\ AFM 100-39 I I R R C M N U V USAF COMMUNICATIONS-ELECTRONICS DOCTRINE SHORT TITLE: CED 3900 COMMUNICATIONS-ELECTRONICS TERMINOLOGY 1 APRIL 1959 EPARTMENT OF THE AIR FORCE For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington 25, D.C. - Price $3.50 0 AFM 100-39 1 APRIL 1959 AIR FORCE MANUAL NO. 100-39 sS . & 7 DEPARTMENT OF THE AIR FORCE WASHINGTON, 1 April 1959 FOREWORD 1. PURPOSE AND SCOPE.—This manual provides a complete cross refer¬ ence listing of those terms, nicknames, designations, abbreviations, and definitions used in military communications and electronics including the field of astronautics. Additional definitions of words not pertaining to military communications or elec¬ tronics are given for clarity and support. The information contained in this manual has been prepared primarily for the C-E Staff officer, every effort has been made to define the terms with the utmost accurcy and carefulness. All classified nick¬ names, abbreviations, terms, and definitions are contained in AFM 100-50, "Class¬ ified CED Extracts” under CED 5039. 2. POLICY.—This manual is an integral part of Communcations-Electronics Doctrine (CED), as described in AFR 100-13. It is both directive and informative for all USAF activities. 3. CHANGES.—Recommendations for changes in the manual will be sub¬ mitted directly to: Commander, Air University, ATTN: C-E Doctrinal Project Office, Maxwell Air Force Base, Alabama. Information regarding additional terms, nicknames, designations, abbreviations, and definitions desired by users is solicited. BY ORDER OF THE SECRETARY OF THE AIR FORCE: OFFICIAL J. L. TARR Colonel, USAF Director of Administrative Services THOMAS D. WHITE Chief of Staff This manual contains no copyright material. This manual supersedes USAF CEI 5100 and 5600 series. 0PI: AF0AC DISTRIBUTION: F;X: CINCAL.1 CINCEUR . 1 CINCPAC . . . ..1 U. S. Documents Officers in SHAPE, AIRCENT, AIRN0RTH, AIRS0UTH ..1 Armed Forces Staff College. Industrial College of the Armed Forces.1 Joint Communications-Electronics Committee.1 Joint Spectrum Evaluation Group . 1 National Security Agency.1 • General Electric Company, Syracuse, N.Y. ....... 1 Trr— 1 APRIL 1959 AFM 100-39 HOW TO USE AFM 100-39 1. The terms, nicknames, designations, abbreviations, definitions, and other matter contained in this manual are used in communications and electronics. Special points of interest are as follows: a. The terms, nicknames, designations, and abbreviations defined, as well as the comments made, relate primarily to Air Force usage. Some words and ab¬ breviations of general interest have been defined, especially when they have been used as key words in the definitions of other words. b. No attempt has been made to define a term in all its senses, unless all senses have some special interest to Air Force users. Thus, when terms are de¬ fined, it is assumed that the reader will understand that these terms may also have other valid meanings not mentioned. c. Abbreviations, historical and current, authorized and commonly used, are entered in normal alphabetical sequence. d. Etymologies and pronunciations are not contained in this manual. 2. For purposes of changes, refer to the Foreword for instructions. iv 1 APRIL 1959 AFM 100-39 A A (ARMY). 1. Land military forces of a nation. 2. Unit of US Army made up of two or more Army Corps. 3. Short for US Army. A/D (AIR DEPOT). Depot providing supply or maintenance for air¬ craft of Air Force organizations. A/G (AIR-TO-GROUND). Pertains to communication from airborne objects to the ground. a/w (ALL WEATHER). Usable or serviceable under any condition of weather or visibility. A-(- (A PLUS OR A POSITIVE). 1. Positive terminal of an A-battery or positive polarity of other sources of filament voltage. 2. Denotes the terminal to which the positive side of the filament voltage source should be con¬ nected. (Reference: F + .) A- (A MINUS OR A NEGATIVE). 1. Negative terminal of an A-battery or nega¬ tive polarity of other sources of filament voltage. 2. On electronic equipment, other than sources of filament voltage, A- denotes the terminal to which the negative side of the filament voltage source should be connected. (Reference: F-.) A-A (AIR-TO-AIR). Used or occurring between or among aircraft in the air. A-AXIS. One of the three equivalent crystallographic A-axes of quartz, perpendicular to the C-axis (Z direction) and intersecting at angles of 120°. The A-axes are of two-fold symmetry and coin¬ cide in position with the Z (or optical) axes. A-BATTERY. Source of energy which heats the filaments of a vacuum tube. A-G GR (AIR-TO-GROUND GUNNERY RANGE). Area set aside or designated for air-to-ground gunnery practice missions. A-INDICATOR. Type of presentation on a cathode-ray indicator in which time is one coordinate (horizontal) and signals appear as deflections in a direction per¬ pendicular to the time scale (vertical). (Refer¬ ence: A-SCAN.) A-N RADIO RANGE. Radio range transmitter that establishes four equisignal zones with off course indication be¬ ing furnished by the audible Morse code letters A or N, and on-course indication being fur¬ nished by a merging of these signals into a con¬ tinuous tone. A-N SIGNAL. Radio-range quadrant-designation signals, which indicate to the pilot whether he is on course, or to the right or left of course. A-OPERATOR. Operator assigned to an A-switchboard. A-POWER SUPPLY. Source of current used to heat filaments of an electron tube. A-SCAN. Presentation on a cathode-ray indicator in which time is one coordinate (horizontal) and signals appear as deflections in a direction perpendicu¬ lar to the time scale (vertical). (Reference: A- INDICATOR.) • A-SCOPE. Oscilloscope that uses an A-scan, presenting the range of the target as the distance along a horizontal line from the transmitted pulse pip to the target, or echo pip. Signals appear as vertical excursions of the horizontal line or trace. A-SUPPLY. A-battery, transformer filament winding, or oth¬ er voltage source that supplies power for heat¬ ing filaments of vacuum tubes. 39-1 AFM 100-39 A-S 1 APRIL 1959 A-SWITCHBOARD. Manual telephone switchboard in a local central office, primarily to receive subscriber calls and to complete connections either directly or through some other switching equipment. AAA (ANTIAIRCRAFT ARTILLERY). Term applied to ground weapons and materials used to locate, illuminate, fire on, and destroy enemy aircraft. AAC (ALASKAN AIR COMMAND). Air Force major air command with the mission of organizing and conducting the air defense of Alaska. AACS (AIRWAYS AND AIR COMMUNICATIONS SERVICE). 1. Service under the Military Air Transport Service providing point-to-point and ground-to- air communication along airways and air routes. 2. Service under the Military Air Transport Service providing military air traffic control and other communication facilities as may be author¬ ized by the Chief of Staff. AAD (ANTIAIRCRAFT DIRECTOR). Army officer, assigned to duty in a direction center, responsible for coordinating antiaircraft action against specified airborne objects. AADCP (ARMY AIR DEFENSE COMMAND POST). Army installation used for collection, display, and evalution of air surveillance information which is used in the assignment of specific bat¬ teries against enemy airborne objects. AAI (AIR-AID-TO-INTERCEPT RADAR). Airborne radar set used in interceptor aircraft to locate, track, and intercept hostile aircraft. AAIS (ANTIAIRCRAFT ARTILLERY INTELLIGENCE SERVICE). System of observers and communication facilities established by antiaircraft artillery units to gath¬ er and transmit information of aerial activities necessary for the proper employment of antiair¬ craft artillery. AAM (AIR-TO-AIR MISSILE). AAO (ANTIAIRCRAFT OFFICER). Army antiaircraft representative, on the battle staff, who advises on employment and capabili¬ ties of antiaircraft weapons. AAOC (ANTIAIRCRAFT ARTILLERY OPERATION CENTER) Antiaircraft artillery installation established for the control of AAA guns, automatic weapons, etc. AAOD (ANTIAIRCRAFT ARTILLERY OPERATION DETACHMENT). AAT (ANTIAIRCRAFT TECHNICIAN). Army enlisted man who assists the antiaircraft director. AB (AIR BASE). Geographical location usually providing space for aircraft operations. AB-POWER PACK. 1. Assembly in a single unit of the A-battery and B-battery for a battery-operated vacuum-tube circuit. 2. Unit that supplies the necessary A and B dc voltages from an ac source of power. ABAMPERE. Centimeter-gram-second electromagnetic unit of current. It is the current which, when flowing through a wire one-centimeter long bent into an arc of one-centimeter radius, produces a magnet¬ ic field the intensity of which is one oersted of the center, provided the remainder of the circuit produces no magnetic field at the center of the arc. One abampere is approximately equal to 10 amperes. ABB (AUTOMATIC BACK BIAS). Technique which consists of one or more auto¬ matic gain control loops to prevent overloading of the receiver by large signals, whether jam¬ ming or actual radar echoes. ABC (AUTOMATIC BASS COMPENSATION). Circuit used in receivers to make bass notes 39-2 1 APRIL 1959 AFM 100-39 ABC sound more natural at low volume settings. The circuit usually consists of a resistor and capaci¬ tor and automatically compensates for the poor response of the human ear to weak sounds. ABCOULOMB. Centimeter-gram-second electromagnetic unit of electrical quantity. It is the quantity of electric¬ ity which passes any section of an electrical circuit in one second when the current is one abampere. One abcoulomb is equal to 10 cou¬ lombs. ABFARAD. Centimeter-gram-second electromagnetic unit of capacitance. It is the capacitance of a capacitor when a charge of one abcoulomb produces a difference of potential of one abvolt between its plates. One abfarad is equal to 10~ 9 farads. ABHENRY. Centimeter-gram-second electromagnetic unit of inductance. It is the inductance in a circuit in which an electromotive force of one abvolt is in¬ ducted by a current changing at the rate of one abampere per second. One abhenry is equal to 10 9 henries. ABMHO. Centimeter-gram-second electromagnetic unit of conductance. A conductor, or circuit, has a con¬ ductance of one abmho when a difference of potential of one abvolt between its terminals will cause a current of one abampere to flow through the conductor. One abmho is equal to 10 -9 mho. ABN (AIRBORNE). 1. Personnel, equipment, etc., transported by air. 2. Material being, or designed to be, transported by aircraft, as distinguished from weapons and equipment installed in and remaining a part of the aircraft. 3. Aircraft, from the instant it becomes entirely sustained by air until it ceases to be so sus¬ tained. A lighter-than-air aircraft is not consid¬ ered to be airborne when it is attached to the ground, except that moored balloons are air¬ borne whenever sent aloft. 4. Track status indicating that an interceptor is airborne. This status exists until detection and initiation are accomplished. ABNORMAL PERFORMANCE. Sampled performance level which deviates mark¬ edly and persistently from the standard (or ref¬ erence) performance level. An unusually high performance level is considered to be as ab¬ normal as an unusually low one, and will be in¬ vestigated for the cause. ABNORMAL PROPAGATION. Phenomena of unstable or changing atmospheric and/or ionospheric conditions acting upon transmitted radio waves, preventing such waves from following their normal path through space, thereby causing difficulties and disruptions of communications. ABNORMAL REFLECTIONS. Sharply defined reflections of radio waves from an ionized layer of the ionosphere, occurring at frequencies greater than the critical (penetra¬ tion) frequency of the layer. (Reference: SPO¬ RADIC REFLECTIONS.) ABOHM. Centimeter-gram-second electromagnetic unit of resistance. It is the resistance of a conductor when, with an unvarying current of one abam¬ pere flowing through it, the potential difference between the ends of the conductor is one abvolt. One abohm is equal to 10 9 ohms. ABORT. 1. To turn back from an aerial mission before completion, for reasons other than enemy action. 2. Switch action taken by weapons directors for interceptor tracks which do not reach airborne status. ABS (AIR BASE SIMULATOR). Individual in the direction center training and battle simulation section responsible for simulat¬ ing an air base operation section. 39-3 AFM 100-39 ABS 1 APRIL 1959 ABSCISSA. Horizontal or X-axis in a chart or graph. ABSENCE-OF-GROUND SEARCHING SELECTOR. In dial (automatic) telephony, an automatic switch which rotates, or rises vertically and ro¬ tates, in search of an ungrounded contact. ABSOLUTE. 1. Adjective used in conjunction with scientific units such as ampere, coulomb, henry, mho, ohm, volt, joule, and watt. 2. An absolute system of units is one in which numbers of units are chosen as fundamental and all other units are derived from them. ABSOLUTE ALTIMETER. Electronic instrument which furnishes altitude data with regard to the surface of the earth or any other object immediately below the instru¬ ment, as distinguished from an aneroid altimeter the readings of which depend on air pressure. ABSOLUTE ALTITUDE. Altitude with respect to the surface of the earth as differentiated from altitude with respect to sea level. ABSOLUTE CEILING. Maximum height above sea level at which a giv¬ en airplane can maintain horizontal flight. ABSOLUTE EFFICIENCY. Ratio of the power output of an electro-acoustic transducer, under specified conditions, to the power output of an ideal electro-acoustic trans¬ ducer. ABSOLUTE SYSTEM. System of units in which numbers of units are chosen as fundamental and all other units are derived from them. ABSOLUTE TEMPERATURE. Temperature measured with respect to absolute zero (-273.1° C, -459.8° F or 0° K). (Refer¬ ence: KELVIN SCALE and ABSOLUTE ZE¬ RO.) ABSOLUTE VALUE. Numerical value of a number or symbol without reference to its algebraic sign. Thus, | 3 | is the absolute value of +3 or -3. To signify abso¬ lute value, vertical lines are placed on both sides of the number or symbol: | Z |. ABSOLUTE ZERO. Lowest possible point on the scale of absolute temperature at which all molecular activity stops. Absolute zero is indicated as -273.1° C, —459.8° F, or 0° K. (Reference: ABSOLUTE TEMPERATURE.) ABSORBER. Material that absorbs radiated electromagnetic energy. ABSORPTION. 1. Phenomena connected with the adherence of molecules of a foreign substance to the surface of a solid or liquid. 2. Loss of energy, due to conversion into heat or other forms, in the transmission of waves over radio or wire paths. 3. The term is usually applied, in wire trans¬ mission, only to loss of energy in extraneous media. ATMOSPHERIC. Loss of energy in transmis¬ sion of radio waves due to dissipation in the atmosphere. AURORAL. Absorption of radio waves as a result of auroral activity. Auroral activity is caused mainly by particle radiation from the sun. GROUND. Loss of energy in transmission of radio waves due to dissipation in the ground. NONDEVIATIVE. Absorption that occurs with¬ out any appreciable slowing up of waves. It is the normal sky-wave absorption. ABSORPTION COEFFICIENT. Measure of sound-absorbing characteristics of a unit area of a given material as compared to the 39-4 1 APRIL 1959 AFM 100-39 ABS sound-absorbing characteristics of an open space (total absorption) of the same area. ABSORPTION CURRENT. Current proportional to the rate of accumulation of electric charges within an imperfect isotropic dielectric. The rate of accumulation and hence the absorption current, decreases with time after any change of the potential gradient, and occurs with both an increase and a decrease of poten¬ tial gradient, so that the absorption current is reversible. ABSORPTION FREQUENCY METER. Frequency-measuring device, incorporating a variable circuit, which absorbs a small portion of the radiated energy under measurement. (Ref¬ erence: WAVEMETER.) ABSORPTION INDEX. Functional relationship between the angle of the sun (at any latitude and local time) and the ionospheric absorption. ABSORPTION LOSS. That part of the transmission loss due to dis¬ sipation or conversion of electrical energy into other forms of energy, either within the medium or attendant upon a reflection. ABSORPTION MODULATION. Inefficient and seldom-used method of ampli¬ tude modulation of the carrier wave of a radio transmitter. This is accomplished by coupling a microphone circuit, either directly or with vacu¬ um-tube amplifiers, to the antenna circuit of the transmitter. This either absorbs the power ra¬ diated by, or varies the radiation resistance of the antenna with the intelligence transmitted. ABSORPTION SPECTRUM. Dark lines or gaps in a spectrum which are due to the absorption of certain rays by a gas, a solu¬ tion, or other absorbing material. ABSORPTION WAVEMETER. Instrument used for measuring the wavelength and/or the frequency of a given source by means of a calibrated resonant circuit, loosely coupled to the source, and indicating resonance as a max¬ imum current in the calibrated circuit. ABVOLT. 1. Centimeter-gram-second electromagnetic unit of electromotive force. With one abampere of current flowing, electric energy is converted to other kinds of energy at the rate of one erg of work per second. 2. Centimeter-gram-second electromagnetic unit of potential difference. It is the potential dif¬ ference between two points when one erg of work is required to transfer one abcoulomb of positive electricity from the point of lower po¬ tential to the point of higher potential. One abvolt is equal to 10~ s volts. AC (ALTERNATING CURRENT). 1. Term applied to electronic equipment indicat¬ ing it is capable of operation from an ac power source only. 2. Current that is continually changing in mag¬ nitude and reversing in polarity. AC (APPROACH CONTROL TOWER). AC (AUXILIARY CONSOLE). Console containing intervention switches, alarms, and warning lights which an operator uses to perform his duties. The auxiliary console may or may not contain a digital-display tube and telephone equipment. AC (ALTERNATING CURRENT) GENERATOR. 1. Rotating electrical machine, generally known as an alternator, that converts mechanical power into alternating current. 2. Vacuum-tube oscillator, or any other device, designed for the purpose of producing alternat¬ ing current. AC (ALTERNATING CURRENT) PLATE RESISTANCE. Internal resistance of a tube to the flow of al¬ ternating current. It is the ratio of a small change in plate voltage to the resulting change in plate current, with other voltages constant, expressed in ohms. AC (ALTERNATING CURRENT) RECEIVER. Radio receiver designed to operate only from an ac source. 39-5 AFM 100-39 AC 1 APRIL 1959 AC (ALTERNATING CURRENT) RESISTANCE. 1. Internal resistance to the flow of alternating current between the cathode and plate of a tube. It is equal to a small change in plate voltage divided by the corresponding change in plate current, and is expressed in ohms. 2. Total resistance offered by a device in an ac circuit. AC&SS (AIR COMMAND AND STAFF SCHOOL). Member college of the Air University which serves as an educational and doctrinal center in the field of command and staff organization, procedure, and techniques. Includes the Com¬ mand and Staff School, Squadron Officer School Air Weapons Course, Air Weapons Orientation Course, and Academic Instructor Course. AC&W (AIRCRAFT CONTROL AND WARNING SYSTEM). Control and warning system established to con¬ trol and report the movement of aircraft. It con¬ sists of observation facilities (radar and/or vis¬ ual), control centers and/or filter centers, and the necessary communications. AC/DC (ALTERNATING CURRENT/DIRECT CURRENT). Term applied to electronic equipment indicating it is capable of operation from either an ac or dc primary power source. AC/DC (ALTERNATING CURRENT/DIRECT CURRENT) RECEIVER. Radio receiver, usually consisting of a few tubes and small power consumption, designed to op¬ erate directly from either an ac or dc source. AC/DC (ALTERNATING CURRENT/DIRECT CURRENT) RINGING. Method of telephone ringing which utilizes ac and dc components: alternating current to oper¬ ate a ringer, direct current to aid the action of a relay which stops the ringing when the called party answers. ACAN (ARMY COMMAND AND ADMINISTRATIVE NETWORK). Domestic and overseas integrated system of fixed radio, wire, cable, and associated facilities providing command and administrative commu¬ nications for the Army. Comparable to the AIRCOM for the Air Force. ACC (AIR CONTROL CENTER). Principal air operations installation (land-or- ship-based) from which all aircraft and air warn¬ ing functions of tactical air operations are con¬ trolled. ACC (AIR COORDINATING COMMITTEE). National committee established to provide for the fullest development and coordination of avi¬ ation policies and activities of federal agencies to formulate the position of US representatives in the international circuit aviation organization. ACCELERATING ANODE OR ELECTRODE. 1. Used in cathode-ray and other electronic tubes to increase the velocity of the electrons in a beam. It is operated at a high positive potential with respect to the cathode. 2. Electrode used for drawing electrons away from a light-sensitive cathode of a Farnsworth image dissector tube for a television camera. ACCELERATION MERIT. Ratio of acceleration (in degrees/-sec 2 ) to angu¬ lar lag (in degrees) in a servo system. ACCELERATION VOLTAGE. Voltage between the cathode and the anode which determines the average velocity of the electrons in the beam. (Reference: BEAM VOLTAGE.) ACCENTUATION. 1. Amplifying or emphasizing any band of fre¬ quencies in the audio spectrum over other audio frequencies. 2. In recording and transmission of FM signals, the pre-emphasis or amplification of the high audio frequencies in the audio amplifier of the recorder or transmitter to improve the signal-to- noise ratio for the higher frequencies. ACCENTUATOR. Network, or circuit, used for pre-emphasis or 39-6 1 APRIL 1959 AFM 100-39 ACC accentuation of a given band of audio frequen¬ cies. ACCEPTOR CIRCUIT. Circuit which accepts a given signal; hence a circuit showing minimum impedance to that signal and therefore in series resonance at that frequency. ACCESS TIME. Time interval which is characteristic of a storage unit in an electronic computer, and is essentially a measure of the time required to communicate with that unit. ACCOMMODATION. Automatic adjustment of the lenses of the hu¬ man eye for seeing objects at different distances. The process whereby the crystalline lens is ad¬ justed to focus sharp, successive, images of ob¬ jects located at various distances from the eye. ACCUMULATOR. 1. Device in an electronic computer which stores a number and which, on receipt of another num¬ ber, adds it to the number already stored, and stores the sum. Note. The term is also applied to devices which function as described but which also have other properties. 2. A storage battery (British usage). ACCURACY. The quality of freedom from mistake or error in an electronic computer, that is, of conformity to truth or to a rule. Accuracy is distinguished from precision as in the following example: a six-place table is more precise than a four-place table. However, if there are errors in the six- place table, it may be either more or less accurate than the four-place table. ACERP (ADVANCED COMMUNICATIONS- ELECTRONICS REQUIREMENTS PLAN). Plan to provide commands with an instrument for soliciting Headquarters, USAF, approval of communications-electronics requirements in ad¬ vance of the detailed effort required for sub¬ mission of the Communications-Electronics Im¬ plementation Plan. ACETATE DISK. Phonograph record made from an acetate com¬ pound. ACFT (AIRCRAFT). 1. Any machine or craft designed to go through the air. 2. Powered fixed-wing airplane. ACHROMATIC. 1. Term used in color television meaning a shade of grey from black to white, or color ab¬ sence. 2. Without color. ACHROMATIC LENS. A lens which has been corrected for chromatic aberration. Such a lens in customarily made to bring all light rays to approximately the same point of focus. ACK (ACKNOWLEDGE). To communicate with the addressee of a mes¬ sage informing originator of a communication that the message has been received and under¬ stood. ACKNOWLEDGEMENT. Message from the addressee informing the originator that his communication has been re¬ ceived and is understood. ACLINIC LINES. Lines on a magnetic map which connect points of equal magnetic inclination or dip. ACLS (AUTOMATIC CARRIER LANDING SYSTEM). Combination radio-radar unit developed for the Navy for use in landing aircraft on carriers under adverse weather conditions. Radar is used to locate the aircraft and determine its position relative to the carrier deck. Altitude, speed, and course are calculated by an electronic com¬ puter and fed into a radio transmitter, which directs the aircraft into the flight pattern. If approach is incorrect, the system will automati¬ cally wave off the approaching aircraft. 39-7 AFM 100-39 ACO 1 APRIL 1959 ACORN TUBE. Button or acorn-shaped vacuum tube, with no base, for UHF applications. ACOUSTIC ABSORPTIVITY. Ratio of sound energy absorbed by a surface to that arriving at the surface. It is equal to one minus the reflectivity of the surface. ACOUSTIC CAPACITANCE. Volume displacement per dyne per square centi¬ meter of a sound medium. The unit of measure¬ ment is dynes per centimeter to the fifth power. ACOUSTIC CLARIFIER. System of cones loosely attached to the baffle of a loudspeaker and designed to vibrate and absorb energy during sudden loud sounds to suppress these sounds. ACOUSTIC COMPLIANCE. 1. Measure of volume displacement of a sound medium when subjected to sound waves. 2. That type of acoustic reactance which corre¬ sponds to capacitive reactance in an electrical circuit. ACOUSTIC FEEDBACK. Feedback of sound waves from a unit of an audio amplifying system to a preceding part of the system causing, when excessive, a howling sound in the speaker. ACOUSTIC FILTER. Sound-absorbing device that selectively sup¬ presses certain audio frequencies. ACOUSTIC IMPEDANCE. Total acoustic resistance of a medium to sound waves. Force per unit area on the surface of the medium divided by the flux through that sur¬ face. This impedance is expressed in ohms and is equal to the mechanical impedance divided by the surface area. Acoustic impedance contains both acoustic resistance and acoustic reactance. ACOUSTIC INERTIANCE. Type of acoustic reactance which corresponds to inductive reactance in an electrical circuit. It is the resistance to movement, or reactance of¬ fered by the sound medium because of the iner¬ tia or effective mass of the medium. It is meas¬ ured in acoustic ohms. ACOUSTIC INTRUSION DETECTOR. Alarm that is responsive to sounds. It generally consists of one or more microphones, concealed or mounted near the object to be protected, con¬ nected to audio amplifiers that transmit a warn- ing signal and give an alarm when sounds ex¬ ceed a predetermined normal level. ACOUSTIC LABYRINTH. Special baffle arrangement used with a loud¬ speaker to prevent cavity resonance and rein¬ force bass response. ACOUSTIC LINE. Equivalent of an electrical transmission line. Baffles, labyrinths, or resonators, are placed at the rear of a loudspeaker, arranged to help re¬ produce the very low audio frequencies. ACOUSTIC OHM. Acoustic resistance, reactance, or impedance which has a magnitude of one acoustic ohm when a sound pressure of one dyne per square centimeter produces a volume velocity of one cubic centi¬ meter per second. ACOUSTIC PICK-UP. Pick-up employed in early nonelectrical phono¬ graphs. ACOUSTIC RADIATOR. That part of an electro-acoustic transducer which initiates the radiation of sound vibrations. ACOUSTIC REACTANCE. That part of acoustic impedance which is due to the effective mass of the medium, that is, to the inertia and elasticity of the medium through which the sound travels. It is the imaginary com¬ ponent of acoustic impedance and is expressed in acoustic ohms. ACOUSTIC REFLECTIVITY. Ratio of the rate of flow of sound energy re¬ flected from a surface, on the side of incidence, to the rate of flow. 39-8 1 APRIL 1959 AFM 100-39 ACO ACOUSTIC REGENERATION. Feedback of sound waves from a unit of an audio amplifying system to a preceding part of the system causing, when excessive, a howling sound in the speaker. ACOUSTIC RESISTANCE. The real component of acoustic impedance. It is responsible for dissipation of energy due to friction between molecules of the air or other medium through which sound travels. It is ex¬ pressed in acoustic ohms and is analogous to electrical resistance. ACOUSTIC SHOCK. Physical pain, dizziness and sometimes nausea caused from hearing a loud, sudden sound. ACOUSTIC SHOCK REDUCER. Piece of telephone-protective equipment usually wired across the receiver leads at the jacks in a switchboard. It is essentially a varistor. When subjected to relatively high voltages, it shunts most of the current from the receiver and thus reduces the intensity of acoustical disturbances. ACOUSTIC STIFFNESS. In a sound medium, that coefficient which when divided by two times the frequency gives the imaginary part of the acoustic impedance which results from the compliance of the medium, or the volume displacement per unit pressure. The unit of measurement is dynes per centimeter to the fifth power. ACOUSTIC SYSTEM. System designed for transmission of sound. ACOUSTIC TRANSMITTIVITY. Ratio of the rate of flow of transmitted sound energy to the rate of incident flow. ACOUSTIC TREATMENT. Use of sound-absorbing materials to give a room a desired degree of freedom from echo and re¬ verberation. ACOUSTICS. 1. Science that deals with production, transmis¬ sion, reception, and effects of sound. 2. Characteristics of a room or location which control reflections of sound waves and thus con¬ trol sound reception in various portions of the room or location. ACP (ALLIED COMMUNICATIONS PUBLICATION). Agreed communications publication prepared in conjunction with other nations. It is approved for United States joint and allied use by mem¬ bers of the United States Joint Communications -Electronics Committee. ACPs are published to provide communications-electronics instructions and procedures that have allied as well as joint application and may also be authorized by each of the United States services for intraservice use. ACS (ARMAMENT CONTROL SYSTEM). System of search and gun-aiming radars which provide the solution to the fire control problem in an aircraft by determining for the pilot the proper course required to intercept a given tar¬ get. The search radar is used to locate targets at long range. When target is within 4000 yards, the gun-aiming radar is used to track target. Target data is supplied to a computer and solu¬ tion to firing problem is presented to pilot on an oscilloscope. ACT. (ACTING). 1. Actively functioning. 2. Doing duty temporarily, or for another. ACTINIC. Capable of producing chemical change, as in the photographic action of light. ACTINIUM. Radioactive element, atomic number 89. ACTINIUM SERIES. One of the principal radioactive series, begin¬ ning with actinium. ACTION ADDRESSEE. Activity or individual to whom a message is directed, by the originator, for action. ACTION TIME. Time required, when used with guided missiles, for a missile to fall from the decision altitude to interception altitude. AFM 100-39 ACT 1 APRIL 1959 ACTIONOMETER. Instrument for measuring the intensity of radia¬ tion received from the sun. ACTIVATION. Make active, as to make certain substances ra¬ dioactive or capable of reacting to radiant ener¬ gy- ACTIVE AIR DEFENSE. Action taken to destroy an enemy air attack. ACTIVE BALANCE. Summation of all return currents, in telephone repeater operation, at a terminal network bal¬ anced against the impedance of the local circuit or drop. ACTIVE COMPUTER. One of two computers at a SAGE center actually performing the air defense mission. ACTIVE ELECTRIC NETWORK. Electrical network containing one or more sources of energy. ACTIVE ELECTRONIC COUNTERMEASURES. That major division of electronic countermeas¬ ures involving actions taken which are of such nature that their employment is detectable by the enemy. Classified definition. (Reference: AFM 100-50.) ACTIVE JAMMING. Intentional radiation or reradiation of electro¬ magnetic waves with the object of impairing the use of a specific portion of the electromagnetic wave spectrum. ACTIVE MATERIAL. Lead oxides or other active substances in the plates of a storage battery. ACTIVE OR ACTUAL POWER. Average of values of instantaneous power taken over one cycle. ACTIVE TRANSDUCER. 1. Transducer whose output is dependent upon sources of power which are controlled by one or more of the waves concerned. 2. Transducer containing one or more sources of power. ACTIVITY. 1. General term used to indicate a unit, forma¬ tion, organization, or establishment. 2. Reference term used to describe the strength or magnitude of oscillation of quartz crystals. ACTUAL HEIGHT. Highest altitude at which refraction of radio waves actually occurs. ACTUATING DEVICE. Manually or automatically operated switch that initiates signal transmission. ACW (AIRCRAFT CONTROL AND WARNING). Activity for detecting, tracking, and reporting airborne objects and for evaluating information received. Its purpose is to furnish air defense warnings and to use air defense weapons to com¬ bat an enemy. ACWO (AIRCRAFT CONTROL AND WARNING OFFICER). Member of the battle staff responsible for air surveillance, identification, and control. ACYCLIC MACHINE. Direct-current machine in which the voltage gen¬ erated in the active conductors maintains the same direction with respect to those conductors, at all times. AD (ATTENTION DISPLAY). Tabular or vector message, computer generated on the display tubes of an operator’s console, drawing attention to a particular situation. ADA (AIR DEFENSE AREA). 1. Specifically defined area within which identi¬ fication of airborne objects is not required if the flights originated in the area, except during periods of air defense emergency. 2. Specifically defined and established territory that includes objectives of possible enemy air attack and for which air defense must be pro¬ vided. 39-10 1 APRIL 1959 AFM 100-39 ADA ADAPTER. Fitting which is designed to adapt a jack, plug, or receptacle so as to make possible electrical connection by means other than those originally intended. HOMING. Device which, when used with an aircraft radio receiver, produces aural and/or visual signals which indicate the direction of a transmitting radio station with respect to the heading of the aircraft. PANORAMIC. Attachment designed to oper¬ ate with a search receiver to provide a visual presentation on an oscilloscope screen, of a band of frequencies extending above and be¬ low the center frequency to which the search receiver is tuned. ADC (AIR DEFENSE COMMAND). Air Force command charged with the execution of North American Air Defense Command pol¬ icies for Air Force participation in air defense. ADCC (AIR DEFENSE CONTROL CENTER). Land based, air-operations installation which with the aid of early-warning installations, air defense direction centers, and other organiza¬ tions and facilities, provides aircraft control and warning, and control and direction of active air defense in a given air defense sector. ADCOCK ANTENNA. Pair of vertical antennas separated by a distance of one-half wavelength or less, and connected in phase opposition to produce a directional pat¬ tern having the shape of a figure eight. ADCOCK DIRECTION FINDER. Spaced antenna, using vertical antennas, design¬ ed to minimize the response due to horizontally polarized components of the waves. ADCOCK RANGE. Range using vertical component transmitting an¬ tennas for A-N airplane navigation. ADCOCK SYSTEM. Radio system utilizing an adcock antenna. ADDC (AIR DEFENSE DIRECTION CENTER). Ground control intercept station that controls interceptors, antiaircraft fire, and reports the pro¬ gress of air defense to the air defense control center. ADDER. 1. Amplifying stage which combines red, green or blue signal from matrix network with Y lum¬ inance signal, and feeds result to a corresponding color output stage; a color television term. 2. Device in an electronic computer which can form the sum of two or more numbers or quanti¬ ties. ADDITIVE. Number, series of numbers, or alphabetical in¬ tervals added to code to encipher it; often re¬ ferred to as the key. ADDRESS. Expression, usually numerical, which designates a particular location in a storage or memory device or other source or destination of informa¬ tion in an electronic computer. (Reference: IN¬ STRUCTION CODE.) ADDRESS GROUP. Group of four letters assigned to represent com¬ mand^), authority(ies), activity(ies), units(s), or geographic location(s); used primarily for the addressing of communications. COLLECTIVE. Address group which repre¬ sents two or more commands, authorities, ac¬ tivities, units, or any combination thereof, in¬ cluding the commander of the organization or group and all subordinate commanders there¬ in. CONJUNCTIVE. Address group, the meaning of which is incomplete unless used in combination with one or more other address groups. GEOGRAPHIC. Address group representing a geographic location or area, which must be used in combination with a conjunctive ad¬ dress group. 39-11 AFM 100-39 ADD ADDRESS INDICATING GROUP. Address group which represents a specific set of action and/or information addresses. address part. In an electronic computer instruction, any part that is usually an address. (Reference- IN¬ STRUCTION CODE.) ADEE (ADDRESSEE). Activity or individual to whom a message is di¬ rected by the originator. Addressees are indi¬ cated as either action or information. ACTION. Activity or individual to whom a mes¬ sage is directed, by the originator, for action. EXEMPTED. Addressee included in the col¬ lective address designation of a message not intended for action or information. INFORMATION. Activity or individual to whom a message is directed by the originator for information. ADES (AIR DEFENSE ENGINEERING SERVICE). Contract organization of specialists from the Western Electric Company and Bell Telephone Laboratories. ADF (AUTOMATIC DIRECTION-FINDING) System which automatically determines’and dis¬ plays the direction of arrival of a radio signal One common type employs a meter with a needle pointing to the bearing. The term usually refers to airborne equipment capable of indicat¬ ing the relative bearings of transmissions in the 100-1750KC band. Normally used for homing purposes. 6 ADIABATIC. Occurring without gain or loss of heat; a change of the properties, such as volume and pressure of the contents of an enclosure, without ex¬ change of heat between the enclosure and its surroundings. ADIV (AIR DIVISION). 1. Unit or its headquarters conventionally on a level of command above wing, composed of two or more combat wings. 1 APRIL 1959 2. Unit on the level of command of a numbered air force. ADIZ (AIR DEFENSE IDENTIFICATION ZONE). 1. Airspace of defined dimensions designated by the Administrator of Civil Aeronautics with¬ in which the ready identification, location, and control of aircraft is required in the interest of national security. 2, Air space above a specified geographical area in which the control and ready classification of airborne objects is required. adjacent channel Channel immediately above or below the refer¬ ence channel. adjacent-channel interference. Interference caused by a transmitter which is as¬ signed for operation in an adjacent channel. ADJACENT-CHANNEL SELECTIVITY. Characteristic of a receiver which governs its ability to reject stations on channels adjacent to that of the desired station. ADJUSTABLE RESISTOR. Resistor whose resistance can be changed me¬ chanically. ADJUSTABLE VOLTAGE DIVIDER. Wire-wound resistor having one or more mov¬ able terminals. Terminals can be moved along the length of the exposed resistance wire until the desired voltage values are obtained. adjustable-speed motor. Electric motor with variable speed. It can be varied over a considerable range by varying either the armature or field current, or both. Usually a shunt-wound motor, which is used with electronic motor control when operated from an ac line. admittance. Lack of opposition to the flow of alternating current in a circuit (the reciprocal of imped¬ ance), usually expressed in mhos. adopted type. Type classification of equipment. Items which 1 APRIL 1959 AFM 100-39 ADO have been adopted for use by the Air Force and are classified as tentative standard, standard, substitute standard, or limited standard. ADPT (ADAPTER). Fitting which is designed to adapt a jack, plug, or receptacle so as to make possible electrical connection by means other than those originally intended. ADRM (AIRDROME). Takeoff and landing area of an air base, with associated runways, hangars, taxi areas, waiting rooms, etc. Does not include maintenance shops. ADSEC (AIR DEFENSE SYSTEMS ENGINEERING COMMITTEE). ADTACS. Classified definition. (Reference: AFM 100-50.) ADVANCE BALL. Rounded support, often of sapphire, that rides ahead of or beside the cutting stylus of a sound recorder. ADVANCED COMMUNICATIONS-ELECTRONICS REQUIREMENTS PLAN. Plan to provide commands with an instrument for soliciting Headquarters, USAF, approval of communications - electronics requirements in ad¬ vance of the detailed effort required for sub¬ mission of the Communications - Electronics Im¬ plementation Plan. ADVISORY GROUP ON AERONAUTICAL RESEARCH AND DEVELOPMENT. Board established by the National Security Act of 1947 to advise Secretary of Defense as to status of scientific research relative to national security and to assist him with research and de¬ velopment problems. Board was abolished by Reorganization Plan No. 6 in 1953. AEC (ATOMIC ENERGY COMMISSION). Civilian governmental agency established by the Atomic Energy Act of 1946 to take over the organization and property of the Manhattan Pro¬ ject and to supervise and control the production of nuclear-fissionable, radioactive materials in the United States. AEDC (ARNOLD ENGINEERING DEVELOPMENT CENTER). Air Force engineering development center lo¬ cated at Tullahoma, Tennessee. Named after general of the Air Force, Henry H. Arnold. AEOLOTROPIC. Showing different properties as to velocity of light transmission, conductivity for heat, or elec¬ tricity, compressibility etc., in different direc¬ tions. AER (AERONAUTICS). 1. Art, skill, or activity of operating aircraft. 2. Science, art, or business of designing, manu¬ facturing, and operating aircraft. AERIAL. The portion, usually wires or rods, of a radio transmitter or receiving station for radiating waves into space or receiving them from space. (Reference: ANTENNA.) AERIAL ARRAY. Antenna arrangement. AERIAL CABLE. Cable connected to a pole or similar overhead structure. AERIAL MOSAIC. Assembly of aerial photos with edges matched to form a continuous photographic presentation of a portion of the earth’s surface. AEROBEE. Research missile developed for the Air Force. It is 20 feet long, 1.3 feet in diameter, and weighs 1690 pounds. The missile is powered by a liquid propellant rocket and uses a solid pro¬ pellant for launching. Maximum speed is Mach 6. Cost per missile is $30,000. AERODROME CONTROL RADIO STATION. Radio station providing communication between 39-13 AFM 100-39 AER 1 APRIL 1959 an aerodrome control tower and aircraft or mo¬ bile aeronautical radio stations. AERODROME CONTROL SERVICE. Air traffic control service for aerodrome traffic. AERODYNAMICS. Branch of dynamics that treats forces exerted by air or other gases upon bodies exposed to them. AEROLOGY. Study of the free atmosphere throughout its vertical extent, as distinguished from investiga¬ tions confined to the layer of the atmosphere ad¬ jacent to the earth’s surface. AERONAUTICAL BROADCASTING SERVICE. Broadcasting service intended for the transmis¬ sion of information related to air navigation. AERONAUTICAL BROADCAST STATION. Radio station which makes broadcasts of meteor¬ ological information and notices to airmen. AERONAUTICAL CHART. Specialized representation of mapped features of the earth, or some part of it, produced to show selected terrain, cultural and hydrographic features, and supplemental information required for air navigation, pilotage or for planning air operations. AERONAUTICAL FIXED SERVICE. Fixed service intended for the transmission of information related to air navigation, prepara¬ tion for, and safety of flight. AERONAUTICAL FIXED STATION. Station in the aeronautical fixed service. AERONAUTICAL GROUND STATION. Radio station operated for the purpose of pro¬ viding air-to-ground communication in connec¬ tion with the operation of aircraft. AERONAUTICAL MARKER BEACON STATION. Radionavigation land station in the aeronautical radionavigation service which provides a signal to designate a small area above the station. AERONAUTICAL MOBILE SERVICE. Mobile service between aircraft stations and aeronautical stations, or between aircraft sta¬ tions. AERONAUTICAL RADIO BEACON STATION. Radionavigation land station in the aeronauti¬ cal radionavigation service, the emission of which is intended to enable an aircraft, or other mobile service to determine its bearing or its position in relation to the aeronautical radio beacon station. AERONAUTICAL RADIO, INCORPORATED. Commercial communications company formed and owned substantially by the scheduled airlines of the United States. It is the liscensee of all domestic airlines enroute communication sta¬ tions. In addition, it furnishes extensive service to international aircraft operations on overseas and foreign routes. The company provides both air/ground and point-to-point service. It coordi¬ nates with industry, government, and manu¬ facturers on the standardization of electronic equipment and represents the aviation industry in RTCA and ICAO on electronic matters. AERONAUTICAL RADIONAVIGATION SERVICE. Radionavigation service intended for the bene¬ fit of aircraft. AERONAUTICAL RADIO SERVICE. 1. Service carried on between aircraft stations and land stations, and between aircraft stations. 2. Special radio for air navigation. AERONAUTICAL RADIO STATION. Land station carrying on a service with aircraft stations. AERONAUTICAL STANDARDS GROUP. Air Force-Navy group concerned with establish¬ ing joint aeronautical standards. AERONAUTICAL STATION. Land station in the aeronautical mobile service, carrying on a service with aircraft stations. 39-14 1 APRIL 1959 AFM 100-39 AER AERONAUTICAL TELECOMMUNICATION AGENCY. Station in the aeronautical telecommunication service. AERONAUTICAL TELECOMMUNICATION SERVICE. Telecommunication service provided for any aero¬ nautical purpose. AERONAUTICAL TELECOMMUNICATION STATION. Station in the aeronautical telecommunication service. AERONAUTICS. 1. Art, skill, or activity of operating aircraft. 2. Science, art, or business of designing, manu¬ facturing, and operating aircraft. AEW (AIRBORNE EARLY WARNING). Air surveillance provided from long-range air¬ craft equipped with search radar and communi¬ cations. Air surveillance information is relayed to surface stations. AEW (AIRBORNE EARLY WARNING) RADAR. High-powered radar set installed in aircraft for the distant detection of approaching enemy air¬ craft. AEW & CON. (AIRBORNE EARLY WARNING AND CONTROL). Air surveillance and control provided from long-range aircraft equipped with search radar and communications. Air surveillance informa¬ tion is relayed to surface stations. AF (AIR FORCE). With specific reference to the United States Air Force. AF (AUDIO FREQUENCY). Frequency which can be detected as a sound by the human ear. The range of audio frequencies extends approximately from 20 to 20,000 cycles per second. AFAC (AIR FORCE ARMAMENT CENTER). AFAUX (AIR FORCE AUXILIARY FIELD). Air base used to aid, or to supplement the facili¬ ties of, another air base. AFB (AIR FORCE BASE). Geographical location that provides space for carrying out an operation, including facilities for offices, warehousing, accomodation of - per¬ sonnel, and takeoff and landing of aircraft. Lo¬ cation is under jurisdictional control of the United States Air Force. AFBU (AIR FORCE BASE UNIT). AFBul (AIR FORCE BULLETIN). Official publication of Headquarters, USAF, con¬ taining matter of an informative or advisory na¬ ture and of continuing interest. AFC (AUTOMATIC FREQUENCY CONTROL). 1. System tending to hold the frequency of an oscillatory circuit constant despite other influ¬ ences that normally would introduce a frequency change. 2. Circuit that holds a radio receiver on the frequency of the station to which it is tuned. AFCOMMSTA. General message originated by the director of communications. Headquarters, USAF, normally containing instructions or changes to publica¬ tions pertinent to the operation of USAF com¬ munications centers. AFCOMMSTACON. General message originated by the director of communications, Headquarters, USAF, normally containing instructions or changes to publica¬ tions pertinent to the operation of USAF com¬ munications centers located within the ConUS. AFCRC (AIR FORCE CAMBRIDGE RESEARCH CENTER). Research center located at Cambridge, Massa¬ chusetts, under the Air Research and Develop¬ ment Command, concerned with electronic, atom¬ ic, geophysical, and other scientific research. AFDCCO (AIR FORCE DEPARTMENTAL CATALOG COORDINATING OFFICE). 39-15 * * AFM 100-39 1 APRIL 1959 AFF AFF (ARMY FIELD FORCES). 1. Ground forces operating in the field. 2. Units, general headquarters, installations, and equipment that comprise the forces in a theater of operation. AFFTC (AIR FORCE FLIGHT TEST CENTER). AFHUFS (ARMED FORCES HEADQUARTERS UNIFICATION FACILITIES SERVICES). AFI (AFRICAN-INDIAN OCEAN REGION). AFL (AIR FORCE LETTER). Administrative Air Force publication, general in application, containing regulatory material con¬ sidered to be temporary in duration, or informa¬ tive matter that may be of either temporary or permanent interest. AFM (AIR FORCE MANUAL). Manual published by order of the Secretary of the Air Force, determined to be of interest, and applicable to two or more major air commands. AFM & SD (AIR FORCE MATERIAL AND SERVICE DIRECTIVE). AFMTC (AIR FORCE MISSILE TEST CENTER). AFNA (AIR FORCE WITH NAVY). AFP (AIR FORCE PAMPHLET). Air Force publication that disseminates informa¬ tion considered of continuing usefulness, but not considered appropriate for issuance in other types of Air Force publications. AFPS (ARMED FORCES PRESS SERVICE). Weekly clipping service, administered by the Army, which supplies materials to interested service newspapers. AFR (AIR FORCE REGULATION). Basic formal order, issued by the Secretary of the Air Force, setting forth rules, policy state¬ ments, procedures, responsibilities, organization¬ al frameworks, or the like for the government and operation of the Air Force, and having a permanent nature. AFRS (ARMED FORCES RADIO SERVICE). Radio service, including maintenance, programs, transcriptions, etc., available to armed forces overseas and to certain service and veteran hos¬ pitals in the United States. AFSAC (ARMED FORCES SECURITY AGENCY COUNCIL). AFSC (AIR FORCE SPECIALTY CODE). 1. Code set up for identifying all Air Force Specialties. 2. Combination of digits, or digits and letters, identifying a particular Air Force Specialty. AFSMAAG (AIR FORCE SECTION, MILITARY ASSISTANCE ADVISORY GROUP). AFSS (AIR FORCE SECURITY SERVICE). AFSSO (AIR FORCE SPECIAL SECURITY OFFICER) SYSTEM. Classified definition. (Reference: AFM 100-50.) AFSWS (AIR FORCE SPECIAL WEAPONS CENTER). Subordinate command of the Air Research and Development Command responsible for the de¬ velopmental testing of atomic and other special weapons. AFTERBURNER. Device for introducing more fuel directly into the thrust chamber of a jet engine to produce more thrust for short periods. AFTERGLOW. Persistence of luminosity in a gas-discharge tube after the voltage has been removed or on the screen of a cathode-ray tube after the electron beam has moved. AFTRC (AIR FORCE AIR TRAINING COMMAND). Major air command with headquarters at Scott Air Force Base, Illinois, having the mission of providing training for Air Force officers and airmen. 39-16 1 APRIL 1959 AFM 100-39 AFU m AFUS (AIR FORCE OF THE UNITED STATES). Designation of the overall USAF. Between 1947 and 1951, this term was used to distinguish the overall organization from its regular component, ambiguously called the United States Air Force. AFWA (AIR FORCE WITH ARMY). AFWAR (AIR FORCE PERSONNEL ON DUTY WITH ARMY). AERONAUTICAL TELECOMMUNICATION. Agency responsible for operating a station or stations in the aeronautical telecommunication service. ARMED SERVICES ELECTRO-STANDARDS. Joint service organization which prepares and promulgates standard joint specifications for the electronic parts and materials used in the communications and electronics equipments of the armed forces. AGARD (ADVISORY GROUP ON AERONAUTICAL RESEARCH AND DEVELOPMENT). Board established by the National Security Act of 1947 to advise Secretary of Defense as to status of scientific research relative to national security and to assist him with research and de¬ velopment problems. Board was abolished by Reorganization Plan No. 6 in 1953. AGENCY OF COMMUNICATION. Facility which embraces personnel and equip¬ ment necessary to provide communications. AGENCY OF SIGNAL COMMUNICATION. Includes all personnel and equipment necessary to operate a signal communication installation. It may include one or more means of communi¬ cation. AGC (AUTOMATIC GAIN CONTROL). 1. Type of circuit used to maintain the output volume of a receiver constant, regardless of var¬ iations in the signal strength applied to the re¬ ceiver. 2. Self-acting compensating device which main¬ tains the output of a transmission system con¬ stant within narrow limits in the face of wide variations in the attenuation of the system. AGING. Allowing a permanent magnet, capacitor, meter, or other device to remain in storage for a period of time, sometimes with voltage applied, until the characteristics of the device become essen¬ tially constant. AGL (AIRBORNE GUN LAYING) RADAR. Airborne radar set, in interceptor aircraft, used for plane-to-plane fire control. 3. Radar circuit which presents saturation of the radar receiver by long blocks of received signals or by a carrier modulated at low frequency. AGCA (AUTOMATIC GROUND-CONTROLLED APPROACH). AGENCY. 1. Office or organization authorized to act for or in behalf of another, as for a commander, for the executive branch of the government, or for any other organization. AGLC (AIR-GROUND LIAISON CODE). Set of symbols for a limited number of words, phrases, and sentences used for communication between air and ground forces. AGONIC LINE. Line on the earth’s surface, at all points of which the magnetic declination is zero. Al (AIRBORNE INTERCEPTION). Airborne interception performed by an inter¬ ceptor equipped with airborne radar. 2. Office or organization serving as an instru- AIA (AIRBORNE INTERCEPTOR AIRCRAFT), ment for accomplishing a definite purpose. Airborne radar set for aircraft interception. 39-17 AFM 100-39 AIC 1 APRIL 1959 AIC (AIR INTERCEPTION CONTROL) COMMON. Designating the communications channel former¬ ly known as ground control interception com¬ mon. AIDED TRACKING. System of tracking a target signal in bearing, elevation, range, or any combination of these variables. AIMING CIRCLE. Instrument for measuring angles in azimuth, site, and for general topographic work. AIP (AIR LIAISON PARTY). AIR (AIRCRAFT). Any machine or craft designed to go through the air. AIR. Air, in radio work, is considered as the most perfect dielectric, and an insulator. A capa¬ citor with air between its plates shows little change of capacity with change of frequency, and in the air dielectric there is no power loss. AIR AID TO INTERCEPT RADAR. Airborne radar set used in interceptor aircraft to locate, track, and intercept hostile aircraft. AIR ALERT MISSION. Air support mission which starts with airborne aircraft awaiting the designation of a target. The aircraft carry a predetermined standard load suitable for attacking any of several types of targets that may be assigned. AIR ATTACHE. Rated Air Force commissioned or warrant officer belonging to an ambassador’s or minister’s dip¬ lomatic staff. His primary duty is to collect, by overt methods, air intelligence information re¬ garding the country in which he is on duty. AIR BASE. Geographical location usually providing space for aircraft operations. AIR BASE SIMULATOR. Individual in the direction center training and battle simulation section responsible for simulat¬ ing an air base operation section. AIR BRAKE. Device fastened to a rope leader ribbon to aid in unwinding the roll. AIR CAPACITOR. Capacitor using air as the dielectric material be¬ tween its plates. AIR COMMAND AND STAFF SCHOOL. Member college of the Air University which serves as an educational and doctrinal center in the field of command and staff organization, procedure, and techniques. Includes the Com¬ mand and Staff School, Squadron Officer School, Air Weapons Course, Air Weapons Orientation Course, and Academic Instructor Course. AIR CONTROL CENTER. Principal air operations installation from which all aircraft and air warning functions of tactical air operations are controlled. AIR CONTROL TEAM. Subordinate operational component of the land- based tactical air control group designed for the control of aircraft from forward observation posts. The air control team operates at division, regiment, or battalion level. AIR CONTROLLER. Individual, in naval usage, specially trained for and assigned the duty of control (by use of radio, radar, or other means) of such aircraft as may be allotted to him for the defense of his area. (Reference: FIGHTER DIRECTOR.) AIR COORDINATING COMMITTEE. National committee established to provide for the fullest development and coordination of aviation policies and activities of federal agen¬ cies and to formulate the position of US repre¬ sentatives in the international circuit aviation organization. AIR DEFENSE. 1. All measures designed to nullify or reduce 39-18 1 APRIL 1959 AFM 100-39 AIR the effectiveness of the attack by hostile aircraft or guided missiles after they are airborne. 2. Sum total of all measures taken for defense against attack on a target area by enemy airborne objects. ACTIVE. Action taken to destroy an enemy air attack. PASSIVE. All measures, other than active de¬ fense, taken to minimize the effects of hostile air action. AIR DEFENSE AIR TRAFFIC CONTROL SYSTEMS INTEGRATION. Joint CAA and military use of air defense and air traffic control radar surveillance facilities for the control of air traffic. AIR DEFENSE AREA. 1. Specifically defined area within which identi¬ fication of airborne objects is not required if the flights originated in the area, except during periods of air defense emergency. 2. Specifically defined and established territory that includes objectives of possible enemy air attack and for which air defense must be pro¬ vided. AIR DEFENSE COMBAT ZONE. That area extending outward from the target areas which has contiguous radar coverage and within which air defense measures are employed. AIR DEFENSE COMMAND. Air Force command charged with the execution of North American Air Defense Command poli¬ cies for Air Force participation in air defense. AIR DEFENSE CONTROL. Control from the ground or ship of all elements engaging in active air defense. AIR DEFENSE CONTROL CENTER. Land based, air-operations installation which, with the aid of early-warning installations, air defense direction centers, and other organiza¬ tions and facilities, provides aircraft control and direction of active air defense in a given sector. AIR DEFENSE DIRECTION CENTER. Ground control intercept station that controls interceptors and antiaircraft fire, and reports the progress of air defense to the air defense control center. AIR DEFENSE EMERGENCY. Declaration of an emergency condition based on any state of events indicating to commander in chief, North American Air Defense Command, or higher authority, that hostile action is in pro¬ gress or imminent. AIR DEFENSE ENGINEERING SERVICE. Contract organization of specialists from the Western Electric Company, and Bell Telephone Laboratories. AIR DEFENSE IDENTIFICATION ZONE. 1. Air space of defined dimensions designated by the administrator of civil aeronautics within which the ready identification, location, and con¬ trol of aircraft is required, in the interest of national security. 2. Air space above a specified geographical area in which the control and ready classification of airborne objects is required. AIR DEFENSE REGION.. Geographical subdivision of an air defense area. AIR DEFENSE SECTOR. 1. Geographical subdivision of an air defense region. 2. Air Force headquarters responsible for the air defense of a sector. AIR DEFENSE SUBSECTOR. Geographical area in which air defense meas¬ ures are accomplished by an air defense direc¬ tion center. 39-19 AFM 100-39 AIR 1 APRIL 1959 AIR DEFENSE SYSTEM. Structure of interdependent elements integrated to accomplish an assigned operational task of air defense. AIR DEFENSE SYSTEMS ENGINEERING COMMITTEE. AIR DEFENSE WARNING. Degree of expected imminence of hostile attack which may be specified under authority of air defense emergency. AIR DEPOT. Depot providing supply or maintenance for air¬ craft of Air Force organizations. AIR DIVISION. 1. Unit, or its headquarters, conventionally on a level of command above wing, composed of two or more combat wings. 2. Unit on the level of command of a numbered air force. AIR DIVISION COC (COMBAT OPERATIONS CENTER). Command post in, or adjacent to, an ADCC for the use of the division commander and his staff in directing and supervising the air defense of the sector. AIR ELECTRONICS OFFICER. USAF officer who manages air electronic activi¬ ties including installation, operation, mainte¬ nance, repair, and modification of airborne elec¬ tronic equipment and commands air electronics units. AIR ENVIRONMENT. General communications-electronics term which is used to define the aggregate of all airborne equipment which is a part of communications- electronics system. This should be distinguished from the equipment which may be installed on the ground, and hence would be termed as be¬ longing to the ground environment. Note. IFF system and navigational aids system may be divided into a ground and air environment. AIR FORCE. With specific reference to the United States Air Force. AIR FORCE AIR TRAINING COMMAND. Major air command with headquarters at Scott Air Force Base, Illinois, having the mission of providing training for Air Force officers and airmen. AIR FORCE AUXILIARY FIELD. Air base used to aid, or to supplement the facili¬ ties of, another air base. AIR FORCE BASE. Geographical location that provides space for carrying out an operation, including facilities for officers, warehousing, accomodation of per¬ sonnel, and takeoff and landing of aircraft. Location is under jurisdictional control of the United States Air Force. AIR FORCE BASE COMPLEX. Air base for support of Air Force units consist¬ ing of landing strips and all components or re¬ lated facilities for which the Air Force has op¬ erating responsibility, together with interior lines of communication and the minimum sur¬ rounding area required for local security. AIR FORCE BULLETIN. Official publication of Headquarters, USAF, containing matter of an informative or advisory nature and of continuing interest. AIR FORCE CAMBRIDGE RESEARCH CENTER. Research center located at Cambridge, Massa¬ chusetts, under the Air Research and Develop¬ ment Command, concerned with electronic, atom¬ ic, geophysical, and other scientific research. AIR FORCE COMMUNICATIONS COMPLEX. All Air Force communications. This term re¬ places GLOBECOM and STRATCOM. AIR FORCE COMMUNICATIONS NETWORK. World-wide integrated teletype tape-relay net¬ work comprised of land lines and radio channels 39-20 1 APRIL 1959 AFM 100-39 AIR designed to carry Air Force message traffic. It is an integral part of the Air Force strategic communications system. AIR FORCE LETTER. Administrative Air Force publication, general in application, containing regulatory material con¬ sidered to be temporary in duration, or informa¬ tive matter that may be of either temporary or permanent interest. AIR FORCE MANUAL. Manual published by order of the Secretary of the Air Force, determined to be of interest and applicable to two or more major air commands. AIR FORCE OF THE UNITED STATES. Designation of the overall USAF. Between 1947 and 1951, this term was used to distinguish the overall organization from its regular component, ambiguously called the United States Air Force. AIR FORCE PAMPHLET. Air Force publication that disseminates informa¬ tion considered of continuing usefulness, but not considered appropriate for issuance in other types of Air Force publications. ARMED FORCES PRESS SERVICE. Weekly clipping service, administered by the Army, which supplies materials to interested service newspapers. AIR FORCE REGULATION. Basic formal order issued by the Secretary of the Air Force setting forth rules, policy state¬ ments, procedures, responsibilities, organization¬ al frameworks, etc., for the government and oper¬ ation of the Air Force, and having a permanent nature. AIR FORCE SPECIAL SECURITY OFFICER SYSTEM. Classified definition. (Reference: AFM 100-50.) AIR FORCE SPECIAL WEAPONS CENTER. Subordinate command of the Air Research and Development Command responsible for the de¬ velopmental testing of atomic and other special weapons. AIR FORCE SPECIALTY CODE. 1. Code set up for identifying all Air Force Specialties. 2. Combination of digits, or digits and letters, identifying a particular Air Force Specialty. AIR FORCE STRATEGIC COMMUNICATIONS COMPLEX. World-wide, long-range, point-to-point, and air- ground-air communications system of the Air Force designed for control of air operations on a global scale. It consists of an integrated and engineered system of interconnected Air Force radio stations, together with other leased or al¬ located long-haul wire and radio channels, nec¬ essary terminal equipment, relay facilities, com¬ munications centers, cryptographic centers, etc., for use by the Air Force as a whole in the accom¬ plishment of its global mission. It does not in¬ clude internal tactical and special-purpose com¬ munications systems of the various commands below the major command level required in the accomplishment of their missions, except as spe¬ cifically designated by Headquarters, USAF. AIR FORCE SUPPLIES. Items or categories of items which are (a) pro¬ vided through Army supply agencies for use by Air Force activities; (b) provided through Army supply agencies for use by the Air Force and in possession of Air Force activities, exclusive of items on a temporary-loan basis from the Department of the Army; (c) Army purchased supplies stored as Air Force credits under cus¬ tody of the Army. AIR GAP. Air space between two objects which are electri¬ cally or magnetically related. AIR INTERCEPTION. Visual or radar contact by a friendly aircraft with an unidentified aircraft. AIR INTERCEPTION CONTROL COMMON. Designating the communications channel form¬ erly known as ground control interception com¬ mon. 39-21 AFM 100-39 AIR 1 APRIL 1959 AIR LIAISON OFFICER. Experienced pilot, familiar with operational pro¬ cedures, capabilities, and limitations of air power. An ALO is provided for each corps and division headquarters furnished tactical air support. The ALO is responsible for technical assistance to the ground staff in formulating requirements for air support and provides continuous guidance on air matters. He is a direct representative of the tactical air force commander. AIR MATERIEL AREA. 1. One of the several areas set up by the Air Materiel Command for expediting Air Force maintenance and the supply of Air Force organi¬ zations and installations within those areas. 2. Organization that operates any one of these areas under the Air Materiel Command, compar¬ able in echelon to a numbered air force. AIR MATERIEL COMMAND. Major air command of the Air Force that pro¬ vides logistic support to the United States Air Force. AIR MINISTRY EXPERIMENTAL STATION. British ground radar station in an early-warning system. AIR MOVEMENT DATA. Flight plan data used in reckoning aircraft move¬ ment. The data may be presented in either a situation or digital display. Correlated Air-Movement Data: Air-movement data which has been associated with a track. Uncorrelated Air-Movement Data: Air-move¬ ment data which has not been associated with a track. AIR MOVEMENTS INFORMATION SECTION. Unit of the civil aeronautics administration which provides flight-plan information to the identification branch of a direction center. Such information pertains to friendly airborne objects which are, or will be, operating in the organiza¬ tions’ area. AIR NATIONAL GUARD. Military force, comprising those units and per¬ sonnel organized and partially maintained by the several states, territories, or District of Columbia, for which certain federal responsibility is vested in the Department of the Air Force, and which, while in the service of the United States, con¬ stitute a component of the United States Air Force. AIR NAVIGATION DEVELOPMENT BOARD. Board, reporting to the department of commerce through the civil aeronautics administration, which was organized to develop a nation-wide air navigation system to serve the needs of civil aviation and nontactical military aviation, and capable of effective integration into any air-de¬ fense system established by the department of defense. AIR NAVIGATION RADIO AIDS. Aeronautical ground stations, radio beacons, di¬ rection finders, and similar aids. AIR PROVING GROUND. Air Force installation operated at Eglin Air Force Base by the Air Proving Ground Com¬ mand. AIR PROVING GROUND COMMAND. Major air command in the USAF organized pri¬ marily to determine the operational suitability of materiel by test and evaluation. AIR POSITION INDICATOR. Airborne computing system which presents a continuous indication of aircraft position on the basis of aircraft-heading, airspeed, and elapsed time. AIR RAID WARNING. Information concerning approaching enemy air¬ craft and/or guided missiles, which is dissemin¬ ated primarily for passive air defense purposes. AIR RAID WARNING CONDITIONS. Degree of air raid probability according to the following: Yellow Alert: Attack likely; intelligence has been received indicating that hostile air¬ craft are over or en route toward the north american continent. 39-22 AFM 100-39 AIR Red Alert: Attack imminent; hostile aircraft have been identified and are within the air de¬ fense sector or within adjacent sectors with a high probability of entering the subject air defense sector. White Alert: All clear; notification to be given when the danger of either yellow-or-red- type air raid warning is over. AIR RESCUE SERVICE. Air Force organization under the Military Air Transport Service that provides air rescue, in¬ cluding search for both civilian and military air¬ craft in remote areas, either on land or sea. AIR RESEARCH AND DEVELOPMENT COMMAND. Major air command in the USAF that carries out the research and development activities required for the accomplishment of Air Force missions. AIR RESERVE OFFICER TRAINING CORPS. Training corps under the control of the USAF, with detachments in colleges and universities, to prepare cadets for service in one of the compon¬ ents of the USAF. AIR ROUTE. Navigable airspace between two points, identi¬ fied to the extent necessary for the application of flight rules. AIR ROUTE TRAFFIC CONTROL CENTER. Civil aeronautics administration facility that es¬ tablishes and monitors routes and altitudes for aircraft flying within a given control area. AIR SOUNDING. Measurements of air conditions at high altitudes by a radiosonde or similar equipment. AIR SPACE PANEL. Agency responsible for ensuring that conflicts in the use of the navigable air space are avoided or reduced by coordinating and resolving joint problems arising from military, civil, and other use of air space. AIR SPEED. Velocity of aircraft relative to the surrounding atmosphere. AIR SURVEILLANCE. Systematic observation of air space by electronic, visual, or other means. Primarily for the purpose of identifying and determining the movements of all aircraft and large missiles, friendly or enemy, in the air space under observation. AIR SURVEILLANCE OFFICER. Officer responsible for the performance of the air surveillance functions. AIR SURVEILLANCE TECHNICIAN. Noncommissioned officer who assists the air surveillance officer. AIR TACTICS OFFICER. Officer responsible for forming hostile tracks into raids and interceptor tracks into groups; also responsible for forwarding summarized da¬ ta on raids and groups to a supervisory organi¬ zation. AIR TACTICS TECHNICIAN. Noncommissioned officer who assists the air tac¬ tics officers. AIR TRAFFIC CONTROL. Service operated by appropriate authority to pro¬ mote the safe, orderly, and expeditious flow of air traffic. The service is administered by air route traffic control centers and airport traffic contol towers. AIR TRAFFIC CONTROL AND NAVIGATION PANEL. Agency responsible for review and coordinating of implementation programs and plans, policies and standards, rules and procedures concerning air traffic control within the United States. AIR TRAFFIC CONTROL CENTER. Principal communications and operations center from which all aircraft are controlled under IFR conditions in the vicinity of an airfield. The complete system consists of a suitable long-range radar installation capable of observing aircraft 39-23 AFM 100-39 AIR along airways, a method of controlling inbound and outbound traffic within the traffic pattern of the airfield, and a precision radar unit capable of providing the pilot of an aircraft with infor¬ mation that will permit a safe landing. AIR TRAFFIC CONTROL CLEARANCE. Authorization by an air traffic control unit for an aircraft to proceed under specified conditions. AIR TRAFFIC CONTROL INSTRUCTIONS. Directions issued by an air traffic control unit for an aircraft to proceed or to delay its flight in a specified manner. AIR TRAFFIC CONTROL PLOTTING DISPLAY. Any type of enlarged radar display which is in tended for use in the control of air traffic and which is so mounted that the display is hori¬ zontal. The radar controller records aircraft posi¬ tions by placing aircraft position markers on the horizontal display and sequences traffic by re¬ ference to the data so displayed. In the event of a failure of the surveillance radar equipment, the markers preserve the pattern of all traffic in the area as it was at the time of the failure and provide initial data for the safe handling of traffic by other means. AIR TRAFFIC CONTROL SERVICE. Service provided to expedite and direct air traffic so as to prevent collisions between aircraft and obstructions or other aircraft. AIR TRAINING COMMAND. Major air command with headquarters at Scott Air Force Base, Illinois; having the mission of providing training for Air Force officers and air¬ men. AIR U (AIR UNIVERSITY). Major air command with headquarters at Max¬ well Air Force Base, Alabama. Functions as an Air Force doctrinal, educational, and research center. Principal components are the Air War College, Air Command and Staff College, School of Aviation Medicine, Institute of Technology, Reserve Officer’s Training Corps, Extension Course Institute, and Research Studies Institute. AIR WAR COLLEGE. School of the Air University charged with the schooling of senior officers for high command and staff duty, and with the development of doc¬ trine on the broad use of air power. AIR WEATHER SERVICE. Service under the Military Air Transport Service providing meteorological service primarily for the armed services. AIR-AIR. Communications between one airborne station and one or more other airborne stations. AIR-BOUND. Lubricating-oil or fuel-oil system may become air-bound when air enters the system through vents or leaks. The air, by being compressed by the fluid flowing through the lines, interferes with the continuous flow of the fuel or lubrica¬ tion and may cause the system to stop operating or cause serious damage. AIR-CORE COIL. Coil without metal in its magnetic circuit. AIR-CORE TRANSFORMER. Transformer (usually RF) having a nonmetallic core. Transformers wound on a solid insulating substance such as isolantite, are assumed to have an air core. AIR-GROUND COMMUNICATIONS. Method or means of conveying information be¬ tween aircraft in flight and ground stations. AIR-GROUND CONTROL RADIO STATION. Aeronautical telecommunication station having primary responsibility for handling communica¬ tions pertaining to the operation and control of aircraft in a given area. AIR-GROUND LIAISON CODE. Set of symbols for a limited number of words, phrases, and sentences used for communication between air and ground forces. AIR-GROUND OPERATIONS SECTION. Part of the joint operation center. (Reference: JOINT OPERATION CENTER.) 39-24 1 APRIL 1959 AFM 100-39 AIR AIR-GROUND OPERATIONS SYSTEM. Operations system operated by the ground forces, in Army and Air Force usage, to provide the ground commander with the means for receiving and processing requests of subordinate ground commanders for air missions and for rapid and continuous exchange of battle information and intelligence. It includes an air-ground operations section, ground liaison officer teams, and the necessary communication facilities. AIR-GROUND RADIO FREQUENCY. Specified frequency agreed upon for transmis¬ sion from an aircraft station to an aeronautical ground station. AIR-GROUND-AIR. Communications between either an airborne sta¬ tion and a ground station, vice versa, or in any combination. Commonly referred to as: air-to- ground, ground-to-air, air-ground, or ground-air. AIR-TO-GROUND. Pertains to communication from airborne objects to the ground. AIR-TO-GROUND COMMUNICATION. One-way communication from aircraft to stations or locations on the surface of the earth. AIR-TO-GROUND GUNNERY RANGE. Area set aside or designated for air-to-ground gunnery practice missions. AIR-TO-SURFACE MISSILE. Missile designed to be dropped from aircraft, which upon release, is guided to a surface target, such as an airfield, by means of an internal hom¬ ing device or radio control. AIR-TO-SURFACE VESSEL. Search radar sets used in aircraft for detecting objects on the surface of the sea. AIR-TO-UNDERWATER MISSILE. Missile designed to be dropped from aircraft, and upon contact with the surface of the water, to pursue or seek out an underwater moving tar¬ get, such as a submarine, by means of an internal or radio guided homing device. AIR-TRANSPORTABLE UNITS. Ground units, other than airborne, which are trained and whose equipment is adapted for movement and delivery by transport aircraft. AIRA (AIR ATTACHE). Rated Air Force commissioned or warrant officer belonging to an ambassador’s or minister’s dip¬ lomatic staff. His primary duty is to collect by overt methods air intelligence information re¬ garding the country in which he is on duty. AIRBORNE. 1. Personnel, equipment, etc., transported by air. 2. Material being, or designed to be, transported by aircraft, as distinguished from weapons and equipment installed in and remaining a part of the aircraft. 3. Aircraft, from the instant it becomes entirely sustained by air until it ceases to be so sustained. A lighter-than-air aircraft is not considered to be airborne when it is attached to the ground, ex¬ cept that moored balloons are airborne whenever sent aloft. 4. Track status indicating that an interceptor is airborne. This status exists until detection and initiation are accomplished. AIRBORNE EARLY WARNING. Air surveillance provided from long-range air¬ craft equipped with search radar and communica¬ tions. Air-surveillance information is relayed to surface stations. AIRBORNE EARLY WARNING AND CONTROL. Air surveillance and control provided from long-range aircraft equipped with search radar and communications. Air-surveillance informa¬ tion is relayed to surface stations. The system can also control friendly airborne objects. AIRBORNE EARLY WARNING RADAR. High-powered radar set installed in aircraft for the distant detection of approaching enemy air¬ craft. AIRBORNE EARLY WARNING SET. Airborne radar equipment providing long-range 39-25 AFM 100-39 AIR detection, identification, and relaying of the ra¬ dar signals to ground or ship-borne stations. AIRBORNE GUN LAYING RADAR. Airborne radar set in interceptor aircraft, used for plane-to-plane fire control. AIRBORNE INTERCEPT RADAR. Short-range airborne radar employed by fighters and interceptors to locate targets. AIRBORNE INTERCEPTION. Interception performed by an interceptor equip¬ ped with airborne radar. AIRBORNE INTERCEPTOR AIRCRAFT. Airborne radar set for aircraft interception. AIRBORNE MOVING TARGET INDICATOR. Capability given to airborne radars so that they may detect moving vehicles of all descriptions. AIRBORNE OBJECT. Any machine or craft in flight in the earth s at¬ mosphere or in outer space. AIRCOM (AIR FORCE STRATEGIC COMMUNICATIONS) COMPLEX. World-wide, long-range, point-to-point and air- ground-air communications system of the Air Force designed for control of air operations on a global scale. It consists of an integrated and en¬ gineered system of interconnected Air Force radio stations, together with other leased or al¬ located long-haul wire and radio channels, nec¬ essary terminal equipment, relay facilities, com¬ munications centers, cryptographic centers, etc., for use by the Air Force as a whole in the accom¬ plishment of its global mission. It does not in¬ clude internal tactical and special-purpose com¬ munications systems of the various commands below the major level required in the accom¬ plishment of their missions, except as specifi- caly designated by Headquarters, USAF. This term replaces GLOBE COM and STRATCOM. AIRCOMNET. World-wide integrated teletype relay network comprised of land lines and radio channels designed to carry Air Force message traffic. It 1 APRIL 1959 is an integral part of the Air Force strategic com¬ munications system. AIRCRAFT. 1. Any machine or craft designed to go through the air. 2. Powered fixed-wing airplane. AIRCRAFT BONDING. Electrically connecting together all of the metal structure of the aircraft, including the engine and metal covering on the wiring. AIRCRAFT CONTROL AND WARNING. Activity for detecting, tracking, and reporting airborne objects and for evaluating information received. Its purpose is to furnish air-defense warnings and to use air-defense weapons to com¬ bat an enemy. AIRCRAFT CONTROL AND WARNING OFFICER. Member of the battle staff responsible for air surveillance, identification, and control. AIRCRAFT CONTROL AND WARNING SYSTEM. Control and warning system established to con¬ trol and report the movement of aircraft. It con¬ sists of observation facilities (radar and/or vis¬ ual), control centers, and/or filter centers, and the necessary communications. AIRCRAFT DB RATING. Rating, in decibels, assigned to each type air¬ craft to indicate its approximate radar cross sec¬ tion. The ratings are used primarily with the ra¬ dar coverage indicator. AIRCRAFT STATION. Mobile station installed onboard any type air¬ craft and continuously subject to human control. AIRCRAFT TRANSMITTER RELAY RACK. Standard size rack for mounting radio or radar components. AIRDROME. Takeoff and landing area of an air base, with associated runways, hangars, taxi areas, waiting rooms, etc. Does not include maintenance shops. 39-26 1 APRIL 1959 AFM 100-39 AIR AIRFIELD. Any aerodrome other than an airport. AIRFIELD APPROACH AREA. Area extending outward from each end of a landing strip within which no natural, or man made object should project above a predetermined safe angle for ascent or descent of aircraft. AIRGLOW. Light source always in the sky, which comes from atmospheric particles which absorb solar energy during the day and radiate it back to earth at night. AIRHEAD. 1. Designated area in a hostile or threatened country which, when seized and held, ensures the continuous air landing of troops and mater¬ ial and provides maneuver space necessary for projected operations. It is normally the area seized in the assault phase of an airborne opera¬ tion. 2. Designated location in an area of operations used as a base for supply and evacuation by air. AIRMAN’S GUIDE. Directory of airports, radio facility data, and notices to airmen published by the civil aeronau¬ tics administration. AIROPNET (AIR OPERATIONS NETWORK). AIRPLANE DIAL. Round radio receiver dial over which a pointer rotates to indicate the frequency of the station being received. AIRPLANE INSULATOR. Insulator used particularly for radio antennas on aircraft. AIRPORT. Any aerodrome at which facilities available to the public are provided for the shelter, servicing or repair of aircraft, and for receiving or dis¬ charging passengers or cargo. AIRPORT BEACON. Beacon (light or radio) located at or near an airport for the purpose of indicating the location of the airport. AIRPORT CONTROL STATION. Furnishes communications limited to actual avia¬ tion needs between an airport control tower and aircraft in the immediate vicinity. AIRPORT RADAR CONTROL. Surveillance radar portion of radar approach control engaged in pick-up, holding, pattern, etc., operations. AIRPORT RUNWAY BEACON. Radio-range beacon that defines one or more approaches to an airport. AIRPORT SURFACE DETECTION EQUIPMENT. Short-distance radar having high resolution and discrimination. It provides, in graphic or pic¬ torial form, for use by traffic control personnel: (a) plan position indication of the airport sur¬ face with the location of runways, taxiways, and ramps clearly defined, and (b) presentation of all aircraft, vehicular, and other traffic, both moving or stationary. AIRPORT SURVEILLANCE RADAR. Radar located on or near an airport to provide an indication of the bearing and distance of each aircraft within the terminal area in which the airport is located. It is employed to vector and give navigational guidance to arriving and de¬ parting aircraft, in the control of air traffic, within the terminal .area; it does not provide data regarding the elevation of aircraft. AIRPORT TRAFFIC CONTROL TOWER. Facility established to provide adequate supervi¬ sion of air traffic within an airport control sector by means of radio, lights, or other signals. AIRSPACE WARNING AREA. Same as danger area but located more than three miles beyond the United States coast line. AIRSTORDEPT (AIR STORAGE DEPOT). Canadian Navy and RCAF abbreviation for air storage depot. Abbreviation will be followed by identifying location. 39-27 AFM 100-39 AIR 1 APRIL 1959 AIRWAY. Control area or portion thereof, established in the form of a corridor equipped with radio navi¬ gational aids. AIRWAY BEACON. Beacon, other than an airport beacon, located on or near an airway, and used for the purpose of indicating the location of the airway. / AIRWAYS AND AIR COMMUNICATIONS SERVICE. 1. Service under the Military Air Transport Serv¬ ice providing point-to-point and ground-to-air communication along airways and air routes. 2. Service under the Military Air Transport Serv¬ ice providing military air traffic control and other communication facilities as may be author¬ ized by the chief of staff. AIRWAYS MODERNIZATION BOARD. Board established for the development on a long-range, full-scale research and development program designed to alleviate the nation’s seri¬ ous air-traffic problems. AIRWAYS STATION. Ground communication installation, established, manned, and equipped to communicate with air¬ craft in flight as well as with other designated airways installations for the purpose of expedi¬ tious and safe movement of aircraft. AJ (ANTIJAMMING). 1. Art of minimizing the effect of enemy elec¬ tronic countermeasures to permit the echoes from targets detected by the radar to be visible on the indicator. 2. Controls or circuit features incorporated to minimize jamming. AJAX. Frequency dispersal radar. AL. International Telecommunications Union desig¬ nation for Aeronautical Radionavigation Land Station. ALAMA. General message originated by the commander, Air Materiel Command, to subordinate units. ALARM. Device such as a lamp, bell, horn or buzzer, or combination of these elements, arranged to call attention to some unusual condition. BATTERY. Signal calling attention to an ab¬ normal power supply condition. CONTACTOR. Signal calling attention to low¬ ered pressure in a cable gas pressure system. CRASH. Relay circuit which functions to con¬ nect the telephones of all emergency services, such as fire department, ambulance, and other personnel affected, from a central location. OFFICE. Signal calling attention to a total or partial failure, or other abnormal condition, in an office. ALASKAN AIR COMMAND. Air Force major air command with the mission of organizing and conducting the air defense of Alaska. ALCOAST. General message originated by the Chief of Naval Operations, promulgating communication information. ALCOMLANT. General message originated by the Chief of Naval Operations as a subdivision of the AL- COM series for the Atlantic and Mediterranean areas. ALCOMPAC. General message originated by the Chief of Naval Operations as a subdivision of the AL- COM series for the pacific areas. ALDIST. General message originated by the Commandant, United States Coast Guard, to provide instruc¬ tions or information of limited applicability, pri¬ marily to district commanders. ALERT. 1. Readiness for action, defense, or protection. 1 APRIL 1959 AFM 100-39 ALE 2. Warning signal of a real or threatened dan¬ ger, such as an air attack. 3. Period of time during which troops stand by in response to an alarm. 4. To forewarn; to ready for action. ALERTING SERVICE. Service provided to notify appropriate organiza¬ tions regarding aircraft in need of search and rescue aid, and assist such organizations as re¬ quired. ALEUTIAN ISLANDS. Chain of islands southwest of Alaska. ALEXANDERSON ALTERNATOR. Mechanical ac generator used in the early days of radio to generate energy. ALFINAF. General message originated by Commander, Air Force Finance Center. ALIGN. 1. Adjust circuits to resonate at a given fre¬ quency. 2. Position objects so that they are all in a straight line. ALIGNING TOOL. Small screw driver, socket wrench, or special tools, constructed partly or entirely of nonmag¬ netic materials, used to align radio ^circuits. ALIGNMENT. 1. Process of adjusting the tuned circuits of a receiver to a given frequency. 2. Process of adjusting two or more components of a system so that their functions are properly synchronized. ALIGNMENT CHART. Chart or diagram on which equations can be solved graphically by placing a straightedge on the two known values and reading the answer where the straight edge crosses the scale for the unknown value. ALIGNMENT PIN. Pin in the center of the base of an octal, loktal, or other tube having a single vertical projecting rib that aids in correctly inserting the tube in its socket. ALIVE. Electrically connected to a source of potential difference, or electrically charged so as to have a potential different from that of the earth. ALJAP. General message originated by the United States joint communications-electronics committee, nor¬ mally containing corrections to or instructions regarding publications published by that com¬ mittee. ALKALINE BATTERY. Secondary cell or battery using an alkaline so¬ lution as the electrolyte. ALL-METAL TUBE. Vacuum tube having a metal envelope, with elec¬ trode leads passing through glass beads fused into the metal housing. ALL-PASS NETWORK. Network designed to introduce phase shift or delay without introducing appreciable attenua¬ tion at any frequency. ALL-PASS TRANSDUCER. Transducer, of which the attenuation constant is practically zero for all frequencies from zero to infinity. ALL-RELAY CENTRAL OFFICE. Automatic dial switchboard, in a central office, using relay circuits only to make line intercon¬ nections. ALL-RELAY DIAL SYSTEM. Telephone system using relays only. ALL-RELAY EXCHANGE. Exchange where all switching is done by relay equipment. ALL-RELAY SYSTEM. Automatic telephone switching system in which 39-29 1 APRIL 1959 AFM 100-39 ALL all switching functions are accomplished by re¬ lays. AIL-WAVE ANTENNA. Receiving antenna that responds to a wide range of frequencies. ALL-WAVE OSCILLATOR. {Reference: ALL- WAVE SIGNAL GENERATOR.) ALL-WAVE SIGNAL GENERATOR. Test instrument capable of genera n g an un¬ modulated or tone-modulated radio-frequency signal at any frequency needed for aligning or servicing radio receivers and amp* lets. ALL-WEATHER. . Usable or serviceable under any conditions of weather or visibility. ALLANTFLT. General message originated by the Commander- in-Chief, United States Atlantic Fleet. ALLIED COMMUNICATION PUBLICATION. Agreed communications publication prepared in conjunction with other nations. It is approved for United States and allied use by members of the United States joint comtnunications-elec- tronics committee. ACP s are published to provide communications-electronics instructions and pro¬ cedures that have allied as well as joint applica¬ tion and may also be authorized by each of the United States services for intra-service use. ALLIED HEADQUARTERS. Allied Headquarters or SHAPE and those estab¬ lished by SHARPE that are international in char¬ acter. ALLEN SCREW. Screw having a hexagonal hole or socket in the head. ALLEN WRENCH. Wrench, consisting essentially of a hexagonal rod, used to turn an alien screw. ALLIGATOR CLIP. Long, narrow spring clip with meshing jaws, primarily used with test leads for temporary con¬ nections. ALLOCATED CHANNELS. AIRCOM complex channel assigned to a specific user. ALLOCATED-USE CURCUIT. Circuit in which one or more channels have been allocated for the exclusive use of one or more services by a proprietary service; it may be uni¬ lateral or joint circuit. ALLOCHROMATIC. Term used to characterize crystals which have photoconductivity because of dispersed micro¬ scopic or submicroscopic particles occurring natur¬ ally or as a result of exposure to certain radia¬ tions. ALLOTROPHY. Existence of more than one form of an element due to differences in the arrangement of atoms or molecules. ALLOTTER. Distributor, associated with the finder control group relay assembly, which allots an idle line- finder in preparation for an additional call. ALLOTTER RELAY. Relay of the linefinder circuit whose function is to preallot an idle linefinder to the next incom¬ ing call from the line, and to guard relays. ALLOWANCE. Copies of a publication authorized in the allow¬ ance tables for automatic distribution to a com¬ mand or activity. ALLOY. Mixture or combination of two or more metals. ALLMAJCOM. General message originated by Headquarters, USAF, addressed to all major air force com¬ mands. ALMAR. General message originated by the commandant, Marine Corps, as the equivalent of ALNAV, NAVOP, but applying to Marine Corps only. 1 APRIL 1959 AFM 100-39 ALM ALMATS. General message originated by Commander, Mil¬ itary Air Transport Service, to Military Air Transport Service subordinate units. ALNAV. General message originated by the Secretary of the Navy, normally concerning the functions of the naval establishment, including Marine Corps. ALNAVSTA. General message originated by the Secretary of the Navy, similar to ALNAV in content, which requires wide dissemination to shore establish ments of the Navy and Marine Corps, including shore based elements of the operating forces. ALNEAC. General message originated by Commander, Northeast Air Command, to subordinate units. ALNICO. Alloy consisting chiefly of aluminum, nickel, and cobalt, with high retentivity; it is used to make small, powerful permanent magnets. ALO (AIR LIAISON OFFICER). Experienced pilot who is familar with operational procedures and the capabilities and limitations of air power. An air liaison officer is provided for each corps, and division headquarters fur¬ nished tactical air support. The air liaison officer is responsible for technical assistance to the ground staff in formulating requirements for air support and provides continuous guidance on air matters. He is a direct representative of the tactical air force commander. ALPACFLT. General message originated by the Commander- in-Chief, United States Pacific Fleet. ALPHA. Greek letter a. Often used to designate angles, or quantities. ALPHA, BETA, GAMMA-FORM OR STAGE. Terms used to distinguish the different modifi¬ cations of an element; for example, these stages of iron depend upon its temperature, and only the alpha iron is highly magnetic. ALPHA, BETA, GAMMA-LINES. Lines of a spectral series, arranged in the order of increasing frequency. ALPHA PARTICLE. Positively charged particle ejected by many ra¬ dioactive substances; actually the nucleus of a helium atom. ALPHA QUARTZ. Name given to the low-temperature modification of silica. ALPHA RAYS. Rays of alpha particles emitted from certain types of radioactive elements. They are slightly de¬ flected by a magnetic field and are powerful ionizers. ALPHA-RAY SPECTRUM. Separation of alpha particles of different speeds, usually by a magnetic field, but in some cases by both magnetic and electric fields. ALPHABET FLAGS. Flags used on an international basis in visual communications to represent the letters of the alphabet. ALPHABET STRIP. Strip containing one mixed alphabet, repeated. ALRAD. General message originated by Commander, Air Research and Development Command, to subor¬ dinate units. ALSTACON. General message originated by the Secretary of the Navy, containing administrative information requiring wide dissemination to all stations with¬ in the ConUS. ALSTAOUT. General message originated by the Secretary of the Navy, containing administrative information 39-31 AFM 100-39 ALS 1 APRIL 1959 requiring wide dissemination to all stations out¬ side the ConUS. ALSTAT. General message originated by the Director of Statistical Services, Headquarters, USAF, to all major air force commands. ALSTATCON. General message originated by the Director of Statistical services, Headquarters, USAF, to all major air force commands in the ConUS. ALTERNATE AIRPORT. Airport specified in a flight plan, to which a flight may proceed when a landing at the in¬ tended point becomes inadvisable. ALTERNATE CHANNEL. Channel, two channels above or below the ref¬ erence channel. ALTERNATE FREQUENCY. Frequency assigned for use at a certain time, or for a certain purpose, to replace or supplement the frequency normally used. ALTERNATING CURRENT. 1. Term applied to electronic equipment indicat¬ ing it is capable of operation from an ac power source only. 2. Current that is continually changing in mag¬ nitude and reversing in polarity. ALTERNATING CURRENT GENERATOR. 1. Rotating electrical machine, generally known as an alternator, that converts mechanical power into alternating current. 2. Vacuum-tube oscillator, or any other device, designed for the purpose of producing alternat¬ ing current. ALTERNATING CURRENT PLATE RESISTANCE. Internal resistance of a tube to the flow of alter¬ nating current. It is the ratio of a small change in plate voltage to the resulting change in plate current, with other voltages constant, expressed in ohms. ALTERNATING CURRENT PULSE. Alternating current wave of brief duration. ALTERNATING CURRENT RECEIVER. Radio receiver designed to operate only from an ac source. ALTERNATING CURRENT RESISTANCE. 1. Internal resistance to the flow of alternating current between the cathode and plate of a tube. It is equal to a small change in plate voltage divided by the corresponding change in plate current, and is expressed in ohms. 2. Total resistance offered by a device in an ac circuit. ALTERNATING CURRENT/DIRECT CURRENT. Term applied to electronic equipment indicating it is capable of operation from either an ac or dc primary power source. ALTERNATING CURRENT/DIRECT CURRENT RECEIVER. Radio receiver usually consisting of a few tubes and small power consumption, designed to op¬ erate directly from either an ac or dc source. ALTERNATING CURRENT/DIRECT CURRENT RINGING. Method of telephone ringing which utilizes ac and dc components; alternating current to operate a ringer, direct current to aid the action of a relay which stops the ringing when the called party answers. ALTERNATING GRID VOLTAGE. Ac component of grid voltage. ALTERNATING OR AC (ALTERNATING CURRENT) COMPONENT OF CURRENT. That portion of a pulsating current represented by the changing rate and/or direction of electron flow; that is, in the absence of the dc compo¬ nent, the average electron displacement is zero. ALTERNATING OR AC (ALTERNATING CURRENT) COMPONENT OF VOLTAGE. That portion of a pulsating voltage which is responsible for the non-uniform electron flow in a conductor to which the pulsating voltage is applied; if the pulsating voltage reverses its 1 APRIL 1959 AFM 100-39 ALT polarity, the ac component is responsible for the reversals of the direction of electron flow as well as for the changes in the rate of flow. ALTERNATING QUANTITY. Periodic quantity, the average value of which is zero over a complete cycle. ALTERNATING VOLTAGE. Voltage developed across a resistance or impe¬ dance through which alternating current is flow¬ ing. This voltage is continually varying in value and reversing its polarity at regular intervals. ALTERNATION. Variation, either positive or negative, of a wave form from zero to maximum and back to zero (equals one-half of a cycle). COLOR PHASE. Periodic changing of color phase of one or more components of the color television subcarrier between two sets of as¬ signed values. ALTERNATIVE FREQUENCY. Frequency or group of frequencies which may be assigned for use on channel, or on a par¬ ticular channel, at a certain time or for a certain purpose to replace or supplement the frequen¬ cies normally used on that channel. ALTERNATIVES, UK (UNITED KINGDOM) JOINT. Two or more cipher or code symbols which have the same plain language equivalent. * ALTERNATOR. Rotating machine which generates alternating current. (Reference: ALTERNATING CUR¬ RENT GENERATOR.) ALTERNATOR TRANSMITTER. Radio transmitter which utilizes power gener¬ ated by a radio-frequency alternator. ALTIMETER. Instrument that indicates the elevation of an air¬ craft with respect to a specific reference level. The reference level may be sea level or the ter¬ rain beneath the aircraft. ALTIMETER STATION. Radio-navigation mobile station in the aeronau¬ tical radio-navigation service, the emissions of which are intended to determine the altitude of aircraft aboard which the altimeter station is lo¬ cated above the earth’s surface. ALTITUDE. True height above sea level; the indicated alti¬ tude corrected for air temperature and barome¬ tric pressure. ALTITUDE DELAY. Synchronization delay introduced between the time of transmission of the radar pulse and the start of the trace on the indicator, for the pur¬ pose of eliminating the altitude hole on the PPI-type display. ALUMINUM. Lightweight silvery white metal used extensively in radio for plates of capacitors, housings, and shielding purposes. ALUMINUM BASE. Aluminum disk on which a lacquer or other coat¬ ing is applied in some types of recording disks. ALUMINUM FOIL. Radio reflector which returns a relatively strong radar echo in proportion to its size. Its effec¬ tiveness is increased when the strips are cut to one-half the radar’s wave length. ALUTS (ALEUTIAN ISLANDS). Chain of islands southwest of Alaska. ALZICOM. General message originated by Headquarters, USAF, addressed to major air force commands within the ConUS. AM (AMPLITUDE MODULATION). 1. Process of superimposing intelligence on a radio-frequency carrier so that the audio-frequen¬ cy variations are superimposed upon the ampli¬ tude of the high-frequency wave. 2. Method of modulating a carrier wave to cause it to vary in amplitude corresponding to the am¬ plitude of the original signal. 39-33 AFM 100-39 AMA 1 APRIL 1959 AMA (AIR MATERIEL AREA). 1. One of the several areas set up by the Air Materiel Command for expediting Air Force maintenance and the supply of Air Force organi¬ zations and installations within those areas. 2. Organization that operates any one of these areas under the Air Materiel Command, com¬ parable in echelon to a numbered air force. AMA (AUTOMATIC MESSAGE ACCOUNTING) SYSTEM. Arrangement of apparatus for recording and processing on continuous tapes the data required for computing telephone charges on certain classes of calls. The system may include provi¬ sion for compiling all charges and credits which affect the customer’s bill and for automatic printing of the bill. AMAS (AMERICAN MILITARY ASSISTANCE STAFF). AMATEUR. Person who operates and experiments with transmitters, receivers, or other electronic equip¬ ment as a hobby and not for profit. AMATEUR BANDS. Bands of frequencies assigned exclusively to radio amateurs. AMATEUR OPERATOR. Person holding a license, issued by the FCC authorizing that person to operate an amateur radio station. AMATEUR PORTABLE STATION. Amateur station that may conveniently be moved about from place to place, but is not operated while in motion. AMATEUR PORTABLE-MOBILE STATION. Amateur station that may be conveniently trans¬ ferred to or from a mobile unit and is ordinarily used while such mobile unit is in motion. AMATEUR RADIO COMMUNICATION. Radio communication between amateur stations solely with a personal aim and without pecuniary interest. AMATEUR SERVICE. Service of self training, intercommunication, and technical investigations carried on by ama¬ teurs, that is, by duly authorized persons interest¬ ed in radio technique solely with a personal aim, and without pecuniary interest. AMATEUR STATION. 1. Radio station owned and operated by an ama¬ teur for personal two-way communication with other amateurs, and licensed accordingly by the FCC or by corresponding authorities in other countries. 2. Station in the amateur service. AMATEUR STATION CALL LETTERS. Group of letters and numbers assigned to a li¬ censed amateur for identification purposes. United States amateur calls begin with W or K, followed by a location-indicating numeral and two or more additional letters. AMB (AIRWAYS MODERNIZATION BOARD). Board established for the development on a long-range, full-scale research and development program designed to alleviate the nation’s seri¬ ous air-traffic problems. AMBER. Yellowish or reddish-brown translucent fossil resin having excellent insulating qualities. AMBIENT. Encompassing on all sides. Ambient temperature means average or mean surrounding tempera¬ ture; ambient noise level means average or mean surrounding noise level. AMBIENT NOISE. Acoustic noise existing in a room or other loca¬ tion; magnitudes are usually measured with a sound level meter. AMBIENT TEMPERATURE. Temperature of the surrounding medium, such as gas or liquid. AMBIGUITY. In navigation, the condition which is obtained when navigation coordinates define more than 39-34 1 APRIL 1959 AFM 100-39 AMC one point, direction, line of position, or surface of position. AMC (AIR MATERIEL COMMAND). Major air command of the Air Force that pro¬ vides logistic support to the United States Air Force. AMD (AIR MOVEMENT DATA). Flight plan data used in reckoning aircraft move¬ ment. The data may be presented in either a situation or digital display. Correlated Air-Movement Data: Air-movement data which has been associated with a track. Uncorrelated Air-Movement Data: Air-move¬ ment data which has not been associated with a track. AMERICAN MORSE CODE. System of dot and dash signals, invented by Samual F.B. Morse, now used to a limited extent for wire telegraphy in North America. It differs considerably from the International Morse code used in radio, having a different spacing method and some entirely different letter codes. AMERICAN RADIO RELAY LEAGUE. Publisher of the monthly magazine QST and is the largest amateur radio organization in the world. AMERICIUM. Element 95. Made synthetically from uranium and plutonium by bombarding U238 and PU239 with 40,000,000 electron volt helium ions. AMES (AIR MINISTRY EXPERIMENTAL STATION). British ground radar station in an early-warning system. AMG (ALLIED MILITARY GOVERNMENT OF OCCUPIED TERRITORY). AMIK (AMERICAN MISSION IN KOREA). AMIS (AIR MOVEMENTS INFORMATION SECTION). Unit of the civil aeronautics administration which provides flight-plan information to the identifi¬ cation branch of a three on center. Such infor¬ mation pertains to i: endly airborne objects which are, or will be, operating in the organiza tion’s area. AMMETER Instrument used for measuring the amount of current in amperes. AMMO (AMMUNITION). 1. Generic term for certain composite objects or substances used up or expended, or intended to be used up or expended, in the process of in¬ flicting damage upon the enemy or practice tar¬ get. 2. Cartridge or shell ammunition for guns, as distinguished from bombs, mines, grenades, etc. AMO (AIRCRAFT MATERIEL OFFICER). AMORPHOUS. Devoid of regular structure, especially of crystal¬ line structure. AMP (AMPERE). Practical unit of current. One ampere will flow through a resistance of one ohm when a differ¬ ence of potential of one volt is applied across terminals. AMP-HR (AMPERE-HOUR). Unit quantity of electricity equal to a current of one ampere flowing, for one hour. Multiplying current in amperes by the time of flow in hours gives the AMP-HR. This rating is used chiefly to indicate the amount of energy that a storage battery can deliver before it needs recharging or that a primary battery can deliver before it needs replacing. AMPERAGE. Amount of an electric current in amperes. AMPERE-HOUR. Quantity of electricity that passes through a cir¬ cuit in one hour when the rate of flow is one ampere. AMPERE-HOUR CAPACITY. Number of ampere-hours that can !*e J iivered 39-35 AFM 100-39 AMP 1 APRIL 1959 by a storage battery or other battery under speci¬ fied conditions. AMPERE-HOUR METER. Meter that registers in ampere-hours the quan¬ tity of electricity consumed. AMPERE-TURNS. Product obtained by multiplying the number of turns in a coil by the current in amperes flowing through the coil. AMPERE’S LAW. Magnetic intensity at any point near a current- carrying conductor can be computed on the as¬ sumption that each infinitesimal length of the conductor produces, at the point, an infinitesi¬ mal magnetic density. The resulting magnetic intensity, at the point, is the vector sum of the contributions of all the elements of the conduc¬ tor. AMPH (AMPHIBIAN). Aircraft designed to take off and land on either water or land. AMPHIBIOUS COMMAND SHIP. Naval vessel from which a commander exercises control in amphibious operations. It is designed primarily to fulfill communication requirements for control of surface, sub-surface, and air units engaged in the landing and supporting of land¬ ing forces. It provides planning and supporting facilities such as aerological, photographic, and map reproduction equipment. AMPLIDYNE. Special type dc generator, used as a power am¬ plifier, in which the response of the output volt¬ age to changes in field excitation is very rapid; used extensively in servo systems. AMPLIFICATION. Increase of magnitude in transmission from one point to another. It may be expressed as a ratio or, by extension of the term, in decibels. CURRENT. Ratio of output to input currents of an amplifier or transducer input circuit. POWER. Process of amplifying a signal to pro¬ duce a gain in power, as distinguished from voltage amplification. VOLTAGE. Ratio of the signal voltage across a specific load impedance of a transducer, to the signal voltage across the transducer input. AMPLIFICATION FACTOR. Ratio of a small change in plate voltage to the small change in control-electrode (grid) voltage required to produce the same change in plate current, with all other electrode voltages and currents constant. It is a measure of the effec¬ tiveness of the control-electrode voltage with respect to that of the plate voltage in control¬ ling the plate current. AMPLIFIED BACK BIAS. Degenerative voltage developed across a fast time constant circuit within a stage of an ampli¬ fier and fed back into a preceding stage. AMPLIFIER. Device employing electron tubes or the control¬ led flow of electrons in solid materials (the transistor) for increasing current or voltage. In a radio receiver, this results in louder sound. In the electron tube form, amplification is achieved by using the incoming signal to control a larger amount of power supplied by a battery or other local power source. BALANCED. Amplifier circuit in which there are two identical signal branches connected so as to operate with the inputs in phase opposi¬ tion and with output connections each bal¬ anced to ground. BUFFER. Amplifier designed to isolate a pro¬ ceeding circuit from the effects of a follow¬ ing or preceding circuit. CLASS A. Amplifier in which the grid bias and alternating grid voltages are such that plate current flows at all times. CLASS AB. Amplifier in which the grid bias and alternating grid voltages are such that plate current flows for appreciably more than half but less than the entire electrical cycle. CLASS B. Amplifier in which the grid bias is approximately equal to the cutoff value so that the plate current is approximately zero when no exciting grid voltage is applied, and 39-36 1 APRIL 1959 AFM 100-39 AMP so that plate current flows for approximately one-half of each cycle when an alternating grid voltage is applied. CLASS C. Amplifier in which the grid bias is appreciably greater than the cutoff value so that the plate current in each tube is zero when no alternating grid voltage is applied, and so that plate current flows for appreciably less than one-half of each cycle when an alter¬ nating grid voltage is applied. DIFFERENTIAL. Amplifier having two similar input circuits connected so as to respond to the difference between two voltages or cur¬ rents and effectively suppress voltages or cur¬ rents which are alike in the two input circuits. DIRECT-CURRENT. Amplifier capable of am¬ plifying direct voltages. It generally employs between stages either resistive coupling alone or resistive coupling combined with other forms of coupling. LINE. Amplifier, common to all channels in one direction, used to compensate for line loss. Normally associated directly with the line. MAGNETIC. Device using one or more satura¬ ble reactors, either alone or in combination with other circuit elements, to secure power gain. MODULATED, Amplifier stage of a transmitter, in which the radio-frequency carrier is elec¬ trically varied or modulated in accordance with another signal such as voice, tone, or visual signals. MONITORING. 1 . Amplifier which absorbs a negligible amount of energy from a circuit for monitoring or measuring purposes. 2. Device which, when connected across a cir¬ cuit, absorbs a negligible amount of energy, but reproduces that energy so it can be heard in a receiver or measured. OVERDRIVEN. Amplifier stage which is de¬ signed to distort the input signal waveform by permitting the grid signal to drive the stage beyond cutoff and/or into plate current saturation. POWER. Amplifier designed to produce a gain in signal power, as distinguished from a volt¬ age amplifier. SINGLE-ENDED. Amplifier in which each stage normally employs one tube or, if more than one tube is used, they are connected in parallel so that operation is asymmetric with respect to ground. TUNED RADIO FREQUENCY. Tuned amplifier, using resonant-circuit coupling, designed to operate at radio frequencies. VOLTAGE. Amplifier designed primarily to in¬ crease the voltage of a signal. AMPLITUDE. 1. Maximum displacement from the zero posi¬ tion of an alternating current or any other per¬ iodic phenomenon. 2. Amplitude is commonly used, in a general sense, to indicate the size or magnitude of a wave or current. PEAK. Value of the maximum amplitude, volt¬ age or current of a wave. PULSE. Maximum instantaneous value of a pulse. Note. Spikes and ripples superimposed on the pulse are commonly considered to be separate transients, and are ignored in considering the dimensions of the pulse itself. AMPLITUDE BALANCE. 1. Device for adjusting the operating limits of a differential gain control. 2. Control for balancing the amplitude of sig¬ nals on separate traces. AMPLITUDE DISTORTION. Changing of a wave shape in amplitude so that it is no longer proportional to its original am¬ plitude. This occurs in an amplifier or other de¬ vice when the amplitude of the output is not 39-37 AFM 100-39 AMP 1 APRIL 1959 exactly a linear function of the input amplitude. AMPLITUDE FADING. Fading in which the amplitudes of all frequency components of a modulated carrier wave are uni¬ formly attenuated. AMPLITUDE LIMITER. Circuit or stage that automatically reduces the amplification for signal peaks exceeding a pre¬ determined value. AMPLITUDE MODULATION. 1. Process of superimposing intelligence on a radio-frequency carrier so that the audio-frequen¬ cy variations are superimposed upon the ampli¬ tude of the high-frequency wave. 2. Method of modulating a carrier wave to cause it to vary in amplitude corresponding to the am¬ plitude of the original signal. AMPLITUDE MODULATION NOISE. Noise produced by undesired amplitude varia¬ tions or a radio-frequency signal. AMPLITUDE NOISE. Effect, on radar accuracy, of the flunctuations in the amplitude of the signal returned by the tar¬ get. These fluctuations are caused by any change in aspect if the target is not a point source. AMPLITUDE RESONANCE. Resonance in which any frequency produces a decrease in the amplitude of the oscillation of the system. AMPLITUDE SEPARATOR. Television receiver circuit that separates the con¬ trol impulses from the video signal. AMPLITUDE SUPPRESSION RATIO. Ratio, in frequency modulation, of the unde¬ sired output to the desired output of an FM receiver when the applied signal has simultane¬ ous amplitude modulation and frequency modu¬ lation. This ratio is generally measured with an applied signal that is amplitude modulated 30 percent at a 400 cycle rate and is frequency modulated 30 percent of maximum system devia¬ tion at a 1000 cycle rate. AMPLITUDE-FREQUENCY RESPONSE CHARACTERISTICS. Transmission gain or loss of a device or system as compared to variations in frequency. AMPLITUDE-MODULATED TRANSMITTER. Radio transmitter sending out a constant fre¬ quency signal varying in amplitude. AMPLITUDE-MODULATED WAVE. Constant frequency wave form varying in ampli¬ tude in accordance with the frequency of an im¬ pressed signal. AMPOULE, CARBON MONOXIDE DETECTOR. Thin glass vial which, when broken, releases a liquid which changes color in the presence of carbon monoxide. AMPLR (AMPLIFIER). Device employing electron tubes or the control¬ led flow of electrons in solid materials (the transistor) for increasing current or voltage. In a radio receiver, this results in louder sound. In the electronic tube form, amplification is achiev¬ ed by using the incoming signal to control a larger amount of power supplied by a battery or other local power source. (Reference: CUR¬ RENT AMPLIFIER, POWER AMPLIFIER AND VOLTAGE AMPLIFIER.) ANAGLYPH. Picture, printed or projected in complementary colors, combining the two images of a stero- scopic pair, which gives a steroscopic image when viewed through spectacles having filters of cor¬ responding complementary colors. ANALOG. Physical system, used in electronic computers, on which the performance of measurements yields information concerning a class of mathe¬ matical problems. ANALOG COMPUTER. Physical system, used in electronic computers, together with means of control for the perform¬ ance of measurements (upon the system) which 39-38 1 APRIL 1959 AFM 100-39 ANA yields information concerning a class of mathe¬ matical problems. ANALYZER. Name given to the second nicol in a polariscope, which in a sense, analyzes the light from the polarizing nicol and intervening crystal section. ANASTIGMAT. Compound lens corrected for astigmatism. ANASTIGMATIC. Free from astigmatism. Usually refers to com¬ pound photographic lenses where the astigma¬ tism of one lens is nullified by the opposite astig¬ matism of the other. ANASTIGMATIC LENS. Lens corrected for astigmatism and curvature of field. ANCHOR. 1. Fastening arranged to prevent movement. For example, a guy wire is fastened to an anchor in the earth. 2. Expansion shield which may be used with a screw or bolt to attach equipment to a concrete or tile surface. EXPANDING. Earth-fastening device with ex¬ panding blades. LOG. Anchor made of a log, split log, or two split logs crossed. SCREW-IN. Spiral or screw-shaped anchor. ' ANCR (AIRCRAFT NOT COMBAT READY). AND-CIRCUIT. Synonym for AND-GATE in an electronic com¬ puter. AND-GATE. 1. Gate, in an electronic computer, whose out¬ put is energized when every input is in its pre¬ scribed state. 2. Electronic circuit, used in astronautics, whose output is energized only when every input is energized. ANDB (AIR NAVIGATION DEVELOPMENT BOARD). Board, reporting to the Department of Com¬ merce through the Civil Aeronautics Administra¬ tion, which was organized to develop a nation¬ wide air-navigation system to serve the needs of civil aviation and tactical military aviation, and capable of effective integration into any air- defense system established by the Department of Defense. This board was disbanded in 1958. ANEMOGRAM. Record traces by a self-registering anemometer. ANEMOMETER. Instrument for measuring the force or speed of the wind. ANEMOSCOPE. Instrument for indicating the existence of wind and showing its direction. ANEROID BAROMETER. Barometer, the operation of which depends upon changes in the shape of an evacuated, hollow, corrugated metal container caused by changes in air pressure. ANEROIDOGRAPH. Aneroid barometer with a mechanism for record¬ ing automatically and continuously the atmos¬ pheric pressure. ANFE (AIRCRAFT NOT FULLY EQUIPPED). ANG (AIR NATIONAL GUARD). Military force, comprising those units and per¬ sonnel organized and partially maintained by the several states, territories, or District of Columbia, for which certain federal responsibility is vested in the Department of the Air Force, and which, while in the service of the United States, consti¬ tutes a component of the United States Air Force. ANGLE. An angle is formed when two straight lines meet. The lines are called the sides of the angle, and the intersection is called the vertex. An acute angle is less than 90°, a right angle is 90°, and an obtuse angle is greater than 90°. AFM 100-39 1 APRIL 1959 ANG BREWSTER. Angle of incidence at which a vertically polarized wave (a wave polarized in the plane of incidence) undergoes a phase shift of 90° on reflection from the surface. CRAB. Angle through which an aircraft is turned into the wind in an attempt to correct for drift. If this angle eliminates the drift and the aircraft thus makes good its desired course, then the crab angle is also the drift correction angle. DRIFT. Horizontal angle between the longitu- diual axis of an aircraft and its path relative to the ground. DRIFT CORRECTION. Angular difference be¬ tween the desired course arid the heading. REFERENCE. Angle formed between the cen¬ ter line of a radar beam as it strikes a reflect¬ ing surface and the perpendicular drawn to that reflecting surface. SLOPE. Direction of a flight path expressed as an angle projected in the vertical plane. STATION. Angle formed between lines drawn from the target to each of two shoran ground stations. ANGLE COMPONENT SOLVER. Machine which resolves an electrical vector into its components. ANGLE MODULATION. Modulation in which the angular velocity of a sine wave carrier is the characteristic subject to variation. Phase and frequency modulation are particular forms of angle modulation. ANGLE NOISE. Tracking error introduced into radar by varia¬ tions in the apparent angle of arrival of the echo from a target due to finite target size. This effect is caused by variations in the phase front of the radiation from a multiple point target as the target changes its aspect with respect to the observer. ANGLE OF ARRIVAL. Angle made between the surface of the earth and the line of propagation of a radio wave arriving at a receiving antenna. ANGLE OF AZIMUTH. Angle measured clockwise in a horizontal plane, usually from the north. The north used may be true north, Y-north, or magnetic north. ANGLE OF BEAM. Angle which incloses the greater part of the energy transmitted from a directional antenna system. ANGLE OF CONVERGENCE. Angle formed by the lines of sight of both eyes in focusing on any line, corner, surface, or part of an object. ANGLE OF DEPARTURE. Angle of the line of propagation of a radio wave with respect to a horizontal plane at the trans¬ mitting antenna. ANGLE OF DEPRESSION. Angle measured at the observer between the horizontal plane and a point below that plane. ANGLE OF DEVIATION. Angle through which a ray of light is bent by a refracting surface; the angle between the sub¬ tended path of an incident ray and the refracted ray. ANGLE OF ELEVATION. Angle measured at the observer between the horizontal plane and a point above that plane. ANGLE OF GROOVE. Angle from wall to wall of an unmodulated groove in a radial plane perpendicular to the surface of a recording disk. ANGLE OF INCIDENCE. Angle between the perpendicular to a reflecting surface at the point at which an electro-magnetic wave strikes a surface and the direction from which the wave approaches the surface. A wave perpendicular to a surface has a zero angle of incidence. ANGLE OF LAG. Angle by which one alternating electrical quan¬ tity lags another of the same cyclic period. 39-40 1 APRIL 1959 AFM 100-39 ANG ANGLE OF LEAD. 1. Time by which one alternating electrical quan¬ tity leads another of the same cyclic period. It is measured as angular velocity and referred to as the angle of lead. 2. Angle through which the commutator brushes of a generator or motor must be moved from the normal position to prevent sparking. ANGLE OF RADIATION. Angle between the surface of the earth and the center of the beam of energy radiated upward into the sky from a transmitting antenna. ANGLE OF REFRACTION. 1. Angle between the perpendicular to a surface separating two different media (at the point at which an electro-magnetic wave passes from the first medium to the second) and the direction which the wave takes in the second medium. 2. Angle measured between a wave, ray, or beam refracted from a surface and the perpendicular to the surface. ANGLE OF SITE. Vertical angle between the horizontal and the line of site (line from gun to target). ANGLE TRACKING NOISE. Any deviation of the tracking axis from the cen¬ ter of reflectivity of a target. It is the resultant of servo noise, receiver noise, angle noise, and arriplitude noise. ANGSTROM UNIT. Unit of measurement of the wave length of light and other radiation, equal to one ten-mil¬ lionth millimeter, which is 10- 8 centimeter; ANGULAR CALIBRATION CONSTANTS. Interior orientation, in a multiple lens camera, of the plate perpendiculars of the several lens- camera units to a common origin of direction. ANGULAR DISTANCE. Distance expressed in radians or equivalent an¬ gular measure. It is equal to 2 radians or 360°, multiplied by the distance in wave lengths. ANGULAR FREQUENCY. Frequency expressed in radians per unit of time. (Reference: RADIAN FREQUENCY.) ANGULAR LENGTH. Length expressed in radians or equivalent angu¬ lar measure equal to 2 radians or 360°, multi¬ plied by the length in wave lengths. ANGULAR PARALLAX. (Reference: PARALLAX.) ANGULAR PARALLAX DIFFERENCE. (Reference: PARALLAX.) ANGULAR PHASE DIFFERENCE. Angular phase difference between two periodic quantities which have the same period is 2 ra¬ dians (360°) times the phase difference in cycles. ANGULAR RATE. Rate of change of bearing. ANGULAR VELOCITY. Rate of change of angle. The angular velocity of a periodic quantity, expressed in radians per second is the frequency multiplied by two. If the periodic quantity can be considered as result¬ ing from the uniform rotation of a vector, the angular velocity is the number of radians per second passed over by the rotating vector. ANGUS PEN RECORDER. Instrument designed to aid in traffic studies by recording permanently the actual amount of time a channel is being utilized for traffic, its maximum capability is 20 channel coverage. ANISTROPIC. Exhibiting different properties when tested along axes in different directions. ANL (AUTOMATIC NOISE LIMITER). Vacuum tube circuit that automatically cuts off all noise peaks that are stronger than the high¬ est peak in the desired signal being received, thereby preventing loud crashing noises due to strong atmospheric or manmade interference. ANNEALING. Heating of metal or alloy followed by slow cool- 39-41 AFM 100-39 1 APRIL 1959 ANN ing, generally resulting in a lowering of tensile strength with a corresponding improvement in ductility. ANNEX. Addition to a basic publication, which becomes an integral part of the publication in which entered. ANNOUNCEMENT SYSTEM. General arrangement for supplying information by means of periodic announcements distributed to the various locations over one-way distribution circuits. It is used for time of day, weather, etc. ANNULAR. Ring-shaped. ANNUNCIATOR. Visual signaling device, operated by relays, which indicates conditions of associated circuits. ANODE. 1. Positive electrode; the plate of a vacuum tube; the positive pole of a tube toward which the electrons move. 2. Positive electrode of an electro-chemical de¬ vice (such as a primary or secondary electric cell) toward which the negative ions are drawn. MAGNESIUM. Bar of magnesium, buried in the earth, connected to an underground cable to prevent cable corrosion due to electrolysis. Forms a battery and keeps the sheath poten¬ tial positive. Used in areas where electrolytic action deteriorates the cable sheaths. ANODE BALANCING COIL. Set of mutually coupled windings used to main¬ tain approximately equal currents in anodes op¬ erating in parallel from the same transformer terminal. ANODE CURRENT. Current flowing in the anode (plate) circuit. ANODE POWER SUPPLY. Means for supplying power to the plate elec¬ trode of a vacuum tube at a properly regulated voltage; usually positive with respect to the cathode. ANODE VOLTAGE. Voltage between the anode and the cathode. ANODE-RAY CURRENT. Current in a varified gas made up of the move¬ ment of positively charged particles, which have their origin in the anode and are of atomic dimensions. ANODIZE. To place a protective film on a metal object by electrolytic action. ANOIN. One of the negative ions that moves toward the anode in a discharge tube, electrolytic cell, or similar apparatus. ANOMALOUS PROPAGATION. Type of radio wave propagation in which radi¬ ated rays are bent excessively by refraction in the lower layers of the atmosphere. This bending creates an effect much as if a duct or waveguide had been found in the atmosphere. The duct, which may be either elevated or ground based, is able to guide part of the radiated energy over distances far beyond the normal range. (Refer¬ ence: ABNORMAL PROPAGATION, TRAP¬ PING.) ANOMALY. Difference between the mean of any meteorologi¬ cal element, or phase of that element, over a given time at a particular place, and the mean of the same element or phase over the same time for all other points on the same parallel of lati¬ tude. ANS (ANSWER). Transmission made by the station called in response to the call received. ANSWER LAMP. Telephone switchboard lamp which lights when an answer cord is plugged into a line jack; goes out when the called telephone answers, and lights when the call is completed. ANSWERING PLUG AND CORD. Plug and cord, in telephone communication, 39-42 1 APRIL 1959 AFM 100-39 ANT used to answer a calling line. ANT. (ANTENNA). ANTENNA. Anything that projects om co pick up sound or electric vibrations; specifically that part of a radar or of a radio-sending or radio-receiving set that projects into the air and contains, or itself consists of, that apparatus that radiates waves or receives them. ADCOCK. Pair of vertical antennas separated by a distance of one-half wave length or less, and connected in phase opposition to produce a directional pattern having the shape of a figure eight. ALL-WAVE. Receiving antenna that responds to a wide range of frequencies. ARTIFICIAL. Device which simulates a real antenna in its essential impedance characteris¬ tics and has the necessary power handling capabilities, but does not radiate or receive radio waves. BASE-LOADED. Vertical antenna, having an inductance in series at the base for loading the antenna to secure a desired electrical length. BEAM. Antenna that concentrates its radiation into a narrow beam in a definite direction. BEVERAGE. Directional antenna consisting of a very long wire, supported a few feet (up to 15) above the ground, running horizon- ally in the direction of the arrival of the in¬ coming waves. BICONICAL. Antenna formed by two conical conductors having a common axis and vertex, excited at the vertex. When the vertex angle of one of the cones is 180°, the antenna is called a discone. BIDIRECTIONAL. Antenna having two direc¬ tions of maximum response. CHEESE. Cylindrical parabolic reflector en¬ closed by two plates, perpendicular to the cylinder, so spaced as to permit the propaga¬ tion of more than one mode in the desired direction of polarization. COAXIAL. Antenna comprised of a quarter- wavelength extension to the inner conductor of a coaxial line and a quarter-wave-length radiating sleeve which closely surrounds the outer conductor of the coaxial line, but is con¬ nected to the outer conductor only at its end. CORNER-REFLECTOR. Antenna consisting of a primary radiating element and dihedral cor¬ ner reflector. COSECANT-SQUARED. Shaped-beam antenna in which the radiation intensity over a part of its pattern in some specified plane (usually the vertical) is proportional to the square of the cosecant of the angle measured from a specified direction in that plane (usually the horizontal). Its purpose is to lay down a uni¬ form field along a line which is parallel to the specified direction, but which does not pass through the antenna. DIELECTRIC. Antenna which employs dielec¬ tric as the major component in producing the required radiation. DIPOLE. Straight radiator, usually fed in the center, and producing a maximum of radiation in the plane normal to its axis. DIRECTIONAL. Antenna which radiates or re¬ ceives radio waves more effectively in some directions than others. The term is usually applied to antennas whose directivity is larger than that of half-wave dipole. DOUBLET. Antenna consisting of two elevated conductors substantially in the same straight line and of substantially equal length, with the power delivered at the center. FANNED-BEAM. Unidirectional antenna so designed that transverse cross-sections of the major lobe are approximately elliptical. FISHBONE. Antenna consisting of a series of coplanar elements arranged in coiinear pairs, loosely coupled to a balanced transmission line. 39-43 AFM 100-39 ANT 1 APRIL 1959 FOLDED DIPOLE. Primary radiating element consisting of two parallel dipoles, separated by a small fraction of the wave length, con¬ nected together at their outer ends, and fed at the center of one dipole. HERTZ. Antenna system which does not de¬ pend, for its operation, upon the presence of ground. Its resonant frequency depends upon its distributed capacitance and inductance, which are determined by its physical length. (Reference: MARCONI ANTENNA.) HORN. Antenna having the shape of a tube whose cross-sectional area increases toward the open end, and through which radio waves pass. IMAGE. Imaginary counterpart of an actual antenna, assumed for mathematical purposes to be located below the surface of the ground, and symmetrical with the actual antenna above ground. ISOTROPIC. Hypothetical antenna radiating or receiving equally in all directions. In the case of electro-magnetic waves, isotropic anten¬ nas do not exist physically but represent con¬ venient reference antennas for expressing directional properties of actual antennas. J. Antenna having a configuration resembling a J, comprising a half-wave antenna end-fed by a parallel wire quarter-wave section. LONG WIRE. Linear antenna which, by virtue of its considerable length in comparison with the operating wavelength, provides a direc¬ tional pattern. LOOP. Antenna consisting of one or more com¬ plete turns of conductor, designed for direc¬ tional transmission or reception. MARCONI. Antenna system of which the ground is an essential part, as distinguished from a Hertz antenna. MULTIPLE-TUNED. Antenna with connec¬ tions to ground or counterpoise through turn¬ ing reactances at more than one point. MUSA. Multiple-unit steerable antenna con¬ sisting of a number of stationary antennas, the composite major lobe of which is electrically steerable. OMNIDIRECTIONAL. Antenna having an essentially nondirectional pattern in azimuth and a directional pattern in elevation. PARABOLIC. Antenna with a radiating ele¬ ment and a parabolic reflector that concen¬ trates the radiated power into a beam. PENCIL-BEAM. Unidirectional antenna so de¬ signed that cross-sections of the major lobe, by planes perpendicular to the direction of maximum radiation, are approximately circu¬ lar. PILL-BOX. Cylindrical parabolic reflector en¬ closed by two plates perpendicular to the cy¬ linder so spaced as to permit the propagation of only one mode in the desired direction of polarization. It is fed on the focal line. ECEIVING. Device for converting received space propagated electro-magnetic energy to electrical RHOMBIC. Directional antenna composed of long wire radiators comprising the sides of a rhombus, the two halves of the rhombus being fed equally in opposite phase at an apex. The antenna is usually terminated in an impedance. SECTIONAL VERTICAL. Vertical antenna in which the continuity is broken at one or more points by the insertion of reactances or driv¬ ing voltages. SERIES-FED VERTICAL. Vertical antenna which is insulated from ground and energized at the base. SHAPED BEAM. Antenna with a directional pat¬ tern of which over a certain angular range, is of a special shape for some particular use. SHUNT-FED VERTICAL. Vertical antenna con¬ nected to the ground at the base and energized at a point suitably positioned above the ground point. 39-44 1 APRIL 1959 AFM 100-39 ANT SLEEVE-DIPOLE. Dipole antenna surrounded in its central portion by a coaxial sleeve. SLEEVE STUB. Antenna consisting of one-half of a sleeve-dipole antenna projecting from an extended conducting surface. SLOT. Radiating element formed by a slot in a conducting surface. STEERABLE. Directional antenna whose major lobe can be readily shifted in direction. TOP-LOADED VERTICAL. Vertical antenna so constructed that because of its greater size at the top there results modified current dis¬ tribution giving a more desirable radiation pat¬ tern in the vertical plane. TRANSMITTING. Device for converting electri¬ cal energy to electro-magnetic radiation cap¬ able of propagating through space. TURNSTILE. Antenna composed of two dipole antennas normal to each other with their axes intersecting at their mid-points. Usually the currents are equal and in phase quadrature. UNIDIRECTIONAL. Antenna that has a single well-defined direction of maximum radiation intensity. V. V-shaped arrangement of conductors, the two branches of the V being fed equally in opposite phase at the apex. WAVE. Directional antenna composed of a sys¬ tem of parallel, horizontal conductors from one-half to several wave lengths long, and terminated to ground at the far end in its characteristic impedance. YAGI. Type of directional antenna array usual¬ ly consisting of one driven one-half wave¬ length dipole section, one parasitically excited reflector and several parasitically excited direc¬ tors. ANTENNA ADAPTER. Device that permits the use of any wall outlet for the antenna and ground connections of a radio receiver. It ordinarily provides connections through capacitors to the power-line wires. ANTENNA ARRAY. Arrangement of antenna elements, usually di¬ poles, which results in desirable directional char¬ acteristics. ANTENNA ASSEMBLY. Complete equipment associated with projecting and receiving radar waves into space. It consists, in general, of a mounting base, gears, and motors for rotating the antenna, synchros, poten¬ tiometers, and antenna proper. A reflector, to¬ gether with associated switches such as those used in sector scanning, are used to set up a ship’s head marker on the PPI scope. ANTENNA BEARING. Bearing of the antenna delivered to the indicator of PPI. ANTENNA COIL. Coil in a radio receiver through which antenna current flows. ANTENNA COINCIDENCE. That instance when two rotating highly direc¬ tional antennas are pointed toward each other. ANTENNA CONTROL. Control governing rotation, direction, speed, servo, slaving, etc., of an antenna. ANTENNA COUPLER. 1. RF transformer used to connect an antenna to a transmission line or to connect a transmis¬ sion line to a radio receiver. 2. RF transformer, link circuit, or tuned line used to transfer RF energy from the final plate tank circuit of a transmitter to the transmission line feeding the antenna. ANTENNA CURRENT. RF current that flows in an antenna. ANTENNA DETECTOR. Device consisting of an antenna and electronic equipment to warn aircraft crew members of their being observed by radar sets. These units are usually located in the nose or tail of the air¬ craft and illuminate a light on one or more panels when radar signals are detected. AFM 100-39 ANT 1 APRIL 1959 ANTENNA DISCONNECT SWITCH. Safety switch or interlock plug used to remove driving power from the antenna to prevent rota¬ tion while work is being performed on it. ANTENNA EFFECT. Spurious effect, in a loop antenna, resulting from the capacitance of the loop to ground. ANTENNA ELIMINATOR. Device that permits the use of any wall outlet for the antenna and ground connections of a radio receiver. It ordinarily provides connections through capacitors to the power-line wires. ANTENNA FIELD GAIN. FCC television standards figure of merit for the effectiveness of a transmitting antenna. It is a measure of the effective free space field inten¬ sity, measured in the horizontal plane, produced by a transmitting antenna at a distance of one mile with an antenna input power of one kilo¬ watt. ANTENNA GAIN. 1. Ratio of the maximum radiation intensity of the antenna in question to the maximum radia¬ tion intensity from a reference antenna with the same power input. 2. Gain of an antenna referred to an isotropic radiator can be measured by measuring the inten¬ sity of the radiated field on the principal axis and at a known distance from the antenna. Knowing the power delivered to the antenna, the field intensity that would have existed with an isotropic radiator is easily calculated. 3. Effectiveness of a directional antenna in a particular direction as compared with a standard dipole antenna. It is usually expressed as the ratio of the standard antenna power to the direc¬ tional antenna power that will produce the same field strength in the desired direction. ANTENNA GROUND SYSTEM. That portion of an antenna closely associated with and including an extensive conducting sur¬ face which may be the earth itself. ANTENNA HEIGHT ABOVE AVERAGE TERRAIN. Average of the antenna heights above the ter¬ rain from two to ten miles from the antenna. In general, a different antenna height will be de¬ termined by each direction from the antenna. The average of these various heights is consid¬ ered as the antenna height above average terrain. ANTENNA MATCHING. Process of adjusting impedances so that the impedance of an antenna equals the characteris¬ tic impedance of its transmission line. ANTENNA MATCHING DEVICE. Passive network which matches an antenna to its transmission line by adding the proper imped¬ ance to the impedance of the antenna at the point of feed to make it appear equal to the characteristic impedance of the line. ANTENNA PATTERN TYPE. Name applied to the configuration of a plot of received signal amplitude versus azimuth when plotted on polar coordinates. ANTENNA PEDESTAL. Support for an antenna assembly containing training motor, gears, synchros, rotating joint, etc. ANTENNA POWER. Square of the antenna current of a transmitter multiplied by the antenna resistance at the point where the current is measured. ANTENNA REFLECTOR. That portion of a directional antenna array which reduces the field intensity behind the array and increases it in the forward direction. ANTENNA RESISTANCE. Quotient of the power supplied to the entire antenna circuit by the square of the effective antenna current referred to at a specified point. ANTENNA SWITCH. Switch used for connecting the antenna into the circuit. ANTENNA SWITCHING UNIT. Unit which switches the receiver out of the 39-46 1 APRIL 1959 AFM 100-39 ANT antenna circuit at the time a pulse is transmitted by the transmitter. (Reference: TR (TRANSMIT- RECEIVE) BOX ) ANTENNA SYSTEM. Assembly of the antenna and the electrical and mechanical devices for supporting, insulating, and/or rotating it. ANTENNA TILT ERROR. Angular difference between the antenna tilt angle shown on the mechanical indicator, and the electrical center of the radar beam. ANTITRANSMIT RECEIVE BOX. Device similar to a transmit-receive box used to tune the transmitter section of the radio fre¬ quency line so that returning echoes do not enter the transmitter. ANTITRANSMIT RECEIVE SWITCH. Automatic device employed in a radar for sub¬ stantially preventing received energy from being absorbed in the transmitter. ANTIAIRCRAFT ARTILLERY. Term applied to ground weapons and material used to locate, illuminate, fire on, and destroy enemy aircraft. ANTIAIRCRAFT ARTILLERY INTELLIGENCE SERVICE. System of observers and communication facilities established by antiaircraft artillery units to gather and transmit information of aerial activi¬ ties necessary for the proper employment of anti¬ aircraft artillery. ANTIAIRCRAFT ARTILLERY OPERATIONS CENTER. Antiaircraft artillery installation established for the control of AAA guns, automatic weapons, etc. ANTIAIRCRAFT DIRECTOR. Army officer, assigned to duty in a direction center, responsible for coordinating antiaircraft action against specified airborne objects. ANTIAIRCRAFT FIRE CONTROL RADAR. Equipment used for precision fire direction and control of antiaircraft artillery. ANTIAIRCRAFT OFFICER. Army antiaircraft representative, on the battle staff, who advises on employment and capabili¬ ties of antiaircraft weapons. ANTIAIRCRAFT TECHNICIAN. Army enlisted man who assists the antiaircraft director. ANTICAPACITANCE SWITCH. Switch designed to have minimum capacitance between its terminals. ANTICATHODE. Target of the X-ray tube, on which the stream of electrons from the cathode is focused and from which X-rays are emitted. ANTICLUTTER GAIN CONTROL. Device which automatically and smoothly in¬ creases the gain of a radar receiver from a low level to the maximum, within a specified period after each transmitter pulse, o that short range clutter producing echoes are amplified less than long range echoes. ANTIHALATION COATING. Light-absorbing coating applied to the back side of the support of a film or plate, or between the emulsion and the support to suppress hala¬ tion. ANTIHUNT. Feed-back signal or network in a servo-mecha¬ nism actiii ; to prevent hunting or oscillation of the system. Special types of antihunt circuits are: anticipator, derivative, velocity feedback, and damper. ANTIJAMMING 1. Art of minimizing the effect of enemy elec¬ tronic countermeasures to permit echoes from targets detected by radar to be visible on the indicator. 2. Controls or circuit features incorporated to minimize jamming. ANTILOGARITHM. Number corresponding to a given logarithm. 39-47 AFM 100-39 ANT 1 APRIL 1959 For example: If the logarithm of 563.2 is 2.75066, then 563.2 is the antilogarithm of 2.75066. ANTIMICROPHONIC. Device specifically designed to prevent micro¬ phonics. ANTINODES. Points, lines, or surfaces of a stationary-wave system which have a maximum amplitude. ANTINOISE MICROPHONE. Microphone with characteristics such that it dis¬ criminates against acoustic noise. ANTIRESONANT CIRCUIT. Parallel-resonant circuit. ANTIRESONANT FREQUENCY. Frequency, of a crystal unit, for a particular mode of vibration at which, neglecting dissipa¬ tion, the effective impedance of the crystal unit is infinite. ANTISIDETONE. Arrangement of telephone set circuit element so that only a small amount of the power generated in a transmitter reaches the associated receiver. ANTISIDETONE CIRCUIT. Circuit, included in telephone sets, which has a balancing network that reduces sidetone. ANTISIDETONE TELEPHONE SET. Telephone set having an antisidetone circuit. antisubmarine. 1* ° f equipment, mines or missiles: Designed to attack or destroy submarines. 2. Of actions: Directed against submarines. 3. Of units or organizations: Set up to search out and attack submarines. ANTRAC. Term associated with radio equipment derived from the JAN nomenclature AN/TRC-( ) with an A added for easier pronunciation. It is applied to the AN/TRC-1, 8, and 24 series of radio equipment. (Reference: VOLSCAN.) AOCP (AIRCRAFT OUT OF COMMISSION FOR PARTS). AP (AIR-POSITION INDICATOR). Airborne computing system which presents a continuous indication of aircraft position on the basis of aircraft heading, airspeed, and elapsed time. APERIODIC. 1. Having no rhythm or repetitive characteristics, or no tendency to vibrate. A circuit that will not resonate in the tuning range is often called aperiodic. 2. Condition of a radio circuit not tuned or re¬ sponsive to any particular frequency. APERIODIC ANTENNAS. Antennas designed to have constant impedance over a wide range of frequencies due to the sup¬ pression of reflections within the antenna sys¬ tem; they include terminated wave and rhombic antennas. APERIODIC DAMPING. Condition of a system when the amount of damp¬ ing is so large that, when the system is sub¬ jected to a single disturbance, either constant or instantaneous, the system comes to a position of rest without passing through that position. While an aperiodically damped system is not strictly an oscillating system, it has such proper¬ ties that it would become an oscillating system if the damping were sufficiently reduced. APERTURE. 1. That portion of a plane surface, in a unidirec¬ tional antenna, near the antenna that is perpen¬ dicular to the direction of maximum radiation through which the major part of the radiation passes. 2. The hole or window in an opaque disc (aper¬ ture plate) which is placed between the copy being scanned and the light-sensitive element or phototube. The image of the copy being scanned is usually focused on the aperture plate, and the size of the hole determines the elemental area scanned by the phototube. 39-48 1 APRIL 1959 APEX OR APEX FACE. Term applied to denote the inclined, terminat¬ ing, rhombohedral faces of quartz. APG (AIR PROVING GROUND). Air Force installation operated at Eglin Air Force Base by the Air Proving Ground Com¬ mand. APGC (AIR PROVING GROUND COMMAND). Major air command in the USAF organized pri¬ marily to determine the operational suitability of materiel by test and evaluation. APHELION. Point at which a planet or comet, in orbit, is farthest from the sun. API (AIR-POSITION INDICATOR). Dead-reckoning computer which integrates head¬ ings and speeds to give a continuous indication of position with respect to the air mass in which the vehicle is moving. APOGEE. Point at which a satellite is farthest from the earth, or its planet. APP (APPENDIX). 1. Tube on a balloon used for inflation and de¬ flation. 2. Attachment to the main text of a document. (Reference: TAB.) APPARATUS. Electrical equipment units, either separately or collectively. APPARENT FIELD OF VIEW. ' Apparent angular size of the field of view as it appears to the eye or the area in which the virtual image is formed; it is equal to the mag¬ nifying power of the instrument times the angle of the true field of view. APPARENT HORIZON. Apparent junction of earth and sky as seen from any specific position on or above the earth. APPARENT POWER. The product of the effective current, at the two AFM 100-39 APE points of entry of a single phase, two wire cir¬ cuit, in one conductor multiplied by the effective potential difference at the two points of entry. APPARENT SAG AT ANY POINT. Departure of the wire at the particular point in the span from a straight line between the two points of support. APPARENT SAG OF WIRE IN A SPAN. Maximum departure of the wire in a given span from the straight line between the two points of support of the span. Where the two supports are at the same level, this is the normal sag. APPENDIX. 1. Tube on a balloon used for inflation and deflation. 2. Attachment to the main text of a document. (Reference: TAB.) APPLEGATE DIAGRAM. Diagram illustrating the behavior of the elec¬ trons in a velocity-modulation tube by showing the positions of electrons along the drift space plotted as vertical coordinates against time along the horizontal axis. APPLETON LAYER. Region of highly ionized air in the ionosphere, capable of reflecting or refracting radio waves, under certain conditions, back to earth. It is made up of the FI and F2 layers; these being above the El and E2 layers that make up the kennelly- heaviside layer. APPLICATION SCHEMATIC DIAGRAM. Pictorial representation in which symbols and lines are used to illustrate the interrelation of a number of circuits. APPLIQUE. Circuit element connected upon a basic circuit without changing the circuit characteristics. APPLIQUE CIRCUIT. Special circuit which is provided to modify exist¬ ing equipment in order to allow for special usage. For instance, some carrier telephone 39-49 AFM 100-39 APP 1 APRIL 1959 equipment designed for ringdown manual op¬ eration can be modified through the use of an applique circuit to allow for use between points having dial equipment. APPROACH CLEARANCE. Clearance issued to the pilot of an aircraft mak¬ ing a flight subject to instrument flight rules authorizing an approach for landing by such air¬ craft. APPROACH CONTROL. Service established for the purpose of control in IFR flights arriving at, departing from, and operating in, the vicinity of airports, by means of direct and instantaneous communication be¬ tween approach-control personnel and all air¬ craft operating under their control. APPROACH CONTROL SERVICE. Air traffic control service for arriving or depart¬ ing IFR flights. APPROACH SCHEDULE. Schedule prepared by the transport commander, in an amphibious operation, in coordination with the battalion landing team commander. It con¬ tains the movement of each scheduled wave of the boat group from the rendezvous area to the line of departure and thence to the assigned beach so that the landing of each wave will be made at the prescribed time. APPROACH SEQUENCE. Order in which two or more aircraft are cleared for approach. APPROPRIATE AERONAUTICAL FACILITY. Normal communications facility with which flight plans or position reports are filed. APPROPRIATION. Authorization by an act of Congress to make payment, for specified purposes within a pre¬ scribed amount out of the Treasury. APPROVED BILL OF MATERIAL. Engineered bill of material that has been edited and approved by an engineering review activity. APPROVED CIRCUITS. Circuit designated by appropriate command in accordance with the joint policy as stated in Article 2424, JANAP 122. The highest classifica¬ tion of information that may be transmitted, in clear, over an approved circuit is dependent upon the classification rating given that circuit. No electrical circuit will be approved for trans¬ mission in the clear of any information having a classification of Top Secret. AQUADAG. Colloidal suspension of graphite deposited on the inner side walls of cathode-ray tubes to serve as an electrostatic shield or an accelerating anode. AR. ITU designation for amateur (radio) station or Army. ARBITRARY CONSTANT. Constant to which various values may be assigned by decision alone, with these values being unaf¬ fected by any of the variables in an equation. ARC. 1. Luminous glow formed by the flow of electric current through ionized air, gas, or vapor be¬ tween separated electrodes, or contacts. 2. Portion of the circumference of a circle. ARC CONVERTER. Form of oscillator utilizing an electric arc as the generator of alternating or pulsating current. ARC FURNACE. Electrothermic apparatus in which heat energy is produced by electric current through one or more arcs internal to the furnace. ARC LAMP. Electric lamp in which the light is produced by an arc made when a current flows through ionized gas between two electrodes. ARC TRANSMITTER. Radio transmitter employing an electric arc in the generation of RF oscillations. 39-50 1 APRIL 1959 AFM 100-39 ARC ARCBACK. Sudden failure of rectifier action in a mercury- vapor rectifier tube due to an internal fault. Sometimes caused by excessive density of mer¬ cury vapor resulting from overheating of the cathode. (Reference: BACKFIRE.) ARCING. Production of an arc, as at the brushes of a motor or the contacts of a switch. ARCING CONTACTS. Special contacts on which the arc is drawn after the main contacts of a switch or circuit breaker have opened. ARCING TIME. 1. Interval between the parting, in a switch or circuit breaker, of the arcing contacts and the extension of the arc. 2. Time elapsing, in a fuse, from the severance of the fuse link to the final interruption of the circuit under the specified condition. ARDC (AIR RESEARCH AND DEVELOPMENT COMMAND). Major air command in the USAF that carries out the research and development activities re¬ quired for the accomplishment of Air Force mis¬ sions. AREA. 1. Surface of anything; the measure of its ex¬ tent. 2. Extent or space on the earth. 3. Scope or extent of something intangible, as the area of responsibility, or the area of study, or the area of power. AIR DEFENSE. 1. Specifically defined area within which identification of airborne objects is not required if the flights originated in the area, except during periods of air defense emergency. 2. Specifically defined and established terri¬ tory that includes objectives of possible enemy air attack and for which air defense must be provided. AIRSPACE WARNING. Same as danger area but located more than three miles beyond the United States coast line. BASE RATE. Area within the exchange in which all types of services are given without mileage charges. CENTRAL OFFICE. Area which receives tele¬ phone service from a central office. EXCHANGES. Areas set up for administrative reasons for telephone service covered by a sin¬ gle rate basis. Usually a single city or large division of town or village. LIGHT LOADING. Territory in which the loading caused by sleet, ice, or wind does not exceed eight pounds per square foot. MAINTENANCE. Territory set up for repair and replacement work. OPERATING. Separation of most of the tele¬ phone company’s work into a large geogra¬ phical unit. An area functions as a complete telephone company up to the executive level. TESTING. Defined territory assigned to one force for trouble locations and routing main¬ tenance tests. AREA AIR DEFENSE CONTROL CENTER. Principal air operations installation from which all aircraft, antiaircraft artillery, ground-to-air guided missiles, and air warning functions of an active air defense area are coordinated. AREA BOMBING. Bombing a target of a general area rather than a small or pinpoint target. AREA CLUTTER GATE. Classified definition. (Reference: AFM 100-50.) AREA COMMAND. Command which is composed of organized ele¬ ments of one or more of the armed services, designated to operate in a specific geographical area, which are placed under a single comman¬ der. AREA CONTROL CENTER. Center established to provide air traffic control 39-51 AFM 100-39 1 APRIL 1959 ARE service to IFR flights. AREA CONTROL SERVICE. Air traffic control service for IFR flights in control areas. AREA MOVING TARGET INDICATOR. Classified definition. (Reference: AFM 100-50.) ArFCoS (ARMED FORCES COURIER SERVICE). ARGON. Colorless, odorless inert gas found in air. When ionized in a vacuum tube, argon gives off a bright red, blue, or purplish glow. ARGUMENT. 1. One of the independent variables upon which the value of a function depends. 2. Angle that fixes the direction of a complex number. 3. Angle between a vector and its reference axis. ARINC (AERONAUTICAL RADIO, INCORPORATED). Commercial communications company formed and owned substantially by the scheduled airlines of the United States. It is the licensee of all domestic airlines enroute communication sta¬ tions. In addition, it furnishes extensive service to international aircraft operations on overseas and foreign routes. The company provides both air/ground and point-to-point service. It coordi¬ nates with industry, government, and manufac¬ turers on the standardization of electronic equip¬ ment and represents the aviation industry in RTCA and ICAO on electronic matters. ARITHMETIC MEAN. Average of a number of quantities, obtained by adding the quantities and dividing the result by the number of quantities involved. ARITHMETIC UNIT. Part used in an electronic computer which per¬ forms arithmetic operations. ARM (ARMATURE). 1. Originally the rotating part of an electrical machine, but in the case of a generator having a rotating field, the stationary part is the arma¬ ture. 2. Piece of ferromagnetic material so positioned with respect to a magnetic field that motion is possible. ARM. 1. Combat branch of a military force or unit. 2. Weapons of war. 3. Furnish a man or troops with weapons. 4. Equip or load an airplane or other vehicle with guns, bombs, rockets, or the like. 5. Make a bomb, torpedo or mine ready for detonation by removal of the safety pin from the fuzes. 6. Prepare a nation for war by producing weap¬ ons, training troops, etc. CABLE EXTENSION. Short arm securing one cable designed to bring another cable in line to throw it out of line to clear an obstruction. CROSS. Horizontal member, usually of wood, attached to a pole or other vertical member, supporting lines, or cables. EXTENSION. Cross arm added vertically to the top of a pole for greater height. GUARD. 1 . Cross arm placed across and in line with a cable to prevent damage to the cable. 2. Cross arm located over wires to prevent foreign wires from falling into them. ARMAMENT CONTROL SYSTEM. System of search and gun-aiming radars which provides the solution to the fire control problem in an aircraft by determining for the pilot the proper course required to intercept a given tar¬ get. The search radar is used to locate targets at long range. When target is within 4000 yards, target data is supplied to a computer and solu¬ tion to firing problem is presented to pilot on an oscilloscope. 39-52 1 APRIL 1959 AFM 100-39 ARM ARMAMENT SYSTEMS OFFICER. USAF officer who manages armament systems maintenance activities including bomb-naviga¬ tion, fire control, turret systems, and related simulated training devices and test equipment, and commands armament units. ARMATURE. 1. Rotating part of an electrical machine, except in the case of a generator having a rotating field, in which the armature is stationary. 2. Piece of ferromagnetic material so positioned with respect to a magnetic field that motion is possible. ARMATURE CORE. Assembly of laminations forming the magnetic circuit of the armature. ARMATURE REACTION. Interaction between the magnetic flux of the armature and that of the field in an electric motor or generator, causing a redistribution of flux that must be taken into account during de¬ sign. The interaction results from the electromo¬ tive force that the armature current produces in the magnetic circuits of the motor or generator. ARMATURE-VOLTAGE CONTROL. Controlling the speed of a motor by changing the voltage applied to its armature windings. ARMED FORCES RADIO SERVICE. Radio service, including maintenance, programs, transcriptions, etc., available to armed forces overseas and to certain service and veteran hos¬ pitals in the United States. ARMED SERVICES ELECTRO-STANDARDS AGENCY. Joint service organization which prepares and promulgates standard joint specifications for the electronic parts and materials used in the com¬ munications and electronics equipments of the Armed Forces. ARMISH (UNITED STATES MILITARY MISSION WITH THE IRANIAN ARMY). ARMOR. Layer or more of extra strength material, in cable construction, such as steel wire or tape to rein¬ force the usual lead wall. ARMOR CLAMP. Fitting for gripping the armor of a cable at the point where the armor terminates or where the cable enters a junction box. ARMORED CABLE. Cable provided with a wrapping of metal, pri¬ marily for the purpose of mechanical protection. ARMSTRONG OSCILLATOR. Indictive feed-back oscillator, that consists of a tuned grid circuit and untuned tickler coil in the plate circuit. Control of feed back is accom¬ plished by varying the coupling between the tickler and the grid circuit. ARMY. 1. Land military forces of a nation. 2. Unit of US Army made up of two or more army corps. 3. Short for US Army. ARMY AIR DEFENSE COMMAND POST. Army installation used for collection, display, and evaluation of air-surveillance information which is used in the assignment of specific bat¬ teries against enemy airborne objects. ARMY COMMAND AND ADMINISTRATIVE NETWORK. Domestic and overseas integrated system of fixed radio, wire, cable, and associated facilities pro¬ viding command and administrative communica¬ tions for the Army. Comparable to the AIRCOM for the Air Force. ARMY FIELD FORCES. 1. Ground forces operating in the field. 2. Units, general headquarters, installations, and equipment that comprise the forces in a theater of operation. ARMY GROUP. Several field armies (primarily a tactical com¬ mand) under a designated commander. 39-53 AFM 100-39 ARM 1 APRIL 1959 ARMY SECURITY AGENCY, Organization, reporting to the Director of Intel¬ ligence, U. S. Army, which directs military com¬ munications security and intelligence operations within the U. S. Army in accordance with the policies and procedures established by the na¬ tional security agency. ARMY WITH AIR FORCE. Army personnel assigned and/or attached as in¬ dividuals or units for duty with the Air Force. Term ARWAF (pronounced as a word) is used to designate this condition. ARNOLD ENGINEERING DEVELOPMENT CENTER. Air Force engineering development center loca¬ ted at Tullahoma, Tennessee. Named after gen¬ eral of the Air Force Henry H. Arnold. ARO (AIRCRAFT RANGE ONLY). AROTC (AIR RESERVE OFFICER TRAINING CORPS). Training corps under the control of the USAF, with detachments in colleges and universities, to prepare cadets for service in one of the compo¬ nents of the USAF. ARR (ARRIVAL). Action or event of an aircraft arriving at a place; an instance of such action, as in the case of an aircraft timetable showing six arrivals and four departures. ARRAY. Combination of antennas with suitable spacing and with all elements excited so as to make the radiated fields from the individual elements add in the desired direction. ANTENNA. Arrangement of antenna elements, usually dipoles, which results in desirable di¬ rectional characteristics. AERIAL. Antenna arrangement. BINOMIAL. Directional antenna array for re¬ ducing minor lobes and providing maximum response in two opposite directions. BROADSIDE. Antenna array in which the di¬ rection of maximum radiation is perpendicu¬ lar to the line or plane of the array. COLLINEAR. Antenna array having a string of halfwave elements excited in phase. END-FIRE. Antenna array whose direction of maximum radiation is along the axis of the array. LINEAR. Antenna array whose elements are spaced along a straight line. PINE-TREE. Array of dipole antennas aligned in a vertical plane known as the radiating cur¬ tain, behind which, is a parallel array of di¬ pole antennas forming a reflecting curtain. ARRESTOR. 1. Protective device used to provide a bypass path directly to ground for lightning discharges that strike an antenna or other conductor. 2. Power-line device that is capable of reducing the voltage of a surge applied to its terminals, interrupting current if present, and restoring it¬ self to original operating conditions. 3. Device which diverts high voltages away from protected equipment to ground. ARRIVAL. Action or event of an aircraft arriving at a place; an instance of such action, as in the case of an aircraft timetable showing six arrivals and four departures. ARRL (AMERICAN RADIO RELAY LEAGUE). Publisher of the monthly magazine QST and is the largest amateur radio organization in the world. ARS (AIR RESCUE SERVICE). Air Force organization under the Military Air Transport Service that provides air rescue, in¬ cluding search for both civilian and military air¬ craft in remote areas, either on land or sea. ART. (ARTICLE). 1. Distinct portion of any writing consisting of 39-54 1 APRIL 1959 AFM 100-39 ART two or more topics. particulars, or treating of various 2. Distinct detail or particular, as of news or conduct. 3. Thing of particular class or kind; a commod¬ ity. ARTCC (AIR ROUTE TRAFFIC CONTROL CENTER). Civil Aeronautics Administration facility that es¬ tablishes and monitors routes and altitudes for aircraft flying within a given control area. ARTICULATION. Percentage, in a telephone transmission system, of the total number of speech units transmitted over the system which are correctly understood by the listener. m ARTICULATION AND INTELLIGIBILITY. Percent articulation or percent intelligibility of a communication system is the percentage of the speech units spoken by a talker or talkers that is understood correctly by a listener or listeners. The word articulation is customarily used when the contextual relations among the units of the speech material are thought to play an unim¬ portant role; the word intelligibility is customa¬ rily used when the context is thought to play an important role in determining the listeners perception. It is important to specify the type of speech material and the units into which it is analyzed for the purpose of computing the per¬ centage. The units may be fundamental speech sounds, syllables, words, sentences, etc. ARTIFICIAL ANTENNA. Device which simulates a real antenna in its es¬ sential impedance characteristics and has the necessary power handling capabilities, but does not radiate or receive radio waves. (Reference: DUMMY ANTENNA.) ARTIFICIAL LINE. Circuit made up of lumped constants, which is used to simulate various characteristics of a transmission line. ARTIFICIAL LINE DUCT. Balancing network simulating the impedance of the real line and distant terminal apparatus, which is employed in a duplex circuit for the pur¬ pose of making the receiving device unresponsive to outgoing signal currents. ARTIFICIAL LOAD. Dissipative, but essentially nonradiating device having the impedance characteristics of an anten¬ na, transmission line, or other practical utiliza¬ tion circuits. (Reference: DUMMY LOAD.) ARTIFICIAL RADIOACTIVITY. Radioactivity produced artificially by radio ele¬ ments. ARTIFICIAL VOICE. Small loudspeaker mounted in a shaped baffle which is proportioned to simulate the acoustical constants of the human head; used for calibrat¬ ing and testing close-talking microphones. ARW (AIR RAID WARNING). Information concerning approaching enemy air¬ craft and/or guided missiles, which is dissemi¬ nated primarily for passive air defense purposes. (Reference: AIR RAID WARNING CONDI¬ TIONS.) ARWAF (ARMY WITH AIR FORCE). Army personnel assigned and/or attached as in¬ dividuals or units for duty with the Air Force. Pronounced as a word, and used attributively as in ARWAF officer or ARWAF unit. AS (ANTISUBMARINE). 1. Of equipment, mines or missiles: Designed to attack or destroy submarines. 2. Of actions: Directed against submarines. 3. Of units or organizations: Set up to search out and attack submarines. ASBESTOS. Noninflammable fibrous mineral used in elec¬ tronics for heat-insulating and fireproofing pur¬ poses, as in a line cord resistor. ASC (AUTOMATIC SENSITIVITY CONTROL). Circuit used for automatically maintaining re¬ ceiver sensitivity at a predetermined level. 39-55 AFM 100-39 ASD 1 APRIL 1959 Similar to automatic gain control, but it affects the receiver constantly rather than during the brief interval selected by the range gate. ASD (AVIATION SUPPLY DEPOT). ASDE (AIR SURFACE DETECTION EQUIPMENT). Short-distance radar having resolution and dis¬ crimination. It provides, in graphic or pictorial form, for use by traffic control personnel: (a) plan position indication of the airport surface with the location of runways, taxiways, and ranges clearly defined, and (b) presentation of all aircraft, vehicular, and other traffic, both moving or stationary. ASDIC. British term for listening devices used on vessels for submarine-detecting purposes. (Reference: SONAR.) ASESA (ARMED SERVICES ELECTRO-STANDARDS AGENCY). Joint service organization which prepares and promulgates standard joint specifications for the electronic parts and materials used in the com¬ munications and electronics equipment of the Armed Forces. ASG (AERONAUTICAL STANDARDS GROUP). Air Force-Navy group concerned with establish¬ ing joint aeronautical standards. ASG (ASSIGNED). Designating personnel, units, equipment, mis¬ sions, etc., that have been assigned in one sense or another. ASH CAN. Depth charge. ASM (AIR-TO-SURFACE MISSILE). Missile designed to be dropped from aircraft, which upon release, is guided to a surface tar¬ get, such as an airfield, by means of an internal homing device or radio control. ASO (AIR SURVEILLANCE OFFICER). Officer responsible for the performance of the air-surveillance functions. ASPB (ARMED SERVICES PETROLEUM BOARD). ASPECT RATIO. Ratio of width to height, as in a television frame. ASPEN. Airborne component of the OBOE navigational system. The nomenclature is AN/APA-9. It con¬ sists essentially of a 10-CM airborne radar bea¬ con which is interrogated by two ground radar stations and directed by them. VCith a different receiver the set is known as ASPEX. British de¬ signations include Album Leaf with Pepperbox receiver and Fountain Pen with Penwiper receiv¬ er. ASPHERICAL LENS. Lens in which the surfaces depart from a true spherical shape. ASPR (ARMED SERVICES PROCUREMENT REGULATION). ASR (AIRPORT SURVEILLANCE RADAR). Radar located on or near an airport to provide an indication of the bearing and distance of each aircraft within the terminal area in which the air¬ port is located. It is employed to vector and give ^ navigational guidance to arriving and departing aircraft in the control of air traffic within the terminal area; it does not provide data regard¬ ing the elevation of aircraft. ASSEMBLY. 1. Combination of parts and/or subassemblies which may be taken apart without destruction and which does not have an application or use of its own, but is essential for the completeness of a more complex item with which it is com¬ bined. Assemblies may be referred to as subas¬ semblies, and sub-sub assemblies, to indicate their relationship to a major assembly. 2. Complete operating unit. ASSIGNABLE CAUSE. Assignable causes are any causes which can be found to account for a quality control reading that falls outside the control limits. There are four major categories of assignable causes: com¬ putational errors, radar performance, weather, and operator performance. 39-56 1 APRIL 1959 ASSIGNED. Designating personnel, units, equipment, mis¬ sions, etc., that have been assigned in one sense or another. ASSIGNED FREQUENCY. Frequency coinciding with the center of the fre¬ quency band in which the station is authorized to operate. ASSIGNER. One who assigns plant interconnections. ASSIST TAKE-OFF. Action of an aircraft taking off with an added boost from a rocket or other device. ASSISTANT. Person who helps or assists another. Used in certain titles, as an assistant for programming. ASSOC (ASSOCIATED REQUISITION). Priority requisition submitted for any material, other than aircraft components covered by AOCP or ANFE requests, the lack of which indirectly affects the performance or mission of an aircraft. 0 ASSOCIATED REQUISITION. Priority requisition submitted for any material, other than aircraft components covered by AOCP or ANFE requests, the lack of which indirectly affects the performance or mission of an aircraft. ASST (ASSISTANT). Person who helps or assists another. Used in certain titles as an assistant for programming. ASSUMPTION. A supposition on the current situation, or a pre¬ supposition on the future course of events, either or both assumed to be true in the absence of positive proof, necessary to enable the commander, in the process of planning, to complete his esti¬ mate of the situation and make a decision on his course of action. AST (AIR SURVEILLANCE TECHNICIAN). Noncommissioned officer who assists the air sur¬ veillance officer. ASTATIC. 1. Without any particular orientation; having no directional characteristics. AFM 100-39 ASS 2. Being in neutral equilibrium; having no ten¬ dency toward any change of position. ASTATIC GALVANOMETER. Sensitive galvanometer consisting of two very small magnetized needles arranged parallel to each other with north and south poles adjacent and suspended inside the galvanometer coil. ASTEROIDS. Many small planets revolving around the sun, largely between Mars and Jupiter. ASTIA (ASSISTANT SERVICES TECHNICAL INFORMATION AGENCY). ASTIGMATISM. Type of spherical aberration in which rays from a single point of an object do not converge in the image. Astigmatism in a lens or mirror causes a blurred image. ASTIGMATIZER. Cylindrical lens which may be rotated into the line of sight of a range finder to cause the ef¬ fect of astigmatism. ASTROGATION. Navigation by the stars while in space. ASTRONAUTICS. Science of space flight. ASTRONOMIC STATION. Point on the earth at which observations are made on heavenly bodies to determine latitude, longitude, or azimuth. ASTROPHYSICS. Physics of astronomical bodies and regions. Deals with the physical constitution of heavenly bodies. ASV (AIR-TO-SURFACE VESSEL). Search radar sets used in aircraft for detecting objects on the surface of the sea. ASW (ANTISUBMARINE WARFARE). ASYMMETRICAL. Not symmetrical. ASYMMETRICAL CELL. Cell, such as a photoelectric cell, in which the 39-57 AFM 100-39 ASY 1 APRIL 1959 impedance to the flow of current in one direc¬ tion is greater than in the other direction. ASYMPTOTIC. Having or pertaining to the characteristics of an asymptote, which is a line representing the limiting position that the tangent of a curve approaches as the point of contact recedes. In electricity, asymptotic breakdown voltage is a voltage, if applied over a long period of time, that will break down a cable. ASYNCHRONOUS. Not synchronous. ASYNCHRONOUS MACHINE. Machine in which the speed of operation is not proportional to the frequency of the system to which it is connected. ASYNCHRONOUS SPARK GAP. Rotary spark gap without provision for sparking at definite points in the cycle of the ac supply. AT BAR. Crystal bar out from X sections with its long direction making an angle with Z equal to the complement of the AT angle (or 90° — 35° 15’ = 54° 45’). AT-CUT CRYSTAL. Oscillator plate of specified dimensions and with an edge parallel to X and the angle Z to Z' = + 350° 15’. AT&T (AMERICAN TELEPHONE AND TELEGRAPH COMPANY). ATAG (AIR TRAINING ADVISORY GROUP). ATAK (ATTACK). Act of offense or act of striking at a physical object with the purpose of inflicting injury, dam¬ age, or destruction. ATC (AIR TRAFFIC CONTROL). Service operated by appropriate authority to pro¬ mote safe, orderly, expeditious flow of air traf¬ fic. The service is administered by air route traf¬ fic control centers and airport traffic control to¬ wers. ATCC (AIR TRAFFIC CONTROL CENTER). Principal communications and operations center from which all aircraft are controlled under IFR conditions in the vicinity of an airdrome. The complete system consists of a suitable long-range radar installation capable of observing aircraft along airways, a method of controlling inboard and outboard traffic within the traffic pattern of the airdrome, and a precision radar unit capable of providing the pilot of an aircraft with infor¬ mation that will permit a safe landing. ATCOM (ATOLL COMMANDER). ATF (ATCUAL TIME OF FALL). ATHERMANOUS. Opaque, to infrared. Not transmitting radiant heat. ATLAS. Surface-to-surface intercontinental strategic bal¬ listic missile being developed for the Air Force. It is powered by rocket engines and uses multi¬ stage construction to acheive the extreme speeds and altitudes required for its range. It will be capable of carrying a nuclear warhead. Maximum altitude may exceed 500 miles. The nomencla¬ ture is SM-65. ATM (ATMOSPHERE). 1. Whole mass of air surrounding the earth. 2. Any gaseous medium. 3. Unit of pressure defined as the pressure of 76 CM of mercury at 0° Centigrade under standard gravity, which is approximately 15 pounds per square-inch. ATMOSPHERE. 1. Whole mass of air surrounding the earth. 2. Arty gaseous medium. 3. Unit of pressure, defined as the pressure of 76 CM of mercury at 0° C(32°F), under stan¬ dard gravity, which is approximately 15 pounds per square inch. EXPLOSIVE. Refers to a condition where the air is mixed with dust, metal particles, or in¬ flammable gas in such proportion that it may ignite or explode. 39-58 1 APRIL 1959 AFM 100-39 ATM I STANDARD. Condition of the atmosphere in which the temperature and moisture content of the air decrease uniformly with height. In the standard atmosphere, the air temperature decreases with increasing altitude from 59°F. (15°C.) at sea level at the rate of 6.5°C. per kilometer (18.8° F. per mile). Although this condition is postulated by standard, it is not necessarily normal at any particular location. The atmosphere is likely to be of standard com¬ position when strong, gusty winds are blow¬ ing, because the turbulence created prevents both stratification of the air and establishment of nonstandard temperature and humidity gra¬ dients. ATMOSPHERIC ABSORPTION. Loss of energy in transmission of radio waves due to dissipation in the atmosphere. ATOMIC BOMB. Bomb that releases a large amount of energy con¬ tained in the nucleus of an atom by splitting the nucleus apart. m ATOMIC ENERGY COMMISSION. Civilian governmental agency established by the Atomic Energy Act of 1946 to take over the or¬ ganization and property of the Manhattan Pro¬ ject and to supervise and control the production of nuclear-fissionable, radioactive materials in the United States. ATOMIC NUMBER. Number representing the position of a given ele¬ ment in the scale of all elements arranged in order of their atomic complexity. This number is supposed also to represent the nuclear charge of the atom, or number of protons in the nucleus, and hence the number of orbital electrons. ATOMIC THEORY. Generally accepted theory, concerning the struc¬ ture and composition of substances and com¬ pounds, that everything is composed of various combinations of atoms. ATMOSPHERIC DUCT. An almost horizontal layer in the troposphere in which the downward curvature of a radio ray exceeds the curvature of the earth. If the wave length is sufficiently short compared to the thickness of the layer, the pressure of the layer may cause appreciable reduction in the attenua¬ tion of radio waves propagated between an¬ tenna in or near the layer. ATMOSPHERIC NOISE. Noise or static due to natural causes, such as thunderstorm activity. ATMOSPHERIC PRESSURE. Pressure of the atmosphere measured from ab¬ solute zero pressure. At sea level, atmospheric pressure is about 14.7 pounds per square inch, decreasing as the altitude increases. ATMOSPHERIC RADIO WAVE. Radio wave that is propagated by reflection in the atmosphere. It may include either the ionospheric wave or the tropospheric wave, or both. ATMOSPHERICS. 1. Electrical disturbances, in the atmosphere, such as lightning, which causes noise that inter¬ feres with intelligible radio communication. 2. Static. 3. Unwanted, extraneous, disturbing currents in¬ duced in wire-line circuits which result from dust, lightning, and snow storms. ATO (AIR TACTICS OFFICER). Officer responsible for forming hostile tracks into raids, interceptors tracks into groups, and also responsible for forwarding summarized da¬ ta on raids and groups to a supervisory organ¬ ization. ATO (ASSIST TAKE-OFF). Action of an aircraft taking off with an added boost from a rocket or other device. ATOM. Smallest particle into which matter can be di ided 39-59 AFM 100-39 ATO 1 APRIL 1959 ATTENUATING. Decreasing electrical current, voltage or power in a communication channel. Refers to audio, radio, or carrier frequencies. ATTENUATION. 1. Attenuation of a wave is the decrease in amplitude which accompanies propagation or passage through equipment lines, or space as in radio. Degree of attenuation is commonly mea¬ sured and stated in decibels. 0 ATOMIC WEIGHT. Relative weight of an atom, based on an atomic weight of 16 for the oxygen atom. On this basis, hydrogen has an atomic weight of 1.0078. ATRAN. Classified definition. (References: AFM 100-50.) ATRAN/ERTIAL. Classified definition. (Reference: AFM 100-50.) ATRC (AIR TRAINING COMMAND). Major air command with headquarters at Scott Air Force Base, Illinois; having the mission of providing training for Air Force officers and air¬ men. ATT (AIR TACTICS TECHNICIAN). Noncommissioned officer who assists the air tac¬ tics officer. ATTACHMENT. 1. Supplementary device composed of parts and/ or assemblies which, when fastened to or mounted on an end item, varies or extends the basic function thereof. 2. Plant elements fastened to a supporting struc¬ ture. ATACHMENTS, TREE. Parts of telephone plant fastened to a tree. ATTACK. Act of offense or act of striking at a physical object with the purpose of inflicting injury, damage, or destruction. ATTENDED TELEPHONE CENTER. Attended telephone center usually is established at Air Force installations by the commercial com¬ munications companies, when necessary, as an aid in handling large volumes of long distance toll calls. Attended telephone centers benefit the commercial communications company primarily, and are of secondary benefit to the Air Force. ATTENTION DISPLAY. Tabular or vector message, computer generated on the display tubes of an operator’s console, drawing attention to a particular situation. 2. Decrease in magnitude in transmission from one point to another. It may be expressed as a ratio, or, by extension of the term, in decibels, or nepers. 3. Of a quantity associated with a traveling wave in a homogeneous medium, the decrease with dis¬ tance in the direction of propagation. Note. In a diverging wave, attenuation in¬ cludes the effect of divergence. CURRENT. Ratio of the current, of a transduc¬ er, in its input circuit to the current in a speci¬ fied load impedance. SPACE. Loss of energy, expressed in decibels, of a signal in free space; caused by such fac¬ tors as absorption, reflection, scattering, and dispersion. VOLTAGE. Ratio of the signal voltage across its input to the signal voltage delivered to a specified load impedance of a transducer. WAVE. Decrease in amplitude with distance in the direction of wave propagation. ATTENUATION CONSTANT. 1. Part of the propagation constant that refers to the decrease of signal amplitude over a given length of the transmission medium. 2. For a traveling plane wave at a given fre¬ quency, the rate of exponential decrease of the amplitude of a field component (or of the vol¬ tage or current) in the direction of the propa¬ gation, in nepers or decibels per unit length. ATTENTUATION DISTORTION. 1. Distortion that causes a decrease in the am¬ plitude of a signal. 39-60 1 APRIL 1959 AFM 100-39 ATT 2. Departure, in a circuit or system, from uni¬ form amplification or attenuation over the fre¬ quency range required for transmission; the ef¬ fect of such departure on a transmitted signal. ATTENTUATION EQUALIZER. Device for altering the total transmission loss of a circuit for various frequencies in order to make substantially equal, the total transmission loss for all frequencies within a certain range. ATTENTUATION-FREQUENCY DISTORTION. Form of wave distortion in which the relative magnitudes of the different frequency compon¬ ents of the wave are changed. ATTENTUATION NETWORK. Arrangement of circuit elements, usually imped¬ ance elements inserted in circuitry to introduce a known loss or to reduce the impedance level without reflections. ATTENTUATION RATIO. Magnitude of the propagation ratio; that is, the ratio which indicates the relative decrease in en- ergy. ATTENUATOR. Device for reducing the amplitude of a wave. Attenuators are most commonly combinations or networks of resistances either fixed or adjust¬ able. In its many different forms and applica¬ tions, the attenuator becomes known variously as pad, gain control, level adjustor, volume con¬ trol, etc. 2. Network of variable resistors which is used to reduce the strength of an audio-frequency or ra¬ dio frequency signal a desired amount without introducing appreciable distortion. The corres¬ ponding nonadjustable device is called a pad. 3. Receiver control similar in operation to a broadcast receiver volume control. It is used to reduce the strength of the signal. ATTRACTION. Force that tends to make two objects approach each other. Attraction exists between two unlike magnetic poles (N and S) or between two un¬ like static charges (+ and —). AUDIBLE. Capable of being heard by the average human ear. The approximate range of human hear¬ ing is between 20 and 20,000 cycles per second, but actual limits vary greatly with different in¬ dividuals. AUDIBLE ALARMS. Alarm provided on each situation-display con¬ sole (and on some auxiliary consoles) to alert an operator to a condition requiring his action or to the fact he has performed an improper action. AUDIBLE BUSY SIGNAL. Audible signal connected to the calling line to indicate that the called line is in use. AUDIBLE RINGING SIGNAL. Audible signal connected to the calling line to indicate that the called station is being rung. AUDIBLE SIGNAL DEVICE. General term, in protective signaling, for bells, buzzers, horns, whistles, sirens, or other devices which produce audible signals. AUDIO. Pertaining to frequencies of normally audible sound waves (between 20 and 20,000 cycles per second). AUDIO AMPLIFIER. Device that amplifies audio-frequency signals. AUDIO BAND. Band used to designate the range of audio fre¬ quencies passed by an amplifier, receiver, trans¬ mitter, etc. AUDIO COMPONENT. Portion of any wave or signal, the frequencies of which are within the audible range. AUDIO FREQUENCY. Frequency which can be detected as a sound by the human ear. The range of audio frequencies extends approximately from 20 to 20,000 cycles per second. AUDIO OSCILLATOR. Instrument designed to generate an electrical sig¬ nal in the audio-frequency range. (Refer¬ ence: AUDIO-FREQUENCY OSCILLATOR.) AUDIO PATCH BAY. Specific patch panels provided for termination of AFM 100-39 AUD 1 APRIL 1959 all audio circuits and equipment used in the chan¬ nel and technical control facility. This equip¬ ment may also be found in transmitting and receiving stations. AUDIO PEAK LIMITER. Circuit used in an audio-frequency system to cut off peaks that exceed a predetermined value. Generally used in the audio system of a radio transmitter to prevent over modulation and to protect equipment from overloading. AUDIO TRANSFORMER. Transformer designed to transfer audio-fre¬ quency signals from one circuit to another. Com¬ monly used to match two different impedances and permit maximum power transfer. AUDIO-FREQUENCY AMPLIFIER. Device that amplifies audio-frequency signals. AUDIO-FREQUENCY CHOKE. Coil used to impede the flow of audio-frequency currents; generally a coil wound on an iron core. AUDIO-FREQUENCY OSCILLATOR. Oscillator unit or circuit producing oscillations at audio frequencies; such as an oscillator used with headphones and a telegraph key for code practices. (Reference: AUDIO OSCILLATOR.) AUDIO-FREQUENCY PEAK LIMITER. Circuit used in an audio-frequency system to cut off peaks that exceed a predetermined value. Generally used in the audio system of a radio transmitter to prevent modulation and to pro¬ tect equipment from overloading. AUDIO-FREQUENCY SHIFT MODULATION. System where a 1500-cycle tone represents picture black, a 2300-cycle tone represents picture white, and frequencies between 1500 and 2300 cycles represent shades of gray. For photographic transmission the black and white frequencies are reversed. This system of modulation is used for sub-carrier frequency shift transmission on a ra¬ dio circuit. The 1500 to 2300-cycle swing is stand¬ ard but other frequencies may be used. AUDIO-FREQUENCY TRANSFORMER. Transformer designed to transfer audio-frequency signals from one circuit to another. Commonly used to match two different circuit impedances and permit maximum power transfer. AUDIOGRAM. Graph plotting hearing loss versus frequency, or percentage of hearing versus frequency. AUDIOMETER. Instrument used to test the power of hearing or the intensity of audibility of sounds. It consists of an audio oscillator having variable calibrated output, capable of generating a wide range of audio frequencies. AUDION. Three electrode vacuum tube. AUDITION. Studio test or rehearsal of all or part of a pro¬ gram prior to a radio broadcast. AUDITORY SENSATION AREA. Area inclosed by the curves of an auditory dia¬ gram defining the maximum tolerable and minimum perceivable intensities appreciated as sound by the ear. AUM (A IR-TG-UNDER WATER MISSILE). Missile designed to be dropped from aircraft, and upon contact with the surface of water, to pursue or seek out an underwater moving target, such as a submarine, by means of an internal or radio guided homing device. AURAL. Pertaining to the ear or to the sense of hearing. AURAL RADIO RANGE. Radio transmitter, the courses of which are nor¬ mally followed by interpretation of an aural sig¬ nal. AURAL SIGNAL. Signal corresponding to the sound portion of a television program. The audible component of a signal. AURAL TRANSMITTER. Radio equipment, in television, for transmission of aural signals. 39-62 1 APRIL 1959 AFM 100-39 AUD AURORA. Caused by particles radiated from the sun that are guided into the polar regions by the earth’s magnetic field. Auroral activity extends from a- bout 65 to 350 miles above the earth and is maxi¬ mum in zones lying about 20 degrees from the earth’s geometric poles. AURORAL ABSORPTION. Absorption of radio waves due to auroral ac¬ tivity. Auroral activity is caused mainly by part¬ icle radiation from the sun. AUTHENTICATION. 1. Security measure designed to protect a com¬ munications system against fraudulent transmis¬ sions. 2. Evidence by proper signature or seal that a military document is genuine and official. NET. Identification used on a communication network to establish the authenticity of several stations. STATION. Security measure designed to estab¬ lish the authenticity of a transmitting or re¬ ceiving station. TRANSMISSION. Security measure embodying self-authentication, message authentication, and station or network authentication, whereby, a station may establish the authenticity of its own transmissions. AUTHENTICATION ELEMENT. Element on which an authentication of a message, transmission, or station, is based. AUTHENTICATION EQUIPMENT. Classified definition. (Reference: AFM 100-50.) AUTHENTICATION MESSAGE. Security measure designed to establish the au¬ thenticity of a message by means of an authen¬ ticator within the transmission derived from cer¬ tain predetermined elements of the message it¬ self. AUTHENTICATION TEST ELEMENT. Element on which an authentication of a message, transmission or station is based. AUTHENTICATOR. Letter, numeral, or groups of letters or numerals, or both, composed in a prearranged manner and usually inserted at a predetermined point within a transmission for the purpose of attesting to the authenticity of the message or transmission. AUTHORIZED FREQUENCY. Portion of the radio spectrum the width of which is the necessary bandwidth of emission plus twice the prescribed frequency tolerance. AUTO (AUTOMATIC). 1. Designating firearms that are fully automatic or semiautomatic. 2. Designating mechanisms that work in reac¬ tion to certain conditions, such as an automatic horn, automatic valve, etc. 3. Designating actions or movements executed by use of automatic equipment, such as an automatic approach, automatic landing, etc. 4. Designating a standard operating procedure observed in distributing or issuing something. AUTODYNE CIRCUIT. Vacuum-tube circuit which serves simultaneous¬ ly as an oscillator and a heterodyne detector. AUTODYNE RECEPTION. System of heterodyne reception through the use of a device which is both an oscillator and a detector. AUTOMATIC. 1. Designating firearms that are fully automatic or semi-automatic. 2. Designating mechanisms that work in reac¬ tion to certain conditions, such as automatic horn, automatic valve, etc. 3. Designating actions or movements executed by use of automatic equipment, such as an auto¬ matic approach, automatic landing, etc. 4. Designating a standard operating procedure observed in distributing or issuing something. AUTOMATIC BACK BIAS. Technique which consists of one or more auto¬ matic gain control loops to prevent overloading of the receiver by large signals, whether jam¬ ming or actual radar echoes. / 39-63 AFM 100-39 AUT 1 APRIL 1959 AUTOMATIC BASS COMPENSATION. Circuit used in receivers to make bass notes sound more natural at low volume settings. The circuit usually consists of a resistor and capacitor and automatically compensates for the poor res¬ ponse of the human ear to weak sounds. AUTOMATIC BRIGHTNESS CONTROL. Circuit used in television receivers to keep the average brightness of the reproduced image es¬ sentially constant. Its action is like that of an automatic volume control circuit. AUTOMATIC CARRIER LANDING SYSTEM. Combination radio-radar unit developed for the Navy for use in landing aircraft on carriers un¬ der adverse weather conditions. Radar is used to locate the aircraft and determine its position re¬ lative to the carrier deck. Altitude, speed, and course are calculated by an electronic computer and fed into a radio transmitter, which directs the aircraft into a flight pattern. If approach is incorrect, the system will automatically wave off the approaching aircraft. AUTOMATIC CHECK. Check performed by equipment built into an electronic computer specifically for that purpose and automatically accomplished each time the pertinent operation is performed. AUTOMATIC CIRCUIT BREAKER. Device that automatically opens a circuit, usually by electromagnetic means, when the current ex¬ ceeds a safe valve. AUTOMATIC CONTROL. Arrangement of electrical controls which pro¬ vides for opening and/or closing switching de¬ vices in an automatic sequence and under prede¬ termined conditions. These switching devices maintain the required character of service and provide adequate protection against all usual op¬ erating emergencies. AUTOMATIC CUTOUT. Device, usually operated either by centrifugal force or by an electromagnet, that automatically removes (cuts out) some part of a circuit at the proper moment. Used on induction motors to cut out the starting winding when operating speed is attained. AUTOMATIC DIGITAL TRACKING AND CONTROL SYSTEM. Classified definition. (Reference: AFM 100-50.) AUTOMATIC DIRECTION FINDING. System, in which the direction finding informa¬ tion is resolved and placed upon the search scopes as an intensified sweep indicating the azi¬ muth bearing of the incoming call. The equip¬ ment is operated automatically by the incoming radio carrier. AUTOMATIC ELECTRONIC DATA SWITCHING CENTER. Communications center designed specifically for the transmission, relay, switching, and reception of digitalized data by automatic electronic meth¬ ods. AUTOMATIC EXCHANGE. Exchange at which communication between sub¬ scribers is effected without the intervention of an operator, by means of switches set in motion by the operation of a dial on the originating sub¬ scriber’s instrument. AUTOMATIC FIRE ALARM SYSTEM. Fire alarm system for automatically detecting the presence of fire and initiating signal tramsmis- sion without human intervention. AUTOMATIC FREQUENCY CONTROL. 1. System tending to hold the frequency of an oscillatory circuit constant despite other influen¬ ces that normally would introduce a frequency change. 2. Circuit that holds a radio receiver on the fre¬ quency of the station to which it is tuned. AUTOMATIC G-BIAS. (Reference. AUTOMATIC GRID BIAS.) AUTOMATIC GAIN CONTROL. 1. Type of circuit used to maintain the output volume of a receiver constant, regardless of vari¬ ations in the signal strength applied to the receiver. 39-64 1 APRIL 1959 AFM 100-39 AUT 2. Self-acting compensating device which main¬ tains the output of a transmission system constant within narrow limits in the face of wide varia¬ tions in the attenuation of the system. 3. Radar circuit which prevents saturation of the radar receiver by long blocks of received signals, or by a carrier modulated at low frequency. AUTOMATIC GAIN STABILIZATION. Circuit, used in certain IFF equipments and ra¬ dar beacon systems, which serves to maintain op¬ timum sensitivity in a superregenerative stage by keeping the noise pulse lead constant. The gain of the tube is controlled so that noise pulse, characteristic of a superregenerative re¬ ceiver, are held to a constant level while receiving signals are permitted to pass without limiting. The system thus prevents random noises from triggering the automatic transmitter associated with the receiver. AUTOMATIC GRID BIAS. Voltage drop formed by the passage of plate cur¬ rent of a vacuum tube through a resistor in its own cathode circuit. AUTOMATIC LEVEL COMPENSATION. System which automatically compensates for var¬ iations in the circuit. (Reference: AUTOMATIC VOLUME CONTROL.) AUTOMATIC MACHINE EQUIPMENT. Equipment that provides automatic control for any type of rotating machine or rectifier. AUTOMATIC MESSAGE ACCOUNTING SYSTEM. Apparatus for recording and processing on con¬ tinuous tapes the data required for computing telephone charges on certain classes of calls. The system may include provisions for compiling all charges and credits which affect the custo¬ mer’s bill and for automatic printing of the bill. AUTOMATIC MORSE TELEGRAPHY. Automatic telegraph transmission usually ac¬ complished by a code wheel or tape. automatic noise limiter. Vacuum tube circuit that automatically cuts off all noise peaks that are stronger than the highest peak in the desired signal being received, thereby preventing loud crashing noises due to strong atmospheric or man-made interference. AUTOMATIC NUMBERING EQUIPMENT. Type of equipment associated with tape trans¬ mitters which automatically transmits a channel number. AUTOMATIC PILOT. Control mechanism which initiates corrections in aircraft control surfaces so as to maintain a steady course without manual assistance. AUTOMATIC RADIO COMPASS. Radio direction finder having provisions for ro¬ tating the loop antenna automatically to the cor¬ rect position, so that a pilot can secure a radio bearing simply by glancing at the indicator dials, without making mechanical adjustments and _1 i.L AUTOMATIC RANGE, BEARING, OR ELEVATION MEASUREMENTS. System in which range, bearing, or elevation is determined automatically by a mechanism act¬ uated by an echo signal. AUTOMATIC RECLOSING. Means provided for automatically reclosing a circuit breaker after it has tripped under ab¬ normal conditions. AUTOMATIC REGULATOR. Device for regulating a system in such a manner that changes in its operation are initiated by changed conditions and carried out without the intervention of an attendant. AUTOMATIC RELAY. Means of selective switching which causes au¬ tomatic equipment to record and retransmit com¬ munications. AUTOMATIC SCANNING RECEIVERS. Receivers which can automatically and contin¬ uously sweep across a preselected frequency either to stop when a signal is found or to plot signal occupancy within the frequency spectrum being swept. AFM 100-39 AUT 1 APRIL 1959 AUTOMATIC SEARCH JAMMER. Intercept receiver and jamming transmitter sys¬ tem which automatically searches for and jams enemy signals of specific radiation characteris¬ tics. AUTOMATIC SENSITIVITY CONTROL. Circuit used for automatically maintaining recei¬ ver sensitivity at a predetermined level. Similar to automatic gain control, but it affects the re¬ ceiver constantly rather than during the brief in¬ terval selected by the range gate. AUTOMATIC SEQUENCING. Ability of a computer to perform successive op¬ erations without human intervention. AUTOMATIC SHORT-CIRCUITER. Device designed to automatically short circuit the commutator bars in some forms of single¬ phase commutator motors. AUTOMATIC START CIRCUIT. Circuit which automatically starts the recording of a facsimile transmission. AUTOMATIC STARTER. Device for starting a system, performing the var¬ ious starting operations in the correct sequence, and requiring no action by an attendant after being given the initial impulse by means of a push button or, similar device. AUTOMATIC STATION. Generating station, substation, radio station, etc. (usually unattended) that, under predeter¬ mined conditions, goes into operation automati¬ cally, and in correct sequence maintains the re¬ quired character of service by automatic means, provides protection against usual operating emer¬ gencies, and goes out of operation by automatic sequence under other predetermined conditions, AUTOMATIC SWITCHBOARD. Telephone switchboard in which the connections are made by using remotely controlled switches. AUTOMATIC SWITCHING. Method by which automatic connection is made between two or more teletypewriter circuits. AUTOMATIC SWITCHING EQUIPMENT. Equipment for making telephone connections au¬ tomatically without the assistance of manual operation. AUTOMATIC TELEGRAPH TRANSMISSION. Form of telegraphy in which telegraph signals are transmitted mechanically from a perforated tape. AUTOMATIC TELEGRAPHY. Method of telegraph operation in which, by the use of automatic apparatus, the manual operations involved are effectively reduced or eliminated. AUTOMATIC TELEPHONE SYSTEM. Telephone system in which telephone connec¬ tions between customers are ordinarily established by electrical and mechanical apparatus controlled by pulses produced by a calling device. AUTOMATIC TOLL TICKETING. System whereby toll calls are automatically re¬ corded, timed, and toll tickets printed, under control of the calling telephone’s dial pulses and without the intervention of an operator. AUTOMATIC TIME SWITCH. Combination of a switch with an electric or spring-wound clock, arranged to turn an appara¬ tus on and off at predetermined times. AUTOMATIC TRACKING. Process, in radar, whereby a mechanism actuated by an echo, automatically keeps the radar beam set on a target and simultaneously, automati¬ cally determines the range of the target. AUTOMATIC TRACKING RADAR. Radar set which can continually and automati¬ cally correct its beam orientation to keep a select¬ ed target in its beam. Some tracking radars also supply range tracking information to computers for fire control systems. AUTOMATIC TRAIN. Automatic training of the antenna in azimuth by automatic following of the target. AUTOMATIC TRANSFER EQUIPMENT. Equipment which automatically transfers a load so that a source of power may be selected from one of several incoming lines. 39-66 1 APRIL 1959 AFM 100-39 AUT AUTOMATIC TRANSFORMER EQUIPMENT. Equipment that provides automatic control for connecting and disconnecting additional trans¬ former capacity at an automatic station in re¬ sponse to overload and underload demands, respectively. AUTOMATIC TRIPPING. Opening of a circuit breaker, under predetermin¬ ed or other conditions, without the intervention of an operator. AUTOMATIC TUNING. . System that tunes a radio receiver automatically to a predetermined station when a button or lever is pressed. AUTOMATIC VIDEO NOISE LIMITING^ Classified definition. (Reference: AFM 100-50.) automatic voltage regulator. Device or circuit which maintains a constant vol tage. AUTOMATIC VOLUME CONTROL. 1. Self-acting compensating device which main¬ tains the output of a transmission system constant within narrow limits in the face of wide varia¬ tions in the attenuation in that system. 2 Self-acting device which maintains the output of a radio receiver or amplifier substantially constant within relatively narrow limits while the input voltage varies over a wide range. automatic volume expansion. Special audio-frequency circuit that increases t e volume range of a radio program or phonograph record by making loud portions louder and weak portions weaker. Since the volume range of a program is generally compressed at the point of broadcast, automatic volume expansion tends to make radio reception more like the actual pro¬ gram. AUTOMATIC-ALARM-SIGNAL KEYING DEVICE. Device capable of automatically keying the radio¬ telegraph transmitter on board a vessel so as to transmit the international automatic-alarm signal. AUTOMATIC-TRACK-WHILE SCAN. Classified definition. (Reference: AFM 100-50.) AUTOMATION. Device or mechanism that imates human actions. AUTOSYN. . . . , Trade name for an angular-position control de vice manufactured by Western Electric Co A telesynchronous device, similar to a selsyn (G.F.) or a synchro (Westinghouse), comprised of two units; a transmitter and an indicator, so arrange electrically that changes in the angular position of the transmitter are reproduced by the rotor of the indicator. autotransformer. 1. Transformer with a single winding (electri¬ cally) in which the whole winding acts as the primary winding, and only part of the winding acts as the secondary (stepdown); or part of the winding acts as the primary and the whole win - ing acts as the secondary (step-up). 2 Voltage, current, or impedance transforming device in which parts of one winding are common to both primary and secondary circuits. AUTOTRANSFORMER STARTER. Motor starter having an autotransformer to fur¬ nish a reduced voltage for starting. It includes the necessary switching mechanism and is fre¬ quently called a compensator or autostarter. iUX (AUXILIARY). That which aids and is additional to. The abbre¬ viation AUX is used in combination only as in ■ ' 1 ' r* n f\ AUTOMATIC-ALARM RECEIVER. Complete receiving, selecting, and warning de¬ vice capable of being actuated automatically by intercepted radio-frequency signals forming the international automatic alarm signal. ;iLIARY CONSOLE. onsole containing intervention switches, alarm , ad warning lights which an operator uses to erform his duties; the auxiliary console may or AFM 100-39 AUX 1 APRIL 1959 may not contain a digital-display tube and tele¬ phone equipment. AUXILIARY CONTACTS. Contacts, in a switching device, in addition to the main circuit contacts, which function with the movement of the latter. AUXILIARY CONTROL UNIT. Unit containing supplementary controls to main control and general control. AUXILIARY DEVICE. Separate piece of equipment used with an instru¬ ment to extend its range, increase its accuracy, or otherwise extend its operation capabilities. AUXILIARY FIRE ALARM BOX. Fire alarm box containing the apparatus necess¬ ary to trip a master fire alarm box from a remote point. AUXILIARY POSITION LIGHT. Light, in aeronautic lighting, used to supplement normal position lights. AUXILIARY RELAY. Relay which operates in response to the opening or closing of its operating circuit to assist another relay or device in the performance of a function. AUXILIARY SWITCH. Switch actuated by some main device such as a circuit breaker, for signaling, interlocking, or other purposes. AUXILIARY TRANSMITTER. Transmitter maintained only for transmitting the regular programs of a station in case of failure of the main transmitter. AUXILIARY-NORMAL CONTROL. Control used for selecting the source of main power to a system. av (AVIATION). Of or pertaining to aviation. The abbreviation av is used in combination only as in avCad mean¬ ing aviation cadet. av (AVIATOR). One whose profession is that of flying heavier- than-air aircraft. AVAILABLE LINE. Portion of the length of a scanning line which can be used for picture signals: Usually expres¬ sed as a percentage of the length of scanning line. For example, the Y-inch diameter drum of the TXC equipment has a circumference of 18.8”^ but 0.5” is required for clamping and 0.3” for variations in phasing; therefore the available line is 18” and the percentage is 96%. AVAILABLE POWER. 1. Available power, in communication practice, at a point in a circuit is the power that would be transferred past that point where the impedance looking toward the load conjugates to the im¬ pedance looking toward the source. 2. Mean square, in a linear source of electric energy, of the open circuit terminal voltage of the source divided by four times the resistive com¬ ponent of the impedance of the source. AVAILABLE-POWER GAIN. Ratio, in an electric transducer, of the available power from the output terminals of the trans¬ ducer, under specified input termination condi¬ tions, to the available power from the driv- ing generator. The maximum available-power gain is obtained when the input termination ad¬ mittance is the conjugate of the driving point admittance at the input terminals of the trans¬ ducer. A VC (AUTOMATIC VOLUME CONTROL). 1. Self-acting compensating device which main¬ tains the output of a transmission system con¬ stant within narrow limits in the face of wide variations in the attenuation in that system. 2. Self-acting device which maintains the output of a radio receiver or amplifier substantially con¬ stant within relatively narrow limits while the input voltage varies over a wide range. AVCS (ASSISTANT VICE CHIEF OF STAFF). AVERAGE NOISE FIGURE. Ratio in a transducer, of total output noise power to the portion thereof attributable to thermal 39-68 1 APRIL 1959 AFM 100-39 AVE noise in the input termination, the total noise being summed over frequencies from zero to in¬ finity, and the noise term temperature of the in¬ put termination being standard (290°K). AVERAGE POWER. Power supplied to the antenna during normal operations, averaged over a time sufficiently long, compared to the period corresponding to the low¬ est frequency encountered in actual modula¬ tion. (Reference: AVERAGE VECTOR POW¬ ER.) AVERAGE POWER OUTPUT. Radio-frequency power, in an audio-modulation transmitter, delivered to the transmitter output terminals, averaged over a modulation cycle. AVERAGE SPEECH POWER. Average value of the instantaneous speech po¬ wer for a given time interval. AVERAGE VALUE. 1. Value obtained by dividing the sum of a num¬ ber of quantities by the number of quantities re¬ presented. 2. Average of many instantaneous amplitude values taken at equal intervals of time during an alternation (half-cycle) of alternating current. The average value of an alternation of a pure sine wave is 0.637 times its maximum or peak amplitude value. AVERAGE VALUE OF A PERIODIC QUANTITY., Average of the values of the quantity taken throughout one period. AVERAGE VECTOR POWER. Power at the points of entry of an electrical cir¬ cuit, averaged over a time interval which con¬ tains a large number of periods of the ac, is equal to the square root of the sum of the squares of the averaged active power during the interval and of the average reactive power during the same interval. AVIATION. Of or pertaining to aviation. AVIATION CHANNEL. Band of frequencies assigned for radio commun¬ ication between aircraft and ground stations. AVIATION SERVICE. Radio communication or special service carried on by aircraft stations, airport control stations, aeronautical stations, aeronautical fixed stations, and flying-school stations. AVIATOR. One whose profession is that of flying heavier- than-air aircraft. AVOGADRO’S NUMBER. Number of molecules in a mass numerically eq¬ ual to its molecular weight. The number is 6.06 x 10 23 . AW (AIR WARNING). AW (AIRCRAFT WARNING). AWC (AIR WAR COLLEGE). School of the Air University charged with the schooling of senior officers for high command and staff duty, and with the development of doc¬ trine on the broad use of air power. AWG (AMERICAN WIRE GUAGE). AWIS (AUTOMATIC-TRACK-WHILE SCAN). Classified definition. (Reference: AFM 100-50.) AWR (AWAITING PARTS). AWS (AIR WEATHER SERVICE). Service under the Military Air Transport Service providing meteorological service primarily for the armed services. AWY (AIRWAY). Control area or portion thereof established in the form of a corridor equipped with radio navi¬ gational aids. AVERAGE VOLTAGE OF A STORAGE BATTERY. Average value of voltage during the period of charge or discharge. AXIAL LEADS. Leads coming out from the ends and along the axis of a resistor, capacitor, or other axial part. 39-69 AFM 100-39 AXI 1 APRIL 1959 AXIS. Straight line, real or imaginary, that passes through a body and about which the body may, or actually does, revolve. RADIOLOGICAL. Line drawn from the center of burst along the mean line of average wind direction. X. Reference axis in a quartz crystal. Y. Line perpendicular to two opposite parallel faces of a quartz crystal. AXIS OF SIGNAL COMMUNICATIONS. 1. Line or route, on which line the starting posi¬ tion and probable future location of the command post of a unit during a troop movement. 2. Main route along which messages are relayed or sent to and from combat units in the field. AXIS OF THRUST. Imaginary line drawn through the motor, along which the thrust or reaction of the motor is direc¬ ted. AXIS OR BORE. Center or straight line through the center of the bore of a gun. AYRTON SHUNT. High-resistance shunt used to increase the range of a galvanometer without changing the damping. AZ-EL DISPLAY. Modified type of PPI presentation showing two separate radar displays on one cathode-ray screen. One display presents bearing information and the other shows elevation. AZIMUTH. 1. Direction in the horizontal plane. Normally used in designating direction of a radio beam. 2. Used as a general term to indicate systems concerned with bearing information, e.g. azimuth scale or azimuth stabilization. 3. Direction, in celestial navigation, of one ob¬ ject from another expressed as an angle mea¬ sured clockwise from north. Measured from true north unless otherwise indicated. AZIMUTH ANGLE. Component of a wave angle which is measured about a vertical axis, clockwise from north, and indicates direction in the plane of the earth’s sur¬ face. AZIMUTH GAIN REDUCTION. Technique which allows control of the radar re¬ ceiver system throughout any two azimuth sec¬ tors. AZIMUTH INDICATING METER. Ground-station receiver used at airports to deter¬ mine the azimuth angle of arrival of signals to determine the azimuth angle of arrival of sig¬ nals from an airplane. The direction of arrival is shown on the screen of a cathode-ray tube and can be radioed to a pilot coming in through fog or darkness. AZIMUTH INSTRUMENT. Telescopic instrument used for measuring hori¬ zontal angles. AZIMUTH MECHANISM. Mechanical means provided for turning an in¬ strument in azimuth (in horizontal plane). It usually contains a worm and wormwheel to give accurate, smooth movement. AZIMUTH RATE. Rate of change of true bearing. (Reference: BEARING RATE.) AZIMUTH STABILIZATION. Presentation of indications on a radar display, so that north, or any specific reference line of direction, is always at the top of the screen. AZIMUTH STABILIZED PLAN POSITION INDICATOR. Presentation of signals on a plan position indica¬ tor arranged so the top of the screen represents a fixed direction and not the plane’s tail-nose axis. The fixed direction may be north or may be es¬ tablished by a gyroscope. 39-70 1 APRIL 1959 t AZON. Two-directional, radio-controlled missile. (Refer¬ ence: RAZON.) AZON BOMB. Ordinary 1,000-pound bomb, fitted with a special AFM 100-39 AZO tail assembly, which enables the bombardier of the plane to steer the bomb a limited degree to the right or left by a radio signal. AZUSA SYSTEM. Apparatus which measures missile velocity and position during flight. 39-71 AFM 100-39 B 1 APRIL 1959 B B (BIG PHOTO). Aircraft of the strategic air command participat¬ ing in training, missions with North American Air Defense Command. B (BOMBER). CAA designation for schedule Broadcast Station (Broadcasts weather at 15 and 45 minutes after the hour; Air Force broadcasts, generally 29 minutes). B-INDICATOR. Radarscope which displays target range and bearing by vertical and horizontal displacement on the radarscope face. (Reference: B-SCOPE.) B-OPERATOR. Operator assigned to a B-switchboard. B-POWER SUPPLY. Power source, for vacuum tubes, which provides a positive voltage for plate and other high-vol¬ tage electrodes. B Letter normally employed to denote the high vol- tage plate power supply for one or more vacuum tubes. B+ (B PLUS or B POSITIVE). The positive terminal of a B-battery or other plate-voltage source for a vacuum tube, or the plate-circuit terminal to which the positive source terminal should be connected. B- (B MINUS or B NEGATIVE). Negative terminal of a B-battery or other plate- voltage source for a vacuum tube, or the plate- circuit terminal to which the negative source terminal should be connected. B-BATTERY. Battery that furnishes required dc voltages to the plate and screen-grid electrodes of the vac¬ uum tubes in a battery-operated circuit. B-DRAWINGS. Schematics and wiring diagrams which are issued to cover special installations. B-ELIMINATOR. Power pack that changes ac power-line voltage to dc source required by vacuum tubes. B-H CURVE. Curve plotted on a graph to show successive states during magnetization of a ferromagnetic material. A normal magnetization curve is a por¬ tion of a symmetrical hysteresis loop, while a virgin magnetization curve shows what happens the first time the material is magnetized. B-SCAN. Radarscope presentation in which the signal ap¬ pears as a bright spot, with bearing as the hori¬ zontal coordinate and range as the vertical coor¬ dinate. B-SCOPE. Radarscope which displays target range and bearing by vertical and horizontal displacement on the radarscope face. (Reference: B-INDICATOR.) B-SUPPLY. Plate power source for vacuum tubes. B-SWITCHBOARD. Manual telephone switchboard in a local central office, primarily to receive and complete connec¬ tions from other central offices. BABBITT. Antifriction metal used to line bearings. BABBLE. 1. Aggregate crosstalk from a large number of disturbing channels. 2. Unwanted disturbing sounds in a carrier or other multiple channel system which result from the aggregate crosstalk or mutual interference from other channels. BABS (BLIND APPROACH BEACON SYSTEM). British pulse-type ground-based navigation bea¬ con used for runway approach. The system makes use of the interrogator-transponder prin¬ ciples utilized in the REBECCA/EUREKA sys¬ tem. The BABS ground beacon is installed be- 39-72 1 APRIL 1959 yond the far end of the runway on the extended centerline. When interrogated by the Rebecca in¬ terrogator it retransmits two diverging beams, one of short duration pulses and the other of longer duration pulses. The beams are trans¬ mitted alternately, but, due to the fast switching, the aircraft receives what appears to be a con¬ tinuous transmission of both beams. The two beams are aligned so as to form a line of equal signal amplitude extended along the centerline of the runway. A CRT in the aircraft displays both long and short pulses, superimposed on each other. If the aircraft is properly aligned with the runway, the pulses will be of equal ampli¬ tude. If to the left, the short pulses will be greater amplitude, and vice versa. Usually an Eureka beacon is provided to home to within range of the BABS beacon, which has a range of 14 to 20 miles when interrogated by aircraft at 1000 feet. BABS is capable of handling up to 30 aircraft at one time. The system does not provide glide path information. BACK. End of a motor or generator, which carries the coupling or driving pulley. BACK BIAS. 1. Degenerative or regenerative voltage which is fed back to circuits before its originating point. It is usually applied to a control anode of a tube. 2. Voltage applied to a grid of a tube (or tubes) to restore a condition which has been upset by some external cause. BACK CONNECTED SWITCH. Switch in which the current-carrying conductors are connected to the stud back of the mounting base. BACK CONTACT. Relay, key, jack, or other contact designed to close a circuit and permit a current to flow when, in the case of a relay, the armature has released or fallen back; in other cases, when equipment is inoperative. BACK ECHO. Echo due to back lobe of an antenna. AFM 100-39 BAC BACK ELECTROMOTIVE FORCE. Voltage developed in an inductive circuit by a changing or alternating current flowing through the circuit. The polarity of the voltage is, at each instant, opposite that of the applied voltage, and its amplitude is never greater than that of the applied voltage. BACK PORCH. Period of time, in a television circuit, immedi¬ ately following a synchronizing pulse during which the signal is held at back level. BACK PRESSURE. Result of resistance to the normal flow of gases and liquids. BACK-SHUNT KEYING OR SIGNALING. Method of keying a radio transmitter, in which RF energy is fed to the antenna when the key is closed and to an artificial load when the key is open. BACK-TO-FRONT RATIO. Ratio used in connection with antennas, metal rectifiers, or any device in which signal strength or resistance in one direction is compared to that in the opposite direction. BACKFIRE. Sudden failure of rectifier action in a mercury- vapor rectifier tube due to an internal fault. Sometimes caused by excessive density of mer¬ cury vapor resulting from overheating of the cathode. BACKGROUND. 1. Picture white of the copy being scanned when the picture is black and white only. Also un¬ desired printing in the recorded copy of the pic¬ ture being transmitted, resulting in shading of the background area. 2. Noise heard during a radio program caused by atmospheric interference or operation of the receiver at such high gain that inherent tube and circuit noises become noticeable. BACKGROUND RADIATION. Radiation indication due to presence of radio-ac¬ tive material in the vicinity of the measuring in¬ strument. 39-73 AFM 100-39 BAC 1 APRIL 1959 BACKLASH. Conditions wherein a gear forming part of a gear train may be moved without moving the next suc¬ ceeding or preceding gear; due to space between the teeth of the meshing gears. BACKSPACER. Mechanism which is designed to retract and re¬ set another item which moves in a predetermined path. BACKUP FACILITY. C-E facility which is established for the purpose of replacing or supplementing another C-E faci¬ lity or facilities, under real or simulated emer¬ gency conditions. The alternate facility is usually some other method of C-E. Frequently, radio al¬ ternate facilities are established to replace or supplement wire facilities. BADGE. (BASE AIR DEFENSE GROUND ENVIRONMENT). BAFFLE. 1. Barrier or partition used to increase the effec¬ tive length of the external transmission path be¬ tween two points in an acoustic system as, for example, between the front and back of an elec¬ troacoustic transducer. Baffle is often used to in¬ crease the acoustic loading of the diaphragm. 2. Shielding structure. 3. Device for deflecting oil or gas in a circuit breaker. BAFFLE PLATE. Metal plate inserted in a waveguide to reduce the cross-sectional area for wave conversion pur¬ poses. BAKELITE. Phenolic compound having good insulating qualities. Widely used in the construction of radio parts. BAL (BASE AUTHORIZATION LIST). List of all equipment specified by the unit allow¬ ance lists of the organizations (except tenant or¬ ganizations) at a particular Air Force base or installation. BALANCE. 1. Proper blending, of the different sounds that make up a radio program to give the desired artistic effect. 2. Proper positioning, in television of the vari¬ ous elements that make up a television scene to give the desired artistic effect. ACTIVE. Summation of all return currents, in telephone repeater operation, at a terminal network balanced against the impedance of the local circuit or drop. BALANCE-TO-UNBALANCE TRANSFORMER. Device for matching a pair of lines, balanced with respect to earth, to a pair of lines not bal¬ anced with respect to earth. BALANCED. 1. Electrically alike and symmetrical with res¬ pect to ground. 2. Arranged to provide balance between cer¬ tain sets or terminals. BALANCED AMPLIFIER. Amplifier circuit in which there are two identi¬ cal signal branches connected so as to operate with the inputs in phase opposition and with output connections in phase, each balanced to ground. (Reference: PUSH-PULL AMPLIFIER.) BALANCED ARMATURE UNIT. Driving unit used in magnetic loudspeakers, con¬ sisting of an iron armature pivoted between the poles of a permanent magnet and surrounded by coils carrying the AF current. Variations in AF current cause corresponding changes in arm¬ ature magnetism and corresponding movements of the armature with respect to the poles of the permanent magnet. BALANCED CIRCUIT. Circuit in which there are substantially equal cur¬ rents, either alternating or direct, in all main wires and substantially equal voltages between main wires and between each main wire and neu¬ tral wire. BALANCED LINE. Line or circuit which utilizes two conductors 39-74 1 APRIL 1959 AFM 100-39 BAL or components instead of one conductor or com¬ ponent and ground (common conductor). A bal¬ anced line is usually preferred when minimum noise and crosstalk are desired. BALANCED METHOD. Method of measurement in which the reading is taken at zero. It may be a visual or audible read¬ ing and in the latter case the null is the no-sound setting. (Reference: NULL METHOD, or ZERO METHOD.) BALANCED MODULATOR. Amplifier in which the tube control grids are connected for parallel operation, the screen grids for push-pull operation (used as injector grids), and the plates for operation in push-pull. In its use in FM transmitters, the original oscillator signal is applied to the control grids and the modulating signal to the screen grids. The out¬ put is a signal of the same frequency as the os¬ cillator, either in phase or 180° out of phase with it, and with an amplitude which depends upon the amplitude of the modulating signal. BALANCE NETWORK. Network designed for use in a circuit in such a way that two branches of the circuit are made substantially conjugate, i.e., such that a voltage introduced in one branch produces no change in current in the other branch. BALANCED OSCILLATOR. Oscillator in which the impedance centers of the tank circuit are at ground potential and the volt¬ age between either end and their centers are equal in magnitude and opposite in phase when os¬ cillating. BALANCED TRANSMISSION LINE. Transmission line having equal conductor resis¬ tances per unit length and equal impedances from each conductor to earth and to other electrical circuits. BALANCED WIRE CIRCUIT. Circuit whose two sides differ only by chance. BALANCER. Circuit used in a radio direction finder to bal¬ ance out the antenna effect due to capacitance \ between the loop and ground. Improves the sharpness of the direction indication. BALANCING NETWORK. 1. Network for use with a hybrid set to simulate the impedance of a transmission line. 2. Any electrical circuit used to conjugate two or more interconnected elements. BALANCING UNIT. 1. Small adjustable capacitors. 2. Small coils of wire added at splices to ad¬ just wire-to-wire capacity. BALLAST LAMP. Resistance lamp which maintains nearly constant current by increasing in resistance as the current increases. BALLAST RESISTANCE. Self-regulating resistance, usually connected in the primary circuit of a power transformer to compensate for variations in the line voltage. BALLAST RESISTOR. Special type of resistor used to compensate for fluctuations in ac power line voltage. It is usual¬ ly connected in series with the power supply to a receiver or amplifier. The resistance of a ballast resistor increases rapidly with increases in cur¬ rent through it, thereby tending to maintain es¬ sentially constant current despite variations in line voltage. BALLAST TUBE. 1. Current-controlling resistance device designed to maintain substantially constant current over a specified range of variations in the applied volt¬ age or the resistance of a series circuit. 2. Resistor consisting of an iron filament mount¬ ed inside an envelope filled with hydrogen. The ballast is rated to operate with the filament at temperatures as high as 690°C (1306°F). Here a crystalline change occurs if the heating current increases slightly. The hydrogen serves to dis¬ sipate the additional heat. BALLASTIC GALVANOMETER. Instrument that indicates the effect of a sudden rush of electrical energy, such as the discharge current of a capacitor. 39-75 AFM 100-39 BAL 1 APRIL 1959 BALLISTIC MISSILE. Missile which travels through most of its tra¬ jectory without guidance or continued propul¬ sion. BALLOON REFLECTOR. Balloon supporting confusion reflectors to pro¬ duce fraudulent echoes. BALLS OF FIRE. Pyrotechnic decoy consisting of free-falling balls which provide an intense source of infrared rad¬ iation. BALUN. 1. Antenna-matching device used to permit ef¬ ficient coupling of a transmitter or receiver hav¬ ing an unbalanced output circuit to an antenna having a balanced transmission line; consists of two bifilar-wound indictors. 2. Device for converting balanced to unbalanced transmission lines, and vice versa, by placing suitable discontinuities at the junction between the lines instead of using lumped components. BANANA JACK. Jack that fits a banana plug. Generally designed for panel mounting. BANANA PLUG. Banana-shaped plug; elongated springs provide a low resistance compression fit. Has a spring metal tip which somewhat resembles a banana in shape. BAND. 1. Range of frequency spectrum between two defined limits. 2. Used as applying to a group of radio chan¬ nels assigned (usually by FCC) to a particular type of radio service. A range of frequencies (per second) within two definite limits. Very low frequency (VLF) 10-30 kilocycles Low frequency (LF) 30-300 kilocycles Medium frequency (MF) 300-3,000 kilocy¬ cles High frequency (HF) 3-30 megacycles Very high frequency (VHF) 30-300 mega¬ cycles Ultra high frequency (UHF) 300-3,000 megacycles Super high frequency (SHF) 3,000-30,000 megacycles 3. Group of tracks on magnetic drum in an elec¬ tronic computer. CITIZEN’S RADIO. Band of frequencies be¬ tween 460 and 470 MC assigned for the use of the general public for communication purposes. BAND ELIMINATION FILTER. Filter network which rejects a given band of fre¬ quencies while passing frequencies to either side of this band. BAND OF FREQUENCIES. Frequencies existing between two definite lim¬ its. BAND PASS. Number of cycles per second expressing the dif¬ ference between the limiting frequencies at which the desired fraction (usually half-power) of the maximum output is obtained. BAND SELECTOR SWITCH. Switch which makes and breaks, at one time, all required connections to all tuning circuits in a receiver or transmitter in order to change over from one band of frequencies to another. BAND SPREAD. Refinement in the tuning system which makes it possible to separate stations on a crowded por¬ tion of the tuning dial. Used mostly in short¬ wave receivers. BAND SPREADING. 1. Spreading of tuning indications over a wide scale range to facilitate tuning in a crowded band of frequencies. 2. Method of double sideband transmission in which the frequency band of the modulating wave is shifted upward in frequency so that the sidebands produced by modulation are separ¬ ated in frequency from the carrier by an amount at least equal to the bandwidth of the original modulating wave, and second order distortion products may be filtered from the demodulator output. 1 APRIL 1959 AFM 100-39 BAN BAND SUPPRESSION FILTER. Filter designed to suppress a given band of fre¬ quencies. BAND SWITCH. Switch which makes and breaks, at one time, all required connections to all tuning circuits in a receiver or transmitter in order to change over from one band of frequencies to another. BANDAGE. Rubber ribbon about four inches wide for tem¬ porarily protecting a splice from moisture. BANDPASS FILTER. Circuit designed to pass, with nearly equal re¬ sponse, all currents having frequencies within a definite band, and to reduce substantially the amplitudes of currents of all frequencies outside that band. BANDPASS RESPONSE. Response characteristic in which a definite band of frequencies is transmitted uniformly. BANDSPREAD TUNING CONTROL. Separate tuning control provided on some short¬ wave receivers to spread stations in a single band of frequencies over an entire tuning dial. BANDSTOP FILTER. Filter having characteristics inverse to those of bandpass, barring frequencies within a defined band and offering low attenuation to those out¬ side. BANDWIDTH. 1. Bandwidth occupied by an emission is the band of frequencies comprising 99 percent of the total radiated power extended to include any discrete frequency on which the power is at least 0.25 percent of the total radiated power. 2. Range within the limits of a band. The width of a bandpass filter is generally taken as the limits between which its attenuation is not more than 3.0 decibels greater than its average atten¬ uation throughout its pass band. Also used in connection with receiver selectivity, transmitted frequency spectrum occupancy, etc. 3. In a given facsimile system, the difference in cycles per second between the highest and low¬ est frequency components required for the ade¬ quate transmission of the facsimile signal. 4. Least frequency interval, of a wave, outside of which the power spectrum of a time-varying quantity is everywhere less than some specified fraction of its value at a reference frequency. CAUTION: This definition permits the spec¬ trum to be less than the specified fraction within the interval. Note: Unless otherwise stated, the reference fre¬ quency is that at which the spectrum has its maximum value. 5. Range of frequencies, of a device, within which performance, with respect to some charac¬ teristic, falls within specific limits. NOMINAL. Maximum band of frequencies as¬ signed to a channel. RF (RADIO-FREQUENCY). Band of frequen¬ cies comprising 99 percent of the total radiated power extended to include any discrete fre¬ quency on which the power is at least 0.25 percent of the total radiated power. BANK. Aggregation of similar devices connected toge¬ ther and used in cooperation. As used in auto¬ matic switching, a bank is an assemblage of fixed contacts over which one or more wipers or brush¬ es move in order to establish electrical connec¬ tions. BANK WINDING. Compact multilayer form of coil winding, for the purpose of reducing distributed capacitance, in which single turns are wound successively in each of two or more layers; the entire winding proceeding from one end of the coil to the other, without return. BANK-AND-WIPER SWITCH. Switch in which electromagnetic ratchet mechan¬ isms are used to move the wipers to a desired group of terminals and to move the wipers over the terminals of this group to the desired bank contacts. 39-77 AFM 100-39 BAN 1 APRIL 1959 BANTAM JR. TUBE. Extremely small vacuum tube with a glass en¬ velope and special base. Used chiefly in hear¬ ing aids. BANTAM TUBE. Vacuum tube having a standard octal base, but a considerably smaller glass tube than a stand¬ ard glass tube. It is identified by the letters GT following the tube type number, and is usually equivalent, electrically, to the standard-size tube. BAR. 1. Centimeter-gram-second absolute unit of pres¬ sure equal to a pressure of one dyne per square centimeter. 2. Subdivision of a crystal slab, obtained by mak¬ ing two parallel saw cuts in planes perpendi¬ cular to the major surfaces of the slab. BAR MAGNET. Bar of hard steel that has been strongly mag¬ netized and holds its magnetism, thereby serving as a permanent magnet. BARIUM. Element; the oxide of which is used in the cat¬ hode coating of vacuum tubes. BARKHAUSEN EFFECT. Succession of abrupt changes in magnetization occurring when the magnetizing force acting on a piece of iron or other magnetic material is varied. grid and negative plate of a triode, caused by oscillatory electrons in the inter-electrode spaces. BARN. Classified definition. (Reference AFM 100-50.) BARRAGE JAMMERS. Electronic jammers which spread their energy over a band which is wide compared to a radar band¬ width. BARRAGE JAMMING. Simultaneous jamming of a number of adjacent channels or frequencies. BARRAGE, RESPONSIVE. Classified definition. (Reference: AFM 100-50.) BARRETTER. Early form of detector which works similar to present thermisters. BARRIER LAYER. Surface of contact between a metal and semi-con¬ ductor. It acts as a rectifier of alternating cur¬ rents. Some barrier layers when illuminated, gen¬ erate a voltage through photovoltaic action. The junction between the copper and cuprous oxide in the photoelectric cell is a barrier layer. (Reference: BLOCKING LAYER.) BARRIER-FILM RECTIFIER. Rectifier in which a film having unilateral (sin¬ gle-direction) conductivity is in contact with metal or other normally conducting plates. BARKHAUSEN INTERFERENCE. Interference caused by Barkhausen oscillations. BARKHAUSEN OSCILLATOR. Type of triode oscillator in which radio frequen¬ cies ranging from 300 to 1,500 me are gener¬ ated. The plate is negative and the grid is posi¬ tive with respect to the cathode. BARKHAUSEN-KURZ OSCILLATOR. Circuit for generating ultra-high frequencies; the operation of which is dependent on the var¬ iation in the electrical field, about the positive BARRIER-LAYER CELL. Type of photovoltaic cell in which light acting on the surface of contact between layers of copper and cuprous oxide causes an electromotive force to be produced. (Reference: BLOCKING-LAY¬ ER CELL.) BARYTRON. Early name for the particle now known as a me¬ sotron. 1. Number upon which a system of logarithms is based, such as 10 in the common system or e (in the natural system equal to 2.718). C 39-78 1 APRIL 1959 2. Bottom, or principal surface on which a switch or vacuum tube is built up. (Reference: POSITIONAL NOTATION.) BASE ALLOWANCE LIST. Variant name for Base Authorization List. BASE AUTHORIZATION LIST. List of all equipment specified by the unit allow¬ ance lists of the organizations (except tenant organizations) at a particular Air Force base or installation. BASE BAND. 1. Band of frequencies, generally extending from near zero frequency, containing all the fre¬ quency components of a multiplex signal. 2. Frequencies containing the intelligence used to modulate the carrier of a radio relay system. BASE FREQUENCY. Frequency, in any wave, which is considered to be the most important. In a driven system, it would, in general, be the driving frequency while in most periodic weaves it would corres¬ pond to the fundamental frequency. BASE INSULATOR. Heavy-duty insulator used to support the weight of an antenna mast and insulate the mast from the ground of some other surface. BASE LINE. Horizontal (or vertical) line formed by the movement of the sweep on a cathode-ray tube. BASE LINK BREAK. Technique in radar which utilizes the character¬ istic break in the base line on an A-scope display due to a pulse signal of significant strength in noise jamming. BASE LOAD. Minimum load, of a power generator, over a given period of time. BASE OPS (BASE OPERATIONS). BASE RATE AREA. Area within the exchange in which all types of service are given without milage charges. AFM 100-39 BAS BASE SECURITY COMMUNICATIONS SYSTEM. Two-way radio communications system consist¬ ing of a base station and one or more portable and/or mobile units, used for the prompt and efficient control of air police and office of spec¬ ial investigations personnel and vehicles. BASE SPEED. Lowest speed, of an adjustable-speed motor, ob¬ tained at rated load, voltage, and temperature. BASE STATION. Land station, in the land mobile service, carry¬ ing on a service with land mobile stations. (A base station may secondarily communicate with other base stations incident to communication with land mobile stations.) Sometimes defined as a station in a land mobile system which remains in a fixed location and communicates with mo¬ bile stations. BASE SUPPORT EQUIPMENT. That equipment provided a base or organiza¬ tion, in addition to unit essential equipment, to enable the base to perform its assigned mission. BASE WIRE AND TELEPHONE SYSTEM. Facilities, both government-owned and commer¬ cial, on and off base, which are part of the over¬ all base switchboard and switching facilities, outside plant, station equipment, and support¬ ing structures. The entire system includes, but is not limited to, the following: 1. Administrative telephone system. (a) Switchboard positions and associated switching equipment, power plant, etc. (b) Local and foreign exchange trunk lines. (c) Tie lines to other Air Force bases or in¬ stallations. (d) PBX stations and bridged stations lo¬ cated on and off base. (e) Long distance toll terminals. (f) Miscellaneous equipment and services offered by the telephone companies un¬ der filed tariffs. 39-79 AFM 100-39 BAS 1 APRIL 1959 2. Message tool telephone service. 3. Message telegraph service. 4. Fire-reporting telephone systems. 5. Aircraft accident emergency alarm communi¬ cations systems. 6. Security telephone systems. 7. Auxiliary and satellite telephone systems. 8. Intercommunicating systems. 9. Public address systems. 10. Local weather disseminating system. 11. Remote lines to radio stations and naviga¬ tional aids, and fixed meteorological facilites. 12. Fire detection and alarm systems which meet technical limitations of telephone cables. BASE-LOADED ANTENNA. Vertical antenna, having an inductance in series at the base for loading the antenna to secure a desired electrical length. BASIC CODE. Code book which is used solely as part of a com¬ posite system, the groups of which are never transmitted unenciphered but are used only to provide groups for use with cipher tables or pads. BASIC NETWORK. Electrical network designed to simulate the im¬ pedance and neglecting dissipation of a line at a particular termination. BASKET WINDING. Winding used on ac machines in which the coils are interlinked with each other like the links of a chain. BASS. Sounds in the low audio-frequency range. On the standard piano keyboard, all notes below middle C (256 cycles per second). BASS COMPENSATION. Emphasizing the low-frequency response of an audio amplifier at low volume levels to offset the lowered sensitivity of the human ear to weak, low frequencies. BASS CONTROL. Control provided in radio receiver or AF ampli¬ fier to attenuate higher audio frequencies and thereby emphasize bass notes. BASS REFLEX. Method of extending the low-frequency range of a loudspeaker; accomplished by an opening in the cabinet enclosing the speaker. BASS RESPONSE. 1. Extent to which a loudspeaker or audio-fre¬ quency amplifier handles low audio frequencies. 2. Ability of any device to pick up or reproduce low audio frequencies. BASS-BOOSTING CIRCUIT. Circuit that attenuates higher audio frequencies in order that low or bass frequencies will be em¬ phasized by comparison. BASSY. Term applied to sound reproduction that over¬ emphasizes low-frequency notes. BAT. (BATTLE). 1. Conflict between individuals, groups of in¬ dividuals, or nations, especially an armed con¬ flict within the framework of a war. Attributed with damage, dress, fatigue gear, formation, etc. 2. Specifically an air battle. Attributed with air¬ craft; comparable to combat. BAT. (BATTLESHIP). One of a class of the largest and most heavily armed and armored vessels. BAT-HANDLE SWITCH. Toggle switch having an actuating lever shaped like a baseball bat. BATHTUB CAPACITOR. Popular name for a type of capacitor inclosed in a metal housing having broadly rounded cor¬ ners like those on a bathtub. 1 APRIL 1959 AFM 100-39 BAT BATTERY. 1. Device for converting chemical energy into electrical energy. 2. Series of several galvanic cells which, when assembled, produce electrical current. Note: The term battery is normally used when referring to a group of dry cells or stor¬ age cells. A. Source of energy which heats the filaments of a vacuum tube. B. Source of energy which causes current to flow in the plate circuit of a vacuum tube. C. Source of energy which supplies a voltage for biasing the grid of a vacuum tube. ALKALINE. Secondary cell or battery using an alkaline solution as the electrolyte. COMMON. System of current supply where all dc energy for a unit of a telephone system is taken from one source in a central office. FILAMENT. Source of energy which heats the filaments of a vacuum tube. FLOATED. Storage battery kept in a state of full charge across the leads of a generator. The generator carries the load but the battery absorbs any peak loads. GRID. Source of energy which supplies a vol¬ tage for biasing the grid of a vacuum tube. LOCAL. Battery made of single dry cells located at the subscriber’s station and distinguished from common battery. PBX (PRIVATE BRANCH EXCHANGE). Source of energy for the operation of a pri¬ vate branch exchange. PLATE. Source of energy which causes current to flow in the plate circuit of a vacuum tube. QUIET. Source of energy of special design or with added filters which is sufficiently quiet and free from interference so that it may be used for speech transmission. SIGNALING. Source of energy used to operate lamps and alarms for calling attention, to show the progress of a call, or to operate stepping magnets. TALKING. Source of energy of special design or with added filters which is sufficiently quiet and free from interference that it may be used for speech transmission. TESTING. High-voltage low-current source of energy used at test boards and test desks for the operation of Wheatstone bridges, and volt¬ meters. BATTERY ACID. Solution that serves as the electrolyte in a stor¬ age battery. In common lead-acid storage bat¬ tery, the electrolyte is dilute sulphuric acid (H 2 so 4 ). BATTERY ALARM. Signal calling attention to an abnormal power supply condition. BATTERY BOX. Case holding dry cells for subscriber’s local set. BATTERY CHARGER. Device used to convert alternating current into a pulsating direct current which can be used for charging a storage battery. BATTERY CLIP. Metal clip having a terminal to which a con¬ necting wire can be attached and spring jaws that can be quickly snapped on a battery termin¬ al or other point to which a temporary connec¬ tion is desired. BATTERY PAIR. Paired conductors for supplying current. BATTERY RECEIVER. Radio receiver that obtains power, required by its vacuum tubes, from batteries. 39-81 AFM 100-39 EAT 1 APRIL 1959 BATTLE. 1. Conflict between individuals, groups of in¬ dividuals, or nations, especially an armed con¬ flict within the framework of a war. Attributed with damage, dress, fatigue gear, or formation, etc. 2. Specifically an air battle. Attributed with air¬ craft; comparable to combat. BATTLE SHORT. Switch for short-circuiting safety interlocks and lighting a red warning light. BATTLE STAFF. Officers of the military services assigned to an organization and designated by its commander to supervise air-defense operations within the organization’s area of responsibility. BATTLE STATIONS. Degree of preparedness that required an inter¬ ceptor or fire unit to be capable of immediately initiating a tactical scramble or an effective en¬ gagement. BATTLESHIP. One of a class of the largest and most heavily armed and armored vessels. BAUD. 1. Unit of signaling speed. The speed in bauds is the number of code elements per second. 2. Term used to define the operating speed of a printing telegraph system. (The total number of mark and space—on and off—code elements per second). A teleprinter, running at such a speed that the maximum line frequency is 22.5 cps, is said to be operating at 45 bauds. BAY. 1. Row of racks on which apparatus, in the form of panels or shelves, is mounted. 2. Vertical compartment in which a radio trans¬ mitter or other equipment is housed. 3. Portion of an antenna array. BAYONET BASE. Base having two projecting pins on opposite sides of a smooth cylindrical base, to engage in corresponding slots in a bayonet socket and hold the base firmly in the socket. BAYONET SOCKET. Socket for bayonet-base tubes or lamps having slots on opposite sides and one or more contact buttons at the bottom. BAZOOKA. 1. Device used to match an unbalanced high-fre¬ quency transmission system into a balanced sys¬ tem, or vice versa. 2. Device used on a coaxial line to isolate the outer conductor from ground. BB (BOMB). 1. Explosive or other lethal agent together with its container or holder, which is planted or thrown by hand, dropped from an aircraft, or projected by some other low-speed device and used to destroy, damage, injure, or kill. 2. Similar to this object in appearance, opera¬ tion, or effect, a leaflet bomb, smoke bomb, pho¬ toflash bomb, a bomb-like container or chamber, etc. 3. To drop a bomb or bombs on a target, as a city, railyard or body of troops. BBC (BRITISH BROADCASTING COMPANY). BC. ITU designation for broadcasting station. BCF. ITU designation for FM broadcasting station. BCI. ITU designation for facsimile broadcasting sta¬ tion. BCST (BROADCAST). Radio broadcast of messages for which re¬ ceiving stations make no receipt. BCT. ITU designation for television broadcasting sta¬ tion. 1 APRIL 1959 AFM 100-39 BEA BEACH MARKER. Device used to identify a beach or certain activi¬ ties thereon, for incoming water-borne traffic. BEACON. 1. Apparatus which transmits radio or radar beams for the purpose of orienting aircraft or radars. 2. Aeronautical light arranged, either through optical design or mechanical motion, to be visi¬ ble at all azimuths, either continuously or con¬ secutively, to designate a particular point on the surface of the earth. AIRPORT. Beacon (light or radio) located at or near an airport for the purpose of indicat¬ ing the location of the airport. AIRPORT RUNWAY. Radio-range beacon that defines one or more approaches to an airport. AIRWAY. Beacon, other than an airport bea¬ con, located on or near an airway, and used for the purpose of indicating the location of the airway. FAN MARKER. Radio beacon which radiates in a vertical fan shaped pattern. The signal can be keyed for identification purposes. H. Nondirectional radio homing beacon which has a power output of 50 to 2000 watts. HAZARD. Light beacon used to designate an extended or particularly dangerous hazard to air navigation. HH. Nondirectional radio homing beacon, which has a power output of 2000 watts or greater. HOMING. Radio transmitter which emits a dis¬ tinctive or characteristic signal used for the determination of bearings, courses, or location. IDENTIFICATION. Code beacon used to iden¬ tify, positively, a particular point on the sur¬ face of the earth. MH. Nondirectional radio homing beacon hav¬ ing an output power of 50 watts or less. OSCILLATING. Beacon having an undulating beam characteristic brought about by periodic motion of the light source near the focal point of the optical system. RADAR. Transponder used as a navigation bea¬ con, which, when used in conjunction with other suitable equipment, permits the determi¬ nation of bearing and/or range from the interrogator to the RACON. RADIO. Radio transmitter which emits a dis¬ tinctive or characteristic signal used for the determination of bearings, courses, or loca- cation. RADIO MARKER. Radio navigation land sta¬ tion in the aeronautical radio navigation serv¬ ice which provides a signal to designate a small area above the station. RADIO RANGE. Radio navigation land station in the aeronautical radio navigation service providing radio equisignal zones. ROTATING. Light beacon having a flashing beam characteristic brought about by mechani¬ cal rotation of the optical system about a verti¬ cal axis. Z MARKER. Equipment identical to the fan marker except that it is installed as part of a four course radio range station at the intersec¬ tion of the four range legs and radiates verti¬ cally to indicate to aircraft when they pass directly over the range station. It is usually not keyed for identification. BEACON COURSE. Equisignal zone created by a radio beacon to guide aircraft along charted courses. BEAD. Glass, ceramic, or plastic insulators through which the inner conductor of a coaxial trans¬ mission line passes, and by means of which the inner conductor is supported in a position coax¬ ial with the outer conductor. BEAD SUPPORT. Ceramic, glass, or plastic beads used to support the inner conductor in coaxial transmission lines. 39-83 AFM 100-39 BEA 1 APRIL 1959 BEADED TRANSMISSION LINE. Line using beads to maintain the inner conduc¬ tor in coaxial transmission lines. BEAM. 1. Directed flow of energy into space. 2. Directional antenna. 3. Directed flow of electrons in a vacuum tube. 4. Constant unidirectional radio signal that is transmitted by an aircraft radio beacon for gui¬ dance of aircraft. An aircraft flying exactly on the course indicated by a radio beam is said to be flying the beam, or on the beam. 5. Angular range over which a microphone or loudspeaker gives maximun response. 6. Shaft or column of light; bundle of rays. PENCIL. Radar beam in which the energy is confined to a narrow, approximately conical portion of space. RADIO. Radio transmission along a very narrow selected path. BEAM ANGLE. Angle between the directions, on either side of the axis, at which the intensity of the radio-fre¬ quency field drops to one-half the value it has on the axis. BEAM ANTENNA. Antenna that concentrates its radiation into a narrow beam in a definite direction. BEAM ATTACK. Attack directed against the side of a target. BEAM CURRENT. 1. Current carried by the electron stream that forms the beam in a cathode-ray tube. 2. Total anode current in a velocity-modulation tube. The actual current in the beam is smaller than the total anode current because focusing is never perfect. BEAM FORMING PLATES. Electron beam focusing elements in power tet¬ rodes, and/or in cathode-ray tubes. BEAM LOBE SWITCHING. Method of determining the direction of a remote object by comparison of the signals correspond¬ ing to two or more successive beam angles, dif¬ fering slightly from the direction of the object. BEAM POWER TUBE. 1. Vacuum tube in which a directed electron beam results in greater power output. Used in the output stages of radio receivers and in other electronic apparatus. 2. Tetrode or pentode in which the electron stream is directed to flow in concentrated beams from the cathode to the plate. BEAM RIDER GUIDANCE. Missile guidance wherein a missile, through a self-contained mechanism, automatically guides itself along a beam. BEAM SWITCHING. Method of obtaining more accurately the bearing and/or elevation of an object by comparing the signals received when the beam is in directions differing slightly in bearing and/or elevation. When these signals are equal, the object lies midway between the beam axis. BEAM TRANSMISSION. Radio transmission concentrated into a beam by specially constructed directional antenna. BEAM VOLTAGE. Voltage between the cathode and anode which determines the average velocity of the electrons in the beam. BEAMWIDTH. 1. Angle between the directions, on either side of the axis, at which the intensity of the radio frequency field drops to one-half the value it has on the axis. 2. Width of the sector of effective radiation (or effective pick-up) of an antenna. Measured in degrees and normally taken as the angle be¬ tween the half power points on the polar pat¬ tern of the antenna. (Reference: BEAM ANGLE.) BEARING. 1. Situation of one point with respect to another. 1 APRIL 1959 AFM 100-39 BEA Unless otherwise stated, all bearings are mea¬ sured at the position of an observer, clockwise from 0° to 360°. 2. Line-of-sight direction, relative to a desig¬ nated point, usually true or compass north, from the observer (radar antenna) to the target. 3. Support for a rotating shaft. CLASS A. Bearing which a direction finding operator may reasonably consider to be accur¬ ate to within plus or minus two degrees. CLASS B. Bearing which a direction finding operator may reasonably consider to be accurate to within plus or minus five degrees. CLASS C. Bearing which a direction finding operator may reasonably consider to be accur¬ ate to within plus or minus ten degrees. GRID. Bearing in which the direction of the reference line is grid north. MAGNETIC. Angular line of position of an ob¬ ject in respect to the earth’s magnetic north pole, expressed in degrees clockwise from that pole. OMNI. Bearing, usually magnetic, of an omni¬ directional radio range as observed from a ve¬ hicle. RADIO. Angle between the apparent direction of a definite source of emission of electromag¬ netic waves and a reference direction, as determined at a radio direction-finding station. A true radio bearing is one for which the reference direction is that of true north. A magnetic radio bearing is one for which the reference direction is that of magnetic north. RECIPROCAL. Bearing plus or minus 180°. RELATIVE. Direction of an object measured clockwise in degrees from a ship or aircraft heading. TRUE. Bearing given in relation to true geo¬ graphic north. BEARING BUZZER. Buzzer and its attendant circuit used to indicate transmission of a bearing to a remote station. BEARING CURSOR. Mechanical bearing line on a PPI-type display for reading target bearing. BEARING DEVIATION INDICATOR. One of the units in an underwater sound system, serving to indicate the direction of an arriving echo with relation to true north or to some major axis of the ship. BEARING RATE. Rate of change of true bearing. BEARING RESOLUTION. Minimum angular separation in a horizontal plane between two targets at the same range that will allow an operator to obtain data on either individual target. BEAT. Periodic variation in amplitude set up by the phenomenon of beating; that is, the interfer¬ ence with each other of two waves of different frequencies. BEAT FREQUENCY. One of the two additional frequencies produced when two different frequencies are combined. One of these beat frequencies is the sum of the two original frequencies and the other is the difference between them. BEAT FREQUENCY OSCILLATOR. Oscillator which produces a desired frequency by combining two frequencies. The frequency may be an audio-frequency produced by combining two radio-frequencies, or it may be some desired radio-frequency, such as the intermediate-fre¬ quency of a superheterodyne circuit. BEAT NOTE. Frequency resulting from combining two differ¬ ent frequencies. It is numerically equal to the difference between these two frequencies. BEAT RECEPTION. Process of reception in which a received high frequency wave is combined in a non-linear de¬ vice with a locally generated wave, with the re¬ sult that in the output there are frequencies eq¬ ual to the sum and difference of the combining frequencies. If the received waves are continuous waves of constant amplitude, as in telegraphy, it 39-85 AFM 100-39 BEA 1 APRIL 1959 is customary to adjust the locally generated fre¬ quency so that the difference of the frequencies is audible. If the received waves are modulated, the locally generated frequency is generally such that the difference frequency is superaudible and an additional operation is necessary to repro¬ duce the original signal wave. BEAT TONE. Musical tone due to beats, produced by the heter¬ odyning of two HF w ave trains. BEATING. 1. Phenomenon in which two or more periodic quantities of different frequencies add linearly to produce a resultant having pulsations of am¬ plitude. 2. Combination of two or more frequencies to produce beats. BEATING-IN. 1. Splicing, by hammering down the end of a lead sleeve so that it fits the cable sheath. 2. Interconnecting two transmitter oscillators and adjusting one until no throbbing is heard in a connected receiver. The oscillators are then at the same frequency. BEATS Periodic variations that result from the super¬ imposition of waves having different frequencies. The term is applied both to the linear addition of two waves, resulting in a periodic variation of amplitude, and to the non-linear addition of two waves, resulting in new frequencies, of which the most important usually are the sum and difference of the original frequencies. BEAVER TAIL. Medium range radar height-finder, AN/CPS-4. This set is air transportable and may be mounted on a vehicle, ground or tower. Operates in the 2700-2900 MC band and has a range of 90 miles. Peak power is 750 kilowatts. (Reference: BIG ABNER.) BEL. Unit of relative power expressing the relation between amounts of signal power and differ¬ ences in sound-sensation levels. The number of bels is equal to the common logarithm of the ratio of the two powers or sound levels involved. Two powers or levels differ by one bel when their actual ratio is 10:1. BELL BOX. Apparatus associated with a desk stand or hand telephone set, comprising a housing (usually ar¬ ranged for w'all mounting) within which are those components of the telephone set not con¬ tained in the desk stand or hand telephone set. BELL CRANK. Lever with two arms generally placed at right angles with a common fulcrum at their junc¬ tion. BELL TRANSFORMER. Small iron-core transformer having a primary coil that connects to an ac primary line and a secondary coil that delivers 10 to 20 volts, for operation of a doorbell, buzzer, or chimes. BELL WIRE. Cotton-covered copper wire, usually number 18, used for doorbell and thermostat connections in homes and for similar low-voltage work. BELLINI-TOSI DIRECTION FINDER. Early radio direction finder that consists of two loop antennas at right angles to each other and connected to a goniometer. BELT, BODY. Heavy belt passed around the waist, equipped with D-rings for fastening the safety belt. Has loops or keepers for tools. BELT, SAFETY. Heavy, adjustable belt passed around a pole and snapped to the D-rings of the body belt. BELT, TOOL. Leather strap worn about the waist with loops and pockets for holding hand tools. BEND. Change in the direction of the longitudinal axis of a waveguide. 1 APRIL 1959 AFM 100-39 BEN BENDER, CABLE. Tool for putting curves or bends in cables when placing them in valuts, manholes, or when rack¬ ing. BENETO. CW navigational system in which the distance to an aircraft is determined on the ground by a phase differential measurement of an audio sig¬ nal transmitted from the ground and retrans¬ mitted by aircraft. Bearing information is obtain¬ ed by ground direction finding of the aircraft signals. BENT-SHANK NEEDLE. Phonograph needle intended for use with heavy phonograph pickups because it lessens needle pressure on the record. BETA. 1. Greek letter B, often used to designate an¬ gles or quantities. 2. Symbol used to denote B-quartz. 3. X-ray frequency. BETA 57-1. Code system, used in astronautics, for identi¬ fying earth satellites. This system was used in the Sputnik II satellite and attached rocket launching vehicle. BETA PARTICLE. Negatively charged particle emitted by cer¬ tain radio active substances. The beta particle is a high-speed electron having energies such as would be obtained by accelerating an electron by a potential of ten thousand to several million volts. While beta particles are emitted by the nu¬ cleus it is believed that they are created (and immediately emitted) by a transformation in tne nucleus. BETA QUARTZ. Name given to the high-temperature hexagonal modification of silica, stable above 373 degrees. BETA RAYS. 1. Electrons given off by radioactive atoms. 2. Rays consisting of beta particles. BETATRON. Induction electron accelerator. It speeds elec¬ trons just as a cyclotron speeds positive particles. BEVERAGE ANTENNA. Directional antenna consisting of a very long wire, supported a few feet (up to 13) above the ground, running horizontally in the direc¬ tion of the arrival of the incoming waves. BEZEL. Holder designed to receive and position the edges of a lens, window, or dial glass. BFO (BEAT FREQUENCY OSCILLATOR). Oscillator which produces an audio frequency by combining two other frequencies. This fre¬ quency may be an audio-frequency produced by combining two radio-frequencies, or it may be some desired radio-frequency, such as the inter- mediate-frequency of a superheterodyne circuit. BIAS. 1. Electrical, mechanical, or magnetic force which is applied to a relay, vacuum tube, or other device, for the purpose of establishing an electrical or mechanical reference level for the operation of the device. 2. DC potential applied to the control grid of a vacuum tube. 3. Bias derived from a direct current, used on signaling or telegraph relays or electromagnets to secure desired time spacing of transitions from marking to spacing. 4. Method of restraining a relay armature, by means of spring tension, to secure a desired time spacing of transitions from marking to spacing. 5. Average dc voltage between the control grid and cathode of a vacuum tube. 6. Effect on teletypewriter signals produced by the electrical characteristics of the line and the equipment. 7. Energy applied to a relay to hold it in a given position. 39-87 AFM 100-39 BIA 1 APRIL 1959 8. Distortion produced by line bias. CATHODE. Method of biasing a vacuum-tube by placing the biasing resistor in the common cathode-return circuit, making the cathode more positive, rather than the grid more nega¬ tive, with respect to ground. FIXED. Bias voltage of constant value, as one obtained from a battery, power supply, or gen¬ erator. GRID. DC voltage applied between the grid and the cathode of an electron tube. RELAY. Bias produced by a spring or an elec¬ tromagnet acting on the armature of the relay, which tends to hold the armature in a given position (usually the spacing condition on a teletypewriter). SELF. Voltage developed as a result of the flow of vacuum-tube current through a resis¬ tor in a grid or cathode lead. SIGNAL. Form of teletypewriter signal distor¬ tion brought about by the lengthening or shortening of pulses during transmission. When marking pulses are all lengthened, a marking signal bias results; when marking pulses are all shortened, a spacing signal bias results. ZERO. 1. Condition in which there is no poten¬ tial difference between the control grid and the cathode. 2. When the received teletypewriter signal is equal to the transmitted signal (neither longer nor shorter), the circuit is said to have zero bias. BIAS CELL. Dry cell used in the grid circuit of a vacuum tube to provide the required C bias voltage. BIAS DISTORTION. Uniform shifting of the beginning of all tele¬ typewriter marking pulses from their proper posi¬ tions in relation to the beginning of the start pulse. BIAS METER. Used in teletypewriter work for measuring sig¬ nal bias directly in percent. A positive reading, on the meter indicates a marking signal bias; a negative reading on the meter indicates a spac¬ ing signal bias. BIAS VOLTAGE. Voltage applied or developed between two vac¬ uum tube electrodes (generally the control grid and cathode) to influence the effect of the sig¬ nal voltage in the input circuit of these two electrodes. BIASED TELEPHONE RINGER. Telephone ringer, the clapper driving element of which is normally held toward side by mech¬ anical forces or by magnetic means, so that the ringer will only operate on half cycles of alter¬ nating current, or on electrical pulses in one direc¬ tion. BIASING RESISTOR. Resistance so connected into a self-biasing vac¬ uum tube circuit that it produces the voltage drop required to provide a desired biasing voltage. BIAXIAL. Having two axes. BICONICAL ANTENNA. Antenna formed by two conical conductors hav¬ ing a common axis and vertex, is excited at the vertex. When the vertex angle of one of the cones is 180°, the antenna is called a discone. BIDIRECTIONAL. Responsive in two opposite directions. An ordin¬ ary loop antenna is bidirectional because it has maximum response from the two opposite direc¬ tions that are in the plane of the loop. BIDIRECTIONAL ANTENNA. Antenna having two directions of maximum re¬ sponse. BIDIRECTIONAL CURRENT. Current which has both positive and negative values. 1 APRIL 1959 AFM 100-39 BID BIDIRECTIONAL PULSES. Pulses, some of which rise in one direction and the remainder in the other direction. BIFILAR. Transformers, inductors, and the like are said to be bifilar wound, when, to achieve a desired balance (similarity between winding), two con¬ ductors are wound simultaneously, side by side. BIFILAR SUSPENSION. Suspension of a body by two vertical wires or similar supports, providing considerable controll¬ ing torque. BIFILAR WINDING. Method of winding noninductive resistors. The wire is first doubled on itself, then wound double, starting from the loop. BIFURCATED. Single contact whose end is divided into two parts or is fork shaped. BIG ABNER. Medium range radar height-finder, AN/CPS-4. A smaller height-finder, the AN/TPS-10 is known as Little Abner. The AN/CPS-4 is air transportable and may be mounted on a vehicle, ground, or tower. It operates in the 2700-2900 MC band. Range is 90 miles and peak power is 750 kilowatts. (Reference: BEAVER TAIL.) BIG PHOTO. Aircraft of the Strategic Air Command partici¬ pating in training missions with North Ameri¬ can Air Defense Command. BILATERAL. Having, or arranged upon, two sides. BILATERAL ANTENNA. Antenna, such as a loop, having maximum re¬ sponse in exactly opposite directions (180° apart). BILATERAL BEARING. Bearing which indicates two possible directions of wave arrival. One of these is the true bearing and the other is a bearing displaced 180° from the true bearing. BILATERAL CIRCUIT. Circuit wherein equipment at opposite ends is managed, operated, and maintained by different services. BILLBOARD ANTENNA. Broadside array with flat reflectors. BILLING PERIOD. Period of service covered by the bill of a com¬ munication company. BIMETALLIC STRIP. Strip formed of two dissimilar metals welded to¬ gether. The metals have different temperature coefficients of expansion, causing the strip to bend or curl when the temperature changes. BIMORPH CELL. Two crystal elements (usually rochelle salt) in rigid combination, arranged to act as a mechani¬ cal transformer in headphones, microphones, pick-ups, and loudspeakers. BINARY. Name of a number system used in electronic com¬ puters, whose successive digits are interpreted as coefficients of the successive powers of the base two. BINARY CELL. Elementary unit of storage which can be placed in either of two. stable states. BINARY CODE. Code in which each element may be either of two distinct kinds of values; for example, the pre¬ sence or absence of a pulse. BINARY NUMBER SYSTEM. Positional number system in which the successive digits are interpreted as coefficients of the suc¬ cessive powers of the base two (just as they are related to successive powers of the base ten in the decimal number system). BINARY POINT. In positional notation, the character, or the loca¬ tion of an implied symbol, which separates the integral part of a numerical expression from its 39-89 AFM 100-39 BIN 1 APRIL 1959 fractional part. For example, it is called the bin¬ ary point in binary notation and the decimal point in decimal notation. If the location of the point is assumed to remain fixed with respect to one end of the numerical expressions, a fixed- point system is being used. If the location of the point does not remain fixed with respect to one end of the numerical expressions, but is re¬ gularly recalculated, then a floating-point system is being used. Note: A fixed-point system usually locates the point by some convention, while a float¬ ing-point system usually locates the point by expressing a power of the base. BINOMIAL ARRAY. Directional antenna array for reducing minor lobes and providing maximum response in two opposite directions. BIOLOGICAL WARFARE. 1. Warfare waged by the employment of liv¬ ing organisms, toxic bacterilogical products, and chemical plant-growth inhibitors to produce death or casualties in man, animals, or plants. 2. Defense against such war fare. BIOLUMINESCENCE. Emission of light by living organisms, as the firefly, certain fungi, and many marine forms. BINARY STAR. Two stars revolving around a common center of gravity. BINARY-CODED-DECIMAL SYSTEM. System of number representation in which each decimal digit is represented by a group of bin¬ ary digits. BINAURAL. Pertaining to the use of two ears of duplicat¬ ing the effect of hearing with two ears. BINAURAL EFFECT. Effect which makes it possible for a person to determine the direction from which a sound is coming. Accomplished by distinguishing the difference in arrival time or intensity of sound at the ears. BINDER. 1. Cement-like material used in carbon resis¬ tors for holding the carbon particles together and providing mechanical strength. 2. Resinous material used in phonograph re¬ cords. BINDING ENERGY. Energy required to separate the positively and negatively charged parts of atoms or molecules. BINDING POST. Bolt and nut terminal for making temporary elec¬ trical connections. BIOPHYSICS. Term used in reference to the physical processes taking place in living organisms. BIPOLAR. Having two poles. BIPOLAR ELECTRODE. Eelctrode, without metallic connection with the current supply, one face of which acts as an anode surface and the opposite face as a cathode sur¬ face when an electric current is passed through the cell.. BIPOLAR MAGNETIC DRIVING UNIT. Headphone or loudspeaker unit having two mag¬ netic poles acting direclyon a flexible iron dia¬ phragm. BIRDNESTING. Clumping together of chaff dipoles after they have been dispensed from an aircraft. BISCUIT. Small slab of the stock material from which a record is pressed as it is prepared for use in the presses. BISECTION. Process used in preparing plain test for en¬ cryption. It consists of breaking the plain text of a message into two segments or portions us¬ ually of unequal length, transposing the seg¬ ments so that the actual beginning and ending NO 39-90 1 APRIL 1959 AFM 100-39 BIS of the message are buried and indicating the true beginning and ending in a distinctive man¬ ner. BISMUTH SPIRAL METHOD. Measurement of magnetic flux by observing the change in resistance of a flat spiral of bismuth wire when placed in an air gap or elsewhere in the magnetic circuit. BIT. (BINARY DIGIT). 1. Single character of a language employing ex¬ actly two distinct kinds of characters. 2. Unit of storage capacity. The capacity, in bin¬ ary digits of a storage device is the logarithm to the base two of the number of possible states of the device. 3. Unit of information content, equal to one bin¬ ary decision, or the designation of one of wo possible and equally likely values or states of anything used to store or convey information. A binary digit may be conveyed by one binary code element. One binary digit equals log of 2 to base 10 times one Hartley. BIVALENT. Substance with two chemical valences. BIZMAC. RCA Computer. BJC-EB (BRITISH JOINT COMMUNICATfONS- ELECTRONICS BOARD). BL (BOMBLINE). Line or boundary, usually marked by terrain fea¬ tures, pyrotechnics, or other devices, that marks the limit to or beyond which bombs may be dropped without endangering friendly ground forces, without causing undesired damage or loss. (Reference: BOMB SAFE TY LINE, FOR¬ WARD BOMBLINES.) BLACK. Signal produced at any point in a facsimile sys¬ tem by the scanning of a selected area of subject copy having maximum density. BLACK AND WHITE TRANSMISSION. Transmission of a television signal wave which represents the brightness values in the picture, but not the chromaticity values. BLACK BODY. Theoretically perfect absorber and emitter of radiation. BLACK SCOPE. Cathode-ray tube operating at the threshold of luminescence when no video signals are being applied. BLACK LEVEL. Instantaneous amplitude of the television signal which corresponds to a black area in the re¬ ceived picture. BLACK LIGHT. Invisible light radiation. It may be either ultra¬ violet or infrared radiation, both of which are invisible. BLACK SIGNAL. Signal at any point in a facsimile system pro¬ duced by the scanning of a maximum density area of the subject copy. BLACK TRANSMISSION. 1. Form of transmission, in an amplitude-modu¬ lation facsimile system, in which the maximum transmitted power corresponds to the maximum density of the copy. 2. Form of transmission, in a frequency-modula¬ tion system, in which the lowest transmitted fre¬ quency corresponds to the maximum density of the copy. BLACK-BODY RADIATION. Radiation from a black body at a given tempera¬ ture. BLACKER-THAN-BLACK LEVEL. Direct voltage value used in an electronic tele¬ vision system for control impulses. It is greater than the value representing black portions of the image. BLACKMARI. Air-to-air identification system developed by the 39-91 AFM 100-39 BLA 1 APRIL 1959 United Kingdom and similar in design to the US Navy’s air-to-air system. This system is not compatible with the Air Force (Hughes Air¬ craft) air-to-air system. BLACKOUT. 1. Interruption of radio communication due to excess absorption caused by solar flares. During severe blackouts, all frequencies above approxi¬ mately 1,500 kc. are absorbed excessively in the daylight zone. 2. Passive defense that consists of interrupting all forms of communication or identification. 3. Temporary fadeout of vision, and/or conscious¬ ness due to effects of rapid acceleration or de¬ celeration, decreasing the flow of blood to the brain. BLADE. Moving contact switch member which enters or embraces the contact clips. BLADE GUIDE. Attachment on a switch to assure proper align¬ ment of blade and contact when closing the switch. BLADE LATCH. Latch used on a hook-operated switch to hold the switch blade in a closed position. BLANK. Result of the final cutting operation on a crys¬ tal. BLANK GROOVE. Groove upon which no modulation is inscribed. BLANK HOLDER. Thin circular holder composed of zinc or other material and perforated with square or other shaped holes which contain and hold the quartz blanks between the upper and lower laps in the lapping process. BLANKETING. Effect produced by an undesired signal so strong that it makes difficult or impossible the recep¬ tion of a desired signal. BLANKING. Process of making a channel or device nonef¬ fective for a desired interval. In television, blanking is the substitution for the picture sig¬ nal, during prescribed intervals, of a signal whose instantaneous amplitude is such as to make the return trace invisible. (Reference: GATING.) BLANKING LEVEL. Level in a composite picture signal that separ¬ ates the range containing picture information from the range containing synchronizing infor¬ mation. BLANKING PULSE. Square wave (positive or negative) used to switch off a part of a television or radar set electroni¬ cally for a predetermined length of time. BLANKING SIGNAL. Wave constituted of recurrent pulses, related in time to the scanning process, used to effect blanking. BLASTING. Distortion due to overloading of a part of a receiver, or public address amplifier. BLEEDER. Resistor connected across a power source to im¬ prove voltage regulation, to drain off the charge remaining in capacitors when the power is turned off, or to protect equipment from ex¬ cessive voltage if the load is removed or sub¬ stantially reduced. BLEEDER CURRENT. Current drawn continuously from a power supply to improve its voltage regulation or to increase the value of the voltage drop across a particular resistor. BLEEDER RESISTOR. 1. Resistor which is used to draw a fixed cur¬ rent. Also used, as a safety measure, to discharge filter condensors after the circuit is deenergized. 2. Resistor placed in the power supply of a radio receiver or other electronic device to stabilize the voltage supply. 39-92 1 APRIL 1959 AFM 100-39 BLE BLEEDING. Appearance of drops of sap or wood preservative, particularly creosote, on the surface of a pole. BLIND APPROACH BEACON SYSTEM. Pulse-type ground-based navigation beacon used for runway approach at airfields primarily in the United Kingdom. BLIND LANDING. Landing with no external visibility. All flight, approach, and landing data used by the pilot are obtained from instruments in the aircraft and from radio-direction finding devices on the ground. BLIND ZONE. Area from which echoes cannot be received; gen¬ erally, an area shielded from the transmitter by some natural obstruction and therefore from which there can be no return. BLINKING. Distinctive signal used in the LOR AN system to indicate unusable pulses. BLIP. Spot of light or base-line irregularity on a cath¬ ode-ray display representing the radar reflection from an object. BLIP SCAN RATIO. Ratio between a single recognizable blip on a cathode-ray display and the number of scans nec¬ essary to produce it. BLISTER. Term used to refer to the housing of an air¬ borne radar antenna. BLOCK. Group of words, introduced to an electronic com¬ puter, considered as a unit. BLOCK DIAGRAM. 1. Diagram in which the essential units of any system are drawn in the form of blocks, and their relation to each other indicated by appro¬ priate connecting lines. 2. Diagram in which the principal divisions or sections of a circuit are indicated by geometric figures and the path of the signal or energy by lines and/or arrows. DISTRIBUTING. Set of punchings, set in hard rubber or other insulating material, mounted on a piece of wood. This assembly is rigidly fastened as to a frame and usually wired per¬ manently on one side, permitting wires to be connected and changed on the other. PROTECTOR. Rectangular piece of carbon, bakelite with a metal insert, or porcelain with a carbon insert which, in combination with each other, make one element of a protector. They form a gap which will break down and provide a path to ground for voltages over 350 volts. TERMINAL. Set of punchings, set in hard rub¬ ber or other insulating meterial, mounted on a piece of wood. This assembly is rigidly fas¬ tened as to a frame and usually wired perman¬ ently on one side, permitting wires to be con¬ nected and changed on the other. WOODEN. Piece of wood simulating carbon blocks used in lightning arresters to keep the springs from grounding when protection is not required. BLOCK PROTECTOR Rectangular piece of carbon, bakelite with a metal insert, or porcelain with a carbon insert which, in combination with each other, make one element of a protector. They form a gap which will break down and provide a path to ground for voltages over 350 volts. BLOCK TELEVISION. Type of aerial television. The block system is a smaller installation of the ring system for use over a shorter distance. BLOCK-GRID KEYING. Method of keying a continuous-wave transmitter by operating the amplifier stage as an electronic switch. During the spacing interval when the key is open, the bias on the control grid becomes highly negative and prevents the flow of plate current so that the tube has no output; during the marking interval when the key is closed, this bias is removed and full plate current flows. 39-93 AFM 100-39 BLO 1 APRIL 1959 BLOCKED IMPEDANCE. Blocked impedance of a transducer is the impe¬ dance measured at the input when the impe¬ dance of the output system is made infinite. (Re¬ ference: DAMPENED IMPEDANCE.) BLOCKED RESISTANCE. Resistance of an AF transducer when its moving elements are blocked so they cannot move. It re¬ presents the resistance due only to electrical losses. BLOCKING. Application of extremely high negative grid bias to a vacuum tube, thus reducing the plate current to zero. BLOCKING CAPACITOR. Capacitor which introduces a comparatively high series impedance for limiting the current flow of low-frequency alternating current or direct cur¬ rent without materially affecting the flow of high-frequency alternating current. BLOCKING LAYER. Surface of contact between a metal and semi-con¬ ductor. It acts as a rectifier of alternating currents. Some barrier layers when illuminated, generate a voltage through photovoltaic action. The junc¬ tion between the copper and cuprous oxide in the photoelectric cell is a barrier layer. (Reference* BARRIER LAYER.) BLOCKING OSCILLATOR. Relaxation oscillator using inductive feedback with its period determined by the time constant of the grid resistor capacitor combination. BLOCKING OSCILLATOR DRIVER. Circuit which develops a square pulse used to drive the modulator tubes, and usually contains a line-controlled blocking oscillator that shapes the pulse into the square wave. BLOCKING-LAYER CELL. Type of photovoltaic cell in which light acting on the surface of contact between layers of copper and cuprous oxide causes an electromotive force to be produced. (Reference: BARRIER-LAYER CELL.) BLOOM. Glare caused by an object reflecting light into the lens of the camera. BLOOMING. Expansion of the spot on a cathode-ray tube due to maladjustment of bias, focus, and intensity. Also the excessive brightness on an intensity-mo¬ dulated radar scope caused by the high inten¬ sity of concentrated signals. BLOOPER. Oscillating radio receiver that is radiating an un¬ desired signal. BLOSSOM. Dispersal of chaff to produce optimum echo. BLOW. Opening of a circuit because of excess current, particularly when the current is heavy and a melt¬ ing or breakdown point is reached. BLOWER. Motor-driven fan used to supply air for cooling purposes. BLOWER ALARM. Indicator light which illuminates if unit over¬ heats, due to blower failure. BLOWHOLE. Gas cavity in a metal casting caused either by evolution of gas released from the solidifying metal, or by steam or air entrapped essentially from the mold. BLOWN FUSE INDICATOR. Special design warning light across a fuse, which illuminates when the fuse is blown. BLOWTORCH. Portable device for producing intense local heat. BLUE BRITTLENESS. Apparent change of the physical properties of steel when heated between 200 and 400°C. In this temperature range, the malleability of the steel decreases and a blue oxide film forms on the surface. 39-94 1 APRIL 1959 AFM 100-39 BLU BLUE GLOW. Glow normally seen in vacuum tubes contain¬ ing mercury vapor due to ionization of the mole¬ cules of mercury vapor. BLUE NEEDLES. Term applied in the grading of quartz which shows up in a mineral oil bath with a bluish- white color under the arc lamp. BLUE STREAK REQUEST. High-priority requisition of an air depot to the Air Materiel Command for projects or programs specifically authorized by Headquarters, USAF; or by the Commanding General, AMC. BLUEING. Operation of heating, to a temperature of about 200°C,, steel which has been subjected to a pickling operation. Blueing is also the term used for producing an oxide film on the surface of steel. BOARD. 1. Switchboard equipped with testing apparatus, so arranged that connections can be made to tele¬ phone lines or central office equipment for testing purposes. 2. Commercial switchboard equipped with ap¬ paratus for making tests and for temporary inter¬ connection and rearrangement of circuits. FORMING. Board used to form cable termina¬ tions at jack mountings, relay mounting plates, terminal strips or similar units^ in which the cable skinners are brought out and turned at a series of nails or holes in the board at the location of the apparatus preparatory to sew¬ ing the form. BOB. (BUREAU OF THE BUDGET). BODY. Body is a definite portion of matter considered separately from other matter. BODY BELT. Heavy belt passed around the waist, equipped with D-rings for fastening the safety belt. Has loops or keeper for tools. BODY CAPACITANCE. Capacitance introduced into an electrical circuit by the proximity of the human body. BOEHME EQUIPMENT. 1. Used for sending International Morse Code characters by passing Wheatstone tape through a keying head. 2. Used for recording International Morse Code characters by ink syphon equipment on a mov¬ ing paper tape. BOHR ATOM. Atom, as conceived by Bohr and Rutherford, con¬ sisting of a positive nucleus about which circu¬ lates a number of orbital electrons. BOLDMETER. Device whose resistance changes in accordance with changes in temperature used in the measure¬ ment of microwave energy. It contains a resistive element, the resistance of which changes as a result of heating by RF power. One type of bold- meter is the barretter, which uses a short length of resistive wire; another type is the thermistot which uses a small mass of resistive material. BOLTZMANN’S CONSTANT. Ratio of mean total energy of a molecule to its absolute temperature. The value is 1.375 x 10 16 ergs per degree. BOM (BILL OF MATERIAL). BOM (BOMBARDMENT). 1. Process of directing high-speed electrons at an electrode, causing secondary emission of elec¬ trons, fluorescence, disintegration, or production of X-rays. 2. Process of directing high-speed particles at atoms to cause ionization or transmutation. BOM (BOMBER). Airplane specifically designed to carry and drop bombs. AFM 100-39 BOM BOM (BOMBING). Action of dropping bombs from an aircraft with the purpose of hitting a target. BOMARC. Surface-to-air guided missile designated as the IM-99 or F-99. It has a gross weight of 8500 pounds, and a maximum speed of Mach 2.5. The BOMARC is intended for air defense of the United States and forward areas. It is a pilotless interceptor type which may ultimately carry air- to-air missiles for launching and then return to base. The wing span is 36 feet; length is 66 feet; and height is 16 feet. Propulsion is by two ramjet engines solid propellant internal rock¬ et booster. This missile will operate up to 60,000 ft. altitude with a range of over 100 miles. Guidance is by means of radar, infrared homing, or command guidance. BOMB. 1. Explosive or other lethal agent together with its container or holder, which is planted or thrown by hand, dropped from an aircraft, or projected by some other slow-speed device and used to destroy, damage, injure, or kill. 2. Similar to this object in appearance, operation, or effect, a leaflet bomb, smoke bomb, photo¬ flash bomb, a bomb-like container or chamber, etc. 3. To drop a bomb or bombs on a target, as a city, railyard, or body of troops. BOMB RELEASE LINE. Imaginary line around a target complex at which point a hostile bomber may be expected to release its first bomb. BOMB SAFETY LINE. Bomb line behind which bombs should not be dropped in order to protect ground forces. (Re¬ ference: BOMBLINE.) BOMBER. CAA designation for scheduled broadcast sta¬ tion. (broadcasts weather at 15 and 45 minutes 1 APRIL 1959 f after the hour; Air Force broadcasts, generally 29 minutes.) BOMBING. Action of dropping bombs from an aircraft with the purpose of hitting a target. BOMBING AREA. Bombing a target of a general area rather than a small or pinpoint target. BOMBLINE. Line or boundary, usually by terrain features, pyro¬ technics, or other, that marks the limit to or be¬ yond which bombs may be dropped without caus¬ ing undesired damage or loss. (Reference: BOMB SAFETY). FORWARD. Line in advance of the bombline, beyond which air units specifically engaged in close air support do not operate unless order¬ ed by the Air Commander. STRAGETIC. Bombline used to indicate the geo- graphical limits to which strategic bombing may be carried out without resulting in unde¬ sired damage or loss. BOND. Electrical interconnection made with low-resis¬ tance material between chassis, metal shield cans, cable shielding braid, and other supposedly' ecjui - potential points, in order to eliminate undersir- able interaction resulting from high-impedance paths between them. BONDING. 1. Maintaining electrical continuity from one element to another. Usually the continuity is immediately or eventually to earth. 2. Connecting together electrically, all the met¬ al parts of an automobile or airplane. 3. Connecting the shields of radio parts, or con¬ necting these parts to the chassis. BONE-CONDUCTION PERCEPTION. Perception in which the sound is conducted to 39-96 1 APRIL 1959 the inner ear by the cranial bones rather than through the ossicles from the outer ear. BOOK CAPACITOR. Two plate trimmer capacitor having the plates hinged together like the pages of a book. The capacitance is varied by changing the angle be¬ tween the plates. BOOK MESSAGE. Book message is one which is destined for two or more addressees and is of such nature that the originator considers that no addressees need to be informed of any other addressees. Each addressee must be indicated as action or infor¬ mation. BOOM. Mechanical support for a micorphone, used in a television or motion-picture studio to suspend the microphone within range of the actors but above the field of view of the camera. BOOST CHARGE. Partial charge of a storage battery, usually at a high rate for a short period. BOOSTER. 1. Small generator inserted in series or parallel with a larger generator in order to maintain nor¬ mal voltage output under heavy loads. 2. Radio station which acts as an intermediate station in transmitting communication signals from one fixed station to another. 3. Propulsion unit, usually a rocket, which serves quickly to accelerate the speed of a plane, mis¬ sile, or rocket to take-off. BOOTSTRAP CIRCUIT. Amplifier in which the output load impedance appears between the negative end of the plate supply and the cathode of the amplifier tube, the signal voltage being applied between the grid and the cathode. The bootstrap circuit dif¬ fers from a cathode follower in that amplifica¬ tion is achieved by applying the input signal be¬ tween grid and cathode where it does not suffer the degeneration caused by the output voltage appearing across the cathode resistor. AFM 100-39 BON BOOTSTRAP DRIVER. Electronic circuit used to produce a square pulse to drive the modulator tube. The duration of the square pulse is determined by a pulse-form¬ ing line. BORE. Interior diameter of an engine cylinder. BORE SIGHT. Sighting device consisting of a breech element and a muzzle element which, when inserted in a gun, is used to determine the axis of the bore and the alignment of other sighting equip¬ ment with the axis of the bore. BORER, INCREMENT. Tool for taking wood samples from a pole to determine depth of creosote treatment or extent of rot. BORON OR BORON HYDRIDE. High energy missile and rocket fuel constituent; one of the so called zip or exotic fuels. BORROW. Receive with the implied or expressed intention of returning or giving an equivalent. BOUND CHARGE. Term used to denote the charge remaining in the dielectric of a capacitor after discharge; the residual charge. BOUNDARY. Lines drawn between specific geographic posi¬ tions which indicate the area of responsibility of air-defense units. BOUNDARY LIGHT. One of the series of lights used to indicate the limits of the landing area of a landing field. BOUNDARY MARKER. Marker, for aircraft, which is installed near the approach end of a landing runway and approx¬ imately in the localizer course line. BOWING. Deflection of a cable from it straight path, due to excessive length in a section or span. 39-97 AFM 100-39 BPC 1 APRIL 1959 BPC (USAF PLANNING-BUDGETING PROGRAM COMMUNICATIONS-ELECTRONICS). BRACE, CROSS ARM. Steel strap mounted from pole to cross arm to hold the cross arm in position. BRACE POLE. Pole set at an angle and bolted to a line pole that cannot be guyed. BRACKETS, POLE. Wooden wedges designed to be nailed to a pole and made to hold an insulator on which a wire may be tied. BRADLEY DETECTOR. Single-stage, locked-in oscillator type of FM de¬ tector (uses a special heptode vacuum tube). BRAGG ANGLE. Glancing angle for X-rays at the reflecting planes of a crystal. Used in X-ray orientation of quartz crystals being cut for radio use. BRAGG’S LAW. Expression specifying the condition under which a system of parallel atomic layers in a crystal will reflect a beam of X-ray with maximum intensity. BRAIN. Rocket or missile guidance system. BRAKING ELLIPSES. Series of orbital approaches to the earth’s or any other planet’s atmosphere for the purpose of slowing up a rocket preparatory to landing. BRANCH. 1. Section in an electronic network, between two adjacent branch points. 2. Major functional subdivision in a combat or direction center. (Reference: CONDITIONAL JUMP.) BRANCH CIRCUIT. Portion, in interior wiring, of a wiring system extending beyond the final overload protective device of the circuit. BRANCH JOINT. Joint used for connecting a branch conductor or cable to a main conductor or cable, where the latter continues beyond the branch. BRANCH POINT. Junction, in an electrical network, where more than two conductors meet. BRANCH-CIRCUIT DISTRIBUTOR CENTER. Distribution center at which branch circuits are supplied. BRASS. Metal made of alloying copper and zinc in vari¬ ous proportions. BRASS BELL. Classified definition. (Reference: AFM 100-50.) BRAUN TUBE. Early type of cathode-ray oscilloscope tube. BRAZING. Joining two metal objects by using a relatively infusible hard solder and direct heat. BREADBOARD. Laboratory idiom for an experimental circuit setup exposed on a board for portability and ease of assembly or disassembly. BREADBOARD CONSTRUCTION. Arrangement in which circuit components are fastened temporarily to a flat surface and wired for experimental work. BREADBOARD MODEL. Assembly of preliminary circuits and parts to prove the feasibility of a device, circuits, equip¬ ment, system or principle in rough or breadboard form, without regard to the eventual overall design or form of parts. BREAK. 1. Break, in a communication circuit, is for the receiving operator or listening subscriber to interrupt the sending operator or talking sub¬ scriber and take control of the circuit. The term is used especially in connection with half-duplex telegraph circuits and two-way telephone circuits equipped with voice-operated devices. 1 APRIL 1959 AFM 100-39 BRE 2. Minimum distance, in a circuit opening device, between the stationary and movable contacts occurs when these contacts are in the open posi¬ tion. 3. Figure represented on the oscilloscope of a radar caused by the echo from an aircraft or other reflecting object. PERCENT. Percentage used in dial pulse testing. It is a percentage expression of the period of time the dial circuit stands open compared to the total time of the dial signal. BREAK CONTACT. Contact of a switching device which opens a cir¬ cuit upon the operation of the device (normally closed). BREAK PERIOD. Time interval, of a dial telephone, during which the circuit contacts are open. BREAK POINT. Place in a routine at which a special instruction is inserted which, if desired, will cause a digital computer to stop for a visual check of progress. BREAK-IN KEYING. 1. Method of operating a continuous-wave radio telegraph communication system in which the receiver is capable of receiving signals during transmission of spacing intervals. 2. Method whereby a telegraph station breaks into the transmission being received from another station. BREAK-IN OPERATION. Method of radio communication in which it is possible for the receiving operator to interrupt or break into the transmission at any time. BREAK-IN RELAY. Relay used in a radio transmitter for break-in operation, automatically permitting reception of incoming signals during keying intervals. BREAKDOWN. Failure of insulation for any reason. Defective insulation may be detected by applying an ex¬ cessive voltage and observing when and where failure occurs when used; this operation is called breaking-down. BREAKDOWN TORQUE. Maximum torque an electric motor will develop with rated voltage applied at rated frequency, without an abrupt drop in speed. BREAKDOWN VOLTAGE. Voltage at which an insulator or dielectric rup¬ tures, or at which ionization and conduction take place in a gas or vapor. BREAKER, CIRCUIT. Automatic device which interrupts the flow of current in a continuous circuit when there is a predetermined deviation of current, voltage, or impedance from a standard value. BREAKER POINT. Transmission system level at which there occurs an abrupt change in distortion or noise which renders operation unsatisfactory. BREIT AND TUVE THEOREM. Relationship between the equivalent triangular path for sky-wave propagation and transmission distance. BREVITY CODE. Code which has as its sole purpose the shorten¬ ing of messages rather than the concealment of their content. BREWSTER ANGLE. Angle of incidence at which a vertically polar¬ ized wave (a wave polarized in the plane of inci¬ dence) undergroes a phase shift of 90° reflection from the surface. BRG (BEARING). 1. Relative position of, or direction taken by, an aircraft, bomb, etc., with respect to a point and line of reference in a horizontal plane, as to a compass point and line. 2. Specifically the position or direction of an ob¬ ject relative to a line between the observer and true north or magnetic north. BRIDGE. 1. Shunt path. 39-99 AFM 100-39 BRI 1 APRIL 1959 2. Device which is used for electrical measure¬ ment of impedance, etc., by comparison with known values. 3. Electrical network usually consisting of four branches; one pair of diagonally opposite corners is connected to the input and the other pair to the output circuit. CAPACITY. Instrument using a modification of the Wheatstone bridge arrangement for meas¬ uring electrical charge capabilities in unit values of farads, microfarads, or micro-micro- farads. IMPEDANCE. Circuit used to measure the com¬ bined resistance and inductance of a device. SLIDE-WIRE. Simplified form of Wheatstone bridge in which the position of a slider on a resistance wire determines the resistance ratio. WHEATSTONE. Null-type resistance-measuring circuit in which resistance is measured by di¬ rect comparison with a standard resistance. WIEN. Network of resistors and capacitors which has voltage characteristics with respect to frequency similar to those of a tuned induct¬ ance-capacitance circuit. BRIDGE CIRCUIT. Network which is so arranged that when an electromotive force is present in one branch, the response of a suitable detecting device in another branch may be zeroed by a suitable adjustment of the electrical constants of still other branches. BRIDGE DUPLEX SYSTEM. Telegraphy duplex system based on the Wheat¬ stone bridge principle in which a substantial neu¬ trality of the receiving apparatus to the sent currents is obtained by an impedance balance. Received currents pass through the receiving relay which is bridged between the points which are equipotendal for the sent currents. BRIDGE RECTIFIER. Full-wave rectifier with four elements connected in a bridge circuit so that direct voltage is ob¬ tained from one pair of opposite junctions when alternating voltage is applied to the other pair. BRIDGE TRANSITION. Method of changing the connection of motors from series to parallel in which all of the motors carry the same amount of current through the transfer due to the XX^heatstone bridge connec¬ tion of motors and resistors. BRIDGED CIRCUIT. Circuit which is shunted. BRIDGED T-NETWORK. Network with the two series impedance of the T, bridged by a fourth impedance. BRIDGED TAP. Portion of a cable pair connected to a circuit which is not a part of the useful path. BRIDGING. Composing a bridge network. BRIDGING CONNECTION. Parallel connection by means of which some of the signal energy in a circuit may be withdrawn. BRIDGING CONNECTOR. Screw fastener for joining drop, bridle, or other wires to open-wire conductors, or to fasten two open wires at a test point. BRIDGING LOSS. Loss resulting from bridging an impedance across a transmission system. It is the ratio of the signal power delivered to that part of the system fol¬ lowing the bridging point, and measured before the bridging, to the signal power delivered to the same part after the bridging. BRIDLE. Tension member which extends longitudinally between supporting structures and is attached to a catenary system or direct-suspension system at points between supports. BRIDLE WIRE. Insulated wire for connecting conductors of an open wire line to associated pole mounted ap¬ paratus. 1 APRIL 1959 AFM 100-39 BRI BRIDLING. Insulated twisted pair wire used on a pole or a cable terminal to connect wire together or to con¬ nect line wires to cable pairs. BRIGHTNESS. Attribute of visual perception in accordance with which an area appears to emit more or less light. Used with cathode-ray tubes. BRIGHTNESS OF IMAGE. Term used to denote the amount of light trans¬ mitted by an optical system to give definition to the image seen by the observer. BRILLIANCE. 1. Degree of brightness and clarity in a repro¬ duced cathode-ray tube. 2. Degree to which the higher audio frequencies sound like the original when reproduced by a receiver or public address amplifier. BRILLIANCE CONTROL. Control, associated with cathode-ray tubes, by which the intensity of the electron beam and hence the amount of light generated by the flu¬ orescent screen is controlled. Generally the con¬ trol adjusts the grid bias of the tube. BRILLIANCE (INTENSITY) MODULATION. Control of the brilliance of the trace on the screen of a cathode-ray tube in conformity with the signal. BRILLIANT. Term applied to sound reproduction in which high frequencies are properly reproduced. BRITISH BROADCASTING CORPORATION. Government-owned corporation in charge of all radio broadcasting in Great Britain, financed by license fees collected from each radio-receiver owner, and carries no commercial programs. BRITISH THERMAL UNIT. Quantity of heat required to raise the tempera¬ ture of one pound of water one degree Fahren¬ heit. The corresponding Metric unit is the Cal¬ orie. BRL (BOMB RELEASE LINE). Imaginary line around a target complex at which point a hostile bomber may be expected to release its first bomb. BROAD. Responding to a wide range of frequencies. Usually applied to tuned circuits. BROAD BAND. Having a wider frequency response than the normal type of circuit at the corresponding mid¬ band frequency. BROAD TUNING. Condition in which two or more radio stations are heard at a single setting of the tuning dial of a receiver, generally due to poor selectivity in the tuning circuits of the receiver. BROAD-BAND CARRIER SYSTEM. Carrier system which is capable of providing 12 or more telephone channels. BROADCAST. Radio transmission of messages for which receiv¬ ing stations make no receipt. BROADCAST BAND. Band of frequencies between 550 and 1,600 kilo¬ cycles. BROADCAST CONTROL. Control exercised by an intercept director trans¬ mitting the location of hostile flights to an inter¬ ceptor pilot who conducts an interception with¬ out further direction. BROADCAST CONTROLLED AIR INTERCEPTION. Interception in which the interceptor is given the area of interception by a surface or air station and effects interception without further control. BROADCAST METHOD. Method of transmitting messages or information to a number of receiving stations which make no receipt. BROADCAST TRANSMISSION. Radio transmission to an unlimited number of receiving locations. 39-101 AFM 100-39 BRO 1 APRIL 1959 r BROADCASTING. Radio transmission, intended for general recep¬ tion. BROADCASTING SERVICE. Radio communication service of transmissions to be received directly by the general public. This service may include transmissions of sound or transmissions by television, facsimile or other means. BROADCASTING STATION. Station in the broadcasting service. BROADSIDE ARRAY. Antenna array in which direction of maximum radiation is perpendicular to the line or plane of the array. BROFICON (BROADCAST FIGHTER CONTROL). System for the transmission of air-defense data to airborne interceptors, using commercial radio broadcasting facilities. BRONZE. Alloy of copper and tin. BRUSH. 1. Conductor, such as a metal or carbon block, serving to maintain electric contact between stationary and moving parts of a generator or motor. 2. Moving member (wiper) of a selector, or other similar device, in communication practice, which makes contact with the terminals of a bank. BRUSH DISCHARGE. Luminous electrical discharge consisting of visi¬ ble streams of charged particles moving through the air between the terminals of a static machine or other high-frequency high-voltage source. BRUSH HOLDER. Device, often adjustable, that holds a brush in the proper position against a commutator or slipring and applies the correct pressure to the brush. BRUSH HOLDER STUD. Intermediate support between the brush holder and the brush yoke. BRUSH, TERMINAL. Brush with long bristles for cleaning fuses and terminals in a terminal box. BRUSH YOKE. Rocker arm, ring, quadrant or other adjustable support for maintaining the brush holders or brush-holder studs in their relative positions. BRUTE-FORCE FILTER. Type of power-pack filter depending on large values of capacitance and inductance to smooth out pulsations, rather than on resonant effects of tuned filters. BSA (BLUE STREAK REQUEST). High-priority requisition of an air depot to the Air Materiel Command for projects or programs specifically authorized by Headquarters, USAF; or by the Commanding General, AMC. BSE (BASE SUPPORT EQUIPMENT). That equipment provided a base or organization, in addition to unit essential equipment, to enable the base to perform its assigned mission. BTO (BOMBING THROUGH OVERCAST). Btu (BRITISH THERMAL UNIT). Quantity of heat required to raise the tempera¬ ture of one pound of water one degree Fahren¬ heit. The corresponding Metric unit is the Cal¬ orie. BU (BUREAU). 1. Government department or office, or one of its subdivisions, for the transaction of business. 2. This abbreviation (BU) in government usage is usually used in conjunction with the preposi¬ tion (of) as in BuAer meaning Bureau of aero¬ nautics. BUCK. Oppose, as one voltage bucking another. BUCKING COIL. Coil connected and positioned in such a way that its magnetic field opposes the magnetic field of another coil. The hum-bucking coil of an elec- trodynamic loudspeaker is an example. a 39-102 1 APRIL 1959 AFM 100-39 BUC BUCKING VOLTAGE. Opposing voltage, have opposite polarity to that of another voltage against which it acts. BUCKLING. Warping of the plates of a battery due to an excessively high rate of charge or discharge. BUFFER. 1. Circuit or component which isolates one electrical circuit from another. Usually refers to electron tube amplifiers used for this purpose. 2. Vacuum tube stage used chiefly to prevent undesirable interaction between two other stag¬ es. In a transmitter, it generally follows the master-oscillator stage. 3. Isolating circuit in an electronic computer, used to avoid reaction of a driven circuit on the corresponding driving circuit. 4. Storage device used to compensate for a dif¬ ference in rate of flow of information or time or occurrence of events when transmitting in¬ formation from one device to another. BUFFER AMPLIFIER. Amplifier designed to isolate a preceding circuit from the effects of a following or proceeding circuit. BUFFER CAPACITOR. Capacitor connected across the secondary of a vibrator transformer or between the anode and cathode of a cold-cathode rectifier tube to sup¬ press voltage surges that might otherwise damage other parts in the circuit. BUFFER STAGE. (Reference: BUFFER.) BUG. 1. Semiautomatic telegraph sending key in which movement of a lever to one side produces a series of correctly spaced dots and movement to the other side produces a single dash. 2. Dial used on echo ranging and radar equip¬ ment to indicate true bearing of the projector, or the position of the projector or antenna with respect to the course of a ship or aircraft. 3. Defect or imperfection present in, or charact¬ eristics of, that equipment. BUILDING OUT. Addition to an electric structure of an element or elements electrically similar to an element or elements of the structure, in order to bring a certain property or characteristic to a desired value. BUILDING-OUT CAPACITOR. Capacitor employed to increase the capacitance of an electric structure to a desired value. BUILDING-OUT CIRCUIT. Short section of transmission line, or a network which is shunted across a transmission line, for the purpose of impedance matching. BUILDING-OUT NETWORK. Network designed to be connected to a basic net¬ work so that the combination will simulate the sending-end impedance, neglecting dissipation, of a line having a termination other than that for which the basic network was designed. BUILDING-OUT SECTION. Short section of transmission line, either open or short-circuited at the far end, shunted across another transmission line for use on an imped¬ ance-matching transformer. BUILDING-UP. Gradual increase in magnetic field strength in a self-excited generator from the residual magne¬ tism value to the normal operation value produced when normal field current is flowing. The resid¬ ual magnetism produces the small initial volt¬ age that starts the building-up process. BULB. Term loosely used to specify the glass envelope that incloses an incandescent lamp or an elec¬ tronic tube. BULL HORN. High power directional loudspeaker. BULLPUP. Air-to-air surface missile developed for the Navy. Nomenclature is XASM-N-7. Length is 11 feet, 39-103 AFM 100-39 BUL 1 APRIL 1959 diameter one foot, and it is powered by a solid propellant rocket motor. BUMBLEBEE. Guided missile identical with TERRIER but with a different guidance principle. BUNCHED PAIR. Group of pairs tied together or otherwise asso¬ ciated for identification. BUNCHER. 1. Input resonant cavity in a conventional klys¬ tron oscillator. 2. Electrode of a velocity-modulated tube which concentrates the electrons in the constant-current electron beam into bunches. BUNCHER RESONATOR. Input cavity resonator in a velocity-modulated tube. It serves to modify the velocity of the elec¬ trons in the beam. BUNCHING. 1. Grouping pairs together for identification and testing. 2. Condition in a vacuum tube where the elec¬ tron flow is in groups rather than a continuous uniform flow. BUNCHING PARAMETER. Single term that combines the effect of a number of factors which determine the theorectical oper¬ ation of a klystron. BUNCHING VOLTAGE. RF voltage between the grids of the buncher resonator in a velocity-modulated tube such as a klystron. Generally, the term implies the peak value of this oscillating voltage. BUNSEN CELL. Primary cell having a zinc negative electrode immersed in sulphuric acid and a positive carbon electrode immersed in nitric acid, with the two liquids separated by a porous cup. BURIED CABLE. Cable installed under the surface of the ground. BURNISHING. Process of turning a thin edge of metal over the beveled edge of a lens to hold it in place in its cell. BURNISHING SURFACE. Portion of the cutting stylus of a burnishing tool, directly behind the cutting edge, which smooths the groove. BURNISHING TOOL. 1. Stylus sometimes used to smooth the groove of a recording. 2. Tool used to restore the surface of relay con¬ tacts. BURNOUT. End of power phase of a rocket engine. BURST. 1. Sudden increase in the strength of a signal. 2. Cosmic-ray effect upon matter, causing a sudden intense ionization that often gives rise to great numbers of ion pairs at once. (Refer¬ ence; COLOR BURST.) BURST PEDESTAL. Rectangular pulse like television signal which may be part of the color burst. The amplitude of the color burst pedestal is measured from the ac axis of the sinewave portion to the horizontal pedestal. BURY. Placing specified elements of a message in other than their usual place, by bisection or other pro¬ cedure. BUS. 1. Term used to specify an uninsulated conductor (a bar or wire); may be solid, hollow, square, or round. 2. Sometimes used to specify a busbar. 3. One or more conductors of an electron com- putor which are used as a path transmitting in¬ formation from any of several sources to any of several destinations. 39-104 1 APRIL 1959 AFM 100-39 BUS BUS REACTOR. Current-limiting reactor for connection between two different buses or two sections of the same bus for the purpose of limiting and localizing the disturbance due to a fault on either bus. BUSBAR. Heavy copper strip or bar used on switchboards and in power plants to carry heavy currents. BUSHING. 1. Lining for a hole intended to insulate and/or protect from abrasion, one or more conductors that pass through it. 2. Metallic sleeve or lining, usually removable, inserted in a body and used as a bearing for a shaft, to reduce friction. BUSY TEST. Test, in telephony, is made to find out whether certain facilities which may be desired, such as a subscriber line or trunk, are available for use. BUTT. Name given to the broken end of a prismatic quartz crystal opposite to the end terminated by rhombohedral faces. BUTT JOINT. Splice or connection formed by placing the ends of two conductors together and joining them by welding, brazing, or soldering. BUTTERFLY CIRCUIT. Frequency-determining element having no sliding contacts, used in UHF oscillator circuits 5 A MODULATOR. Class A amplifier which is used specifically for the purpose of supplying the necessary signal power to modulate a carrier. 1 APRIL 1959 AFM 100-39 CLA CLASS A OPERATION. Operation of a vacuum tube with grid bias such that the operating point is. at or near the center of the straight portion of its Ip Eg (plate-cur¬ rent grid-voltage) characteristic curve. Plate current flows throughout the entire operating cycle and distortion is kept to a minimum. CLASS A POSITION. Position which may be expected to be accurate to within five nautical miles. CLASS A TELEPHONE. Telephone authorized for the transaction of of¬ ficial business, with access to all facilities, includ¬ ing long distance trunks at government expense. CLASS AB AMPLIFIER. Amplifier in which the grid bias and alternating grid voltages are such that plate current flows for appreciably more than half but less than the entire electrical cycle. CLASS AB OPERATION. Operation of a vacuum tube with grid bias such that the operating point is approximately half way between class A and class B. CLASS ABl Circuit operation in which the input signal never exceeds the bias voltage, so that the grid is never driven positive and no grid current flows. CLASS AB 2 . Circuit operation in which the input signal is greater than the bias voltage, driving the grid positive and causing grid current to flow. y CLASS B AMPLIFIER. Amplifier in which the grid bias is approxi¬ mately equal to the cut-off value so that the plate current is approximately zero when no exciting grid voltage is applied, and so that plate current flows for approximately one-half of each cycle when an alternating grid voltage is applied. CLASS B BEARING. Bearing which a direction finding operator may reasonably consider to be accurate to within plus or minus five degrees. CLASS B MODULATOR. Class B amplifier which is used specifically for the purpose of supplying the necessary signal power to modulate a carrier. In such a modulator the class B amplifier is normally connected in push-pull. CLASS B OPERATION. Operation of a vacuum tube with grid bias at or very near cutoff, so that the operating point is at the lower bend of the Ip Eg with no input signal to the grid, and flows, for approximately the positive half of each cycle of the input signal. CLASS B POSITION. Position which may be expected to be accurate to within 20 nautical miles. CLASS B TELEPHONE. Telephone authorized for the transaction of of¬ ficial business, but may be used for unofficial service, with access to long distance trunks at sub¬ scriber’s expense. CLASS C AMPLIFIER. Amplifier in which the grid bias is appreciably greater than the cut-off value so that the plate current in each tube is zero when no alternating grid voltage is applied, and so that plate current flows for appreciably less than one-half of each cycle when an alternating grid voltage is applied. CLASS C BEARING. Bearing which a direction finding operator may resonably consider to be accurate to within plus or minus ten degrees. CLASS C OPERATION. Operation of a vacuum tube with grid bias con¬ siderably greater than cutoff. The plate current is zero with no input signal to the grid, and flows for appreciably less than one-half of each cycle of the input signal. CLASS C POSITION. Position which may be expected to be accurate to within 50 nautical miles. AFM 100-39 CLA 1 APRIL 1959 CLASS C TELEPHONE. Telephone authorized for the transaction of of¬ ficial business, but restricted to intra-base com¬ munication, with no access to long-distance trunks. CLASS D TELEPHONE. Telephone restricted to special classes of service such as fire alarm, guard alarm, and watchman services. CLEAR. 1. When security of military information is not involved in plain text, messages are ordinarily sent in the clear rather than in cipher or code. 2. To restore a storage or memory device to a prescribed state, usually that denoting zero. (Reference: RESET.) CLEAR TEXT. Text or language which conveys an intelligible meaning in the language in which it is written, with no hidden meaning. CLEARANCES. Usual meaning of separation, with special appli¬ cation to the separation of telephone plant from power plant or hazardous structures. CLEARING ENDS. Operation of removing the sheath from the end of a cable and eliminating all moisture and check¬ ing for crosses, shorts, and grounds in prepara¬ tion for testing. CLEAVAGE. Tendency of a crystalline substance to split along definite planes, called cleavage planas, which correspond to the layers of atoms making up the crystalline structure. CLICK FILTER. Device to reduce or eliminate the key clicks in a radiotelegraph transmitter. (Reference- KEY- CLICK FILTER.) CLIMBERS, LINEMAN’S. Shaped irons with straps for fastening to the tegs, equipped with sharp spurs, for climbing poles. CLINOMETER. Instrument for measuring the degree or percent of slope. CLIPPER. 1. Device which automatically limits the instan¬ taneous value of the output to a predetermined maximum value. The term is usually applied to devices which transmit only portions of an input wave lying on one side of an amplitude bound¬ ary. 2. Radio circuit which removes those portions of a signal wave exceeding a specified amplitude. CLIPPER-LIMITER. Transducer which gives output only when the input lies above a critical value and a constant output for all inputs above a second higher cri¬ tical value. (Reference: SLICER.) CLIPPING. Perceptible mutilation of signals or speech syl¬ lables during^transmission. CLN (COLON). Punctuation character(:) used in writing and printing. CLOCK. Primary source of electronic computer synchro¬ nizing signals. CLOSE CONTROL. Positive control exercised by an intercept director with communications contact over which he can deliver vectoring instructions to a friendly air¬ borne object. Such instructions are based upon computations derived from radar surveillance of the target and interceptor. CLOSE COUPLING. Degree of coupling greater than the critical cou- pling. CLOSE SUPPORT MISSION. Mission with the primary purpose of direct close support of friendly ground forces in the accom¬ plishment of their immediate objective and/or preventing front line enemy forces from carry¬ ing out their objectives. It requires close coordi¬ nation of air and ground activities, prior to, and 39-140 1 APRIL 1959 during the mission, and may include ground or air control, air to air control, and the positive establishment of bombing and strafing lines or zones prior to the mission. CLOSE-UP. Shot taken at close range in which the object or person practically fills the screen. CLOSED. Status indicating an air base is officially closed, for any reason, to the operation of aircraft. CLOSED CIRCUIT. 1. Program source that is not broadcast for gen¬ eral consumption but is fed to remote monitoring units by wire. 2. Completed circuit. CLOSED CIRCUIT SIGNALING. Signaling in which current flows in the idle con¬ dition, and a signal is initiated by increasing or decreasing the current. CLOSED CIRCUIT SYSTEM. Telegraph system in which, when no station is transmitting, the circuit is closed and current flows through the circuit. CLOSED CIRCUIT TELEVISION. Television signals which are not broadcast but are transmitted over a closed circuit and received only by interconnected receivers. CLOTH, WIPING. Material used by splicers in working molten lead into position when completing a splice. ' CLOUD CHAMBER. 1. Mechanism for making subatomic particles visible. 2. Closed shape containing saturated water vapor which, upon sudden expansion, reveals the pre¬ sence of condensation particles by the visible droplets formed upon them, or in which rapidly moving particles are revealed by the streaks of droplets, or tracks. CLOUD TRACK. Row or streak of droplets formed in a cloud AFM 100-39 CLO chamber by the passage through it of an ioniz¬ ing particle, the path of which is thus revealed. CLOVER-LEAF ANTENNA. Antenna having radiating units shaped like a four leaf clover. CLUTCH. Mechanical element which allows the synchron¬ ous motor to rotate while the phasing mechanism is stopped. This allows a facsimile machine to be phased without stopping the synchronous drive mechanism. CLUTTER. Unwanted signals, echoes, or images on the face of a cathode-ray tube which interfere with ob¬ servation of desired signals. (Reference: GRASS, NOISE.) Cm -1 . Unit of frequency employed chiefly in infrared spectroscopy. One cm-1 is equal to one divided by the wave length in centimeters. CMA (COMMA). Punctuation character (,) used in writing and printing. CMBT (COMBAT). Action or situation in which hostile military forces are in direct contact. CMLC (CHEMICAL CORPS). CMTC (COMMUNICATIONS MESSAGE TRAFFIC CONTROL). Unit responsible for the authorization, supervi¬ sion, and regulation of on-call patching and tele¬ conference service in a tape-relay center. This responsibility is delegated to this unit by the Director of Communications-Electronics. CMTCU (COMMUNICATION MESSAGE TRAFFIC CONTROL UNIT). CN (CONTROL TOWER, NAVY). CNC (CHIEF OF NAVAL COMMUNICATIONS). CNJC (CABLE NETWORK JOINT COMMITTEE). CNO (CHIEF OF NAVAL OPERATIONS). CO (COMMANDING OFFICER). 39-141 AFM 100-39 CO 1 APRIL 1959 CO. International Telecommunications Union desig¬ nation for station open to official correspondence exclusively. CO-CHANNEL INTERFERENCE. Interference caused oh one communication chan¬ nel by a transmitter operating in the same chan¬ nel. COARSE CONTROL. Control used for making rough adjustments of any of the adjustable features of electronic equip¬ ment such as intensity, gain, volume, tuning, COAST STATION. Land station in the maritime mobile service car¬ rying on a service with ship stations (a coast sta¬ tion may secondarily communicate with other coast stations, incidents to communicate with ship stations). COASTING PHASE OR COAST-IN-FLIGHT. Period in multi-stage rocket flight when no pow¬ er is applied, the rocket moving inertially until another engine fires. COATED LENS. Lens with air-glass surfaces coated with a thin transparent film of such index of refraction as to minimize the light loss by reflection. COAX (COAXIAL). Having one axis within another, as a coaxial cable, with a single cylindrical conductor sus¬ pended in the center of another conductor. COAXIAL ANTENNA. Antenna comprised of a quarter-wavelength ex¬ tension to the inner conductor of a coaxial line and a quarter-wavelength radiating sleeve which closely surrounds the outer conductor of the coaxial line, but is connected to the outer con¬ ductor only at its end. COAXIAL CABLE. Cable, used as a transmission line, consisting of one conductor, usually a small copper tube or wire, within and insulated from another con¬ ductor of larger diameter, usually copper tubing % or copper braid. The outer conductor may or may not be grounded. Radiation from this type of line is practically zero. (Reference: CONCENTRIC LINE, COAXIAL LINE.) COAXIAL LINE. Long metal tube having at its center a conductor supported by insulators. It is used as a transmis¬ sion line for radio or television signals. (Refer¬ ence: PIPELINE, COAXIAL CABLE CON¬ CENTRIC LINE.) COAXIAL-LINE FREQUENCY METER. Shorted section of coaxial line which acts as a resonant circuit and is calibrated in terms of fre¬ quency or wave-length. COAXIAL STUB. Short length of coaxial which is joined as a branch to another coaxial. Frequently a coaxial stub is short-circuited at the outer end and its length is so chosen that a high or low impedance is presented to the main coaxial in a certain frequency range. COAXIALLY FED LINEAR ARRAY. Beacon antenna having a uniform aximuth pat¬ tern. r COBALT. Metal having slight magnetic characteristics; combined with iron and steel to make special alloys used in permanent magnets. COC (COMBAT OPERATIONS CENTER). Physical facility from which territorial or regional supervision is exercised over air-defense opera¬ tions performed by subordinate organizations. CODAN (CARRIER-OPERATED DEVICE ANTI-NOISE). Device commonly used to mute the audio output of a receiver during standby or no carrier periods. Usually, the AVC voltage is used to control a squelch tube, which in turn controls the bias ap¬ plied to the first audio tube so that it is permit¬ ted to operate only when a carrier is present at the receiver input. Thus, the receiver output is heard when a signal is received, and is muted when no signal is present. 39-142 1 APRIL 1959 AFM 100-39 COD CODAN LAMP. Visual indication that a usuable transmitted sig¬ nal has been received by a particular radio re¬ ceiver. CODAN (CARRIER-OPERATED ANTI-NOISE) RECEIVER. Noise automatically suppressed by reduction of receiver gain during intervals when no carrier is present. Gain is restored to normal by arrival of a carrier. CODE. 1. System of communication in which arbitrary groups of symbols represent units of plain text of varying length. Codes may be used for brevity or for security. 2. Coded book (or document) arranged in sys¬ tematic form, containing a list of letters, sylla¬ bles, words, phrases or sentences each accom¬ panied by one or more arbitrary groups of sym¬ bols used as equivalents in cryptograms. 3. System of signaling utilizing dot-dash-space, mark-space or other method where each letter or figure is represented by prearranged combina¬ tions. 4. System of characters and rules for represent¬ ing information. 5. Loosely, the set of characters resulting from the use of a code. 6. Prepare a routine in machine language for a specific computer. , 7. Encode; to express given information by means of a code. (Reference: LANGUAGE.) BASIC. Code book which is used solely as part of a composite system, the groups of which are never transmitted unenciphered but are used only to provide groups for use with ci¬ pher tables or pads. BREVITY. Code which has as its sole purpose the shortening of messages rather than the concealment of their content. CABLE MORSE. Three-element code, used mainly in submarine cable telegraphy, in which dots and dashes are represented by positive and negative current impulses of equal length, and a space by absence of current. COLOR. System of colors used to specify the electrical value of a radio part or to identify terminals and leads. COMBAT. Code or cipher, the purposes of which are simplicity and speed in addition to as much security as is possible without pre¬ judicing unduly such simplicity and speed. HATTED. Randomized code consisting of an encoding section. The plain text groups are arranged in alphabetical or other significant order, accompanied by their code groups ar¬ ranged in a non-alphabetical or random order. INTERNATIONAL MORSE. Code on which letters and numbers are represented by specific groupings of dots and/or dashes. The Inter¬ national Morse Code is used especially in radio, telegraph and visual communications. INTERNATIONAL SIGNAL. Code adapted by many nations for international communication. The code uses combinations of letters to stand for words, phrases and sentences. The let¬ ters are transmitted by the hoisting of inter¬ national alphabet flags or by transmitting their dot and dash equivalents in the International Morse Code. N-ARY. Code in which each code element may be any one of N distinct kinds or values. NONHATTED. Plain text elements are arrang¬ ed in alphabetical or numerical order accom¬ panied by their code groups also arranged in alphabetical, numerical, or other systematic order. ONE-PART. Code in which the plain text ele¬ ments are arranged in alphabetical or numeri¬ cal order accompanied by their code groups also arranged in alphabetical, numerical or other systematic order. PANEL OR SURFACE. Prearranged code de¬ signed for visual communications between ground units and friendly aircraft. 39-143 AFM 100-39 COD 1 APRIL 1959 PREARRANGED MESSAGE. Code adapted for the use of units which require special or techni¬ cal vocabulary and composed almost exclusive¬ ly of groups representing complete or nearly complete messages. PRIVACY. Code employed to protect the con¬ tents of a message from casual reading by un¬ authorized individuals, but which does not af¬ ford (and is not intended to afford) any secur¬ ity against organized cryptanalysis. PYROTECHNICS. Prearranged code in which meanings are assigned to the various colors and arrangements of pyrotechnics. RINGING. System of spaced rings to call in different subscribers on the same line. TELEGRAPH. Impulse combinations corres¬ ponding to letters and figures used in tele¬ graphic communications. TELETYPEWRITER. Code used in teletype¬ writer communication in which each code group is made up of five units or elements, of equal length. These elements are known as marking or spacing impulses. TERNARY. Code in which each code element may be any one of three distinct kinds of values. TWO-PART. Randomized code, consisting of an encoding section and a decoding section. In the encoding section the plain text groups are ar¬ ranged in an alphabetical or other significant order accompanied by their code groups ar¬ ranged in a nonalphabetical or random order. In the decoding section the code groups are arranged in alphabetical or numerical order and are accompanied by their meanings as given the encoding section. CODE BEACON. Beacon having the characteristics of a code light. CODE BOOK. Book or document, used in a code system, ar¬ ranged in a systematic form containing a list of letters, syllables, words, phrases, or sentences each accompanied by one or more arbitrary groups of symbols for use as equivalents in cryptograms. CODE CHARACTER. Particular arrangement of code elements, used in a code to represent a single value or symbol. CODE ELEMENT. Discrete condition or event in a code. CODE GROUP. Fixed arbitrary combination or permutation of symbols assigned to represent a plain text ele¬ ment in a code book. CODE WORD. Word which conveys a meaning other than its conventional one, prearranged by the correspon¬ dents. CODED PASSIVE REFLECTOR. Object intended to reflect Hertzian waves and having variable reflecting properties according to a predetermined code, for the purpose of produc¬ ing an indication on a radar receiver. CODER. 1. Device which sets up a series of signals in code form. 2. Beacon circuit which takes the trigger pulse output of a discriminator, forms it into a series of pulses, then feeds these pulses to a modulator circuit. CODING DELAY. Arbitrary time delay in the transmission of pulse signals, usually inserted at the transmitting sta¬ tion. CODING DISK. Disk with small projections for operating con¬ tacts to give a certain predetermined code to a transmission. CODRESS. Type of message in which the complete address is contained only in the encrypt text. COEF (COEFFICIENT). 1. Number or symbol placed before another symbol or combination of symbols as a multiplier. 39-144 1 APRIL 1959 AFM 100-39 COE 2. Number expressing the amount of some change or effect under certain conditions. COEFFICIENT OF COUPLING. Numerical indicator of the degree of coupling existing between two circuits. COEFFICIENT OF REFLECTION. Square root of the ratio of the reflected power leaving a reflecting surface to the power inci¬ dent to the same surface. COEFFICIENTS. System of transmission ratings denoting the im¬ pairment to teletypewriter signals in various types of wire or radio facilities. COFFING HOIST. Block and tackle used in telephone outside plant construction work for pulling the slack from a suspension strand. COHERENT MTI. Process of matching the phase of a reference os¬ cillator to that of the transmitter at each trans¬ mitted pulse. This can be done by allowing a sufficient amount of power from the transmitter to enter the resonant cavity of the oscillator, which is then forced into step with the transmit¬ ter. COHERENT PULSE OPERATION. Method of pulse operation in which the phase of the radio frequency waves is maintained through successive pulses. COHERENT REJECTION. Classified definition. (Reference: AFM 100-50.) COHO. Type of local oscillator which is used to provide a reference phase in a coherent pulse doppler system. It is locked in phase to the transmitter pulse every time a pulse is sent out. (Reference. STALO.) COI (COMMUNICATIONS OPERATING INSTRUCTIONS). COIL. Turns of wire wound on an iron core or on a coil form made of insulating material so as to be self-supporting. A coil offers considerable opposition to the passage of alternating current but very little opposition to direct current. CHOKE. Inductor (reactor) which is used to limit or suppress the flow of alternating cur¬ rent without appreciably affecting the flow of direct current. (Reference: IMPEDANCE COIL.) EXPLORING. Loop of wire, with or without a magnetic core, for locating current by induc¬ tion. Used with a current indicating device. HEAT. Protective device which grounds or opens a circuit, or does both, by means of a mechanical element which is allowed to move when the fusible substance that holds it in place is heated above a predetermined tem¬ perature by current in the circuit. Provides overcurrent protection. HEAT DUMMY. Substitute for a heat coil which is not operated by excessive current. Used when protection is not desired. HELMHOLTZ. Variometer, having horizontal and vertical balanced coil windings, which is used to vary the angle of phase difference be¬ tween any two similar wave forms of the same frequency. HYBRID. Four-winding coil wound and con¬ nected so that incoming and outgoing currents in a two wire path are separated and kept from interfering with each other. IMPEDANCE. Coil primarily used to impede the flow of alternating current by its induc¬ tive reactance. (Reference: RETARDATION COIL, CHOKE COIL.) INDUCTION. 1. Transformer used in a tele¬ phone set for interconnecting the transmitter, receiver and line terminals. 2. Transformer for converting interrupted di¬ rect current into high voltage alternating cur¬ rent. LOADING. Coils of wire around a magnetic core constituting inductances which can be in¬ serted in a circuit at regular intervals to im¬ prove transmission. 39-145 AFM 100-39 COI 1 APRIL 1959 PHANTOM Originally a coil used in a phantom circuit for impedance matching. Now general¬ ly, any coil, side or phantom in a phantom cir¬ cuit. When the term is used the meaning should be made clear. REPEATING. 1. Audio-frequency transformer, usually having a one-to-one ratio, which is used to connect two sections of telephone line inductively so as to permit the formation of simplex and phantom circuits. 2. General term for a transformer in a speech or signal circuit. RETARDATION. Telephony, a high-inductance coil which offers high impedance to voice-fre¬ quency currents, but permits the passage of ringing current. SIDE CIRCUIT. One of a pair of repeating coils used on each of two pairs of wire to de¬ rive a phantom circuit. SIMPLEX. Repeating coil used on a pair of wires to derive a simplex circuit. SOLENOID. Tubular coil of wire which, when traversed by an electric current, will act as a magnet and tend to pull a movable iron core to a central position. VOICE. Moving coil which activates the dia¬ phragm of a dynamic speaker. COINCIDENCE. Agreeing as to position; corresponding. In a coincidence-type range finder, when the two half images of a distant object are aligned, they are said to be in coincidence. COINCIDENCE AMPLIFIER. Amplifier which has an output only when two pulses are applied simultaneously to the tube. COINCIDENCE PRISM. Compound prism, consisting of a system of small prisms cemented together, used in a coincidence range finder to bring the images from the two objectives to a single eyepiece for viewing. COINCIDENCE RANGE FINDER. Self-contained distance measuring device operat¬ ing on the principle of triangulation. Half imag¬ es, observed from points of know distance, are matched to determine the range. COLD. Idiomatic expression applied in general to elec¬ trical circuits that are disconnected from voltage supplies and at ground potential. Opposed to "hot”, which means "carrying an electrical charge.” COLD CATHODE. Cathode that is not heated. Electrons may be pulled out of it by a sufficiently high voltage applied to an anode. The cathode of a phototube may be considered in this class since it emits elec¬ trons when exposed to light rather than heat. COLD CATHODE TUBES. Tubes in which no external source is used for heating the cathode. These include vacuum tubes such as photoelectric cells and rectifiers, gas glow tubes such as voltage regulators. COLINEAR ARRAY. Antenna array having a string of half wave ele¬ ments excited in phase. COLLATION. Classified definition. (Reference: AFM 100-50.) COLLECT CHARGES. Collect charges are those paid by the addressee covering the cost of a received telegraph mes¬ sage, or the charges paid by the called party covering the cost of a received telephone toll call. COLLECTION. Classified definition. (Reference: AFM 100-50.) COLLECTIVE ADDRESS GROUP. Address group which represents two or more commands, authorities, activities, units, or any combination thereof, and includes the comman¬ der of the organization or group and all subordi¬ nate commanders therein. COLLECTIVE CALL SIGN. Call sign which represents two or more facilities, commands, authorities, or units. The collective 39-146 1 APRIL 1959 AFM 100-39 COL call sign for any of these includes the comman¬ ders thereof and all subordinate commanders therein. COLLECTIVE LENS. Convex or positive lens used in an optical sys¬ tem to collect the field rays and bend them to the next optical element. COLLECTOR. Electrode in a velocity-modulated vacuum tube on which the spent electron bunches are col¬ lected. COLLIMATE. 1. Render parallel to a certain line or direction. 2. Render parallel, as rays of light. 3. Adjust the line of sight of an optical instru¬ ment so that it is in its proper position relative to the other parts of the instrument. COLLIMATING TELESCOPE. Telescope with an outer cylindrical surface that is concentric with its optical axis. COLLIMATION. Process of aligning the axis of the optical ele¬ ments to the mechanical axis of an instrument. COLLIMATOR. Optical device for artificially creating a target at a predetermined distance (a beam of parallel rays of light) used in testing and adjusting cer¬ tain optical instruments. COLLINEAR ARRAY. Antenna array in which halfwave elements are arranged end-to-end on the same vertical or hori¬ zontal line. COLLISION COURSE. Course toward a selected object which, if main¬ tained, will cause the aircraft or missile to pass directly over, or into the object. COLLISION FREQUENCY. Number of collisions between an electron and a molecule of a gas per unit time. It is dependent on the velocity of the electron and the mean free path between molecules. COLON. Punctuation character (:) used in writing and printing. COLOR BANDS. Bands of a smoky color arranged with a quartz crystal parallel to prism or rhombohedral growth faces. COLOR BREAK-UP. Spurious color caused by difference in observa¬ tion condition from one field to the next. Color television term. COLOR BURST. Color television portion, of the composite color signal comprising the few sine-wave cycles of color subcarrier frequency (and the color burst pedestal, if present) which is added to the hori¬ zontal pedestal for synchronizing the color-car¬ rier reference. COLOR CODE. 1. System of colors used to specify the electrical value of a radio part or to identify terminals and leads. 2. System of colors applied to the wrapping of cable conductors to distinguish one from anoth¬ er. COLOR DECODER. Section, including demodulators and phase split¬ ters which derive red, green, and blue signals from composite color video signal. Color televi¬ sion term. COLOR DIFFERENCE SIGNAL. Combination of I and Q signals in proper polar¬ ity which are added to Y monochrome signal to produce signals representing tristimulus values (red, green, blue) transmitted. Resulting signals applied to the television picture tube. COLOR EDGING. Spurious color at the boundaries of differently colored areas in a picture. COLOR FRINGING. Spurious colors introduced into picture by change in position of televised object from field to field. 39-147 AFM 100-39 COL 1 APRIL 1959 COLOR GAMUT. Restricted range of colors which can be matched by primaries. COLOR KILLER. Television circuit between color sync and video sections which cuts off chrominance channel when monochrome signal is being transmitted. COLOR KINESCOPE. Cathode-ray picture tube, used in color televi¬ sion receivers, in which electrical signals are translated into a visible picture in natural color on a luminescent screen usually comprising sev¬ eral different color-emitting phosphors. COLOR PHASE. Phase difference between color television I or Q and carrier chrominance signal. COLOR PHASE ALTERNATION. Periodic changing of color phase of one or more components of the color television subcarrier be¬ tween two sets of assigned values. COLOR PICTURE SIGNAL. Monochrome component plus subcarrier modu¬ lated with color information, excluding synchro¬ nizing signals. Color television term. COLOR SIGNAL. General term for any signal, excluding lumi¬ nance or monochrome, which controls chroma- ticity values. Color television term. COLOR SUBCARRIER. Color television, carrier whose modulation side¬ bands are added to the monochrome signal to convey color information. COLOR TELEVISION. Television system that reproduces an image in its original colors. ACHROMATIC. Shade of grey from black to white, color absent. COLOR TEMPERATURE. Color temperature of a source of light is the temperature at which a black body must be oper¬ ated to give a color matching that of the source in question. COLOR TRANSMISSION. Transmission of a signal wave which represents both the brightness values and the chromaticity values in the television picture. COLOR-CARRIER REFERENCE. Color television continuous signal having the same frequency as the color subcarrier and hav¬ ing fixed phase with respect to the color burst. This signal is used for the purposes of modula¬ tion at the transmitter and demodulation at the receiver. COLORIMETRY. Measurement of color. COLPITTS OSCILLATOR. Vacuum tube oscillator in which a parallel-tuned tank circuit is connected between grid and plate, with the tank capacitance containing two voltage- dividing capacitors in series, with their common connection at cathode potential. When the two voltage-dividing capacitances are the plate-to- cathode and the grid-to-cathode capacitances of the tube, the circuit is known as the ultra-audion oscillator. COLUMN. 1. Vertical sequency of symbols or groups there¬ of. 2. Electronic computer synonym for place. COLUMN CO-ORDINATE. Symbol normally at the top of a matrix identify¬ ing a specific column of cells. COM (COMMAND, COMMANDER, COMMANDANT, COMMUNICATION). COMA. Aberration affecting the sharpness of images off the axis (caused by the fact that rays from an object point off the axis) passing through a given circular zone of the lens, come to a focus in a circle rather than a point, and the circles formed by rays through different zones are of different sizes and are located at different dis¬ tances from the axis. The image of a point object is comet shaped. 1 APRIL 1959 AFM 100-39 COM COMAIRCANLANTSUBAREA (COMMANDER AIR CANADIAN ATLANTIC SUB AREA). COMAIRNELANTSUBAREA (COMMANDER AIR NORTHERN EUROPEAN ATLANTIC SUB AREA). COMAIRNORTH (COMMANDER ALLIED AIR FORCES NORTHERN EUROPE). COMAIRSOUTH (COMMANDER ALLIED AIR FORCES SOUTHERN EUROPE). COMALAIRNOREUR (COMMANDER ALLIED AIR FORCES NORTHERN EUROPE). COMALNAVNOEUR (COMMANDER ALLIED NAVAL FORCES NORTHERN EUROPE). COMAT (COMMANDER MILITARY AIR¬ TRANSPORT SERVICE). COMBAT. Action or situation in which hostile military forces are in direct contact. COMBAT AIR PATROL. Air patrol over any area or force usually for the purpose of intercepting and attacking hostile airborne objects before they can reach their ob¬ jective. COMBAT CENTER. Physical facility from which a NORAD exercises supervision of air-defense operations by its sub¬ ordinate SAGE direction center. The combat cen- ^ ter is equipped with AN/FSQ-8 Combat Control Central. COMBAT CODE. Code or cipher, the purposes of which are sim¬ plicity and speed in addition to as much security as is possible without prejudicing unduly such simplicity and speed. COMBAT INFORMATION CENTER. Agency charged with the function and responsi¬ bility of keeping the commanding officer and higher commands together with other control sta¬ tions, informed of the location, identity, and movements of friendly and/or enemy aircraft, large missiles, and surface ships within the air defense area. COMBAT INTELLIGENCE OFFICER. Member of the battle staff responsible for all intelligence matters. COMBAT OPERATIONS CENTER. Physical facility from which territorial or re¬ gional supervision is exercised over air-defense operations performed by subordinate organiza¬ tions. COMBAT SCENE OF ACTION FREQUENCY. Simplex channel for tactical communications in combat operations in which two or more ele¬ ments of the same, or different, arms are em¬ ployed in circumstances precluding the prior agreement of a communication plan. COMBAYOFBISCAYSUBAREA (COMMANDER BAY OF BISCAY SUB AREA). COMBINATION CABLE. Cable having conductors grouped in both quads and pairs. COMBINATION DISTRIBUTOR FRAME. Frame which combines the functions of a main distributing frame and an intermediate distribut¬ ing frame. COMBINED ROUTING INDICATOR PLAN. 1. Plan designed to meet requirements of allied military tape relay communications which are world-wide in scope. 2. Plan designed to meet requirements of allied military teletypewriter (teleprinter) communica¬ tions which are confined to a localized theater. COMBINED TELEPHONE SET. Telephone set including in a single housing all the components required for a complete tele¬ phone set except the handset which it is arranged to support. COMBINER. Circuit for mixing video, trigger, and scan data from synchronizer for modulation of link. 39-149 AFM 100-39 COM 1 APRIL 1959 COMBRAX (COMMODORE RCN BARRACKS). COMCANLATNSUBAREA (COMMANDER CANADIAN ATLANTIC SUB AREA). COMCM (COMMUNICATIONS COUNTERMEASURES). COMD (COMMAND). COMDG (COMMANDING). COMDT (COMMANDANT). COME ALONG. Slang expression which refers to a block and tackle, or other equipment, used to remove the slack from a strand of wire, messenger, or sus¬ pension strand. COMET. Loose body of gases and solid matter revolving around the sun. COMFLOGWING (COMMANDER FLEET LOGISTIC AIR WING). COMFLIBASTILLES (COMMANDER U S ATLANTIC FLEET BASES ANTILLES). COMINT (COMMUNICATIONS INTELLIGENCE). Communications intelligence is the information obtained from the analysis of intercepted foreign communication transmissions. COMJEF (COMMANDER JOINT EXPEDITIONARY FORCE). COML (COMMERCIAL). 1. Produced or producible in large quantities and available as mercantile. 2. Aircraft used as a common carrier by a com¬ pany or private firm. COMLANDDENMARK (COMMANDER ALLIED LAND FORCES DENMARK). COMLANDGREECE (COMMANDER ALLIED LAND FORCES GREECE). COMLANDNORWAY (COMMANDER ALLIED LAND FORCES NORWAY). COMLANDSOUTH (COMMANDER ALLIED LAND FORCES SOUTHERN EUROPE). COMLANDSOUTHEAST (COMMANDER ALLIED LAND FORCES SOUTHEAST EUROPE). COMLANDTURKEY (COMMANDER ALLIED LAND FORCES TURKEY). COMLOGNET (COMBAT LOGISTICS NETWORK). World-wide integrated network comprised of land lines, cable, and radio channels designed to carry Air Force digitalized data traffic between all major air commands, Air Force bases, air materiel areas, depots, Air Force contractors, and other department of defense data systems points of entry and other locations as authorized. COMM (COMMUNICATION). Means of conveying information of any kind from one person or place to another except by direct unassisted conversation or correspondence. COMM CEN (COMMUNICATION CENTER). Agency responsible for the receipt, transmission, and delivery of messages. It normally consists of a message center section, message section, cryp¬ tocenter section, and such other means of oper¬ ation sections (radio, wire, teletypewriter, etc) required by the headquarters or echelon served by the communication center. COMM Z (COMMUNICATIONS ZONE). That area adjoining the combat zone and con¬ taining lines of communication, establishments for supply and evacuation, and other facilities and agencies required for the immediate support and maintenance of troops in the field. COMMA. Punctuation character (,) used in writing and printing. COMMAND. 1. Set of characters which defines an operation. 2. One of a set of several signals (or groups of signals) which occurs as a result of an electronic computer instruction. COMMAND GUIDANCE. Form of missile guidance wherein control sig¬ nals transmitted to the missile from an out¬ side agency cause it to traverse a directed path through space. 39-150 1 APRIL 1959 AFM 100-39 COM COMMAND HEADING. Vector or steer calculated by a computer (based upon a computer-generated interception point) to enable interceptors to complete an assigned mission. COMMAND NET. Communication system or network by which a commander maintains control of subordinate headquarters or units under his command. COMMAND POST. 1. Physical facility within a combat center or direction center from which division or sector supervision or air-defense operations is exercised. 2. Station of a unit’s headquarters where the commander and the staff perform their activities. In combat, a unit’s headquarters is often divided into echelons. COMMAND TRACKING. Process by which a computer performs automatic tracking of interceptors; in this process, the com¬ puter uses inserted or computer-generated head¬ ing, speed, and altitude, rather than that infor¬ mation derived from the automatic-tracking pro¬ gram. COMMANDER IN CHIEF. 1. Officer or official having supreme command of the armed forces of a country. 2. Commander of a theater of war 3. Commander of a force directly under the Joint Chiefs of Staff. COMMANDER IN CHIEF NORTH AMERICAN AIR DEFENSE COMMAND. Commanding officer of the combined command for air defense of the ConUS, Canada, Alaska, and Northeast area. COMMANDING GENERAL. General officer commanding an installation or organization, such organization normally being a wing or larger organization. Usually called a commander in the Air Force. COMMARMOC (COMMANDER MARITIME FORCES, MOROCCO). COMMERCIAL FACILITIES. Facilities for which direct charge is made for handling messages. COMMON BATTERY. System of current supply where all dc energy for a unit of a telephone system is supplied by one source in a central office or exchange. COMMON BATTERY CIRCUITS. Telephone circuits through which the talking and signaling currents of electricity are supplied from a central office source, usually a central office switchboard installation. COMMON BATTERY SYSTEM. Telephone system which has current supplied from a central source. COMMON BATTERY TELEPHONE SET. Telephone set for which both the transmitter current and the current for signaling by the tele¬ phone station are supplied from a centralized power source. COMMON BATTERY TELEPHONE SYSTEM. Telephone system which has current supplied to it from a central source. COMMON SERVICING. Servicing performed by one department for one or more departments for which no charge is made to the other departments. COMMON SUPPLIES. Supplies common to two or more services. COMMON SYSTEM. System of air navigation and air traffic control facilities designed to meet the requirements of all uses of air space in the ConUS, except tac¬ tical military units. The basic plans for the sys¬ tem were developed by special committee 31 of the radio technical commission for aeronautics. The plan outlines the requirement for develop¬ ment of new equipments and their integration into existing systems over an extended period of time. COMMON USE CIRCUIT. Circuit that is shared by two or more services, 39-151 AFM 100-39 COM 1 APRIL 1959 either on a concurrent or time sharing basis. It may be a unilateral, bilateral, or joint circuit. COMMON-USER CHANNELS. Communication channels which are available to all Air Force agencies for transmission of com¬ mand, administrative, and logistic traffic. COMMUNICATION. Means of conveying information of any kind from one place to another except by direct, unassisted conversation or correspondence. AGENCY OF. Facility which embraces person¬ nel and equipment necessary to provide commun¬ ication. AGENCY OF SIGNAL. Includes all personnel and equipment necessary to operate a signal communication installation. It may include one or more means of communication. AIR-GROUND. Method or means of conveying information between aircraft in flight and ground stations. INTERIOR. Rapid communication facilities, elec¬ trical, acoustical, or mechanical, that intercon¬ nect the various operational spaces of a naval vessel, aircraft, or other activity. JOINT. Common use of communication facilities by two or more services of the same nation. LINE. Use for communication purposes of a phy¬ sical path, such as wire or waveguide, be¬ tween terminals. RADIO. Use of radio for communication facili¬ ties. VISUAL. Use of optical signs, such as flags and lights, for communication purposes. COMMUNICATION BAND. Communication band consists of the band of fre¬ quencies due to modulation (including keying) necessary for a given type of transmission. COMMUNICATION CENTER. Agency responsible for the receipt, trans¬ mission, and delivery of messages. It normally consists of a message center section, message sec¬ tion, cryptocenter section, and such other means of operating sections (radio, wire, teletypewriter, etc.) required by the headquarters or echelon served by the center. COMMUNICATION CHANNEL. Part of a radio or wire circuit, or a combination of wire and radio, which connects two or more terminals. COMMUNICATION FACILITY. Device or system, in its entirety, that promotes the sending of intelligence from one point to another. COMMUNICATION GUARD, RADIO. Communication station designated to listen for and record transmission, and to handle traffic on a designated frequency for a certain unit or units. COMMUNICATION SECURITY. Protection resulting from all measures designed to deny to unauthorized persons information of value which might be derived from a study of communications. COMMUNICATIONS COUNTERMEASURES. Electronic countermeasure used specifically a- gainst communications. COMMUNICATIONS COVER. Classified definition. (Reference: AFM 100-50.) COMMUNICATIONS COVER AND DECEPTION. Classified definition. (Reference AFM 100-50) COMMUNICATIONS DECEPTION. Use of devices, operations, and techniques with the intent of confusion or misleading the user of a communications link or a navigation system (Reference: AFM 100-50.) COMMUNICATIONS IMPROVEMENT MEMORANDUM. COMMUNICATIONS INTELLIGENCE. Intelligence developed from listening in on, in¬ tercepting, or observing enemy, or potential en¬ emy, communication transmissions. (Reference: AFM 100-50.) 1 APRIL 1959 AFM 100-39 COM COMMUNICATIONS JACKAL. Series of airborne barrage jammers, AN/ART-7, -9, -10 and -11. These sets vary in power from 105 watts to 150 watts and together cover the frequency band from 27 to 57 me. They are frequency-modulated and operate unattended dur¬ ing flight to jam AM enemy signals. Each set weighs approximately 75 pounds. COMMUNICATIONS JAMMING. Deliberate interference with radio communica¬ tions by electronic means. It may consist of par¬ tial or complete obliteration of the message con¬ tent, it may take the form of annoyance or dis¬ traction to the operator, or it may modify or add to the message. COMMUNICATIONS MESSAGE TRAFFIC CONTROL. Unit responsible for the authorization, super¬ vision, and regulation of on-call patching and teleconference service in a tape-relay center. This responsibility is delegated to this unit by the Director of Communications-Electronics. COMMUNICATIONS NETWORK. Interconnection of specific organizations or geo¬ graphical locations by communications means for functional or command purposes. Two or more networks interconnected make up a com¬ munications system. For instance, the AIRCOM- NET, AIROPNET, and SACCOMNET are net¬ works which are a part of the AIRCOM. (Re ference: COMMUNICATIONS SYSTEM.) COMMUNICATIONS OFFICER. Officer who manages communications activities including construction, installation, operation, maintenance, repair, and modification of ground communications equipment such as radio, tele¬ type, telephone, telegraph, facsimile, crypto¬ graphic, and television, and commands commun¬ ications units. COMMUNICATIONS OPERATIONS INSTRUCTIONS. . Series of instructions issued for the technical con¬ trol and coordination of communications agen¬ cies of a command. COMMUNICATIONS SECURITY. Protection resulting from all measures designed to deny unauthorized persons, information of value which might be derived from the posses¬ sion and study of electrical communications. COMMUNICATIONS SERVICE AUTHORIZATION. Call or subsidiary contract upon the general con¬ tracts with the communications companies to provide specific facilities and services within the prescribed limits of the Communications Service Authorization. COMMUNICATIONS ZONE INDICATOR. Device developed by Raytheon to indicate whe¬ ther or not long distance high frequency broad¬ casts are successfully reaching their destinations. The equipment will also indicate approximately how strong the signals are when they arrive. It could be used by the Voice of America to check the effectiveness of their broadcasts, and also as an aid in increasing the efficiency and reli¬ ability of any long distance radio communica¬ tions system. To test a signal, COZI sends out from the radio stations own antenna, a radar beam along the same path taken by the radio waves. The interruption in broadcasting is so brief the listeners do not notice the break. The radar beam returns and is measured for both its in¬ tensity and the time interval of its travel. From these measurements of "back-scatter energy, the equipment produces values that tell the op- ' erator, with a high degree of accuracy, the "skip distance” of the wave and its probable strength when it arrives at its destination. Under certain conditions, it is also possible to detect various evidences of deliberate "jamming” through var¬ iances in the calculated energy of the back- scatter return. COMMUNICATIONS SYSTEM. Series of interconnected communications net¬ works, circuits, stations, and facilities for ful¬ filling communications needs on a broad scale. (Reference: COMMUNICATIONS NET¬ WORK.) 39-153 AFM 100-39 COM 1 APRIL 1959 COMMUNICATIONS/SIGNAL CENTER. Agency charged with the responsibility for re- ceipt, transmission and delivery of messages. It normally includes message center, transmitting and receiving facilities. COM MUNI CATIONS-ELECTRON ICS. Field of specialization which covers radio and wire communications and electronic devices and their uses. COMMUNICATIONS-ELECTRONICS DOCTRINE. Series of Air Force manuals authorized by AFR 100-13. These manuals contain C-E directives, data, instructions, and related information cover¬ ing basic concepts, policies, planning systems, and operating instructions. Specialized informa¬ tion required by C-E staffs to plan, implement, and operate C-E systems and facilities is included in CED Manuals. COMMUNICATIONS-ELECTRONICS FACILITY. Combination of communications and/or electro¬ nics material which will, when properly installed and manned, function to satisfy the operational requirement for a communications-electronics ser¬ vice. COMMUNICATIONS-ELECTRONICS FIELD. Element of air power concerned specifically with the collection and transmission of informa¬ tion. Communications-electronics provides the facilities by which commanders, separated from the elements of their command, may exercise ad¬ ministrative, logistical, and tactical direction. It provides facilities to enhance or control the op¬ erational capabilities of aircraft or missiles. The field of communications-electronics does not in¬ clude communications that take place by methods of direct conversation or correspondence. COMMUNICATIONS-ELECTRONICS INSTRUCTIONS. Replaced by a series of Air Force Manuals in the 100 series called communications-electronics doctrine. COMMUNICATIONS-ELECTRONICS OFFICER. Member of the battle staff responsible for all matters pertaining to proper functioning of radio, wire, and electronic devices. COMMUNICATIONS-ELECTRONICS SCHEME. Document which translates an approved opera¬ tional requirement into the engineering data and supply information necessary to obtain action to place a communications-electronics facility in an operational condition. COMMUNICATIONS-ELECTRONICS SCHEME DESIGNATOR. Combination of symbols, numbers, and letters which are used to correlate the communications- electronics scheme to the port call authorization during the preparation, processing, and installa¬ tion phases. In essence, the designator is a short title which can be used for reference, reporting, and control purposes. COMMUNICATIONS-ELECTRONICS STAFF OFFICER. Officer who has charge, under the direction of his organizational commander, of all military communications duties. This includes books, pa¬ pers, and devices connected therewith, includ¬ ing electromagnetic and electro-mechanical ap¬ paratus. He has the duty of collecting and trans¬ mitting information for the Air Force by elec¬ tromagnet vehicles, and all other duties us¬ ually pertaining to military communications- electronics. COMMUNITY AUTOMATIC EXCHANGE. Small dial office serving a community. COMMUTATION. Mechanical process of converting the alternating current which flows in the armature of dc gen¬ erators into the dc generator output. COMMUTATOR. 1. Device used on electric motors or generators to maintain a unidirectional current. 2. Device used in a multiplex system to connect the line to various channels. COMNAVGER (COMMANDER U S NAVAL FORCES IN GERMANY). 39-154 1 APRIL 1959 ComNavMarianas (COMMANDER U S NAVAL FORCES, MARIANAS). ComNavNorth (COMMANDER ALLIED NAVAL FORCES NORTHERN EUROPE). ComNavSouth (COMMANDER ALLIED NAVAL FORCES SOUTHERN EUROPE). ComNorEastSubArea (COMMANDER NORTH EASTERN SUB AREA). ComOceanAnt (COMMANDER OCEAN ATLANTIC). COMP (COMPOSITE). Operating one telephone and two dc telegraph or teletypewriter circuits over one pair of wires. COMPANDER. Device which combines the function of a com¬ pressor with an expander. It is a combination of a compressor at one point in a communication path for reducing the volume range of signals, followed by an expander at another point for restoring the original volume range. Usually its purpose is to improve the ratio of the signal to the interference entering in the path between the compressor and expander. Permits the trans¬ mission of a signal having a small volume range. COMPANDING. Process in wh h compression is followed by ex¬ pansion. Companding is often used for noise re¬ duction, in which case the compression is applied before the noise exposure and the expansion af¬ ter the exposure. COMPARATOR. Optical instrument for measuring rectangular co¬ ordinates of points on a plane surface, such as a photographic plate. COMPASS. Instrument used to determine direction. FLUXGATE. Gyrostabilized remote indicating compass which is used as a compass and azi¬ muth control system in conjunction with auto¬ matic pilots. RADIO. Direction-finding radio set which pro¬ vides indications concerning the bearings of AFM 100-39 COM radio transmitters with respect to a reference point. COMPASS BEARING. Bearing measured relative to magnetic north. COMPASS COURSE. Course in which the direction of the reference line is north, as indicated by a magnetic compass. COMPASS DIRECTION. Direction with reference to magnetic north in¬ dicated by a compass. COMPASS ERROR. Angle formed by the north-south compass line and the true meridian passing through the cen¬ ter of the compass. COMPASS LOCATOR. Non-directional radio beacon of low power as¬ sociated with a recognized instrument landing system. COMPASS NORTH. Direction indicated by the north-seeking end of the needle of a magnetic compass. COMPASS TRANSMITTER. Sensitive element of a compass system which picks up the directive force of the earth’s magnetic field. COMPATABILITY. , Nature of a color television system which permits normal monochrome reception of color trans- * missions by unaltered monochrome receivers. COMPENSATED VOLUME CONTROL. Device in a radio receiver that changes the tonal balance of the loudspeaker output for dif¬ ferent output levels to compensate for corres¬ ponding variations in the response character¬ istics of the human ear. COMPENSATION THEOREM. If an impedance AZ is inserted in a branch of a network, the resulting current increment pro¬ duced in any branch in the network is equal to the current that would be produced at that point by a compensating voltage acting in series with the modified branch, whose value is - AZ, where 39-155 AFM 100-39 COM 1 APRIL 1959 I is the original current that flowed where the impedance was inserted before the insertion was made. COMPENSATOR. 1. Portion of a direction finder which automat¬ ically applies to the direction indication, all, or a part of, the correction for magnetic deviation. from which the light originally comes, cannot be seen sharply defined by the reflected or trans¬ mitted light. COMPLEX REFLECTORS. Structure or group of buildings with many re¬ flection surfaces, oriented in many different di¬ rections. 2. Device that compensates for electrical losses, such as a cable compensator. COMPLEMENT. 1. Number, in an electronic computer, whose re¬ presentation is derived from the finite positional notation of another by one of the following: a. True complement: Subtract each digit from one less than the base; then add 1 to the least significant digit, executing all carries required. b. Base minus one’s complement: Subtract each digit from one less than the base. 2. To form the complement of a number. Note. In many machines, a negative number is represented as a complement of the cor¬ responding positive number. COMPLEMENTARY BAR. Rectangular cut at the complement of the AT or BT angle in X-sections of crystals. COMPLEMENTARY COLORS. Two colors are complementary if when added to¬ gether, such as by projection, they produce white light. COMPLEMENTARY WAVE. Wave brought into existence at the ends of a coaxial cable, or two conductor transmission line, or at any discontinuity along the line. COMPLETE CARRY. (Reference: CARRY.) COMPLETE DIFFUSION. Diffusion in which the diffusing medium scat¬ ters the light incident upon it so that none is regularly reflected or transmitted, and objects, COMPLIANCE. Acoustical and mechanical equivalent of cap¬ acitance. COMPONENT. 1. Major item, not a complete operating set, which may be part of an operating set, or which may be used to extend the functions or to sup¬ plement the facilities of the set. 2. Electrical or mechanical unit in an assembly or subassembly of radio parts. COMPOSITE. Method of simultaneously operating telephone and telegraph or teletypewriter circuits by the use of a single pair of conductors. COMPOSITE CABLE. Cable in which conductors of different gauges or types are combined under one sheath. COMPOSITE COLOR SIGNAL. Color signal, including blanking, luminance and chrominance information, and sync signals. Co¬ lor television term. COMPOSITE PICTURE SIGNAL. Television signal which consists of the blanked picture signal and the synchronizing signals. COMPOSITE SET. Device, consisting of capacitors and retard coils, which permits the operation of a ground-return telegraph circuit on each wire of a pair. COMPOSITION PLANE OR SURFACE. Name applied to the boundary surface between two crystals growing together symmetrically. COMPOUND LENS. Two or more separate pieces of glass. 39-156 1 APRIL 1959 AFM 100-39 COM COMPRESSION. 1. Diminishing of the audio volume range of the input signal so that the minimum output signal contains less noise and the maximum out¬ put signal less distortion. 2. Reduction in the black-to-white amplitude range or frequency swing occurring between two points in the system or reduction of the contrast of a facsimile signal. 3. Process in which the effective gain applied to a signal is varied as a function of the signal magnitude, the effective gain being greater for small signals. COMPRESSOR. 1. Transducer which, for a given amplitude range of input voltages, produces a smaller range of output voltages. One important type of compres¬ sor employs the envelope of speech signals to reduce their volume range. 2. Electrical device which compresses the volume range of a signal. COMPROMISE, CRYPTOGRAPHIC. Discovery of cryptographic information or plain text of messages by unauthorized persons through cryptoanalytic methods. COMPROMISE, PHYSICAL. Availability of material to unauthorized persons through loss, capture, recovery by salvage, defec¬ tions of individuals, unauthorized viewing, or any other physical means. COMPROMISE NETWORK. 1. Network employed in conjunction with a hy¬ brid coil to balance a subscriber’s loop, which is adjusted for an average loop length or an aver¬ age subscriber’s set, or both, to secure compro¬ mise (not precision) isolation between the two directional paths of the hybrid. 2. Hybrid balancing network which is designed to balance the average of the impedances that may be connected to the switchboard side of a hybrid arrangement of a repeater. COMPUTER. 1. Instrument for calculating various quantities such as range, speed, altitude, etc., from the in¬ formation supplied. 2. Machine for carrying out calculations. 3. Machine for carrying out specified transfor¬ mations on information. 4. Electronic instrument which facilitates the so¬ lution of mathematical problems. ACTIVE. One of two computers at a SAGE cen¬ ter actually performing the air-defense mission. ANALOG. Physical system, used in electronics, together with means of control for the per¬ formance of measurements (upon the system) which yields information concerning a class of mathematical problems. COURSE-LINE. Airborne equipment which ac¬ cepts bearing information from a VHF omni¬ directional range receiver and distance infor¬ mation from the distance-measuring equipment interrogator and processes it to provide devia¬ tion information and distance-to-go informa¬ tion with respect to a pilot-selected way point within the coverage of the VHF omnidirec¬ tional range and distance-measuring equip¬ ment indications to instruments mounted on the instrument panel of an aircraft. DIGITAL. Computer in which quantities are re¬ presented in numerical form and which gen¬ erally is made to solve complex mathematical problems by iterative use of the fundamental processes of addition, subtraction, multiplica¬ tion, and division. FLIGHT-PATH. Computer which performs all of the functions of a course-line computer and, in addition, provides means for controlling the altitude of an aircraft in accordance with a desired plan of flight. COMRAZ. System for determining the air-to-air or ground- to-air range between any two stations equipped with communications (AN/ARC-27) and range/ azimuth (AN/ARA-25) equipment. A range-de¬ termining feature of COMRAZ increases the functional utility of existing navy communica¬ tions equipment as a navigational aid. 39-157 AFM 100-39 COM 1 APRIL 1959 COMSECACT (COMMUNICATION SECURITY ACTIVITY). ComUSLantSubArea (COMMANDER U S ATLANTIC SUB AREA). ComYard (COMMANDER OF THE DOCKYARD). Used to identify area dockyard commanders, such as ComYardNorfolk, meaning the comman¬ der of the dockyard, Norfolk, Virginia. CON (CONSUL). Official appointed by the government to reside in a foreign country, to care for the commercial interests of the citizens of the United States. CON (CONTROL). 1. Parts of a digital computer which effect the carrying out of instructions in proper sequence, the interpretation of each instruction, and the ap¬ plication of the proper signals to the arithme¬ tic unit and other parts in accordance with this interpretation. 2. One or more of the components in any me¬ chanism responsible for interpreting and carry¬ ing out manually-initiated directions. Sometimes called manual control. ConAc (CONTINENTAL AIR COMMAND). One of the major air commands in the United States, the headquarters of which is located at Mitchell AFB, New York. CONBAL (CONSOLIDATED BASE ALLOWANCE LIST). CONCAVE. Hollowed and rounded like the inside of a sphere. CONCAVE LENS. Lens that is curved inward on one side and is flat on the other side. CONCAVE-CONVEX LENS. Lens that is curved inward on one side and is curved outward on the other side. CONCENTRIC CABLE. 1. Cable in which one conductor is accurately centered inside another. Used primarily for the transmission of telephone, radio, and television signals. 2. Cable, used as a transmission line, consisting of one conductor, usually a small copper tube or wire, within and insulated from another con¬ ductor of larger diameter, usually copper tubing or copper braid. The outer conductor may or may not be grounded. (Reference: COAXIAL CAB¬ LE.) CONCENTRIC LINE. Long metal tube having at its center a conduc¬ tor supported by insulators. It is used as a trans¬ mission line for radio or television sigqals. (Re¬ ference: PIPELINE, COAXIAL CABLE, CO- XIAL LINE.) CONCEPT OF OPERATIONS. Verbal or graphic statement, in broad outline, of a commander’s assumptions or intent in regard to an operation or series of operations. The con¬ cept of operations frequently is embodied in campaign plans and operations plans. The con¬ cept is designed to give an overall picture of the operation. It is included primarily for addi¬ tional clarity of purpose. COND (CONDUCTOR). 1. Material which permits the passage of an elec¬ tric current. 2. Transmission, distribution, or wiring system which actually carries the current. 3. Live wire in an open wire system. CONDENSATION CODE. Code which has as its sole purpose the shortening of messages rather than the concealment of the content. CONDENSER. 1. Lens or lens system designed to concentrate the illumination from a light source upon a limited area. 2. Air or gas compressor. 3. Tubing in a relatively cold bath. 4. Two or more conductors separated by a non¬ conductor (dielectric) such as glass, paper, air, oil or mica. (Reference: CAPACITOR.) 1 APRIL 1959 AFM 100-39 CON ELECTROLYTIC. Capacitor which makes use of a very thin, chemically formed, dielectric. CONDENSER MICROPHONE. Microphone which depends for its operation on variations in capacitance. CONDENSER PICK-UP. Phonograph pick-up, the electrical output of which is generated by a mechanical variation of its capacitance. CONDITIONAL JUMP. Electronic computer instruction which will cause the proper one of two (or more)addresses to be used in obtaining the next instruction, depend¬ ing upon some property of one or more numerical expressions or other conditions. CONDITIONAL TRANSFER OF CONTROL. (Reference: CONDITIONAL JUMP.) CONDOR. CW navigational system, similar to BENITO, which automatically measures bearing and dis¬ tance from a single ground station. The distance is determined by phase comparison, and the bearing by automatic direction finding. Distance and bearing are displayed on a cathode ray in¬ dicator. CONDUCTANCE. Ability of a material to conduct or carry an elec¬ tric current. It is the reciprocal of the resistance and is expressed in mhos. CONDUCTION CURRENT. Power flow parallel to the direction of propa¬ gation expressed in w'atts per square meter. CONDUCTIVITY. Measure of the ability of a material to act as a path for electron flow. It is the reciprocal of resistivity and is expressed in mhos/meter. 1. Material which permits the passage of an electric current and has relatively low resistance. 2. Transmission, distribution, or wiring system which actually carries the current. 3. Line wire in an open wire system. CONDUIT. Tube of tile, steel, wood, or other material through which cables can be passed. CONDUIT RUN. Arrangement of conduit providing one or more continouous ducts between two points. (Refer¬ ence: DUCT BANK.) CONE. 1. One of the two types of light-sensitive ele¬ ments or visual cells in the retina of the eye which permit sight. 2. Cone-shaped part of a loudspeaker that actual¬ ly moves the air. CONE OF NULLS. Antenna practice, a conical surface formed by directions of negligible radiation. CONE OF SILENCE. Inverted-cone-shaped space directly over the aer¬ ial towers of some forms of radio beacons in which signals are unheard or greatly reduced in volume. CONELRAD (CONTROL OF ELECTROMAGNETIC RADIATIONS). Plans for controlling electromagnetic radiations during times of emergency, as directed by Execu¬ tive Order 10312, 10 December 1951. The pur¬ pose is to deny the enemy aircraft the use of electromagnetic radiations for navigation, while still providing essential services. With reference to. commercial broadcast stations, procedures might include sequential transmission of the same program material on one frequency by several stations in the same general area. Another procedure is to have all stations in a general area broadcast the same program material sim¬ ultaneously on the same frequency. This would prevent an aircraft from taking a bearing on any one station. The two assigned frequencies for CONELRAD operations by commercial broad¬ cast stations are 640 KC and 1240 KC. The au¬ thority for promulgating the CONELRAD plans under Executive Order 10312 has been dela- gated to the Federal Communications Commis¬ sion in the case of non-government radio services, and to the responsible operating agency in the 39-159 AFM 100-39 CON 1 APRIL 1959 case of government radio services. A Depart¬ ment of Defense CONELRAD plan and detailed implementing plans have been prepared. CONFERENCE COMMUNICATIONS. Communications facilities whereby direct speech conversation may be conducted between three or more locations simultaneously. CONFERENCE CONNECTION. Special connection for a telephone conversation among more than two stations. CONFIGURATION. Relative distribution or arrangement of parts in a structure, as in an antenna array. CONFUSION REFLECTOR. Radio wave reflector used for creating echoes for confusion purposes against radars, proximity fuzes, and guided missiles. CONICAL HORN. Horn with an equivalent cross-sectional radius which has a constant rate of increase along its axis. CONICAL SCAN. Process of swinging the radar beam about an axis a few degrees off the center of the beam so that the beam describes a cone in space, the apex of which is located at the antenna. CONICAL SCANNING. Type of antenna beam scanning in which the tilt angle is fixed so that the axis of the RF beam generates a cone, the vertex angle of which is usually from five to 10 degrees. CONJUGATE DISTANCE. For every position that an object may occupy with respect to a lens, there is a corresponding position for the image. The distances of object and image from the nodal points of the lens are called conjugate distances. CONJUGATE FILTERS. Classified definition. (Reference: AFM 100-50.) CONJUGATE FOCAL POINTS. Pairs of points on the principal axis of a mirror or lens so located, that light emitted from either point will be focused at the other. CONJUGATE IMAGE RAYS. Rays connecting each of a set of conjugate image points with its particular perspective center. CONJUGATE IMPEDANCES. Impedances having resistance components which are equal and reactance components which are equal in magnitude but opposite in sign. CONJUNCTIVE ADDRESS GROUP. Address group, the meaning of which is incom¬ plete unless used in combination with one or more other address groups. CONNECTION, ROSIN. Connection or joint of a conductor to a piece of equipment or another conductor, supposedly securely soldered, but actually held together by rosin flux. CONNECTION DIAGRAM. Sketch showing the position of components and connections in an apparatus. CONNECTOR. 1. Coupling device that joins two or more parts, as two cables. 2. Name given to the switch or relay group sys¬ tems that find the line being called as a result of digits being dialed. This switch also has the function of causing interrupted ringing voltage to be placed on the called line or of returning a busy tone to the calling party if the line is busy. BRIDGING. Screw fastener for joining drop, bridle, or other wires to open-wire conductors, or to fasten two open wires at a test point. CABLE. Connector used to splice, terminate, or tap a power cable. REGULAR. Final unit in the dialing link by which the calling subscriber is connected to the called subscriber. In the all relay system, it is operated by the last three digits dialed. It consists of control, counting, sequence, and the final tens and units relays. TEST. 1. Device, usually operated by a spring, to connect the leads from portable meters and apparatus to other equipment or conductors. 39-160 1 APRIL 1959 AFM 100-39 CON 2. Manual connector controlled by an operator or from the test-desk to connect them to a subscriber’s line. TEST AND OPERATOR’S VERIFICATION. Circuit connecting the attendant switchboard operator or wire chief’s test desk to any line through the connector switch or test or veri¬ fication through the test distributor circuit. TRUNK-HUNTING. Circuit which automatically hunts for an idle line in a group of lines that services one station, department, or office. WIRE CHIEF TEST. Circuit by means of which the wire chief or switchboard operator may con¬ nect to any line through the regular connector circuits for test or verification. CONNECTORS. Switching mechanism for connecting a trunk to a subscriber line or another line. It may be de¬ signed to hunt for an idle terminal. CONOSCOPE. Instrument used for determining the position of the Z or optical axis of a quartz crystal. CONS (CONSTRUCTION). 1. Process, art, or manner of constructing; act of devising and forming; also a thing constructed, structure. 2. Act or result of construing, interpreting, or explaining a declaration or fact; interpretation. CONSOL. Long range radio aid to navigation, the emis¬ sions of which, by means of their audio fre¬ quency modulation characteristics, enable bear¬ ings to be determined. CONSOLAN. Long-range, directional navigation system, AN/ FRN-5, that transmits a slowly rotating keyed radio field pattern. It is the American version of the German SONNE and British CONSOL sys¬ tems. CONSOLAN differs from these systems in the following respects. Two radiators instead of three are used to obtain a line of position. Each radiator is excited by its own transmitter, and RF energy is transmitted between towers over RF cable at one-half the operating frequency. These modifications have minimized night effect as a source of error. The operating principle of CONSOLAN is based upon the interference pat¬ tern resulting from the excitation of two vertical radiators with equal radio frequency intensity but variable relative phase. In-phase excitation produces a distinctive pattern of a certain number of lobes. Out-of-phase excitation (180°) pro¬ duces a distant pattern with the same number of lobes but oriented so that the peaks of the in- phase lobes correspond to the nulls of the out- of-phase lobes. The number of lobes depends on the spacing between radiators in wavelengths. The two radiators then are alternately excited in- phase and out-of-phase, the duration of one ex¬ citation being four times as long as the other, thus producing dots and dashes. Ater each switch¬ ing operation, the RF phase between radiators is shifted five electrical degrees until a total of 180° is reached. The relative intensities between the dots and dashes change gradually as the keying cycle progresses. The precision of the system varies with azimuth and with maximum accuracy on the perpendicular bisector of the line of an¬ tennas. The system is capable of 10- to 20-mile accuracy at 1500 miles range. The only airborne equipment required is a standard radio receiver tunable to the CONSOLAN frequency. This system has been extensively tested, and is cur¬ rently in use in Europe. CONSOLE. 1. Control and monitoring position. 2. Main operating unit of a radar or electronic group in which indicators and general controls are installed. CONSONANCE. Either electrical or acoustical resonance occurring between bodies or circuits which are not connected directly with each other. CONSTANT. 1. Anything invariable or not subject to change. 2. In mathematics, a magnitude that is supposed not to change its value in a certain discussion or stage of investigation. AFM 100-39 CON 1 APRIL 1959 DECAY. Exponential constant of a heterogen¬ eous mixture of radioactive material calculated from its observed rate of decay. DIELECTRIC. Ratio of the capacitance of a cap¬ acitor with a given dielectric between the elec¬ trodes to the capacitance with air as the di¬ electric. FAST TIME. Type of coupling circuit used in radar receivers to permit discrimination a- gainst echo pulses of duration longer than the transmitted pulse. PHASE. Phase constant is the imaginary com¬ ponent of the propagation constant. PROPAGATION. 1. Propagation constant per unit length of a uniorm line is the natural logarithm of the ratio of the current at a point of the line to the current at a second point, at unit distance from the first point along the line in the direction of transmission, when the line is infinite in length, or is terminated in its characteristic impedance. 2. Propagation constant per section of a period¬ ic line is the natural logarithm of the ratio of the current entering a section to the current leaving the same section, when the periodic line is infinite in length, or is terminated in its iterative impedances. 3. Propagation constant of an electric trans¬ ducer is the natural logarithm of the ratio of the current entering the transducer to the current leaving the transducer, when the trans¬ ducer is terminated in its iterative impedances. CONSTANT AMPLITUDE. Recordings wherein all frequencies of the same intensity are inscribed at the same amplitude. CONSTANT AMPLITUDE RECORDING. Mechanical recording characteristic wherein, for a fixed amplitude of a sinusoidal signal, the re¬ sulting recorded amplitude is independent of frequency. CONSTANT-CURRENT MODULATION. Method of amplitude modulation in which a con¬ stant-current source supplies a radio-frequency generator and a modulation amplifier in paral¬ lel, the variations in the current taken by the latter causing equal and opposite variations in the former, resulting in corresponding modula¬ tion of the carrier output. CONSTANT-K NETWORK. Ladder network whose product of series and shunt impedances is independent of frequency within the range of interest. CONSTANT LUMINANCE TRANSMISSION. Method of color television transmission in which the carrier color signal controls the chromaticity of the produced image without affecting the lum¬ inance. CONSTANT VELOCITY. Recordings wherein frequencies of a given in¬ tensity are inscribed with the same maximum vel¬ ocity of the cutting stylus. CONSTANT VELOCITY RECORDING. Mechanical recording characteristic wherein, for a fixed amplitude of a sinusoidal signal, the re¬ sulting recorded amplitude is inversely propor¬ tional to the frequency. CONSTRICTOR, CABLE SHEATH. Tool for creasing rings in cable sheaths when making gas-tight plugs. CONSTRUCTION. 1. Process, art, or manner of constructing; act of devising and forming; also a thing constructed; structure. 2. Act or result of construing, interpreting, or explaining a declaration of fact; interpretation. CONSTRUCTION CENTER. Installation, located near or in a command-post area, where trunks and local circuits converge for entrance to the telephone central. CONSTRUCTION CHIEF. Noncommissioned officer in charge of the instal¬ lation and maintenance of the trunk and long local circuits in the wire system of his unit. CONSUL. Official appointed by the government to reside in a foreign country, to care for the commercial interests of the citizens of the United States. 39-162 1 APRIL 1959 AFM 100-39 CON CONT (CONSTANT). 1. Anything invariable or not subject to change. 2. In mathematics, a magnitude that is supposed not to change its value in a certain discussion or stage of investigation. CONTACT. Part of an equipment, usually an alloy, some¬ times of silver and platinum, designed to touch a similar contact to permit current to flow, or designed to break this union to cause a current to cease. BACK. Relay, key, jack, or other contact de¬ signed to close a circuit and permit a current to flow when, in the case of a relay, the arma¬ ture has released or fallen back. FRONT. Contact on a movable member which closes a circuit when the associated device is operated. MARKING. Contact of a telegraph relay which is closed when marking current is controlling the relay operation. NORMAL. Contact which closes a circuit, per¬ mitting current to flow, when in its normal position. RADAR. Aircraft is said to be in radar con¬ tact when its radar echo can be seen on the PPI tube and is properly identified. SPACING. Contact of a telegraph relay which is closed when a spacing impulse is controlling the relay operation. WET. Contact through which direct current flows. CONTACT BANK ASSEMBLY. Group of two or three banks with each bank containing 100 or 200 individually insulated brass contacts. CONTACT MICROPHONE. Microphone designed to pick up mechanical vi¬ brations directly from the sound source and con¬ vert them into corresponding electrical currents or voltages. CONTACT RECTIFIER. Rectifier consisting of two materials in contact, in which rectification is due to greater conductiv¬ ity across the contact in one direction than in the other. CONTACT REPORT. Report of the enemy made by a field unit, ship, or aircraft which is in visual, radio, SONAR, or radar contact with the enemy. The report, giving the information immediately available when the contact is first made, is known as an initial con¬ tact report. Subsequent reports containing addi¬ tional information are referred to as amplifying reports. (Reference: SIGHTING.) CONTACT-SPRING FILE-UP. Number of springs arranged one above the other. CONTACTOR. 1. Device for closing and opening electrical cir¬ cuits remotely. 2. Heavy duty relay which controls electrical cir¬ cuits. 3. Device acted on by changes in gas pressures to open or close a signal circuit. CONTACTOR ALARM. Signal calling attention to lowered pressure in a cable gas pressure system. CONTAMINATING MATERIAL. Denaturing material used in making uranium 235 or plutonium. CONTAMINATION. 1. Deposition of cathode emitting material on grid of tube, causing unwanted grid emission. 2. Exposure to radioactive radiation. 3. Condition existing in a given area due to the presence of unwanted radioactive or toxic mater¬ ial. CONTIGUOUS RANGE GATES. Classified definition. (Reference: AFM 100-50.) CONTINENTAL AIR COMMAND. One of the major air commands in the US, the AFM 100-39 CON 1 APRIL 1959 headquarters of which is located at Mitchel AFB, New York. CONTINENTAL CODE. International Morse Code, universally used for radiotelegraphy. CONTINUOUS CURRENT. Another term for direct current. CONTINUOUS RECORDER. Recorder whose record sheet is a continuous strip or web rather than individual sheets. CONTINUOUS SPECTRUM. Spectrum which exhibits no structure and appears to represent a continuous variation of wave¬ length from one to the other. CONTINUOUS WAVES. Successive oscillations of waves, identical under steady-state conditions. Generally, radio waves are of a constant amplitude and constant fre¬ quency. CONTINUOUS-WAVE RADAR. System in which a transmitter sends out a con¬ tinuous flow of radio energy to the target which reradiates (scatters) the energy intercepted and returns a small fraction to a receiving antenna. CONTINUITY. The presence of a complete path through which current can flow. CONTINUITY TEST. Electrical test to determine the existence of a broken connection. CONTOUR GRINDING. Process of hand lapping an oscillator crystal plate to provide convex surfaces. CONTOUR VIBRATION. Shear mode of vibration. CONTRACT. 1. Term used in air defense operations. 2. Method by which the scale of a situation dis¬ play is decreased from normal setting. CONTRACT TECHNICAL SERVICES. Services to provide indoctrination of Air Force personnel during the introduction of complex equipment into Air Force units. CONTRACT TECHNICIAN. Employee, paid by the Air Force, representing a commercial concern under contract with the con¬ cern. A contract technician provides technical service on specified complex equipment or sys¬ tems and is particularly qualified in the mainte¬ nance and operation of such equipment. CONTRAST. 1. Actual difference in density between the highlights and the shadows. Contrast is not con¬ cerned with the magnitude of density but only with the difference in densities. 2. Amplitude ratio between picture white and picture black. CONTROL. 1. Parts of a digital computer which effect the carrying out of instructions in proper sequence, the interpretation of each instruction, and the ap¬ plication of the proper signals to the arithmetic unit and other parts in accordance with this in¬ terpretation. 2. One or more of the components in any mecha¬ nism responsible for interpreting and carrying out manually-initiated directions. Sometimes called manual control. AUTOMATIC BRIGHTNESS. Circuit used in tel¬ evision receivers to keep the average bright¬ ness of the reproduced image essentially con¬ stant. Its action is like that of an automatic volume control circuit. CIRCUIT. Authority assigned to a specific of¬ fice on a toll circuit to direct overall service continuity operations. CRYSTAL. Control of the frequency of an os¬ cillator by means of a specially designed and cut crystal. DIFFERENTIAL GAIN. Device for altering the gain of a radio receiver at appropriate times so as to equalize the amplitude of multiple signals at the output of the receiver. 1 APRIL 1959 AFM 100-39 CON EN ROUTE RADAR. Portion of the long-range radar operation as applies to the positive fix¬ ing and/or control of aircraft operating be¬ tween two terminal areas. FREQUENCY. Regulation of the frequency of a generating system. LANDING RADAR. Precision radar system of radar approach control engaged only in land¬ ing operations. LOCAL. System or method of radio-transmitter control whereby the control functions are per¬ formed directly at the transmitter. PRIMARY. Local agency, control tower, surveil¬ lance radar, or other, who will exercise con¬ trol over an aircraft within the airport control area prior to assumption of control of the air¬ craft by precision approach control. RADAR APPROACH. Combination of a sur¬ veillance and precision radar system engaged in the complete radar control of aircraft op¬ erating within a designated airport control zone. RADIO. Control of mechanism or other appara¬ tus by radio waves. REMOTE. System or method of radio-transmit¬ ter control whereby the control functions are performed from a distance, electrically, over intervening wire or radio circuits. SENSITIVITY TIME. Circuit which acts to vary the amplification of a radio receiver in a pre¬ determined manner as a function of time, in order to adjust or compress signals which may be received. TERMINAL AREA RADAR. Combination of a high resolution surveillance radar and preci¬ sion radar system engaged in the complete radar control of aircraft operating within a designated terminal control area and/or con¬ trol zone. CONTROL AND REPORTING CENTER. Operational center immediately subordinate to an air control center responsible in a certain area for control and reporting of aircraft and certain warning services. CONTROL AND REPORTING POST. Radar installation capable of providing medium high altitude long range radar cover. Low cover to be consistent with line of sight ranges and siting restrictions. A control and reporting post must be capable of performing the follow¬ ing functions: a. Tactical control of fighter aircraft as directed by the air control center or the control and re¬ porting center. b. Radar surveillance and raid reporting. c. Operational supervision of associated report¬ ing posts. d. Providing assistance to fighters on ground support missions (tactical only). e. Filtering. CONTROL CHARACTERISTIC. Relation between critical grid voltage and anode voltage. CONTROL CHART. Plotted graph showing performance or quality along the vertical scale, against time along the horizontal scale. It contains two horizontal lines called control limits, and usually a central line called median. CbNTROL ELECTRODE. Electrode on which a voltage is impressed to var) the current flowing between two or more other electrodes. CONTROL GRID. Grid electrode, ordinarily placed between the cathode and anode of an electron tube, for use as a control electrode. CONTROL GRID BIAS. Average dc voltage between the control grid and cathode of a vacuum tube. CONTROL GRID PLATE TRANSCONDUCTANCE. Ratio of the amplification factor of a vacuum tube to its plate resistance, combining the effects of both into one term. AFM 100-39 CON 1 APRIL 1959 CONTROL LIMITS. Two parallel horizontal lines drawn directly on the control chart. One is the upper control limit, and the other is the lower control limit. Plots which fall between the two limits are usually considered normal or cause-free plots. CONTROL OF ELECTROMAGNETIC RADIATIONS. Plan for controlling electromagnetic radiations during times of emergency, as directed by Execu¬ tive Order 10312, 10 December 1951. The pur¬ pose is to deny the enemy aircraft the use of elec¬ tromagnetic radiations for navigation, while still providing essential services. With reference to commercial broadcast stations, procedures might include sequential transmission of the same pro¬ gram material on one frequency by several sta¬ tions in the same general area. Another proce¬ dure is to have all stations in a general area broadcast the same program material simultane¬ ously on the same frequency. This would pre¬ vent an aircraft from taking a bearing on any one station. The two assigned frequencies for CONELRAD operations by commercial broadcast stations are 640 KC and 1240 KC. The authority for promulgating the CONELRAD plans under Executive Order 10312 has been delegated to the Federal Communications Commission in the case of non-government radio services, and to the responsible operating agency in the case of gov¬ ernment radio services. A Department of Defense CONELRAD plan and detailed implementing plans have been prepared. CONTROL PANEL. Used to mount and protect electrical equipment. CONTROL TOWER. 1. Facility at an airfield, usually a tower with its special equipment, for controlling the move¬ ment of airdrome traffic and for controlling ground vehicles in the takeoff and landing area. 2. Personnel operating the tower. CONTROL TRANSFER POINT. Point in the airspace, usually defined by a radio navigational aid, at which the control of an air¬ craft is transferred from one air traffic control facility to another, or from one controller within a facility to another within the same facility. CONTROL TRANSFORMER. Synchro in which the electrical output of the rotor is dependent on both the shaft position and the electrical input to the stator. (Refer¬ ence: SYNCHRO CONTROL TRANSFORM¬ ER.) CONTROL WINDING. Winding by means of which a controlling mag¬ netomotive force is applied to a core. CONTROL ZONE. Airspace of defined dimensions, designated by competent authority, extending upwards from the surface, including one or more airports, and within which, rules additional to those govern- ing flight in control areas apply for the protec¬ tion of air traffic. CONTROLLED AIRSPACE. Airspace is defined as the dimensions within which air traffic control service is provided to IFR flights. CONTROLLED CARRIER. System of modulation wherein the carrier is am¬ plitude modulated by the signal frequencies, and, in addition, the carrier is amplitude modulated in accordance with the envelope of the signal, so that the modulation factor remains constant regardless of the amplitude of the signal. CONTROLLED DEVICES COUNTERMEASURE. Controlled electronic countermeasure against guided missiles, pilotless aircraft, proximity fuzes, or similar devices. CONTROLLED INTERCEPT. Intercept wherein the friendly aircraft are con¬ trolled from a ground or ship station. CONTROLLED INTERCEPTION. Interception during which friendly airborne ob¬ jects are vectored by directions from an airborne or surface station. CONTROLLED MAP. Precise scale map with horizontal and vertical ground control as a basis. 39-166 1 APRIL 1959 AFM 100-39 CON CONTROLLER. 1. Ship or ground personnel charged with the responsibility of controlling aircraft in an air de¬ fense area. 2. Air Force officer qualified as an intercept con¬ troller and assigned to duty at a NORAD divi¬ sion. FEEDER. Surveillance radar controller respon¬ sible for funneling aircraft into a runway ra¬ dar control pattern. FIGHTER. Officer on the staff of a tactical air controller, charged with coordination and evaluation of air warning reports and opera¬ tional control of aircraft allocated to him. FINAL. Radar air traffic control systems, the precision radar controller responsible for the information and control procedures required to complete the actual landing. During PPI assists, this responsibility becomes the func¬ tion of the PPI operator engaged in the opera¬ tion. FORWARD AIR. Officer in charge of a tactical air control party. PICK-UP. Surveillance radar controller who first contacts and identifies new' arrivals and advises them of current airport operations in use. RADAR. Air traffic controller or other responsi¬ ble person proficient in the use and interpre¬ tation of radar and capable of performing one or more of the following functions: a. Surveillance controller. b. Traffic director. c. Final controller. SENIOR. Officer who is responsible for the op¬ eration of an air defense control center, and for the conduct of air defense operations. SURVEILLANCE. Radar controller proficient in the use and interpretation of search and/or height finding radar equipment and trained in the dissemination of the information so gained so as to assist in the expeditious flows of air traffic, aircraft separation, position re¬ ports and emergency situation. TACTICAL AIR. Officer in charge of all op¬ erations of the tactical air control center. Fie is responsible to the tactical air commander foi the control of all aircraft and air warning facilities within his area of responsibility. CONTROLLER CIRCUIT. Circuit established for the purpose of passing air-defense information from the controller of one installation to the controller of another in¬ stallation. CONNECTOR. Switching mechanism for connecting a trunk line to a subscriber line, etc. It may be designed to hunt for an idle terminal. ConUS. (CONTINENTAL UNITED STATES). CONVECTION. Circulation in a fluid of nonuniform tempera¬ ture, due to differences of density. CONVECTION CURRENT. Current in which electricity is carried by mov¬ ing masses heavier than electrons. CONVENIENCE RECEPTACLE. Contact device installed at an outlet for the con¬ nection of a portable lamp or appliance by means of a plug and flexible cord. CONVENTION. Symbol which may represent anything selected as long as it is agreed on. CONVERGE. Direct so that two lines of sight meet at a com¬ mon focal point and form an angle from the point. CONVERGENCE. Meeting and crossover of three electron beams in a color picture tube at a common point on shadow' mask. Color television term. CONVERGENCE CONTROL. Variable resistor in high-voltage section controls voltage applied to three-gun picture tube. Color television term. 39-167 AFM 100-39 CON 1 APRIL 1959 CONVERGENT BEAM. Beam of light rays that meet (converge) at a point. CONVERGING CONVERGENT, CONVEX, OR COLLECTIVE LENS. Lens that will converge parallel light. It is al¬ ways thicker at the center than at the edge. (Ref¬ erence: POSITIVE LENS.) CONVERSION GAIN. 1. Ratio of the IF output voltage to the input signal voltage of the first detector of a super¬ heterodyne receiver. 2. Ratio of the available IF power output of a converter or mixer to the available RE power input. CONVERSION TRANSCONDUCTANCE. 1. Characteristic associated with the mixer func¬ tion of vacuum tubes, and used in the same man¬ ner as mutual conductance. It is the ratio of the IF current in the primary of the first IF trans¬ former to the RF signal voltage producing it. 2. Transducer in which the signal undergoes frequency conversion. The gain or loss of a conversion transducer is specified in terms of the useful signal. 3. Quotient of the magnitude of the desired out¬ put-frequency component of current by the mag¬ nitude of the input-frequency component of volt¬ age when the impedance of the output external termination is negligible for all of the frequen¬ cies which may affect the result. Note: Unless otherwise stated, the term refers to the cases in which the input-frequency voltage is of infinitesimal magnitude. All direct electrode voltages and the magni¬ tude of the local-oscillator voltage must be specified, fixed values. CONVERSION VOLTAGE GAIN. Ratio of the magnitude of the output-frequency voltage across the output termination, with the transducer inserted between the input-frequency generator and the output termination, to the mag¬ nitude of the input-frequency voltage across the input termination of the transducer. CONVERTER. 1. Section of a superheterodyne radio receiver which converts the desired incoming RF signal to a lower carrier frequency known as the inter¬ mediate frequency. 2. Rotating machine consisting of an electric motor driving an electric generator for the pur¬ pose of changing alternating current to direct current. 3. Facsimile device that changes the type of mod¬ ulation delivered by the scanner. 4. Facsimile device which changes amplitude modulation to audio frequency shift modulation. Generally called a remodulator. 5. Device which changes audio frequency shift modulation to amplitude modulation. General¬ ly called a discriminator. 6. Conversion transducer in which the output frequency is the sum or difference of the in¬ put frequency and an integral multiple of the local oscillator frequency. Note. The frequency and voltage or power of the local oscillator are parameters of the conversion transducer. Ordinarily, the output signal amplitude is a linear func¬ tion of the input signal amplitude over its useful operating range. ARC. Form of oscillator utilizing an electric arc as the generator of alternating or pulsating current. LINE BALANCE. Device used at the end of a coaxial line to isolate the outer conductor from ground. (Reference: BAZOOKA.) OMNI-BEARING. Electto-mechanical device which combines an omni-range signal with air¬ craft heading information to furnish electrical signals for the operation of the pointer of a radio magnetic indicator. An omni-bearing con¬ verter bcomes an omni-bearing indicator when a pointer and dial are added. TWENTY-CYCLE. Source of 20-cycle ringing current obtained from a dc battery by means 1 APRIL 1959 AFM 100-39 CON of a tuned pole change and transformer cir¬ cuit. CONVERTER TUBE. Multielement vacuum tube used both as a mixer and an oscillator in a superheterodyne receiver. It creates a local frequency and combines it with an incoming signal to produce an intermediate frequency. CONVERTER UNIT. Unit of a radar system in which is located the mixer and usually two stages of IF amplification. Usually placed relatively close to the radar an¬ tenna. It performs a preamplifying operation. CONVEX. Rounded and bulging outwardly as the outer surface of a sphere. CONVEX LENS. Lens curved outward on one side and flat on the other. (Reference: CONVERGING LENS.) CONVEX-CONCAVE LENS. Lens with one convex and one concave surface. CONVOTROL. Type of dry-disc rectifier. COOLING WATER. Fluid which circulates through the jacket space of cylinders and cylinder heads to prevent exces¬ sive heating of the castings. COOPER-HEWITT LAMP. Mercury-vapor lamp that produces a bluish- green light having a high ultra-violet content. COORDINATE CONVERSION. System of transferring a polar-grid presentation to a rectangular-grid presentation. COORDINATE SYSTEM. Group of quantities which, when taken together, serve to define the position of a point in two or three dimensional space. COORDINATED TRANSPOSITIONS. Transpositions which are installed in either elec¬ tric supply or communication circuits or in both for the purpose of reducing inductive coupling and which are located effectively with respect to the discontinuities in both the electric supply and communication circuits. COORDINATE, COORDINATION, COORDINATOR. 1. Geographically, any one of two or more mag¬ nitudes that determine position. 2. To carry out coordination with a person or department. 3. Coordination; the act of informing a depart¬ ment or person of a course of action so that he can either fit his own actions into the pro¬ posed course of action, or take steps to modify the proposed course of action to make it fit his own. 4. Coordinator; one who coordinates. COPPER-CLAD WIRE. Steel wire lightly coated with copper. COPPER-OXIDE RECTIFIER. Copper disks coated on one side with cupreous oxide. COPY. 1. Maintain a continuous receiver watch and a complete log. 2. Material in graphic form which is to be trans¬ mitted for facsimile reproduction by the recorder. Also referred to as subject or subject copy. COPYING TELEGRAPHY. ' Obsolete term used to designate a facsimile sys¬ tem for transmitting only black and white copy. COR (COMBAT OPERATIONS REPORT). COR (CORPS). Army tactical unit usually made up of two or more divisions such as the Corps of Engineers. CORD (COORDINATE, COORDINATION, COORDINATOR). 1. Geographically, any one of two or more mag¬ nitudes that determine position. 2. To carry out coordination with a person or department. 3. Coordination; the act of informing a depart¬ ment or person of a course of action so that he AFM 100-39 COR 1 APRIL 1959 can either fit his own actions into the proposed course of action, or take steps to modify the pro¬ posed course of action to make it fit his own. 4. Coordinator; one who coordinates. CORD. Flexible conductor, or several conductors under one cover, equipped with terminals. ANSWERING. Cord nearest the face of the switchboard which is used for answering sub¬ scriber’s calls and incoming trunks. BACK. Switchboard cord of a pair nearest the jackfield. CALLING. Cord farthest from the face of the switchboard which is used for completing an incoming call to the called subscriber or to an outgoing trunk. It may be arranged to transmit dial pulses to the called line. COMMON BATTERY. Cord circuit used in common battery office. It may be of either the repeating coil or impedance coil bridge type. DIAL. Separate cord used to transmit dial pulses to the called lines. FRONT. Switchboard cord of a pair nearest the operator. IMPEDANCE BRIDGE. Method of connecting the common office battery to the cord circuits by connecting the battery to the mid-points of a retardation coil bridged across the cord cir¬ cuit. REPEATING COIL BRIDGE. Method of connect¬ ing the common office battery to the cord circuits by connecting the battery to the mid¬ points of a repeating coil, bridged across the cord circuit. PATCH. Cord equipped with one or more con¬ ductor plugs at each end for interconnecting jack-terminated equipment. SWITCHBOARD. Plug-ended cords, usually in pairs, for completing telephone connections. TEST. 1 . Cord used for testing. 2. Cord end at a frame of a trunk to a testing position. THRU SWITCHING. Cord circuit by which in¬ coming and outgoing interoffice trunks may be connected for thru traffic not terminating at the switchboard. UNIVERSAL. Cord circuit arranged to give supervision over either common battery of magneto (ringdown) line to which the cord circuit may be connected. CORD CIRCUIT. Connecting circuit terminating in a plug at one or both ends and used at switchboard positions in establishing telephone connections. CORDLESS SWITCHBOARD. Manual telephone switchboard which uses man¬ ually operated keys to make connections. CORE. 1. Magnetic material placed within a coil to in¬ crease the intensity of the magnetic field. 2. Magnetic material inside a relay or inductor coil winding. 3. Conductors of a cable inside a sheath. 4. Central forming ring about which a roll of rope is wound. CORE HITCH. Attachment to a cable core to permit pulling it into a duct without damaging the sheath. CORE MEMORY. High-speed electromagnetic storage device with¬ in a computer. CORNER. 1. Abrupt change in the direction of the axis of a waveguide. 2. Point at which a line changes direction, re¬ quiring special construction. CORNER CUBE REFLECTOR. Device attached to a small balloon. CORNER REFLECTOR. 1. Device made in the form of three planes, mutually perpendicular; as the three sides of a cube that meet at a corner. It is very effective in returning a strong radar echo. 39-170 1 APRIL 1959 AFM 100-39 COR 2. Device consisting of two flat surfaces at right angles to each other. It is used with dipole an¬ tennas to add directivity to the radiation pattern. CORNER-REFLECTOR ANTENNA. Antenna consisting of a primary radiating ele¬ ment and dihedral corner reflector. CORONA. , Luminous discharge due to ionization of the air surrounding a conductor around which exists a voltage gradient exceeding a certain critical value. CORPORAL. Tactical, surface-to-surface guided missile de¬ veloped for the Army. It is rocket powered and has a speed of Mach 3, a ceiling of 260,000 feet, and a range of 150 miles. The nomenclature is XSSM-A-17. The missile is 40 feet long, 25 feet in diameter, and weights 12,000 pounds. Guid¬ ance is by the beam-rider technique, with ballistic trajectory after motor cut-off. Either conventional or atomic warheads may be employed. CORPS. Army tactical unit usually made up of two or more divisions such as the Corps of Engineers. CORPUSCULAR THEORY. Theory that the sensation of light was due to bombardment of the retina of the eye by tiny particles given off by a luminous body. CORRECTED LENS. , . , Compound lens, the various surfaces of whic have been so designed with respect to each other than the lens are reasonably free from one or more aberrations. CORRECTED RADIO BEARING. Observed radio bearing to which all known cor¬ rections have been applied. CORRECTION. , „ 1. Difference in mathematics, between the true value and a calculated or observed value in the computer field. A quantity (equal in absolute magnitude to the error) added to a calculated or observed value to obtain the true value is called a correction. 2. Computer or data-processing system, incor¬ rect step, process, or result. In addition to the mathematical usage in the computer field, the term is also commonly used to refer to macnine malfunctions as machine errors and to human mistakes as human errors. CORRECTION WEDGE. Range finder or height finder, rotating a wedge- shaped element, used precisely to divert the line of sight to correct errors in the optical sys¬ tem caused by temperature variations. CORRECTION WINDOWS. Optical wedges of very small angles. They admit light, seal out dirt and moisture, and are so mounted that they may be rotated to compensate for the accumulated errors in the entire system. CORRECTIVE OR SHAPING NETWORK. Electrical network designed to be inserted in a circuit to improve its transmission properties, its impedance properties, or both. CORRELATED RADAR DATA. Radar data which a computer associates with ten¬ tative or established tracks. CORRELATING LATERALTOLD-INC. Track status associated with surveillance infor¬ mation from an adjacent semiautomatic organi¬ zation which can be correlated with radar data at the receiving organization. , CORRELATION. , Process of associating related items with each other. CORRELATION DISTANCE. Term used in tropospheric scatter propagation. It is the minimum spatial separation between an¬ tennas which will give rise to independent fad¬ ing of the received signals. CORRODE. , Western Electric test project which supplies the required data for the design of equipment and subsequent installation of the distant ear y- warning time. CORROSION PROOF CABLE. Cable with a special protective cover over the sheath to reduce damage from electrolysis. 39-171 AFM 100-39 COR 1 APRIL 1959 CORT (ESCORT). 1. Airplane or airplanes flying, or assigned to fly, as protection to other aircraft. 2. Action of such flying, or the protection given by it. 3. To accompany other aircraft or vessels as pro¬ tection. COSECANT-SQUARED ANTENNA. Shaped-beam antenna in which the radiation in¬ tensity over a part of its pattern in some specified plane (usually the vertical) is proportional to the square of the cosecant of the angle measured from a specified direction in that plane (usually the horizontal). Its purpose is to lay down a uniform field along a line which is parallel to the specified direction, but which does not pass through the antenna. COSECANT SQUARED BEAM. Radar beam patern designed to give approxi¬ mately uniform signal intensity for echoes re¬ ceived from distant and nearby objects. COSMIC. Security warning used as a designator for certain types of information within the North Atlantic Treaty Organization. The word cosmic is un¬ classified, but the related meaning of the word is confidential. COSMIC NOISE. Radio static, the origin of which is due to sources outside the earth s atmosphere. The source may be similar to sunspots, or spots on other stars. COSMIC RAYS. Extremely fast particles which continually enter the earth’s upper atmosphere from interstellar space. COSMOLOGY. Scientific study of the universe. COSMONAUTICS. Word coined in recent years to describe the science, as yet merely academic, of travel beyond the solar system by using radically new form of propulsion. COST PLUS FIXED FEE CONTRACT. Contract in which the government agrees to reimburse the contractor for costs incurred in producing the articles or performing the services covered by the contract, and to pay a fixed fee in addition. COTAR (CORRELATED ORIENTATION TRACKING AND RANGE SYSTEM) (RADAR). COULOMB. Measure of the quantity of electricity that passes a given point in a circuit in a given time. One coulomb is equal to a current of one ampere flow¬ ing for one second. COULOMBMETER OR COULOMETER. Instrument for measuring a quantity of electri¬ city by the amount of electro-deposition produced from an electrolyte. COULOMB’S LAW. Law of electrostatic attraction. COUNT. Numerical sequency of pairs from a cable as terminated in a central office. USAGE. Count indicating the number of times a circuit or piece of equipment is used during a certain period. COUNT-DOWN. Ratio, expressed as a percentage, of the differ¬ ence between the number of synchronized replies received by an aircraft and the number of its in¬ terrogations. COUNTDOWN. Series of events that take place from the start of rocket-launching operations until the rocket lifts off the launch stand. Countdown starts with a missile in the ready condition, progresses through loading of propellants and pressuriza¬ tion gas, activating the circuits, last-minute check¬ out of components, starting the rocket engines, and building up the thrust to the required force for lift-off. COUNTER. 1. Device capable of changing from one to the next of a sequence of distinguishable states upon each receipt of an input signal. 39-172 1 APRIL 1959 AFM 100-39 COU 2. Circuit which counts input pulses. One specific type is a circuit which produces one out¬ put pulse each time it receives some predeter¬ mined number of input pulses. The same term may also be applied to several such circuits con¬ nected in cascade to provide digital counting. RING. Loop of interconnected bi-stable elements such that only one is in a specified state at any given time and such that, as input sig¬ nals are counted, the position of the one speci¬ fied state moves in an ordered sequence around the loop. COUNTER CIRCUIT. Circuit which receives uniform pulses represent¬ ing units to be counted and produces a voltage in proportion to their frequency. COUNTER-COUNTERMEASURES. Employment of antijamming techniques and cir¬ cuits designed to decrease the effects of electronic countermeasure activities against electronic equip ment. COUNTER-EMF (ELECTROMOTIVE FORCE) CELL. Cell using nickel and sodium hydroxide to op¬ pose the voltage of the central office battery. COUNTER-INTELLIGENCE CORPS. Organization responsible for activities to prevent enemy intelligence from accomplishing its mis¬ sion. COUNTERMEASURES 1. Military science which, by the employment of devices and/or techniques, has as its objective the impairment of the operational effectiveness of enemy activity. 2. Antiradar devices, usually aluminum foil called windows or chaff, and electronic detectors and jammers. COUNTERMEASURES OF OPPORTUNITY. Electronic countermeasure techniques which may be made ineffective by changes in operational procedures and tactics, or by minor equipment changes. COUNTERPOISE. . System of wires used in conjunction with an antenna. The wires are placed a short distance above the ground and are insulated from it. They serve as an earth ground by virtue of their cap¬ acity to ground and are used when actual ground connections are not practicable. COUNTING CIRCUIT. Circuit which receives uniform pulses represent¬ ing units to be counted and produces a voltage in proportion to their frequency. COUNTING DOWN CIRCUIT. Frequency divider. COUPLED IMPEDANCE. Effect produced in the primary winding of a transformer by the influence of the current flow¬ ing in the secondary winding. COUPLER. Arrangement of inductance coils or capacitors so placed with reference to each other that there is electromagnetic or electrostatic coupling be tween their circuits. COUPLING. . Association of two circuits so that electrical en¬ ergy may be transferred from one to another. CAPACITIVE. Type of interconnection between stages of an amplifier which employs a cap- acitator in the circuit between the plate of one tube and the , grid of the succeeding one. CRITICAL. Degree of coupling between two cir¬ cuits independently resonant to the same fre¬ quency which results in optimum transfer of energy at the resonant frequency. CROSS. Unwanted coupling between two differ¬ ent communication channels or their compon¬ ent parts. CROSSTALK. Ratio of the power in the disturb¬ ing circuit to the induced power in the dis¬ turbed circuit, observed at definite points of the circuits and under specified terminal con¬ ditions. DIRECT. Association of two or more circuits by means of a self-inductance, capacitance, resis¬ tance or a combination of these which is com¬ mon to the circuits. 39-173 AFM 100-39 COU 1 APRIL 1959 IMPEDANCE. Use of a tuned circuit or an im- pendance coil as the coupling element be¬ tween two circuits. INDUCTIVE. 1. Association of two or more circuits with one another by means of induc¬ tance mutual to the circuits. 2. Interrelation of neighboring electric supply and communication circuits by electric or mag¬ netic induction or both. LOOSE. 1. Degree of coupling less than the cri¬ tical coupling. 2. Less than optimum coupling. Coupling pro¬ viding little transfer of energy. MUTUAL-INDUCTANCE. Coupling of two cir¬ cuits by means of their mutual inductance. RC (RESISTIVE-CAPACITIVE). Coupling between two or more circuits, usually amplifier stages, by means of a combination of resistive and capacitive elements. RESISTANCE. 1. Method of interconnection be¬ tween stages in an amplifier which connects the plate of one tube to the grid of the follow¬ ing tube by means of a resistor. 2. Method of transferring energy from one circuit to another by means of resistance com¬ mon to both circuits. TIGHT. More than enough coupling to give maximum transfer of energy at the resonant frequency. Greater than optimum coupling. TRANSFORMER. Coupling of circuits by means of a transformer. COUPLING CAPACITOR. Capacitor used to couple two circuits together. Coupling is accomplished by means of capacitive reactance common to both circuits. COUPLING COEFFICIENT. Measure of the degree of coupling that exists between two circuits. It is equal to the ratio of the mutual impedance to the square root of the product of the total self-impedances of the coupl¬ ed circuits, all impedances being of the same kind. COUPLING ELEMENT. Means by which energy is transferred from one circuit to another, the common impedance nec¬ essary for coupling. COUPLING TRANSFORMER. Transformer used to couple two circuits by means of its mutual inductance. COURSE. Projected path of an object, usually expressed in terms of true bearing. COURSE ERROR. Angular difference between the intended course and the course made good. COURSE LIGHT. Light directed along the course of an airway so as to be chiefly visible from points on or near that airway. COURSE LINE. Line which is the projection in the horizontal plane of the proposed path of travel, composed of the course and element of distance. COURSE LINE COMPUTER. Airborne equipment which accepts bearing in¬ formation from a VHF omnidirectional range re¬ ceiver and distance information from a distance¬ measuring equipment interrogator and processes it to provide deviation information and distance- to-go information with respect to a pilot-se¬ lected way point within the coverage of the VHF omnidirectional range and distance-measuring equipment ground station. Course line computers supply the navigation indications to instruments mounted on the instrument panel of the air¬ craft. COURSE LINE DEVIATION. Difference between the track and the course line, expressed in terms of either angular or linear measurement. COURSE LINE DEVIATION INDICATOR. Cross-pointer instrument which indicates devia¬ tion from a course line. COURSE LINE SELECTOR. Instrument which provides means to select the course to be flown. 39-174 1 APRIL 1959 AFM 100-39 COU COURSE MADE GOOD. . Resultant direction of actual travel projected in the horizontal plane, expressed as an angle from the reference line to a line extending in the di¬ rection of actual travel, and usually measure clockwise from the reference line. This is the equivalent of the bearing of the aircraft from t e point of departure. COURTESY LIGHT. Auxiliary position light. COVER. , . , 1. Maintain a continuous receiver watch wit transmitter calibrated and available but not nec¬ essarily available for immediate use. 2. Classified Definition. (Reference: AFM 100- 50.) COZI (COMMUNICATIONS ZONE INDICATOR). Device developed by Raytheon to indicate whe¬ ther or not long distance high frequency broad¬ casts are successfully reaching their destina¬ tions. The equipment will also indicate appro¬ ximately how strong the signals are when they arrive. It could be used by the Voice of Amer¬ ica to check the effectiveness of their broad¬ casts, and also as an aid in increasing the efficiency and reliability of any long distance ra¬ dio communications system. To test a signa, COZI sends out from the radio stations own an¬ tenna, a radar beam along the same path taken bv the radio waves. The interruption in broad- , casting is so brief the listeners do not notice the break. The radar beam returns and is measured for both its intensity and the time interval of its travel. From these measurements of back-sca - ter energy, the equipment produces values that tell the operator, with a high degree of accuracy the skip distance of the wave and its strength when it arrives at its destination^ certain conditions, it is also possible to detec various evidences of deliberate "l-ming through variances in the calculated energy of the back-scatter return. CP (COMMAND POST). ,• Physical facility within a combat center or tion center from which division or sector super¬ vision of air-defense operations is exercise . CPFF (COST PLUS FIXED FEE CONTRACT). * Contract in which the government agrees to re¬ imburse the contractor for costs incurred in pro¬ ducing the articles or performing the services covered by the contract, and to pay a fixed fee in addition. CPS (CYCLES PER SECOND). One complete sequence of variations in an alter¬ nating current, including a rise to a maximum in one direction, a return to zero, a rise to a max¬ imum in the opposite direction, and a return to zero. The number of cycles occurring in one second is called frequency. CR 1. International Telecommunications Union de¬ signation for station open to limited public cor¬ respondence. 2 Abbreviation associated with specific keys on a teletypewriter such as CR, LF, LIRS, or FIGS, which, when operated cause the teletypewriter to perform mechanical functions in order that a message may be received in proper form. "^Turning of an airplane which causes its longi¬ tudinal axis to vary from the track of the plane. Angle through which an aircraft is «™d m” the wind in an attempt to correct for drift If this angle eliminates the drift and the aircraft thus makes good its desired course, then the crab an g le is also the drift correction angle. CR Te F rm usually applied to small ships, including all boats, launches, tankers, tugs, s ips, sels under the jurisdiction and responsibility of the transportation corps. C Trt of the crankshaft which is in the form of a crank and crankpin. CR Lower^part of the engine structure surrounding the crankshaft working parts. 39-175 AFM 100-39 CRA 1 APRIL 1959 CRANKPIN. Part of the crank to which the connection rod is connected. CRANKSHAFT. Part of the engine which transmits the recip¬ rocating motion of the piston to the driven unit in the form of rotary motion. That part to which the connection rod and flywheel are attached. That part which actually does the delivering of the power developed above the piston. CRANKSHAFT MAIN BEARING. Part of the shaft which revolves in the bearing in the crankcase which is the main support of the crankshaft. CRANKSHAFT PIN BEARING OR JOURNAL. Part of the crankshaft on which the connecting rod is attached and rotates. CRANKSHAFT WEB. Part of the crankshaft that connects the crank- pin with the main bearing of the crankshaft. CRASH ALARM. Relay circuit which functions to connect the tele¬ phones of all emergency services, such as fire department. CRASH-FIRE SYSTEM. Two-way radio-communications system consisting of a base station and one or more portable and/or mobile units, used for the prompt and efficient control of fire, crash, and crash-ambulance ve¬ hicles and personnel. CRATPR. 1. Cavity formed in the positive carbon electrode of an electric arc. 2. Depression at the termination of an arc weld. CRATER LAMP. 1. Glow discharge type vacuum tube, whose brightness is proportional to the current passing through the tube. The glow discharge takes place in a cup or crater rather than on a plate as in a neon lamp. 2. Gaseous lamp, usually containing neon. Pro¬ vides a point source of light that can be modu¬ lated with a signal. CRC (CONTROL AND REPORTING CENTER). Operational center immediately subordinate to an air control center responsible in a certain area for control and reporting of aircraft and certain warning services. CREEP METAL. Slow deformation which metals undergo when subjected to prolonged stress with or without exposure, simultaneously to high temperature, depending on the particular metal. CREOSOTE. Oil that is derived from distilling coal tar or wood tar. Used to preserve wood, particularly poles. CREST FACTOR. Ratio of the peak value to the effective (root- mean-square) value of an ac or pulsating wave. CREST VALUE. Crest value of any quantity which varies with time is the maximum value which the quantity attains during the time interval under consi¬ deration. CRF (CARRIER FREQUENCY TELEPHONE REPEATER). CRITERIA. Standards. CRITICAL ANGLE. 1. Maximum angle at which a radio wave may be emitted from an antenna, in respect to the plane of the earth, and still be returned to the earth by refraction in the ionosphere. 2. Angle at which radiation, about to pass from a medium of greater density into one of lesser density, is refracted along the surface of the denser medium. CRITICAL AREA. Portion of the subject copy which is seen by the facsimile scanner at any instant. (Reference: ELE¬ MENTAL AREA.) 1 APRIL 1959 AFM 100-39 CRI CRITICAL COUPLING. . Degree of coupling between two circuits inde¬ pendently resonant to the same frequency which results in maximum transfer of energy a resonant frequency. CRITICAL DAMPING. . . C Point of change between aperiodic and periodic damping. CRITICAL DIMENSION. Dimension of waveguide cross section determines the cut-off frequency. CRITICAL FREQUENCY. 1 Limiting frequency below which a wave com¬ ponent is reflected by, and above which it pe trates through, an ionospheric layer of vertica incidence. 2. Highest frequency which may be emitted from an antenna at 90 degrees (vertical incidence) and still be returned to the earth by refractio from one of the layers of the ionosphere. CRITICAL grid current. Instantaneous value of grid current when the anode current starts to flow in a gas filled vacuum tube. CRITICAL grid voltage. Instantaneous value of grid voitage when the anode current starts to flow in a gas filled vacu um tube. “SS ab-Ierodrome elevation at which the instrument approach should be disont.nued if vis- ual reference is not established. C "Essential' item which is in short supply or ex- pected to be short supply. CRITICAL MATERIAL. . , Raw or semiprocessed materials required . I essential uses in a national emergency, which are not expected to be available in quantity, in qua - ity, or in time, to meet requirements. CR Minhn L um Z !mount of material which will sup- port a chain reaction. CRITICAL STRAIN. Point at which no recrystallization will take place on annealing, and above which abnormal gram growth occurs on annealing. CRITICAL WAVELENGTH. Wave length corresponding to the critical o threshold frequency in a quantum process brought about by radiation. Area over which a bombing plane engaged in horizontal ot glide bombing must maintain straight flight so that the bomb sight can be operated properly and bombs dropped accur- ately. CRM (COUNTER-RADAR MEASURES). lamming signals and metalized foil ca led win- dows, chaff rope, flak paper, and maiden s hair spread in the air to upset enemy radar. CRO (CATHODE RAY OSCILLOSCOPE). Cathode-way tube used to show the waveform o a changing current or voltage. ^Accidental contact between wires of different pairs. ^Horizontal member, usually of wood, attached to a pole or other vertical member, supporting lines, or cables. CROSS ARM BRACE. Steel strap mounted from pole to cross arm hold the cross arm in position. CROSS CONNECTIONS OR CROSSCUTS. ? Easily changed or removed wire that is loose¬ ly run between equipment and circuit terminals. 2 Unwanted modulation produced by one car¬ rier, altering, in some manner, another carrier. 3. Jumpers on a main frame. 4. Connections made at distributing framesland selectors, switch and relay bays using )umpe Wire for connecting the subscriber s line to the switching train and for distributing the various circuit paths in a graded multiple at the selector bays. 39-177 AFM 100-39 1 APRIL 1959 CRO CROSS COUPLING. Unwanted coupling between two different com¬ munication channels or their component parts. CROSS MODULATION. 1. Cross modulation is unwanted modulation produced by one frequency altering, in some manner, another frequency. Cross modulation usually results from non-linear circuits of overloading of equipment and generally causes crosstalk, either intelligible or unintelligible. 2. Type of crosstalk in which the carrier fre¬ quency being received is interfered with by an ad¬ jacent carrier, so that the modulated signal of both are heard at the same time. CROSS TRAIL. Distance of the point of impact of a bomb down¬ wind from the nearest point on the ground over which the aircraft passes. CROSS-BANDING. Use of combinations of interrogation and reply frequencies such that either one interrogation fre¬ quency is used with several reply frequencies or one reply frequency is used with several interro¬ gation frequencies. CROSS-COLOR. Interference in receiver chrominance channel caused by crosstalk from monochrome signals. Color television term. CROSS-CONNECTIONS, GRADED. System of cross connecting the circuits between the local selector relay bays and the first selectors switching bays in order to distribute the traffic evenly over the first selectors. CROSS-EYE. Classified definition. (Reference: AFM 100-50.) CROSS-LEVEL ANGLE. Angle between the plane of the ships deck and a horizontal plane, measured in the plan per- perpendicular to the side of the level angle ly¬ ing in the ship’s deck. This quantity is positive if the right side of the deck, as seen by an ob¬ server facing the target, is raised. CROSS-NEUTRALIZATION. Method of neutralization used in push-pull am¬ plifiers whereby a portion of the plate-cathode ac voltage of each vacuum tube is applied to the grid-cathode circuit of the other vacuum tube through a neutralizing capacitor. CROSS-OVER FREQUENCY. Frequency at which a recording process changes from a constant amplitude process (used for the low frequencies) to a constant velocity process (used for the high frequencies). CROSS-OVER RANGE. Classified definition. (Reference: AFM 100-50.) CROSS-OVER SPIRAL. Reference made to indicate the cross-over point when using 16-gauge 4-spiral (disc-insulated) toll-entrance cable. CROSSBAR. Switching system using mechanisms called cross¬ bar switches, consisting of rectangular fields of contact springs operated in coordination by hor¬ izontal and vertical members. CROSSBAR DIAL SYSTEM. Dial operated telephone system using crossbar switches in the switching train and directly controlled by the dials in a straight forward decimal numbering system for making connec¬ tions within its own network. CROSSBAR EXCHANGE. Exchange in which switching is done by crossbar apparatus. CROSSBAR SWITCH. Switch having a plurality of vertical paths, a plurality of horizontal paths, and electromag- netically operated mechanical means for inter¬ connecting any one of the vertical paths with any one of the horizontal paths. ARMATURE RESIDUAL. Metal clip of non-mag- netic material fastened to an armature to pre¬ vent the armature from sticking to the core due to residual magnetism. FINGER SPRING. Flexible U shaped spring which engages the select lever. GUIDE FINGER. Metal tab welded to the select rod that supports the finger spring. 39-178 1 APRIL 1959 CRO AFM 100-39 HOLD ARMATURE. Armature provided on each vertical that is pivoted between and supported by the front and rear rails of the switch. It is actuated by the hold magnet when it is de¬ sired to close a crossprint in its associated ver¬ tical. HOLD MAGNET. Coil and ion core, mounted on the rear of the switch. HOLD PILOT SPRINGS. Stack of contact springs that are operated when the associated hold magnet is energized. HORIZONTAL. Stack of flexible metal strips, insulated from each other, which run the full length of the switch. The horizontal strips are equipped with twin contact lever springs. LADDER. Phenol-fiber member linking all the lever springs at any one crosspoint. LADDER BACK REST. Adjustable bar associated with each vertical, located directly beneath the ladders. Used to hold the ladders in place and adjust the ladder to the required contact separation. SELECT MAGNET. Coil and ion core, mounted on the end of the switch under each wing of the select magnet armature, which moves the armature in the desired direction. SELECT MAGNET ARMATURE. Wing-shaped twin armature, mounted on one end of a select rod, which rotates the select rod a few degrees when one associated select magnet is energized. SELECT MAGNET OFF NORMAL SPRINGS. Stack of contact springs associated with each select magnet that is actuated when the magnet is energized. SELECT ROD. Metal rod located under the switch supported and pivoted on the select rod bearings. VERTICAL. Stack of rigid stampings which run the full width of the switch from front to back. The vertical strips are each equipped with ten or more sets of contacts multiplied to¬ gether. CROSSBAR SYSTEM. Automatic telephone switching system which is generally characterized by the following features: a. Selecting mechanisms are crossbar switches. b. Common circuits select and test the switching paths and control the operation of the selecting mechanisms. c. Method of operations in which the switching information is received and stored by controlling mechanisms which determine the operations nec¬ essary in establishing a telephone connection. CROSSFIRE. Interference from one telegraph circuit to another circuit, or which causes the faulty operation of the relays in a telephone circuit. CROSSING, RAILROAD. Where the line crosses over a railroad in pole line construction. The crossing requires special clearance and strength. CROSSTALK. 1. Unwanted sound reproduced by an electro¬ acoustic receiver associated with a given trans¬ mission channel resulting from cross coupling to another transmission channel carrying sound- controlled electric waves or, by extension, the electric waves in the disturbed channel which result in such sound. 2. Undesired power injected into a communica¬ tion circuit from other communication circuits. May be intelligible or unintelligible. 3. Interference caused by energy being coupled from one circuit to another by stray electromag¬ netic, or electrostatic coupling. 4. Sound heard in a receiver associated with a given telephone channel resulting from tele¬ phone currents in another telephone channel. Note. Crosstalk may be measured either by the loudness of the overhead sounds or by the magnitude of the coupling between the 39-179 AFM 100-39 CRO 1 APRIL 1959 ( disturbed and disturbing channels. In the latter case, to specify the loudness of the overhead sounds, the volume in the dis¬ turbing channel must also be given. CROSSTALK COUPLING. Ratio of the power in the disturbing circuit to the induced power in the disturbed circuit, ob¬ served at definite points of the circuits and under specified terminal conditions. CROSSTALK UNIT. Crosstalk measurement unit representing one millionth of zero decibel power value (10 -G db). toll-entrance cable. CROSSTALK LEVEL. Volume of crosstalk energy, measured in db, re¬ ferred to a base. CROWN. Top of an engine piston. CROWN GLASS. One of the two principal types of optical glass. CRP (CONTROL AND REPORTING POST). CRPL (CENTRAL RADIO PROPAGATION LABORATORY). Organization, reporting to the Department of Commerce through the Bureau of Standards, which is responsible for the collection, correla¬ tion, and analysis of data on which radio-propa¬ gation predictions are based, the issuance of ra¬ dio-propagation predictions, and research on ra¬ dio-propagation measurement methods and stan¬ dards. CRT (CATHODE-RAY TUBE). Vacuum tube in which the instantaneous position of a sharply focused electron beam deflected by means of electrostatic and/or electro magnetic fields is indicated by a spot of light produced by the impact of the electrons on a fluorescent screen at one end of the tube. CRU (CRUISER). Man-of-war less heavily armed and armored than a battleship, having superior speed. CRUTCH. Auxiliary inputs to inertial bombing-navigation sub-systems. crypto (CRYPTANALYSIS). The process by which a cryptographic system is discovered by analysis cryptograms intercepted, or by analysis of the machine that sends the cryp¬ tograms. crypto (CRYPTANALYST). One trained in cryptanalysis. crypto (CRYPTANALYTIC). crypto (CRYPTOGRAPHER). One who encrypts or decrypts messages, or has a part in making cryptographic systems. crypto (CRYPTOGRAPHIC). crypto (CRYPTOGRAPHY). Art or science concerned with encrypting and de¬ crypting. CRYPTO-OPERATING INSTRUCTIONS. Instructions describing the methods to be em¬ ployed in the operation of a general cryptosys¬ tem. This includes a description of the general cryptosystem as well as the method of application of specific keys. CRYPTOBOARD. Personnel assigned to encrypting and decrypting messages. CRYPTOCENTER. Establishment maintained for the encrypting and decrypting of messages. CRYPTOCHANNEL. 1. Complete system of cryptocommunication be¬ tween two or more holders. 2. U.S. Navy flag ship, or station in a given cryptochannel which can communicate with any other flagship, or station in that cryptochannel just as any flagship, or station on a radio circuit can communicate with any other flagship, or sta¬ tion on that circuit. CRYPTODATE. Date which indicates the key employed. CRYPTOGRAM. Encrypted communication in visible writing. 39-180 ( 1 APRIL 1959 AFM 100-39 CRY CRYPTOGRAPHER. One who encrypts or decrypts messages or has a part in making a cryptosystem. CRYPTOGRAPHIC COMPROMISE. Recovery of cryptographic information or plain text of messages by unauthorized persons through cryptoanalytic methods. CRYPTOGRAPHIC MATERIAL. Cryptographic equipment, instructions, and key¬ ing materials used in the encryption and decryp¬ tion of classified communications. CRYPTOGRAPHIC SYSTEM, HIGH GRADE. Inherently resisting solution for a comparatively long period or indefinitely, thus providing lasting security. CRYPTOGRAPHIC SYSTEM, LOW GRADE. Provides temporary security. CRYPTOGRAPHY. Art or science which treats of the various means and methods for rendering plain text unintel¬ ligible and reconverting unintelligible text into intelligible language or the application thereof by means other than cryptanalysis. CRYPTOLOGIC EQUIPMENT. Cryptographic and special communications inter¬ cept equipment employed in Air Force communi¬ cation and intelligence activities. CRYPTONET. Crypto-communication network. ✓ CRYPTOPART. One of several portions of a cryptotext. Facn cryptopart bears a different message indicator. CRYPTOSECURITY. Component of communication security which results from the provision of technically sound cryptosystems and their proper use. CRYPTOSECURITY OFFICER. Officer appointed by the commander of a head¬ quarters to represent the command in all matters relating to cryptosecurity and the physical security of cryptographic material. CRYPTOSYSTEM. Associated items of cryptomatenal which are used as a unit and which provide a single means of encryption and decryption. GENERAL. Basic method employing certain in¬ variable elements to encrypt and decrypt. SPECIFIC. Application of a specific set of rules and aids to a general cryptosystem. CRYPTOTEXT. Test of visible writing which conveys no intel¬ ligible meaning in any language or which appar¬ ently conveys an intelligible meaning that is not the real meaning. CRYSTAL. 1. Natural substance, such as quartz or tourma¬ line, which is capable of producing a voltage when under pressure or stress, or producing pressure when under an applied voltage. It has the prop¬ erty of responding only to a given frequency when cut to a given thickness. It is therefore a valuable medium to control the frequency of radio transmitters. 2. Nonlinear element, such as galena or silicon, in which case the piezoelectric characteristic is not exhibited. PIEZOELECTRIC. Piece of natural quartz or other material capable of demonstrating a pie¬ zoelectric effect. A quartz crystal can be ground to dimensions such that it will vi¬ brate naturally at a desired radio frequency when placed in . an electric circuit of appro¬ priate components. X_cuT. Crystal which is so cut that its major flat surfaces are perpendicular to an electrical (X) axis of the original quartz crystal. XY-CUT. Crystal which is so cut that its charac¬ teristics are between those of the X-cut and the Y-cut crystals. It has a very low tempera¬ ture coefficient. Y-CUT. Crystal which is so cut that its major flat surfaces are perpendicular to a mechanical (Y) axis of the original quartz crystal. CRYSTAL ANALYSIS. Study of the arrangement of atoms, ions, or mole¬ cules in crystals, chiefly by X-ray methods aided by the theory of space groups. AFM 100-39 CRY 1 APRIL 1959 CRYSTAL AXES. Term used to refer to the imaginary reference line of direction used in cutting crystals. The three major axes are arbitrarily called the X, Y, and Z-axes. CRYSTAL AXES. Specific reference line of direction within a cry¬ stal. CRYSTAL BURN-OUT. Impairment of a crystal by exposure to excessive RF power. CRYSTAL CALIBRATOR. Crystal controlled oscillator used as a reference to check and set the frequency tuning of a re¬ ceiver. CRYSTAL CHECK. 1. Measurement of forward and backward cry¬ stal resistance. 2. Inspection of the piezoelectric quality of a crystal. CRYSTAL CONTROL. Control of the frequency of an oscillator by means of a specially designed and cut crystal. CRYSTAL CONTROLLED TRANSMITTER. Radio transmitter whose carrier frequency is dir¬ ectly controlled by a crystal oscillator. CRYSTAL DETECTOR. 1. Mineral or crystalline material which allows electrical current to flow more easily in one dir¬ ection than in the opposite, thus converting al¬ ternating current to pulsating current. 2. System composed of a metal wire and a cry¬ stal, which offers a higher resistance to currents in one direction than to currents in the other direction. CRYSTAL FACE. One of the surfaces of a cut crystal. CRYSTAL DIODE. Rectifying element comprising a semi-conducting crystal having two terminals designed for use in circuits in a manner analogous to that of vacuum-tube diodes. CRYSTAL FILTER. Circuit employing a crystal as a selective ele¬ ment. Used to descriminate against all signals except those at the center frequency of the cry¬ stal. CRYSTAL HOLDER. Case of insulating material for mounting the os¬ cillator-plate therein, and external prongs for plugging into a suitable socket. CRYSTAL LOUDSPEAKER. Loudspeaker in which the mechanical displace¬ ments are produced by piezoelectric action. CRYSTAL MICROPHONE. Microphone which depends on the generation of an electromotive force by the deformation of a crystal having piezoelectric properties for its operation. CRYSTAL MIXER. Housing containing the crystal inputs for signal and local oscillator, and the IF output. Used in heterodyne detection for converting the received signal to a lower frequency before amplification. CRYSTAL OPERATION. Operation using crystal controlled oscillators. CRYSTAL OSCILLATOR. Oscillator circuit in which a crystal is used to control the frequency and to reduce frequency instability to a minimum. CRYSTAL OVEN. Container, maintained at a constant temperature, in which a crystal and its holder are inclosed in order to reduce frequency drift. CRYSTAL PICKUP. Phonograph pickup which depends for its oper¬ ation on the generation of an electric charge by the deformation of a body (usually crystal¬ line) having piezoelectric properties. CRYSTAL RECTIFIER. Electrically conductive, or semiconductive sub¬ stance, natural or synthetic, which has the pro¬ perty of rectifying small radio-frequency voltages. 39-182 1 APRIL 1959 AFM 100-39 CRY CRYSTAL SPEAKER. Loudspeaker in which the mechanical forces re¬ sult from the deformation of a crystal having converse piezoelectric properties. CSgO (CHIEF SIGNAL OFFICER). CST (CENTRAL STANDARD TIME). ' Mean time based on the 90th meridian, west longitude. CRYSTAL SYSTEM. . . Group which includes all crystals containing the same number and kind of planes of symmetry. There are six crystal systems: isometric (cubical), tetragonal, orthorhombic, monoclinic, triclinic, and hexagonal. CRYSTAL-AUDIO RECEIVER. Similar to the crystal-video receiver except or the path detection bandwidth which is audio rather than video. CRYSTAL-VIDEO. Type of receiver in which the radio frequency energy is converted directly to video energy as it comes from the antenna by means of a silicon crystal. CRYSTAL VIDEO RECEIVER. Broad-tuning receiver consisting of a crystal de¬ tector and a high-gain video amplifier. Usually an intercept receiver. CRYSTALLINE LENS. Flexible inner lens of the eye which accommodation for sharply focusing near provides and dis¬ tant objects. CRYSTALLIZATION. Condition where metal is changed the smooth consistency of the to small, sharp granules due to age, temperature change or movement. CRYSTALLOGRAPHY. Branch of physical science which deals with the geometrical form of crystals. CS. ■steel. Material designation for copper wire A (COMMUNICATIONS SERVICE ITHORIZATION). Call or subsidiary contract upon the general con¬ tracts with communications companies to provide specific facilities and services within the pre¬ scribed limits of the Communications Service Au¬ thorization. CT. ITU designation for coastal telegraph station, Carrier telephone channel. CT CUT - ... , Oscillator crystal plate of specified dimensions with an edge parallel to the X-axis and making an angle of ±38° with the Z-axis. CTC (CENTER-TO-CENTER). CTCF (CHANNEL AND TECHNICAL CONTROL FACILITY). • • u ATurnM Facility in a tape-relay station in the A1K.CUM NET which provides on-call patching. CTE (COMMANDER TASK ELEMENT). CTF (COMMANDER TASK FORCE). CTG (COMMANDER TASK GROUP). CTU (COMMANDER TASK UNIT). CU. Material designation for copper wire. CU RADIATION. X-radiation emitted from a copper target (anti¬ cathode), or anode .of an X-ray tube and ordinar¬ ily employed for the examination of quartz. CUBICAL ANTENNA. Antenna array, the elements of which are posi¬ tioned to form a cube. CUE SHEET. Orderly tabulation of scheduled motion picture programs, indicating all cues. CUPPINESS. , , „ Defect in wire drawing which leads to fracture of the cut and cone type. CUR. (CURRENT). Drift of electrons past a reference point, ihe passage of electrons through a conductor. Mea¬ sured in amperes. 39-183 J— AFM 100-39 T APR,L 1959 CUR CURIE. Unit quantity of radium emanation of radon, de¬ fined as that quantity which is in equilibrium with one gram of radium. CURIE X CUT. Cut of piezoelectric crystal having its edges par¬ allel to the X-, Y-, and Z-axes, flattened perpen¬ dicular to the X- and somewhat elongated par¬ allel to the Y-axis. CURIUM. Element 96, made synthetically from uranium and plutonium by bombarding U238 and PU239 with 40 megavolt helium ions. CURRENT. Drift of electrons past a reference point. The passage of electrons through a conductor. Mea¬ sured in amperes. ABSORPTION. Current proportional to the rate of accumulation of electric charges within an im¬ perfect isotropic dielectric. The rate of accumu¬ lation and hence the absorption current, de¬ creases with time after any change of the poten¬ tial gradient, and occurs with both an increase and a decrease of potential gradient, so that the absorption current is reversible. ALTERNATING. Current continually changing in magnitude and periodically reversing in po¬ larity. ANODE. Current flowing in the anode (plate) circuit. ANODE RAY. Current in a varified gas made up of the moment of positively charged part¬ icles, which have their origin in the anode and are of atomic dimensions. BLEEDER. Current drawn continuously from a power pack to improve its voltage regulation or to increase the voltage drop value across a particular resistor. DIRECT. Current which is constant in direction and essentially constant in magnitude. EDDY. Current induced in a metal by a chang¬ ing electromagnetic field. GRID. Current between the cathode and the grid of vacuum tube. GROUND RETURN. Vector sum of the currents in all conductors in an electrical supply line. LONGITUDINAL. Current which flows in the same direction in the two wires of a pair using the earth as its return path. OSCILLATORY. Current whose direction of flow periodically reverses as a result of a bal¬ ance between the inductance and capacitance in the circuit through which it flows. PEAK PLATE. Maximum instantaneous plate cur¬ rent flowing in a tube. PLATE. Current flowing in the plate circuit of a vacuum tube. PULSATING. Current of varying magnitude but constant direction. RESIDUAL. Vector sum of the currents in sev¬ eral wires of an electrical supply circuit. SATURATION. Current produced in the plate circuit of a vacuum tube when all of the elec¬ trons emitted by the cathode pass to the plate. It is sometimes referred to as the emission cur¬ rent. SNEAK. Current which, while not particularly excessive, is above the carrying capacity of the equipment through which it flows. SPACE. Total current flowing between the cath¬ ode and all other electrodes in a tube. This includes the plate current, grid current, screen grid current, and any other electrode current which may be present. WAVELENGTH CHARACTERISTIC. Relation usually shown by a graph between the direct anode current per unit energy of the incident radiant flux and the wavelength of the flux. CURRENT AMPLIFICATION. Ratio of output to input currents of an ampli¬ fier, or transducer input circuit. 39-184 1 APRIL 1959 AFM 100-39 CUR CURRENT AMPLIFIER. Amplifier capable of delivering considerable cur¬ rent at a low voltage. CURRENT, ANTENNA. RF current that flows in an antenna. CURRENT ATTENUATION. Ratio of the current, of a transducer, in its input circuit to the current in a specified load im¬ pedance. CURRENT INTELLIGENCE. Spot information or intelligence that is of im¬ mediate interest and value to the users and which is usually furnished to them without delays incident to complete evaluation and interpre¬ tation. CURRENT MARGIN. Difference between the steady-state currents flow¬ ing through a telegraph receiving instrument corresponding, respectively, to the two positions of the telegraph transmitter. CURRENT SATURATION. Condition in which the plate current of a vacuum tube cannot be further increased by increasing the plate voltage. (Reference: PLATE SATURA¬ TION, VOLTAGE SATURATION.) CURSOR. 1. Mechanical or electronic generated line which moves back and forth over another surface to delineate accurate readings. 2. Mechanical bearing line on a PPI-type display for reading target bearing. (Reference: BEAR¬ ING CURSOR.) CURSOR TARGET BEARING. Target bearing as measured by a PPI cursor. CURVATURE OF FIELD. Aberration affecting the longitudinal position of images off the axis in such a manner that objects in a plane, perpendicular to the axis, are imaged in a curved or dish-shaped surface. CURVE. 1. A bending without angles. 2. Analytically, a line or lines that may be pre¬ cisely defined by an equation or equatious. 3. Geometrically, a curve is the intersection of two surfaces, or the path of a moving point, or the envelope of a moving line. FREQUENCY RESPONSE. A graphical repre¬ sentation of the manner in which a circuit responds to different frequencies within its operating range. GAS PRESSURE. Curve plotted on special paper and indicating the pressure read at selected valves in a gas pressure system (vertical) a- gainst the length of the cable (horizontal) used for locating leaks. RESONANCE. Graphical representation illus¬ trating the manner in which a tuned circuit responds to the various frequencies in the vic¬ inity of the resonant frequency. CURVE OF PURSUIT. Type of interception in which the friendly air¬ borne object is always headed towards the target. CUSRPG (CANADA, UNITED STATES, REGIONAL PLANNING GROUP). CUSTODIAN, U S (UNITED STATES) JOINT, UK (UNITED KINGDOM) ARMY. Officer charged with the actual custody, hand¬ ling, and safe-guarding of the publications issued. CUT. (CUTTER). Electromechanical transducer which transforms an electrical input into a mechanical output, typified by mechanical motions which may be in¬ scribed into a recording medium by a cutting stylus. (Reference: MECHANICAL RECORD¬ ING HEAD.) CUT. 1. Crystal plane section with two parallel major surfaces cut in any orientation. Any given cut is specified by the direction normal to the major surface, or by special distinguishing symbols. 2. Two station fix in radio direction finding. 3. Disconnect; to open a circuit so that communi¬ cations cannot be carried on. CUT DOUBLE, TRIPPLE, ETC. Make two (three, etc.) original recordings sim¬ ultaneously. CUT-OVER. Rapid transfer of lines from one termination to another or from one facility to another. 39-185 AFM 100-39 CUT 1 APRIL 1959 CUTS-OFF. Fails to permit satisfactory transmission above, or below, a specific frequency limit. CUTS-OUT. Interruption of communication as when an open circuit occurs. Implies a come and go condition. CUTLER FEED. Resonant cavity at the end of a waveguide, which feeds RF energy to the refelector of the spinner assembly. CUTOFF. 1. Minimum value of bias which cuts off, or stops, the flow of plate current. With a constant plate voltage and no signal decreasing the bias from the cutoff valve will permit the plate current to flow again, while increasing it to or beyond the cutoff point keeps the plate cur¬ rent at zero. 2. Frequency at which the transmission loss ex¬ ceeds by 10 db the loss at 1,000 cycles. 3. Frequency above or below which a selective circuit fails to respond. CUTOFF ATTENUATOR. Variable length of waveguide used below its cut¬ off frequency to introduce variable non dissi¬ pative attenuation. CUTOFF FREQUENCY OF AMPLIFIER. Frequency or frequencies at which the normal gain of an amplifier begins to decrease sharply. CUTOFF FREQUENCY OF FILTER EQUIPMENT. Frequency or frequencies at which attenuation begins to rise sharply. CUTOFF FREQUENCY OF LINE. Upper frequency limit, usually of a loaded trans¬ mission circuit, beyond which attenuation rises very rapidly. CUTOFF LIMITING. Limiting the maximum output voltage of a vac¬ uum-tube circuit by driving the grid beyond cut¬ off. CUTOFF SAW. Crystal sawing machine with a downward hand-or-gravity-controlled movement; the work being held stationary. CUTOFF WAVELENGTH. Free space wavelength which corresponds to the cutoff frequency of a waveguide. CUTOUT. Pairs brought out of a cable and terminated at some place other than at the end of the cable. CUTTER. Electromechanical transducer which trans¬ forms an electrical input into a mechanical out¬ put, typified by mechanical motions which may be inscribed into a recording medium by a cut¬ ting stylus. (Reference: MECHANICAL RE¬ CORDING HEAD.) CUTTER DISPENSER. Device which, in operation, cuts window to a selected length and dispenses it. CUTTING STYLUS. Toll which cuts the groove into an original re¬ cording. CV. International Telecommunications Union desig- ;% nation for station open exclusively to the corre¬ spondences of a private agency. CV (CRYSTAL-VIDEO) RECEIVER. Receiver consisting of an antenna, a crystal de¬ tector and a video amplifier, the frequency band of operation being determined by the an¬ tenna only. CW (CONTINUOUS WAVE). Successive oscillations of waves, identical under steady-state conditions. Generally, radio waves are of constant amplitude and frequency. CW (CARRIER WAVE) DOPPLER. Comparison of transmitted and echo frequen¬ cies to give an aural indication of moving target. CW (CARRIER WAVE) TRACK BREAKING OR VELOCITY GATE STEALING. Classified definition. (Reference: AFM 100-50.) CX (COMPOSITE, COMPOSITE LEG). 39-186 1 APRIL 1959 AFM 100-39 CYC CYC (CYCLE). 1. One complete positive and one complete nega¬ tive alternation of an alternating current. 2. Complete set of any recurrent valves. DOT. One cycle of a periodic alternation between the signaling conditions, each condition having unit duration. Thus, in two-condition signal¬ ing, it consists of a dot, or marking element, followed by a spacing element. DUTY. Cycle of starting, running, and stop¬ ping operations performed by equipment on intermittent duty. (Reference: DUTY FAC¬ TOR.) SUNSPOT. Sunspot activity follows a cycle with an average of 11.1 years between successive minima. The usual cycle shows the variation of the 12-month running average sunspot num¬ ber plotted against the months. CYCLES PER SECOND. One complete sequence of variations in an alter¬ nating current, including a rise to maximum in one direction, a return to zero, a rise to a maxi¬ mum in the opposite direction, and a return to zero. The number of cycles occuring in one sec¬ ond is called the frequency. CYCLIC SHIFT. Electronic computer operation which produces a word in which characters are obtained by a cyclic permutation of the characters of a given word. CYCLOTRON OR ATOM SMASHER. Apparatus for imparting high speeds to elec¬ trons or ions by causing them to move in semi¬ circular paths in a magnetic field. CYL (CYLINDER). Cylindrical part of the engine in which the piston moves, and combustion takes place. CYLINDER. Cylindrical part of the engine in which the piston moves, and combustion takes place. CYLINDER BLOCK. Number of cylinder bores all cast in line and in one piece. CYLINDER BORE. Part of the cylinder in which the piston slides or moves. CYLINDER HEAD. Part which covers and seals the end of the cy¬ linder and usually contains the valves. CYLINDRICAL CONCAVE MIRROR. Curved reflecting surface like the inside of one- half of a cylinder, used to focus light rays to a line. CYLINDRICAL CONVEX LENS. Lens having a straight surface in its longer di¬ mension and a spherically curved surface at right angles to this direction. CYLINDRICAL LENS. Lens ground with a cylindrical surface instead of a spherical one. CYLINDRICAL WAVE. Wave whose equiphase surfaces form a fam¬ ily of coaxial cylinders. CYROGENIC. Pertaining to low temperatures or to apparatus for producing them. 1 APRIL 1959 AFM 100-39 D D D (DISTANTLY CONTROLLED). D 30° ITU designation for directive antenna having maximum radiation in the direction of 30° (ex¬ pressed in degrees from true North; from 0-360 degrees clockwise). D/L (DATA LINK). Electronic equipment which permits automatic transmission of information in digital form. D/O (DIRECTOR (DEPUTY) OPERATIONS). Member of the battle staff responsible for super¬ vision of air-defense operations within the orga¬ nization area of responsibility. D-CABLE. Two-conductor cable, each conductor having the shape of the capital letter D, with insulation be¬ tween the conductors and between the conductors and the sheath. D-INDICATOR. Radar indicator which combines types B-and C- indicators. The signal appears as a bright spot with azimuth angle as the horizontal coordi¬ nate and elevation angle as the vertical coordi¬ nate. Each horizontal trace is expanded verti¬ cally by a compressed time sweep in order to facilitate separation of signal from noise and to give a rough range indication. D-LAYER. One of the lowest regular ionospheric layers. Sky waves normally are not reflected by this lay¬ er, but are absorbed by it. D-REGION. Region of the ionosphere below the E region or about 90 kilometers from the earth’s surface. D-SCAN. Presentation combining B and C types. The sig¬ nal appears as a bright spot with azimuth angle as the horizontal coordinate, and elevation angle as the verticle coordinate. Each horizontal trace is expanded vertically by a compressed time sweep to facilitate separation of signal from noise and gives a rough range indication. D-SCOPE. (Reference: D-SCAN). DAILY KEYING ELEMENT. Part of the specific key that changes at predeter¬ mined intervals, usually daily. DA (DEPARTMENT OF THE ARMY). DAF (DEPARTMENT OF THE AIR FORCE). Executive part of the Air Force establishment at the seat of government. Includes the Secretary of the Air Force, Headquarters, USAF, and the supporting staffs. DAGMAR. Project to synthesize the various return-to-base procedures for aircraft into a standard manual system. Average traffic capability of this system is 30 to 40 aircraft per hour, with a peak rate of up to 60 for very brief periods. Equipment for the system may include the AN/CPN-18 and AN/GPX-9 radar-IFF combination, plus the FPN-16 precision approach radar. Air traffic controllers and tower operators are also re¬ quired. DAMPENED IMPEDANCE. Blocked impedance of a transducer is the imped¬ ance measured at the input when the impedance of the output system is made infinite. (Refer¬ ence: BLOCKED IMPEDANCE.) DAMPED OSCILLATION. Oscillation which, because the driving force has been removed, gradually dies out, each cycle be¬ ing smaller than the preceding in smooth, regu¬ lar decay. DAMPEN. Place sound-absorbing material, such as draper¬ ies, in a radio studio or in an auditorium to pre¬ vent echoes. DAMPENED WAVES. Waves that progressively decrease in amplitude during successive cycles. DAMPING. 1. Reduction of energy in a mechanical or elec¬ trical system by absorption or radiation. 2. Act of reducing the amplitude of the oscilla¬ tions of, an oscillatory system; hindering or pre¬ venting oscillation or vibration; diminishing the 39-188 AFM 100-39 DAM 1 APRIL 1959 sharpness of resonance of the natural frequency of a system. DAMPING CONSTANT. Napierian logarithm of the ratio of the first to the second to two values of an exponentially de¬ creasing quantity separated by unit time. DAMPING DIODE. Vacuum tube which damps the positive or negative half-cycle of an ac voltage. DAMPING FACTOR. Damping factor of any underdamped motion is, during any complete oscillation, the quotient ob¬ tained by dividing the logarithmic decrement b^ the time required by the oscillation. DAMPING FACTOR OF AN INSTRUMENT. Ratio of the deviations of the pointer (or mark¬ ing device) in two consecutive swings from the position of equilibrium, the greater deviation being divided by the lesser. For practical pur¬ poses, it is sometimes convenient to express the performance of an instrument in terms of the reciprocal of the damping factor. This reciprocal of the ratio of the excess of the maximum momentary deflection (over the steady deflec¬ tion) to the steady deflection, both expressed in angular degrees, when expressed as a precentage, is denoted by the term percentage overshoot. DAMPING OF AN INSTRUMENT. Dissipation of the kinetic energy of the moving element of the instrument. Two general classes of damping are: periodic, in which the pointer oscillates about the final position before coming to rest; and aperiodic, in which the pointer comes to rest without overshooting the rest posi¬ tion. DANIELL’S CELL Cell having a copper electrode in a copper sul¬ phate solution and a zinc electrode in dilute sul¬ phuric acid or zinc sulphate solution, with the two solutions separated by a porous partition. It generates an essentially constant electromotive force of about 1.1 volts. DAOD. Classified definition. (Reference: AFM 100-50.) DARAF. Unit of elastance, which is the reciprocal of capa¬ citance. DARK CONDUCTION. Residual electrical conduction in a photosensi¬ tive substance when not illuminated. DARK DISCHARGE. Electric discharge, occurring in a gas, that has no visible luminosity. DARK SPOT. Sometimes observed in a reproduced television image. Caused by the formation of electron clouds in front of the mosaic screen in the camera tube at the television transmitter. DARK-SPOT SIGNAL. Signal existing in a television system during scanning of a dark spot by the television camera. DARK-TRACE TUBE. Cathode-ray tube with a screen composed of a halide of sodium or potassium. The screen norm¬ ally is nearly white, and wherever the electron beam strikes, it turns a magenta color which is of long persistence. The screen can be illumi¬ nated by a strong light source so that the re¬ flected image may be made intense enough to be projected. (Reference: SKIATRON.) DARMAR. Classified definition. (Reference: AFM 100-50.) D’ARSONVAL CURRENT. High-frequency, low-voltage current of compara¬ tively high amperage. D’ARSONVAL GALVANOMETER. Dc galvanometer consisting of a narrow, rectan¬ gular coil, freely suspended between the poles of a permanent magnet. Current sent through the coil produces the magnetic field that interacts with the permanent field and causes rotation of the coil. D’ARSONVAL MOVEMENT. Meter movement commonly used in precision in¬ struments for dc measurements. It consists essen¬ tially of a small, lightweight coil of wire sup¬ ported on jeweled bearings between the poles of 39-189 1 APRIL 1959 AFM 100-39 DAS a permanent magnet. Spiral sprints provide con¬ nections to the coil and keep the coil and its attached pointer at the zero position on the meter scale. When the direct current to be measured is sent through the coil, its magnetic field inter¬ acts with that of the permanent magnet and causes rotation of the coil and pointer. DASH. Dash is defined as three unit lengths of sus¬ tained signal (when transmitted, a dash will automatically be followed by one unit length of silence). Term used in radiotelegraphy. DASHPOT. Device using a gas or liquid to absorb energy, or retard the movement of the moving parts of a circuit breaker or other electrical device. DATA. 1. Plural term collectively used to designate material serving as a basis for discussion; mate¬ rial may or may not be technical in nature. The singular of data is datum. 2. Information, particularly that used as a basis for mechanical or electronic computation. DATA CIRCUIT. Communication facility permitting transmission of digital data. DATA LINK. Electronic equipment which permits automatic transmission of information in digital form. DATA-TIME-GROUP. Date and time, expressed in digits and zone suf¬ fix, at which the message was prepared for transmission. (Expressed as six digits followed by zone suffix; first pair of digits denoting the date, second pair the hours, third pair the min¬ utes.) DATAC. Computer in the VOLSCAN system of automatic air traffic control. It receives continuous position reports on aircraft from automatic tracking-while¬ scanning channels called ANTRACs. The com¬ puter then automatically selects a scheduled ar¬ rival time for each aircraft and calculates head¬ ing and altitude orders which will make good this schedule. Thus, DATAC is an automatic controller. The DATAC control orders may be relayed to the aircraft by voice or sent automati¬ cally over a data Link. The computer always se¬ lects the earliest possible time of arrival which does not conflict with aircraft already scheduled. Where such a schedule is possible, DATAC is¬ sues a control order which heads the aircraft along the shortest possible path, or tangent path, to the final turn circle. In case there is a conflict with another schedule, DATAC selects the earliest later 30-second interval which has no reservation. It then orders pilot to take a head¬ ing which is off-set from the tangent path head¬ ing. Thus, as the aircraft progresses along this longer path, it is delayed. As delay time drops, the magnitude of the heading offset gradually reduces until finally, when the delay has been accomplished, the aircraft, now on time, is on a tangent path. Thus, by heading control, delays are gradually used up, and the aircraft are deliv¬ ered to the final turn with precise timing. DATE. 1. Point of time at which a transaction or event takes place. 2. Point or period of time to which anything is referred as present, as to usage, style, know¬ ledge, etc. DAUPHINE TWINING. Electrical twining. DAVISSON COORDINATES. Special system of curvilinear coordinates, used in plotting the emission characteristics of a vacuum tube. DAY. D. Term used to designate the unnamed day on which an operation commences, or is to commence. This operation may be the com¬ mencement of hostilities, the date of assault landing, a bombardment, etc. If more than one such event is mentioned in a single plan, any letter (except M) may be used. 39-190 AFM 100-39 DAY 1 APRIL 1959 M. Term used to designate the day on which mobilization is to begin. Though the term is M-day, related figures, unless otherwise spe¬ cified, will refer to months before or after M- day. P. Earliest point in time after D-day at which the rate of production of an item equals or exceeds the rate at which the item is required by the Armed Forces. From D-day to P-day, mobilization reserves are used to fill the gap between production and requirements. S. Sailing date for a scheduled operation. db (DECIBEL). One-tenth of a bel, the number of decibels de¬ noting the ratio of the two amounts of power being 10 times the logarithm to the base 10 of this ratio. The abbreviation db is commonly used for the term decibel. DB (DOUBLE-BRAIDED). DB METER. Meter having a scale calibrated to read directly in decibel values at a reference level that must be specified (usually one milliwatt equals zero db). Used in AF amplifier circuits of broadcast stations, public address systems, and receiver output circuits to indicate volume level. DB OVER ISOTROPIC SOURCE. Measure of the directivity, and hence the direc¬ tive gain, of an antenna relative to a hypotheti¬ cal point source of radiation (the isotropic source). DBA. Expression used in conjunction with noise meas¬ urements. The reference level is -90bm, and the adjustment is dependent on the frequency band characteristics of the measuring device. DBM. 1. Unit used for measuring absolute power levels; power in decibels measured for a one- milliwatt reference level. 2. Facsimile power level expressed as being a given number of db above or below a reference level of one milliwatt. DBRN. Unit of measurement of electrical circuit noise in which the noise is referred to as zero, or refer¬ ence power level of one micromicrowatt at 1000CPS (90 db below one milliwatt). DBU. Measure of field strength expressed in decibels below one watt per square meter. DBW. Measure of power expressed in decibels below one watt. DBWP (DOUBLE-BRAIDED,WEATHERPROOFED.) DC (DIRECTION CENTER). Physical facility of an air defense sector head¬ quarters from which active air defense functions are directed. The direction center is equipped with an AN/FSQ-7 combat direction central. dc (DIRECT CURRENT). Unidirectional current which has an essentially constant average value. DC AMPLIFIER. Amplifier that is capable of amplifying small variations in direct current. DC GENERATOR. Rotating electric machine that converts mechani¬ cal power into dc power. DC INSERTER STAGE. Television transmitter stage that adds to the video signal a dc component known as the pedes¬ tal level. DC PATCH BAY. Specific patch panels provided for termination of all dc circuits and equipment used in an in¬ stallation. DC PICTURE TRANSMISSION. Transmission of the dc component of the tele¬ vision picture signal. This component represents the background or average illumination of the overall scene, and varies only with overall illum¬ ination. DC PLATE RESISTANCE. Value or characteristic used in vacuum-tube com¬ putations. It is equal to the dc plate voltage 39-191 1 APRIL 1959 AFM 100-39 DC DCS/M (DEPUTY CHIEF OF STAFF, MATERIEL). DCS/O (DEPUTY CHIEF OF STAFF, OPERATIONS). DCS/P (DEPUTY CHIEF OF STAFF, PERSONNEL). divided by the dc plate current and is given the sign Rp. DC RECEIVER. Radio receiver designed to operate from direct current power lines. DC RESISTANCE. Opposition to current flow offered by a circuit or body to an unvarying current. DC RESTORATION. Imposition, on a recurrent wave form, of a value of steady potential, obtained by rectification from that wave form, such that the trough or crest of the wave form reaches a desired level. DC RESTORER. Circuit which holds either amplitude extreme of a television or radar signal wave form to a given reference level of potential. DC TRANSFORMER. 1. Device for measuring large values of direct current, in which the line current magnetizes an iron core surrounding the conductor or inclosed by a few turns of the conductor. 2. Term sometimes applied to a rotating machine used to convert direct current from one voltage to another. DC TRANSMISSION. Transmission of a television signal in such a way that the dc component of the picture signal is still present. DCA (DIRECTION CENTER ACTIVE). Complete direction center computer program which directs the computer in the performance of air-defense functions. DCD (DOUBLE CHANNEL DUPLEX). DCDS (DOUBLE-COTTON, DOUBLE-SILK- COVERED). DCR (DIRECT CURRENT RESTORATION). DCS (DOUBLE CHANNEL SIMPLEX). DCS (DOUBLE-COTTON SINGLE-SILK COVERED). DDD (DIRECT DISTANCE DIALING). Method of making toll calls under which the call can be dialed directly without the services of a telephone company operator. DDM (DIFFERENCE IN DEPTH MODULATION). In directive systems employing overlapping lobes as modulating signals, such as Instrument Landing Systems, a fraction obtained by subtract¬ ing from the percentage of modulation of the larger signal, the percentage of modulation of the smaller signal, and dividing by 100. DDR (DIGITAL DATA RECEIVER). Device for accepting digital signals in audio form from a data circuit and for presenting these sig¬ nals in pulse form to digital equipment. DDT (DIGITAL DATA TRANSMITTER). Device for transmitting digital signals in pulse form and presenting these signals in audio form to digital equipment. DE BROGLIE EQUATION. Expression for the wavelength of the de Broglie wave associated with a moving electron. It states that the wavelength is equal to Planck’s constant divided by the momentum of the elec¬ tron. DE BROGLIE WAVE. Wave or wave group assumed in wave mechanics to be associated with an elementary moving parti¬ cle such as an electron or a proton. (Reference: PHASE WAVE.) DE-EMPHASIS. Restoration of a pre-emphasized signal wave to its original form. DE-ENERGIZE. Stop the flow of current in a circuit, or remove the voltage from a circuit, as by opening a switch. 39-192 AFM 100-39 DE 1 APRIL 1959 DE-ENERGIZED. State of an apparatus or system when all power has been removed, as relay with no current flowing through its coil. DE-ICER. Heating circuit to melt ice from antenna assem¬ bly. DE-ION CIRCUIT BREAKER. Arc that forms when circuit is broken is magnet¬ ically blown into a stack of insulated copper plates, giving the effect of a large number of short arcs in series. Each arc becomes almost in¬ stantly de-ionized when the current drops to zero in the ac cycle, and the arc cannot re-form. DE-IONIZATION POTENTIAL. Potential at which ionization of the gas within a gas-filled tube ceases and conduction stops. DE-IONIZATION TIME. Time required for the control grid of a gaseous tube to regain control after plate current has been interrupted. DEACCENTUATOR. Network, or circuit, required in a frequency-mod¬ ulation receiver to offset the pre-emphasis action introduced at the higher audio frequencies in a frequency-modulation transmitter. (Reference: DE-EMPHASIS.) DEAD. Free from any electric connection to a source of potential difference and from electric charge; not having a potential different from that of earth. The term is used only with reference to current-carrying parts which are sometimes alive or charged. DEAD END. 1. End of a sound studio that has the greater sound-absorbing characteristics. 2. Portion of a tapped coil through which no current is flowing at a particular band-switch position. 3. Termination of a single open wire or group of wires on a cross arm, bracket, or knot. 4. Termination of a suspension strand. DEAD END TOWER. Antenna or transmission line tower designed to withstand unbalanced mechanical pull from all the conductors in one direction together with the wind strain and vertical loads. DEAD LINE. Telephone circuit disconnected from a central of¬ fice. DEAD RECKON. Computer action resulting from a manually in¬ serted instruction on a track, this action projects a track for six frames. This is accomplished by logical conclusions based on the assumption of continuity of previously known data. It temporar¬ ily prevents a track from being dropped. DEAD RECKONING. Procedure of advancing a known position to a given position at a later time by the addition of one or more vectors representing courses and distances. The expression estimated position is used when allowance is made for wind and current. DEAD RECKONING TRACER. Mechanical device on which a moving spot of light automatically indicates the approximate geographical position of the ship on which it is used. The direction of motion of the light is con¬ trolled by synchro data from the gyro compass. DEAD ROOM. Room so thoroughly sound-proofed that practi¬ cally all sound is absorbed, and there is little reflection or echo. DEAD SHORT. Short circuit having minimum resistance. DEAD SPACE. Area or zone which is within range of a radio transmitter, but in which a signal is not received. DEAD SPOT. 1. Geographic location in which signals from one or more radio stations are received poorly or not at all. 39-193 1 APRIL 1959 AFM 100-39 DEA 2. Portion or spot in the tuning range of a re¬ ceiver in which stations are heard poorly or not at all. DEAD TIME. Time interval, in a counter vacuum tube, after recording an ionizing event required for the sheath of positive ions to move away from the anode wire to a position corresponding to the threshold field. DEAD-CENTER POSITION. Position in which a brush would be placed on the commutator of a dc motor or generator if the field flux were not distorted by armature reac¬ tion. DEAD-FRONT SWITCHBOARD. Switchboard having no live parts on the front of the panels. DEADBEAT. Coming to rest without vibration or oscillation. Thus, the pointer which a highly damped meter or galvanometer moves to a new position without overshooting and vibrating about its final posi¬ tion. (Reference: APERIODIC.) DEADMAN. 1. Type of anchor for soft ground, usually made from short lengths of poles, logs, etc. 2. Support used in setting a pole with pikes. DEATH RAY. Ray capable of killing living cells. Ultra-violet rays of certain frequencies can kill bacteria; radio waves of certain frequencies can kill in¬ sects; X-rays have still greater destructive power. DEBUG. Term used in troubleshooting* meaning: to clear away the difficulties arising from imperfect de¬ sign or construction of a set, and to make it operate satisfactorily. DEBUNCHING. Space charge effect that tends to destroy the elec¬ tron bunching in a velocity-modulation vacuum tube. DECADE BOX. Special type of variable resistor or variable capa¬ citor used chiefly in laboratory work. It contains two or more sections, with each section having 10 times the value of the preceding section and with each section divided into 10 equal parts. Each section has a 10-position selector switch or equivalent arrangement such that the box can be set to any desired value in its range. DECADE RESISTANCE BOX. Decade box containing two or more sets of 10 precision resistors. DECAL. Decalcomania; sometimes used for large charac¬ ters in place of stenciling. DECAY. Disintegration of the nuclei of an unstable ele¬ ment due to the spontaneous emission of charged particles or energy quanta. Elements which decay are called radioactive. DECAY CONSTANT. Exponential constant of a heterogenous mixture of radioactive material calculated from its ob¬ served rate of decay; a means of predicting future contamination intensities in given areas. DECAYING CONDUCTION CURRENT. Current which is related to the conduction cur¬ rent by a decreasing function of the time. DECCA. British continuous wave, differential distance, hyperbolic radio aid to navigation, in which the receiver measures and integrates the relative phase difference between the signals received from two or more synchronized ground stations. Because of the phase comparison technique used, the system has a high accuracy, with changes in position of a few yards being detecta¬ ble. Range with accuracy is limited by sky-wave transmission which interferes with the uniform phase pattern of the signals. DECCA operates in the 70-130 kc frequency band. It is somewhat similar to LORAN, except that it utilizes con¬ tinuous waves rather than pulses, and phase dif¬ ferences in RF signals rather than the difference AFM 100-39 DEC 1 APRIL 1959 in arrival times. The transmissions from the master and slave stations are on different fre¬ quencies. These two frequencies are so related, however, that their multiplication by different whole numbers such as three or four will pro¬ duce the same frequency. Phase comparison fol¬ lows this frequency multiplication; a complete 360-degree shift occurring each time the receiv¬ ing point moves from one hyperbolic line of posi¬ tion to the next adjacent line. This distance is called a "lane.” More than one position line is required for a fix. The general arrangement of transmitters is one master station and three slave stations arranged in a star formation, and ordi¬ narily referred to as the red, green, and purple slaves. The master and each slave for a pair of stations, and three complete systems of hyper¬ bolic lines are formed to permit accurate full cov¬ erage of the area. The transmitters are unmodu¬ lated, continuous wave. However, the slave sta¬ tions are more complex than the master because of the necessity of phase-locking and synchroniz¬ ing their RF signals with the master. The dis¬ tance between master and slave station is 80-100 miles. Operational range is about 250 miles. The system was originally designed for maritime navigation. Zone of "land” ambiguity is solved by a superimposed lower order of accuracy sys¬ tem, which is turned on systematically to assist the pilot or navigator. DECCA is widely used in Europe where the service is provided on a rental basis. It has been advocated as a helicopter navigation system in the U.S. It provides good service down to ground level, as it is not de¬ pendent upon line of sight transmission. ANDB is evaluating DECCA and other systems to de¬ termine the most suitable one for helicopter nav¬ igation. DECEPTION. Deliberate production of false or misleading echoes on enemy radars by the radiation of spurious signals synchronized to the radar, or by the reradiation of the radar pulses from extran¬ eous reflectors. 2. Classified definition. (Reference: AFM 100-50.) ELECTRONIC. Radiation or reradiation of elec¬ tromagnetic waves in a manner intended to mislead the enemy in the interpretation of data received by his electronic equipment. IMITATIVE. Transmission of messages in the enemy’s communication channels with the in¬ tention of deceiving the enemy. MANIPULATIVE. Manipulation of traffic in friendly communication channels with the intention of deceiving the enemy. RADIO. Employment of radio sets to deceive the enemy. Radio deception includes sending false dispatches, using deceptive headings, employing enemy call signs, etc. DECEPTION IN CHALLENGE. Classified definition. (Reference: AFM 100-50.) DECEPTION IN REPLY. Classified definition. (Reference: AFM 100-50.) DECIBEL. Unit used to indicate the ratio between power voltage, currents, amplitudes, signal levels, etc., and a base or zero level. The common zero level now used is one milliwatt in 600 ohms and when so used the unit is abbreviated as "dbm”. Plus db’s indicate a gain, minus db’s indicate a loss. When used to express the voltage gain of an amplifier, the db is only correctly used when input and output impedances are the same. Db’s equal 10 log 10 (power ratio) or 20 log 10 (voltage or current ratio). DECIBELS, ADJUSTED. Expression used in conjunction with noise meas¬ urements. The reference level is 90 dbm, and the adjustment is dependent on the frequency band weighting characteristics of the measuring de¬ vice. Measurements may be made with a Western Electric 2B measuring set or equivalent. DECIBELS ABOVE OR BELOW ONE MILLIWATT. Quantity of power expressed in terms of its ratio to one milliwatt. 39-195 1 APRIL 1959 AFM 100-39 DEC DECIMAL ATTENUATOR. System of attenuators so arranged that a voltage or current can be reduced decimally. DECIMAL NUMBER SYSTEM. (Reference: POSITIONAL NOTATION.) DECIMAL POINT. (Reference: POINT.) DECIMETRE WAVES. Electromagnetic waves having wavelengths be¬ tween 0.1 and 1 meter. DECIPHER. Convert an enciphered message into its equiva¬ lent plain text by means of a cipher system. DECISION. Clear and concise statement of the line of action intended to be followed by the commander as the one most favorable to the successful accom¬ plishment of his mission. DECISION ALTITUDE. Term used in connection with guided missiles. It is the highest altitude at which a defender can identify a missile. (Reference: UNMASKING ALTITUDE.) DECK-TILT CORRECTION. When a spinner base is tilted with respect to the horizontal, changing the elevation of the reflec¬ tor causes a small rotation about a true vertical axis. Thus, a bearing error is introduced since bearing is read directly from the rotation of the spinner base. Removal of this error is called the deck-tilt correction. DECLASSIFY. Remove the security classification of an item of classified matter such as a document or an item of material. DECLINATION. 1. Arc between a point and the equator meas¬ ured on a great circle passing through the poles and perpendicular to the equator. 2. Angular difference between the normal in¬ dication of a magnetic compass and that of true north and south. DECLINOMETER. Instrument for measuring magnetic declina¬ tion, consisting essentially of a delicately sus¬ pended magnet and a means for measuring the angular position of the magnet with respect to true north. DECODE. 1. Convert an encoded message into its equiva¬ lent plain text. 2. Section of a code book in which the code groups are in alphabetical, numerical or other systematic order. DECODER. 1. Device for decoding a series of coded signals. 2. Automatic telephone relay tape translator which determines, from the office code of each call, the information required for properly re¬ cording the call through the switching train. Each decoder has means, such as a cross-connect¬ ing field, for establishing the controls desired and for readily changing them. 3. Electronic computer network or system in which a combination of inputs is excited at one time to produce a single output. (Reference: MATRIX.) DECODING MATRIX. Device which can decode many input lines into a single output line. DECOMPOSITION POTENTIAL. Minimum potential at which an electrochemical process can take place continuously at an appre¬ ciable rate. DECONTAMINATE. Process of restoring the original condition of low emission to the grid of contaminated oscillator vacuum tubes in radar equipment. DECOUPLER. Circuit for eliminating the effect of common impedance coupling. DECOUPLING. Prevention of transfer or feed back of energy from one circuit to another. 1 APRIL 1959 AFM 100-39 DEC decoupling CIRCUIT. . Circuit used to prevent interaction of one circ with another. decoupling filter. Filter used in a decoupling circuit to prevent interaction of two circuits. DECOUPLING NETWORK. ! Network which is used to prevent the inter¬ action of two circuits. 2 Network of capacitors and chokes, or resis¬ tors, placed in leads which are common to two or more circuits to prevent unwanted and harm¬ ful interstage coupling. decoupling resistance. Resistor, usually of high value, used to prevent interaction of two circuits. DECOY. , , Reflecting object used in radar deception, such as a spar buoy, a group of streamers hung from a captive balloon, etc. decrement. r . Progressive diminution in the value of a variab e quantity and the amount by which a variable is decreased. When applied to damped oscillations, it is usually called damping factor. Instrument for measuring the logarithmic decre¬ ment (damping) of a train of waves. decrypt. , , Convert a cryptogram into plain text by reversa of the encryption process. British radionavigational aid which is designe to provide navigational coverage over sections of a specific route, especially over long oceanic crossings. This system uses a technique similar to existing DECCA installations, and is com¬ prised of a pair of transmitting stations, a master and a slave, at each end of the route. DECCA indicating equipment can be used with this sys- tem. DEEP FREEZE. Contract with Commercial Cable Company or lease of teletype channels in their proposed new transatlantic cable linking the US, Nova Scotia, Newfoundland, Greenland, Iceland, an t e UK. DEFENSE VISUAL FLIGHT RULES. Rules applicable to visual flight rules (VF ) which originate within or penetrate an air de¬ fense identification zone. deferred. . , A message precedence designation (Reference PRECEDENCE DESIGNATIONS, MESSAGE.) definition or resolution. I Fidelity with which the detail of an image is reproduced. When the image is sharp and has definite lines and boundaries, the definition is said to be good. 2. Definition in a given direction is equal to the width of the narrowest isolated line of subject copy perpendicular to that direction, for which the response of the facsimile system will just reach the steady-state value attained for a larger area of the same density. deflecting coil. . Inductor used to produce a magnetic field that will bend the electron beam a desired amount in a cathode-ray tube of an oscilloscope, television receiver, or television camera. DEFLECTING ELECTRODE. Electrode to which a potential is applied for t purpose of moving an electron beam in a hon- , zontal or vertical direction. deflecting force of recording INSTRUMENT. Force at the recording point, in the direction of its motion, produced by the electrical quantity to be measured and acting through the instru¬ ment. deflection. , , Movement of the electron beam in a cathode-ray tube created by electromagnetic or electrostatic fields, which are varied to cause the light spot 39-197 AFM 100-39 DEF 1 APRIL 1959 to txaverse the face of the tube in a predeter¬ mined pattern. ELECTROSTATIC. Deflecting an electron beam by applying a voltage between plates mounted inside a cathode-ray tube. MAGNETIC. System using electromagnetic fields for the deflection of electron beams, as in cathode-ray tubes. DEFLECTION COILS. Coils placed about the yoke of a cathode-ray tube to cause the displacement of the electron stream by the magnetic field produced within the tube as the result of current flowing in the coils. DEFLECTION FACTOR. Reciprocal of the deflection sensitivity of a cathode-ray tube. It is, therefore, the amount of change in the deflecting field that will cause unit displacement of the electron beam at the screen. It may be expressed as volts per inch or deflect¬ ing coil current per inch. DEFLECTION PLATES. Two pairs of parallel electrodes, the pairs set one forward of the other and at right angles to each other, parallel to the axis of the electron stream, within cathode-ray tube. In applied po¬ tential produces an electric field between each pair which, by varying the applied potential may be varied, to cause a desired angular displace¬ ment of the electron stream. DEFLECTION POLARITY OF AN OSCILLOSCOPE. Relationship between the direction of displace¬ ment and the polarity of the applied signal wave. DEFLECTION SENSITIVITY OF A CATHODE-RAY TUBE. Quotient of the displacement of the electron beam at the place of impact by the change in the deflecting field. Usually expressed in milli¬ meters per volt applied between the deflection plates, or in millimeters per gauss of the deflect¬ ing magnetic field. DEFLECTION YOKE. Assembly of one or more coils, the magnetic fields of which deflect an electron beam. DEFRUSTING. Method by which asynchronous returns are elimi¬ nated in radar beacon systems. DEG (DEGREE). 1. Division identified by a whole number on a thermometer. One degree change in temperature in the centigrade system is equal to one-hun¬ dredth of the difference in temperature between that of melting ice and boiling water, while one degree in the Fahrenheit system is equal to 1/180th of this difference in temperature. 2. Angular unit of measure equal to l/360th of a circle. DEGASSING. Process of driving out and exhausting any gases that are occluded in the electrodes and other parts of a vacuum tube and that would not be removed by evacuation alone. DEGAUSSING. Term used to describe a means of neutralizing the magnetic field of the hull of a ship or a submarine as a protection against magnetic mines or magnetic anomaly detectors. DEGAUSSING CABLE. Cable arranged around the hull of a ship and fed with a current of the correct value to neu¬ tralize the magnetic effect of the hull. The ad¬ justment is made at a degaussing station equip¬ ped with underwater equipment to indicate when the resultant magnetic field has been sufficiently weakened so that it will not actuate the mag¬ netic striker of a mine. DEGENERACY. Resonant device condition where two or more modes have the same resonant frequency. degeneration. Process whereby a part of the output power of an amplifying device is returned to its input cir¬ cuit in such a manner that it tends to cancel the input. (Reference: NEGATIVE FEED¬ BACK.) DEGRADATION OF ENERGY. 1. Process whereby available energy becomes unavailable as by conversion into heat. If the 1 APRIL 1959 AFM 100-39 DEG unavailable energy is allowed to escape, the term dissipation is more apt to be used. 2. Transformation of radiation of given type into a form having lower frequency and lower quantum energy. 1. Division identified by a whole number on a thermometer. One degree change in temperature in the centigrade system is equal to one-hun- dreth of the difference in temperature between that of melting ice and boiling water, while one degree in the Fahrenheit system is equal to 1 /180th of this difference in temperature. 2. Angular unit of measure, equal to l/360th of a circle. degree of current rectification. Ratio between the average unidirectional current output and the RMS value of the alternating- current input from which it was derived. degree of voltage rectification. Ratio between the average unidirectional volt¬ age and the RMS value of the alternating volt¬ age from which it was derived. DEHUMIDIFIER. , . . Mechanical refrigerating device used in central offices to remove moisture from the air. DEHYDRATING UNIT. Used for removing moisture from the air DEL (DELEGATION). One or more persons commissioned to represent others, as in a convention. DELAY. , , 1. Time required for a signal to pass throug a device or a conducting medium. 2 Time which elapses between the instants at which any designated point of a transmitted wave passes any two points of a transmission circuit between which the delay is measured or specified. Such delay is primarily determined by the con¬ stants of the circuit, and is measurable in milli¬ seconds or microseconds. ABSOLUTE. Time interval between the trans¬ mission of two synchronized signals. ALTITUDE. Synchronization delay introduced between the time of transmission of the radar pulse and the start of the trace on the indi¬ cator, for the purpose of eliminating the alti¬ tude hole on a PPI-type display. INTERROGATION SUPPRESSED TIME. Over¬ all fixed time delay between transmission of an interrogation and reception of the reply to this interrogation at zero distance. SKY-WAVE TRANSMISSION. Amount by which the time of transit from transmitter to receiver of a pulse, carried by sky waves re¬ flected once from the E-layer, exceeds the time of transit of the same pulse carried by ground waves. TRANSPONDER SUPPRESSED TIME. Overall fixed time delay between reception of an in¬ terrogation and transmission of a reply to this interrogation. DELAY BRAKE. Device employed to delay the opening of a unit of window. DELAY CIRCUIT. 1 Circuit which introduces a time delay in the passage of a pulse or signal from one part of a circuit to another. 2. Circuit which stores a pulse for a specified time. DELAY DISTORTION. 1. Form of distortion which occurs when the en¬ velope delay of a circuit or system is not constant over the frequency range required for trans¬ mission. 2. Form of distortion which results from incon¬ stancy in the relation between intrinsic delay and frequency due to nonlinear phase vs. frequency relation. 3. Amount of variation in delay for various frequency components of the facsimile signal. 39-199 AFM 100-39 DEL usually expressed in micro-seconds from an aver- age delay time. Note. Delay distortion of a communication cir¬ cuit used for TXC equipment should be not more than 300 micro-seconds for good picture quality. DELAY EQUALIZER. '■ Devke which add * delay at certain frequencies to a circuit such a manner as to reduce the delay distortion. the C r eCti n e , netWOrk Which is desi « ned t0 the phase delay or envelope delay of a circuit or system substantially constant over a desired frequency range. delay line. Lfd' ° r a , rtifiCial transmission line or equiva¬ lent device designed to introduce time delay in a signal or wave. ' 2. Color television transmission line or similar elay device ,n luminance channel which delays . to compensate for phase differences in transmission primary channels. DELAY PPI (p LAN POSITION INDICATION) Indicator m which the start of the sweep is de- ayad after the trigger, allowing distant targets to be displayed on a short-range scale that pro- ides an expanded presentation. DELAY unit. Unit of a radar system in which pulses may be delayed a controllable amount. DELAY-LINE MEMORY. (Reference: DELAY-LINE STORAGE.) DELAY-LINE STORAGE. Electronic computer storage or memory device consisting of a delay line and means for regen Ly hfe Md re,nSer,in8 info ™ation into the^e- delayed automatic volume control Automatic volume-control circuit that acts only 1 APRIL 1959 Signals above a certain strength. It thus per- ts reception of weak signals even though y may be fading, whereas normal automatic volume control would make the weak signals weaker. The delayed action is obtained by intro¬ ducing a bias voltage that is in series with and opposes the automatic volume-control voltage. DELAYED SWEEP. f„ We T 'u' f ,eCtr0 " beam 0f a cathode-ray tube n which the beginning of the „ J or a time after the pulse which initiates Ihe sweep. c DELAYED TEST. Service test of a battery made after a specified period of time and is usually made for compari son with an initial test to determine shelf depre- DELEGATION. One or more persons commissioned to represent others, as in a convention. DELINEATION. Accurate representation on a map of physical nd cultural features of the earth by means of lines and symbols. delivery group. Group of letters assigned to represent a com- and, activity, or unit assigned to facilitate de- livery of messages. delivery indicating group. Delivery group which, while indicating a sped- ftc set Of addresses, may also indicate the identity action ° r ' 8 ' nat0r and show wh ich addresses are action or information. delivery stroke. Stroke of a pump during which the fluid in the pump is forced out of the cylinder. DELLINGER EFFECT. Sudden ionospheric disturbances which affect all in the d ^ i8ht p ort ‘° n of earth Field intensities are reduced greatly due to this cause. s y ( 39-200 1 APRIL 1959 AFM 100-39 DEL DELRAC. , . , British radionavigational system designed to pro¬ vide worldwide coverage using 21 pairs of mas¬ ter-slave stations; 3000-mile range for each pair of stations is claimed, using frequencies in the 10-14 kc band. A continuous ambiguity-resolv¬ ing process is included. DECCA indicating equipment can be used with this system. delta circuit. . Combination of three resistors or other circuit components connected in series to form a tri¬ angle. DELTA CONNECTION. Connection of a three-phase system so that the phases form a triangle. delta matching transformer. Method of matching an open-wire transmission line to half-wave antenna by spreading out t e upper end of the line and connecting them dir¬ ectly to the antenna to form a triangle. DELTA RAYS. , , , , , Electrons emitted by substances when bombarded by alpha particles. demagnetization curve. Portion of the hysteresis loop of a magnetic mat¬ erial, giving practically all the required char¬ acteristics of the material for use as a permanent magnet. The curve shows the peak value of resi¬ dual induction (Br) and the manner in which magnetization reduces to zero as demagnetizing force (El) is applied. DEMAGNETIZE. . Remove magnetism from a magnetized object, as by heating or by placing it in a strong ac field. demand factor. Power distribution ratio of the maximum demand of a system to the total connected load of the system. DEMAND METER. , , , , Device which indicates or records the demands. A demand meter records or indicates the maxi¬ mum average load over any specified time inter¬ val, or the average load over a number of equal time intervals. DEMAND OF AN INSTALLATION OR SYSTEM. , Load at the receiving terminals averaged over a specified interval of time. Expressed in kilo¬ watts, amperes, or other suitable units. DEMAND RECORDER. Instrument that records graphically the average value of the load in a circuit during successive short periods. DEMODULATION. 1. Process wherein a wave resulting from pre¬ vious modulation is employed to derive a wave having substantially the characteristics of the original modulating wave. 2. Process of extracting the signal intelligence from a modulated carrier wave. (Reference: DE¬ TECTION.) demodulator. 1. Facsimile device which detects an amplitude- modulated signal and produces the modulating frequency as a dc signal of varying amplitude. This type of unit is used to provide keying sig¬ nal for a frequency-shift exciter unit for radio facsimile transmission. 2 Device which operates on a carrier wave so as to recover the wave with which thegarner^was originally modulated. (Reference: DETECTOR.) DE Sied definition. (Reference: AFM 100-50.) DEMOUNTABLE TUBE. Hieh-power radio tube having a metal envelope with porcelain insulation. It can be taken apart for inspection and for renewal of electrodes. denature. . . 1. Term used for controlling or contaminating the explosive qualities of plutonium. 2. Make alcohol unfit to drink. dendrite. , , „ Crystal skeleton which grows from a nucleus dur¬ ing the solidification of metals. densitometer. . „ r Form of photometer used especially for me - suring the density of silver deposits on photo¬ graphic plates or films. 39-201 AFM 100-39 DEN 1 APRIL 1959 DENSITY. 1. Measure of the light-reflecting or transmit¬ ting properties of an area. 2. Ratio of the mass of a substance to the volume of the specimen. 3. Term expressing the closeness of any space distribution. 4. Measure of the light-reflecting properties of an opaque type of facsimile copy or the light- transmission properties of a film. Expressed as log io (% light reflected for opaque copy or transmitted for film). DENSITY STEP TABLET. Facsimile test chart consisting of a series of areas. The density of the areas increases from a low value to a maximum value in steps. (Refer¬ ence: STEP TABLET.) DEP (DEPUTY). 1. Person authorized to act for, or in the place of, his immediate superior. 2. Title given an officer who performs the du¬ ties of his superior during his absence. 3. Title given a staff officer subordinate to a vice commander or to a vice chief of staff, head¬ ing one of the major subdivisions of the staff. DEPARTMENT OF DEFENSE. 1. Entire military establishment of the United States. 2. Main subdivision of the executive branch of the federal government, charged with adminis¬ tration, management, and policy determination of the entire military establishment of the US. DEPOLARIZER. Chemical used in some primary cells to prevent polarization (formation of bubbles of hydrogen) at the positive electrode. DEPOSITION. Depositing a coating on a surface, as by elec¬ troplating. DEPOT. Facility for the receipt, classification, storage, accounting, issue, maintenance, procurement, manufacture, assembly, research or salvage of supplies, or for the reception, processing, train¬ ing, assignment, and forwarding of personnel replacements. It may be an installation or activity of the ConUS or area of operations. DEPOT MAINTENANCE. Maintenance of material which involves a major overhaul or complete rebuilding of parts, sub- assemblies, and/or the end item as required. Such maintenance is intended to augment stocks of serviceable equipment or to support lower levels of maintenance by the use of more exten¬ sive shop equipment and persor-«el of higher technical skill than are available :r organizational or field maintenance activities. DEPRESSION. Sensitivity-time control adjustment of initial gain at zero range. DEPRESSION CONTOUR. Closed contour, inside which the ground is at a lower elevation than outside. DEPTH. Limits, with respect to distance, within which objects may be seen with satisfactory definition under a given set of conditions. DEPTH OF CUT. Depth of which the stylus penetrates the record¬ ing lacquer of a recording disk. DEPTH PERCEPTION. Ability to see in depth or three dimensions. DERIVED UNITS. Units of a system of units which are derived from the fundamental units by the application of physical laws. DES (DESTROYER). Name occasionally applied to certain twin-en¬ gined fighter-bombers before and during World War II, namely the FW-187 and A-20 aircraft. DESICCANT. Chemical, such as silica gel, having the ability to absorb water from the air. Used to dehumidify packaged equipment. AFM 100-39 DES DESICCATOR. Unit containing a chemical which absorbs water from the air. Often used to keep the air dry in¬ side of a piece of equipment. design objectives. Electrical performance characteristics for com¬ munication circuits which are based on reason¬ able engineering estimates of the performance required, but which have not been confirmed by actual measurement of operating circuits. A design objective is, in reality, a projected stan¬ dard, to serve until such time as a system sta- dard can be established by actual measurement, under operating conditions, of the developed circuit. DESIGNATED ENGINEERING-INSTALLING AGENCY. , . „ Agency designated to perform the installation engineering or installation of a particular facil¬ ity. Designations conform to Air Force direc¬ tives, and while these responsibilities normally are Assigned to airways and air communications services or to air materiel commands, other major air commands also may be so designated. DESIGNATION. Name plate or marker; also, the information con¬ tained thereon. DESIGNATION STRIP. Strip of paper with a transparent covering used to mark the assignment of jacks or other appara¬ tus below it. DESK FAX. Western Union system employing compact fac¬ simile sets installed on the desk of the user. Connected to local Western Union facilities, the set eliminates the delivery and pickup of telegrams. DESK STAND. Movable pedestal or stand (adapted to rest on a desk or table) which serves as a mounting for a transmitter of a telephone set, and which ordinarily includes a hook for supporting the associated receiver when not in use. 1 APRIL 1959 DESTROYER. Name occasionally applied to certain twin-engined fighter-bombers before and during World War II, namely the FW-187 and A-20 aircraft. DESTRUCTOR Small unit containing an explosive charge, some¬ times used to damage the interior of a piece of equipment so that the enemy cannot use or re¬ construct the equipment. (Reference: DETONA¬ TOR.) DET (DETACHMENT). 1. Part of a unit separated from its main organ¬ ization for duty elsewhere. 2. Temporary military or naval unit formed from other units or parts of units. 3. Military or naval unit smaller than a com¬ pany. DETAIL. , , , 1. Measure of the sharpness of a recorded facsimile copy. Generally related to the number of lines scanned per inch. 2. Square root of the ratio between the number of scanning lines per unit length and the de¬ finition in the direction of the scanning line. A measure of the sharpness of the recorded fac¬ simile copy. DETECTION. 1. Process of extracting the audio or video-fre¬ quency component from the modulated RF sig- 2. Classified definition. (Reference: AFM 100- 50.) HETERODYNE Detection (or conversion) by Is of the heterodyne principle; used in the generation of the intermediate frequency of a superheterodyne receiver, and in making CW signals audible. PLATE Operation of a vacuum-tube detector at or near plate cutoff, so that the input signal is rectified in the plate circuit. RADIO. Detection of the presence of an object by radio location, without precise determination of its position. 39-203 1 APRIL 1959 AFM 100-39 DET DETECTOPHONE. Instrument for listening to conversation secretly, without the knowledge of the speakers. It con¬ sists essentially of a high-sensitivity, nondirec- tional microphone concealed in the room and con- ected to an amplifier and headphones in a near¬ by room. Sometimes the microphone feeds into a small radio transmitter of a wired wireless transmitter broadcasting over power lines, per¬ mitting the listener to be farther away. DETECTOR. 1. Rectifier tube, crystal, or dry disc by which a modulation envelope on a carrier, or the sim¬ ple off-on state of a carrier, may be made to drive a lower-frequency device. 2. Stage or circuit in a radio set that demodulates the RF signal into its audio or video component. 3. Receiver circuit which derives the desired sound from the modulated carrier wave. ANTENNA Device consisting of an antenna and electronic equipment to warn aircraft crew members of their being observed by radar sets. These units are usually located in the nose or tail of the aircraft and illuminate a light on one or more panels when radar signals are detected. BRADLEY. Single-stage, locked-in oscillator type of FM detector which uses a special hep- tode vacuum tube. DIODE. Diode used in a demodulation circuit. Detection may be half or full wave rectifica¬ tion. FIRST. Vacuum tube in a superheterodyne re¬ ceiver in whose circuit the signal being re¬ ceived and the local-oscillator signal are com¬ bined to produce the IF signal. (Reference: MIXER.) GRID-LEAK. Triode or multi-electrode tube in which rectification occurs because of electron current to the grid. The voltage associated with this flow through a high resistance in the grid circuit appears in amplified form in the plate circuit. HETERODYNE. Detector incorporating a local oscillator (called a beat-frequency oscillator), used to convert an incoming RF signal to an audible tone by the heterodyning process. PLATE-CIRCUIT. Detector functioning by vir¬ tue of nonlinearity in its plate-circuit charac¬ teristic. POWER. Detector tube which operates with plate voltage sufficiently high to allow hand¬ ling of strong input signals without appreci¬ able distortion. SECOND. Superheterodyne receiver stage that separates the intelligence from the modulated intermediate frequency. TRAVELING. RF probe which incorporates a detector; used to measure the standing wave ratio in a slotted-line section. DETECTOR BALANCED BIAS. Circuit that automatically limits the current through the second detector after a delay deter¬ mined by the constants. DBB prevents occur¬ rence of spurious signals. It is similar to the FPC. DETECTOR CIRCUIT. Portion of a receiver which recovers the audible signal from the modulated RF carrier wave. DETENT. Stop or checking device, as a pin, lever, etc., on a ratchet wheel or the like. DETONATOR. Small unit containing an explosvie charge, some¬ times used to damage the interior of a piece of equipment so that the enemy cannot use or re¬ construct the equipment. (Reference: DESTRUC¬ TOR.) DETUNE. Adjusting a circuit so that it is not resonant to an applied frequency. DEUTERIUM. Hydrogen isotope, the atomic weight of which is approximately 2, its atomic structure is the same as that of hydrogen except that a neutron is added to the nucleus. 39-204 1 APRIL 1959 AFM 100-39 DEU DEUTERON. Nucleus of deuterium, a hydrogen isotope hav- ing an atomic weight or mass of approxi¬ mately 2. DEV (DEVELOP). Subject to the action of chemical agents for the purpose of bringing to view the invisible or latent image produced by the action of light on a sensitized surface. DEVELOPMENTAL BROADCAST STATION. Station licensed to carry on development and research for the advancement of broadcast ser¬ vices. DEVELOPMENTAL MODEL. Model designed to meet performance require¬ ments of the specification or establish technical requirements for production equipment. This model need not have the required final form factor or necessarily contain parts of final de¬ sign. It may be used to demonstrate the repro¬ ducibility of the equipment. DEVIATION. 1. Term used in frequency modulation to indi¬ cate the amount by which the carrier or resting frequency increases or decreases when modu¬ lated. It is usually expressed in kilocycles. 2. Turning aside from a course. 3. Bending of light from its path. FLIGHT-PATH. Difference between the flight track of an aircraft and the flight path, expressed in terms of either angular or linear measurement. FREQUENCY. Frequency-modulation peak dif¬ ference between the instantaneous frequency of the modulated wave and the carrier fre¬ quency. MAXIMUM SYSTEM. Greatest deviation in fre¬ quency specified in the operation of a system. PHASE. Phase modulation peak difference be¬ tween the instantaneous angle of the modulated wave and the angle of the carrier. SLOPE. Difference between the projection in the vertical plane of the actual path of movement of an aircraft and the planned slope for the aircraft expressed in terms of either angular or linear measurement. DEVIATION ALARM. Unit which gives warning indication when syn¬ chroerror exists due to failure of excitation, am¬ plifier, etc. DEVIATION DISTORTION. Distortion in an FM reciever due to inadequate bandwidth and inadequate amplitude-modulation rejection or to inadequate discriminator linearity. DEVIATION RATIO. Term used in frequency modulation to indicate the ratio of the maximum amount of deviation of a fully modulated carrier to the highest audio frequency being transmitted. DEVIATIVE ABSORPTION. Absorption that occurs at frequencies near the critical frequency. It occurs in conjunction with the slowing up of radio waves near the critical frequency, upon reflection from the ionosphere. DEW. Atmospheric moisture which condenses, in liq¬ uid form, upon objects cooler than the air, es¬ pecially at night. DEW LINE (DISTANT WARNING LINE). Automatic radar warning net or fence which will extend for 3000 miles along the Arctic circle from Alaska to Greenland. This net is intended to give the earliest possible warning of the ap¬ proach of enemy planes. When hostile planes are, detected, a warning will be flashed to air defense command centers in Canada. From these centers, the alert will be relayed in a few seconds to American air defense centers. Automatic fea¬ tures incorporated in the radar equipment will eliminate the need for constant attention by hu¬ man observers. Hence, operation of the DEW LINE stations will require a greatly reduced number of personnel than that required by a standard radar station. DEW POINT. Temperature at which, under ordinary conditions, 39-205 AFM 100-39 DEW 1 APRIL 1959 condensation begins in a cooling mass of air. It varies with the specific humidity. DEXTROROTATORY. Name applied in the field of optics to sub¬ stances which rotate the plane of polarization to the right. DF (DIRECTION FINDER OR DIRECTION). 1. Radio aid to navigation which determines the direction of arrival of a radio signal by mea¬ suring the orientation of the wavefront or of the magnetic or electric vector of a radio wave. Direction-finding sets can be combined into nets to provide a fix on a transmitted signal. In addi¬ tion to purely navigation functions, such nets can be used for SAR and balloon tracking pur¬ poses. 2. Used by the British to indicate radar. DG (DOUBLE-GROOVE). Descriptive terminology of insulators. DG (DIFFERENTIAL GENERATOR) SYNCHRO AMPLIFIER. Synchro differential generator driven by servo system. Generally used with oscillator servo or deck-tilt correction. DGDP (DOUBLE-GROOVE, DOUBLE¬ PETTICOAT). Descriptive terminology of insulators. Dl (DEVIATION INDICATOR). DIAGNOSTIC ROUTINE. Electronic computer routine designed to locate either a malfunction in the computer or a mis¬ take in coding. (Reference: CHECK, PRO¬ GRAMMED.) DIAGONAL SYMMETRY AXIS. Synonymous with A-axis or X direction. DIAGRAM. Visual aid such as: schematics, maps, prints, charts, etc. APPLICATION SCHEMATIC. Pictorial repre¬ sentation in which symbols and lines are used to illustrate the interrelation of a number of circuits. BLOCK. Diagram in which the essential units of any system are drawn in the form of blocks, and their relation to each other indicated by appropriate connecting lines. SCHEMATIC CIRCUIT. Functional circuit dia¬ gram in which the component parts are repre¬ sented by schematic symbols. TACTICAL CIRCUIT. Line drawing of the cir¬ cuits of a communications net, showing the number, kind, and location of lines and all headquarters and subordinate units, within security requirements, by code names and co¬ ordinates. TRAFFIC. Chart, illustration, or drawing used to show the movement and control of traffic over a communication system. WIRING. Drawing that shows electrical equip¬ ments and/or component parts together with all the wiring that interconnects these equip¬ ments and/or parts. DIAL. Manually operated rotating device for producing direct current impulses for the control of dial switching equipment. START LAMP. Lamp used with automatic posi¬ tion dialing to indicate that the connecting circuit is ready to receive dial pulses. DIAL CABLE. Braided cord or flexible wire cable used to make a tuning knob control the position of the pointer or dial which indicates the frequency to which a radio receiver is tuned. DIAL CENTRAL OFFICE. Telephone or teletypewriter office where neces¬ sary automatic equipment usually is located for connecting two or more users together by wires for communication purposes. DIAL CORD. (Reference: DIAL CABLE.) DIAL EXCHANGE. Exchange in which all calls originate by mechani¬ cal dialing. DIAL LIGHT. Pilot lamp which illuminates dials such as the 39-206 1 APRIL 1959 AFM 100-39 DIA tuning dial of a radio receiver. DIAL OF A METER. Graduated circle, or circular arc, over which a dial pointer moves. DIAL POINTER OF A METER. Part of the register which moves over the dial and points to the number on the divisions of the dial. DIAL PULSE. Interruption in the direct current flowing through the loop of a calling telephone, produced by the opening and closing of the dial pulse springs of a calling telephone in response to the dialing of a digit. The current in the calling line loop is interrupted as many times as there are units in the digit dialed. That is, dialing of the digit 7, for example, generates 7 dial pulses (inter¬ ruptions in current flowing through the loop of the calling telephone). DIAL PULSE SPRINGS. Pair of normally closed springs of a dial assembly, which is opened and closed by the pulse cam a number of times corresponding to the digit dialed. DIAL SHUNT SPRINGS. Set of contact springs of a dial assembly which operate and shunt the receiver and transmitter of a dial telephone set whenever the dial is off normal (operated). Shunting of the receiver pre¬ vents pulse clicks from being heard in the re¬ ceiver during dialing. Shunting of the trans¬ mitter prevents its variable resistance from af¬ fecting the pulses generated in the calling line loop. DIAL SPEED AND PULSE RATIO TEST CIRCUIT. Test circuit, or component, of a test desk. DIAL SPEED AND PULSE RATIO TEST SET. Portable test set or a component of a test desk used to check the pulse speed and pulse ratio (percent make) of dials of dial telephone sets. A milliammeter on the front panel of the test set has two scales, one scale for registering dial pulse speeds in pulses per second, another scale for registering pulse ratios. DIAL SPEED INDICATOR. Portable dial speed test set or a component of a desk used to measure the pulse speed of dials. DIAL SPEED TEST UNIT. Unit used to measure dial speed at pulses per second. DIAL SYSTEM A BOARD. (Reference: SWITCHBOARD.) DIAL TELEPHONE. Type of calling device which, when wound up and released, generates pulses required for es¬ tablishing connections. DIAL TELEPHONE SET. Telephone set equipped with a dial. DIAL TELEPHONE SYSTEM. Telephone system in which telephone connec¬ tions between customers are ordinarily established by electronic and mechanical apparatus, con¬ trolled by manipulations of dials by the calling parties. DIAL TONE. Tone employed in a dial telephone system to in¬ dicate that the equipment is ready for the dial¬ ing operation. DIAL TRAIN OF A METER. Gear wheels and pinions used to interconnect the dial pointers. DIALING. To make connections with, by means of a dial; to manipulate a dial. COMPOSITE. Method of dialing between dis¬ tant offices over one leg of a composite set. LOOP. Return-path method of dialing in which the dial pulses are sent out over one side of the interconnecting line or trunk and are re¬ turned over the other side; limited to short- haul traffic. POSITION. Dialing over the regular position cord circuits by means of a relay circuit under control of a dial of the regular cord circuits. 39-207 AFM 100-39 DIA 1 APRIL 1959 SIMPLEX. Method of dialing over the simplex leg of a phantom group. VOICE FREQUENCY. Method of dialing by which the direct current pulses from the dial are transformed into voice-frequency, ac pulses. Used in long-haul intertoll dialing. DIALING CORD. Method of dialing by which the operator’s dial is connected to the outgoing line of trunk by means of a cord. DIALING KEY. Method of dialing in which a set of numerical keys is used to originate dial pulses instead of a dial. Generally used in connection with voice- frequency dialing. DIALYTE. Type of duplex lens in which the inner surfaces of the two elements of each half of the system are ground to different curvatures to correct for aberrations. The dissimilar faces cannot be cemented together. DIAM (DIAMETER). Any chord passing through the center of a figure or body. DIAMAGNETIC. Magnetic permeability less than one and hence less than that of a vacuum. Examples are Bis¬ muth and Antimony. DIAMAGNETIC MATERIAL. Material having a permeability less than that of a vacuum. DIAMOND ANTENNA. Horizontal rhombic antenna having four con¬ ductors forming a diamond pattern or rhombus. DIAPHRAGM. 1. Thin, flexible membrane used in various elec¬ troacoustic transducers to produce AF vibra¬ tions when actuated by electric impulses or ac¬ tuated by AF vibrations to control the produc¬ tion of electric impulses. 2. Electrolytic porous or permeable membrane, usually flexible, separating anode and cathode campartments. 3. Waveguide plate (or plates) placed trans¬ versely across the waveguide, not completely closing it, and usually introducing a reactive im¬ pedance. DIAPHRAGM RING FILTER. Waveguide filter in the form of an annular slot in a diaphragm. DIAPHRAGMLESS MICROPHONE. Microphone having no mechanical vibrating sys¬ tem. Instead, sound waves act directly on a frame, an arc, a glow discharge, or the ionized space between a Nernst glower and a cold electrode. DIATHERMY. Therapeutic use of HF current to generate heat within some part of the body. DICHROISM. Property of showing different colors when viewed in different directions. DICHROMATISM. Form of night blindness. DICING. Process in which a crystal wafer is sawed into blanks. DICKE FIX. Classified definition. (Reference: AFM 100-50.) DICTAPHONE RECEPTION. Recording of high-speed, radiotelegraph signals with a dictaphone or phonograph, which after¬ ward can be run slower for reading or copying the message. DID (DIGITAL INFORMATION DISPLAY). SAGE presentation of digital information in tubular form on the face of a digital-informa¬ tion-display tube. DIE CASTING. Casting of alloys in metal moulds or dies. There are pressure and gravity die casting, according to whether the metal is forced into the die. DIELECTRIC. Term applied to the insulating material between the plates of a capacitor. Air, paper, mica and oil are dielectrics. 39-208 1 APRIL 1959 AFM 100-39 DIE DIELECTRIC ABSORPTION. Property of imperfect dielectric whereby all electric charges within the body of the material caused by an electric field are not returned to the field. DIELECTRIC ANTENNA. Antenna which employs dielectric as the major component in producing the required radiation. DIELECTRIC CONSTANT. Property of a dielectric material that determines how much electrostatic energy can be stored per unit volume when unit voltage is applied. In effect, it is the ratio of the capacitance of a ca¬ pacitor filled with a given dielectric to that of the same capacitor having only a vacuum as dielectric. (Reference: PERMITTIVITY, SPE¬ CIFIC INDUCTIVE CAPACITANCE.) DIELECTRIC CURRENT. 1. Current flowing at any instant through any surface in an isotropic dielectric which is in a changing electric field. 2. Absorption current. 3. Decaying conduction current. DIELECTRIC FATIGUE. Property of some dielectrics in which its in¬ sulating quality decreases after a voltage has been applied for a considerable time. DIELECTRIC GUIDE. Class of waveguides consisting of a dielectric cy¬ linder surrounded by air. It is capable of pro¬ pagating electromagnetic waves through its in¬ terior in much the same way as sound waves travel through a speaking tube. DIELECTRIC HEATING. Use of RF energy to heat nonmetallic materials such as wood, plastics, or chemicals by causing them to act as a dielectric. The heat is produced by molecular friction. DIELECTRIC HYSTERESIS. Lagging of the electric field produced by appli¬ cation of an alternating voltage to a dielectric. It causes a dielectric hysteresis loss analogous to that of magnetic hysteresis. DIELECTRIC LOSS. Time rate at which electric energy is transformed into heat in a dielectric when it is subjected to a changing electric field. DIELECTRIC LOSS ANGLE. Difference between 90 degrees and the dielec¬ tric phase angle. DIELECTRIC LOSS FACTOR. Product of the dielectric constant of a material and the tangent of its dielectric loss angle. DIELECTRIC MATCHING PLATE. Waveguide dielectric plate used as an impe¬ dance transformer for matching purposes. DIELECTRIC PHASE ANGLE. Angular difference in phase between the sin¬ usoidal alternating potential difference applied to a dielectric and the component of the result¬ ing alternating current having the same period as the potential difference. DIELECTRIC POWER FACTOR. Cosine of the dielectric phase angle or sine of the dielectric loss angle. DIELECTRIC SEPARATOR. Apparatus for separating minerals from other ma¬ terials on the basis of differences in the dielec¬ tric constants of the materials to be separated. DIELECTRIC STRENGTH. Maximum potential gradient that a dielectric ma¬ terial can withstand without rupturing. The value obtained for the dielectric strength will depend on the thickness of the material and on the meth¬ od and conditions of test. DIELECTRIC SUSCEPTIBILITY. Polarization in a material per unit electric inten¬ sity. When k is dielectric susceptibility and K is the dielectric constant, k = (K-l)/4. DIELECTRIC TESTS. Tests which consist of the application of a volt¬ age higher than the rated voltage for a specified time for the purpose of determining the ade¬ quacy against breakdown of insulating materials and spacings under normal conditions. 39-209 AFM 100-39 DIE 1 APRIL 1959 DIELECTRIC WIRE. Waveguide consisting of a solid dielectric rod of the desired length, made of an insulating ma¬ terial. Used for transmission of radio waves over short distances between parts of a circuit at ultra-high frequencies. DIESEL. Internal-combustion engine differing from other internal-combustion engines in that its compres¬ sion is high enough to cause combustion to be spontaneous. DIESEL CYCLE. Cycle of events which occur in diesel engines similar to gasoline (Otto cycle) engines except that air without fuel is compressed to a high pressure. At the end of the compression stroke, fuel is injected into the hot compressed air and it burns immediately. DIESEL-ELECTRIC DRIVE. Self-contained system of power conversion in which a diesel engine operates an electric genera¬ tor that develops and supplies power to an elec¬ tric driving motor. DIFFERENCE IN DEPTH MODULATION. In directive systems employing overlapping lobes as modulating signals, a fraction obtained by sub¬ tracting from the percentage of modulation of the larger signal, the percentage of modulation of the smaller signal, and dividing by 100. DIFFERENCE OF POTENTIAL. Voltage between two points. DIFFERENTIAL. Pertaining to, or involving, a difference; for ex¬ ample, a differential current device is one which operates upon the basis of a difference in two current values. DIFFERENTIAL AMPLIFIER. Amplifier having two similar input circuits con¬ nected so as to respond to the difference be¬ tween two voltages or currents and effectively suppress voltages or currents which are alike in the two input circuits. DIFFERENTIAL ANALYZER. Electromechanical mathematical computer for solving linear and nonlinear problems. DIFFERENTIAL DUPLEX SYSTEM. System in which the sent currents divide through two mutually inductive sections of a receiving apparatus, connected respectively to the line and to a balancing artificial line in opposite direc¬ tions, so that there is substantially no net effect on the receiving apparatus. The received currents pass mainly through one section, or through the two sections in the same direction, and operate the apparatus. DIFFERENTIAL GAIN CONTROL. Device for altering the gain of a radio receiver in accordance with expected change of signal level, in order to reduce the amplitude differ¬ ential between the signals at the output of the receiver. DIFFERENTIAL GALVANOMETER. Galvanometer having two similar but opposed coils with currents that tend to neutralize each other. A zero reading is obtained when the currents are equal. DIFFERENTIAL INSTRUMENT. Galvanometer or other measuring instrument hav¬ ing two circuits or coils, usually identical, through which currents flow in opposite direc¬ tions. The difference or differential effect of these currents actuates the indicating pointer. DIFFERENTIAL MICROPHONE. Double-button carbon microphone. Extra sensi¬ tivity is obtained by using two carbon elements, one on each side of the diaphragm, so that a decrease in resistance of one button is accom¬ panied by an increase in resistance of the other button. DIFFERENTIAL PERMEABILITY. Ratio of the positive increase of normal induc¬ tion to the positive increase of magnetizing force when these increases are vanishingly small. DIFFERENTIAL PROTECTION. Effect of a device operative on a difference be¬ tween electrical quantities in excess of a prede¬ termined amount of ratio to cause and maintain the interruption of power in the circuit. 39-210 1 APRIL 1959 AFM 100-39 DIF DIFERENTIAL RELAY. 1. Relay that functions by reason of the differ¬ ence between two quantities of the same nature, such as two currents or two voltages. 2. Relay with two windings which assist or op¬ pose each other in moving the armature. DIFFERENTIAL SEL5YN. Selsyn in which both rotor and stator have similar windings that are spread 120° apart. The position of the rotor corresponds to the alge¬ braic sum of the fields produced by the stator and rotor DIFFERENTIAL SHRINKAGE. Difference in unit contraction along the grain structure of the material as compared to the unit contraction across the grain structure; frequently applied to photographic film and papers and to mapping in general. DIFFERENTIAL SYNCHRO. (Reference: SYNCHRO DIFFERENTIAL GEN¬ ERATOR, SYNCHRO DIFFERENTIAL MO¬ TOR.) DIFFERENTIAL WINDING. Coil winding arranged so that its magnetic field, and hence its effect, is opposite to that of a nearby coil. DIFFERENTIAL WOUND FIELD. Type of motor or generator field having both series and shunt coils that are connected to oppose each other. DIFFERENTIATING CIRCUIT. Circuit which produces an output voltage sub¬ stantially in proportion to the rate of change of the input voltage or current. Differentiating circuits employ time constants that are short com¬ pared to the duration of the pulse applied, thus differentiating the input pulse. DIFFERENTIATOR. 1. Electronic computer device, usually of the analog type, whose output is proportional to the derivative of an input signal. 2. Transducer whose output wave form is sub¬ stantially the time derivative of its input wave form. Such a transducer preceding a frequency modulator makes the combination a phase modu¬ lator; or, following a phase detector, makes the combination a frequency detector. Its ratio of output amplitude to input amplitude is propor¬ tional to frequency and its output phase leads its input phase by 90 degrees. DIFFERENTIATOR CIRCUIT. Circuit which produces an output voltage sub¬ stantially in proportion to the rate of change of the input voltage of current. Differentiating circuits employ short time constants compared to the time duration of the pulse applied. DIFFRACTED WAVE. When a wave in a medium of certain propaga¬ tion characteristics is incident upon a discontin¬ uity or a second medium, the diffracted wave is the wave component that results in the first medium in addition to the incident wave and the waves corresponding to the reflected rays of geometrical optics. DIFFRACTION. Effect produced when waves (light, sound, or radio) encounter a barrier and bend around it. DIFFRACTION ANGLE. Angle between the direction of an incident beam of light and any resulting diffracted beam. DIFFRACTION GRATING. Screen having 1,000 to 50,000 lines per inch on a polished metal or glass surface, used to pro¬ duce a spectrum by interference between colors of light passing through or reflected by the grat¬ ing. DIFFUSE. In all directions, not in any sharply defined path. Applicable to reflection, refraction, or transmis¬ sion of light and other waves. DIFFUSE REFLECTION. Type of reflection obtained from a relatively rough surface in which the reflected rays are scattered in all directions. DIFFUSE REFLECTOR. Reflector or mosaic of reflectors that scatter in¬ cident radiation in all directions. 39-211 AFM 100-39 DIF 1 APRIL 1959 DIFFUSED SOUND. Sound is said to be in a perfectly diffused state when in the region considered, the energy den¬ sity, averaged over portions of the region com¬ pared to the wavelength, is uniform and when all directions of energy flux at all parts of the region are equally probable. DIFFUSING SURFACES AND MEDIA. Surfaces which break up the incident light and distribute it more or less in accordance with the cosine law, as, for example, rough plaster and opal glass. DIFFUSION. Scattering of radiation by reflection or transmis¬ sion. Diffused reflection results when light strikes an irregular surface such as a frosted win¬ dow or the surface of a frosted or coated light bulb. When light is diffused, no definite image is formed. DIFFUSION PUMP. Type of vacuum pump in which mercury vapor or other heavy molecules in a stream or jet carry gas molecules before them. Mercury vapor diffu¬ sion pumps are extensively used in producing high vacuums in vacuum tubes. DIG (DELIVERY INDICATING GROUP). Delivery group which, while indicating a speci¬ fic set of addressees may also indicate the iden¬ tity of the originator and show which addressees are action or information. DIG-IN ANGLE. Stylus cutting angle such that the point is driving into the coating. It is the opposite of drag angle. DIGIT. 1. One of the successive series of pulses incom¬ ing from a dial to operate a switching train. (Reference: POSITIONAL NOTATION.) DIGITAC. Airborne digital computer developed by Hughes Aircraft Co. It was designed for use in tactical bombing and navigation. Although Digitac itself never went into production it served as a proto¬ type for further development of airborne digital computers. One digital computer will perform all the functions which require individual analog computers, such as fire control, navigation, and automatic flight control. Digital computers will also handle new or different problems without major internal change. DIGITAL COMPUTER. Computer in which quantities are represented in numerical form and which generally is made to solve complex mathematical problems by inera- tive use of the fundamental processes of addition, subtraction, multiplication, and division. DIGITAL DATA. Information expressed in numerical values based upon some particular base numbering system. DIGITAL DATA RECEIVER. Device for accepting digital signals in audio form from a data circuit and for presenting these signals in pulse form to digital equipment. DIGITAL DATA TRANSMITTER. Device for transmitting digital signals in pulse form and presenting these signals in audio form to digital equipment. DIGITAL INFORMATION DISPLAY. Presentation of digital information in tubular form on the face of a digital-information-display tube. DIGITAL INFORMATION DISPLAY TUBE. Small cathode-ray tube on which digital infor¬ mation is displayed. DIGITALIZED DATA. Data presented in a number of digit forms for electrical transmission. This data includes output information from electronic data processing equipment (EDPE), high speed data transmis¬ sion terminals, digital computers, data transceiv¬ ers, magnetic tape, punched card readers, tele¬ type and digitalized facsimile, and voice equip¬ ment. DIHEPTAL BASE. Vacuum tube base having 14-pin sockets, used for cathode-ray tubes. 39-212 1 APRIL 1959 AFM 100-39 DIM DIMMER. Control for varying the intensity of illumination on pilot, scale, or dial lights. DINA. Airborne radar jamming transmitter, AN/APT-1. It operates in the 92-210 MC band with an output of 30 watts, and weighs 70 pounds. Ener¬ gy radiated is noise, contained in one sideband. The carrier and other sideband are suppressed. This set is similar to the Navy AN/SPT-1 equip¬ ment. It is used on spot or barrage jamming. DIODE. Vacuum tube with two electrodes, a cathode and a plate; used principally as: (1) detector and as (2) rectifier for converting alternating currents to pulsating currents. DIODE CUPPER. Two element vacuum tube which can be adjusted to remove any unwanted portion, positive or negative, of a signal by biasing. (Reference: CLIPPER.) DIODE DETECTOR. Diode used in a demodulation circuit. Detection may be half or full wave rectification. DIODE LIMITER. Peak limiting circuit employing a diode that be¬ comes conductive when signals peaks exceed a predetermined value. DIODE MIXER. Diode in an RF line which mixes incoming radio frequency and local oscillator signals to produce an intermediate frequency. (Reference: MIXER.) DIODE PEAK DETECTOR. Diode used in a circuit to indicate when audio peaks at the transmitter exceed a predetermined value. DIODE RECTIFICATION. Half-wave rectification by means of a diode which depends on the fact that a diode passes current in one direction only. DIODE SWITCH. Diode which is made to act as a switch by the successive application of positive and negative biasing voltages to the anode (relative to the cathode). This allows or prevents, respectively, the passage of other applied wave forms within certain limits of voltage. DIODE-PENTODE. Vacuum tube having a diode and a pentode in the same envelope. DIODE-TRIODE. Vacuum tube having a diode and a triode in the same envelope. DIOPTER. Unit of optical measurement which expresses the refractive power of a lens or prism. DIOPTER MOVEMENT Term applied to adjustment of the eyepiece of an instrument to provide accommodation for eye¬ sight variations of individual observers. DIOPTER SCALE. Scale usually found on the focusing nut of the eyepiece of an optical instrument. It measures the change in refracting power of the eyepiece in diopters to introduce a correction to compen¬ sate for the nearsightedness or farsightedness of the individual observer. It permits presetting of the instrument if the observer knows his diopter correction. DIPLEX OPERATION. Simultaneous transmission or reception of two signals using a specified common feature, such as a single antenna or a single carrier. DIPLEX TRANSMISSION. Simultaneous transmission of two signals by means of some common feature, such as a single carrier or a single antenna. DIPLEXER. 1. Coupling system which allows a radar and a communications transmitter to utilize simultane¬ ously or alternately the same antenna. 2. Coupling unit in radio which allows more than one transmitter to operate together on the same antenna. 39-213 AFM 100-39 DIP 1 APRIL 1959 DIPOLE. Molecule in which the centroid (effective cen¬ ter) of the positive charges is at a different point from the centroid of the negative charges. DIPOLE ANTENNA. Straight radiator, usually fed to the center, and producing a maximum of radiation in the plane normal to its axis. DIPOLE DISK FEED. Antenna consisting of a dipole near a disk, which is used to reflect energy to the disk. DIRECT COMPONENT OF CURRENT. Drift of electrons in one direction while current is flowing, whether or not there are reversals of the direction of electron flow at regular intervals during the period of current flow. DIRECT COMPONENT OF VOLTAGE. Portion of a pulsating voltage which is responsi¬ ble for the drift of electrons in one direction while the pulsating voltage is applied to a con¬ ductor. DIRECT COUPLING. 1. Association of two or more circuits by means of a self-inductance, capacitance, resistance or a combination of these which is common to the cir¬ cuits. 2. That type of interconnection between tubes in amplifiers or other electronic equipment wherein the plate of the preceding tube is connected di¬ rectly to the grid of the following tube. DIRECT CURRENT. Unidirectional electric current flowing through a circuit in one direction, and essentially constant in magnitude. DIRECT CURRENT AMPLIFIER. Amplifier capable of amplifying dc voltages. It generally employs between stages either resis¬ tive coupling alone or resistive coupling com¬ bined with other forms of coupling. DIRECT DISTANCE DIALING. Method of making toll calls under which the call can be dialed directly without the services of a telephone company operator. DIRECT DRIVER. Direct shaft-to-shaft connection between the driv¬ ing and driven parts of a rotating system, avoid¬ ing the use of belts and pulleys. DIRECT ELECTROMOTIVE FORCE. Unidirectional electromotive force in which the changes in values are either zero or so small that they may be neglected. DIRECT FEEDER. Feeder which connects a generating station, sub¬ station, or other supply point to one point of utilization. DIRECT GRID BIAS. Direct component of grid voltage; commonly called grid bias. DIRECT INDUCTIVE COUPLING. Association or linking of one circuit with anoth¬ er by means of inductance that is common to both circuits. Often obtained by connecting one circuit directly to a tap on a coil in another circuit. DIRECT MANUAL CONTROL. Arrangement of controls in which the control handles are directly attached to their switching devices. DIRECT OPERATION. Operation by means of a mechanism connected directly to the main operating shaft, or an ex¬ tension of it. DIRECT PIEZOELECTRICITY. Name sometimes given to the piezoelectric ef¬ fect in which an electric charge is developed on a crystal by the application of mechanical stress. DIRECT POINT. Device which receives signals over a line and re¬ peats corresponding signals directly into another line or lines without the interposition of any other repeating or transmitting apparatus. DIRECT RECORDING. Facsimile recording where the record sheet is usable without further processing. Examples of direct recording are barbon pressure, electrolytic, Stenafax, Timefax, and Teledeltos. 39-214 1 APRIL 1959 AFM 100-39 DIR DIRECT RESISTANCE-COUPLED AMPLIFIER. Amplifier in which the plate of one stage is con¬ nected either directly or through a resistor to the control grid of the next stage, with the plate load resistor being common to both stages. Used to amplify small changes in direct current. DIRECT RHOMBOHEDRON. Identical with the major r (1010) rhombohedron of a crystal. DIRECT SCANNING. Scanning method in which the subject is illum¬ inated at all times and only one elemental area of the subject is viewed at a time by the televi¬ sion camera. DIRECT VOLTAGE. Voltage that forces electrons to move through a circuit in the same direction continuously, thereby producing a direct current. DIRECT WAVE. 1. Wave that travels directly between the trans¬ mitter and receiver without reflections from any object. 2. Wave that is propagated directly through space. DIRECT-ACTING RECORDING INSTRUMENT. Recording instrument in which the working de¬ vice is mechanically connected to, and directly operated by, the moving element. DIRECT-ARC FURNACE. Furnace in which the heat-producing arc is formed between the electrodes and the charge. DIRECT-CURRENT BALANCER. Machine which comprises two or more similar dc machines connected in series across the outer conductors of a multiple-wire system of distri¬ bution, for the purpose of maintaining the po¬ tentials of the intermediate conductors of the system which are connected to the junction points between the machines. DIRECT-CURRENT COMMUTATING MACHINE. Rotating machine which consists of a magnetic field excited from a dc source (or formed of permanent magnets), an armature, and a com¬ mutator. Specified types of dc commutating ma¬ chines are: generators, motors, synchronous con¬ verters, boosters, balancers, and dynamotors. DIRECT-CURRENT CONDUCTANCE. Conductance for an unvarying potential differ¬ ence (usually called single conductance). Direct- current conductance is the reciprocal of dc re¬ sistance. DIRECT-CURRENT DISTRIBUTION. Supply to points of utilization of electric energy by direct current from its point of generation or conversion. DIRECT-CURRENT ERASING HEAD. Magnetic recording head which uses direct cur¬ rent to produce the magnetic field necessary for erasing. Dc erasing is achieved by subjecting the medium to an unidirectional field. Such a medi¬ um is, therefore, in a different magnetic stage than one erased by alternating current. DIRECT-CURRENT QUADRUPLEX SYSTEM. Dc telegraph system which affords simultaneous transmission of two messages in each direction over the same line, operating by superposing neutral telegraph upon polar telegraph. DIRECT-CURRENT RESISTANCE. Circuit resistance to an unvarying current. DIRECT-CURRENT RESTORER. Means, used in a circuit incapable of transmit¬ ting slow variations but capable of transmitting components of higher frequency, by which a dc or low frequency component is reinserted after transmission. (Reference: CIRCUIT, CLAMP¬ ING.) * DIRECT-CURRENT TELEGRAPHY. Form of telegraphy in which, to form the trans¬ mitted signals, direct current is supplied to the line under the control of the transmitting ap¬ paratus. DIRECT-CURRENT TRANSMISSION. Transfer of electrical energy by direct current from its source to one or more main receiving stations. 39-215 AFM 100-39 DIR 1 APRIL 1959 DIRECT-RELATION TELEMETER. Telemeter in which the translating means (volt¬ age, current, frequency, etc.) increases in value with an increase in the measured quantity. DIRECT-WIRE CIRCUIT. In a supervised protective signaling circuit usu¬ ally consisting of one metallic conductor and a ground return and having signal-receiving equip¬ ment responsive to either an increase or a de¬ crease in current. DIRECTED NET. Net in which no station other than the net con¬ trol station may communicate with any other sta¬ tion, except for the transmission of urgent mes¬ sages, without first obtaining the permission of the net control station. DIRECTION. Position of one point in space relative to another, without reference to the distance between them; may be either three-dimensional or two-dimen¬ sional. Direction is not an angle, but is often indicated in terms of its angular distance from a reference direction. DIRECTION CENTER. Physical facility of an air defense sector head¬ quarters from which active air-defense func¬ tions are directed. The direction center is equip¬ ped with an AN/FSQ-7 Combat Direction Cen¬ tral. DIRECTION CENTER ACTIVE. Complete direction center computer program which directs the computer in the performance of air-defense functions. DIRECTION FINDER. Radio aid to navigation which determines the di¬ rection of arrival of a radio signal by measuring the orientation of the wavefront or of the mag¬ netic or electric vector of a radio wave. Direction finding sets can be combined into nets to provide a fix on a transmitted signal. In addition to purely navigational functions, such sets can be used for SAR and balloon tracking purposes. DIRECTION FINDER BEARING INDICATOR. Instrument which is used with an airborne radio direction finder to indicate the relative, magnetic, or true bearing of a station from an aircraft, or the reciprocal of this bearing. A direction¬ finder bearing indicator of the manual type is known as an MDF bearing indicator, and one of the automatic type is known as an ADF bearing indicator. DIRECTION OF INDUCED CURRENT. Current induced in a conductor as a result of the conductor’s motion in a magnetic field in such a direction as to exert a mechanical force opposing the motion. DIRECTION OF LAY. Lateral direction in which the strands of a cable run over the top of the cable as they recede from an observer looking along the axis of the cable. DIRECTION OF POLARIZATION. 1. Direction of electrical lines of force. 2. For a mode possessing at any cross section two, and only two, axes of symmetry or antisym¬ metry at right angles, the direction of polariza¬ tion is the direction of the electric field at, or limitingly near to, the intersection of the axes. 3. In a linearly polarized wave, the direction of the displacement vector. In an electromagnetic wave, the direction of the electric displacement is taken as the direction of polarization. DIRECTION OF PROPAGATION. Point in a homogeneous isotropic medium where the direction of propagation is the normal to an equiphase surface taken in the direction of in¬ creasing phase lag. DIRECTION RECTIFIER. Rectifier which supplies a dc voltage varying in magnitude and polarity with the magnitude and relative polarity of an ac selsyn error voltage. DIRECTION-FINDER DEVIATION. Sum of the systematic and random angular dif¬ ference between the indicated bearing and the correct bearing caused by characteristics of the receiving aircraft or station. 39-216 1 APRIL 1959 AFM 100-39 DIR DIRECTION-FINDING RECEIVERS. Receivers used in conjunction with radio direc¬ tion finders. (Reference: DIRECTION FIND¬ ER.) DIRECTION-FINDING STATION. Shore radio station having equipment for deter¬ mining the direction of arrival of radio waves from ships or aircraft. DIRECTIONAL ANTENNA. Antenna which radiates or receives radio waves more effectively in some directions than others. The term is usually applied to antennas whose directivity is larger than that of a half-wave di¬ pole. DIRECTIONAL CHARACTERISTIC. Expression of the behavior of an antenna or electroacoustic transducer with respect to direc¬ tion. DIRECTIONAL CONTROL. Qualifying term applied to a protective relay or relay scheme which indicates a means for prevent¬ ing the protective relay or scheme from function¬ ing until the power is in a predetermined direc¬ tion. DIRECTIONAL COUPLER. 1. Coupling between a waveguide and another waveguide or external circuit in such manner that the direction of energy flow in the latter is re¬ lated to the direction of energy flow in the former. 2. Device used to extract a portion of the RF energy moving in a given direction in a transmis¬ sion line. Energy moving in the opposite direc¬ tion is rejected. (Reference: DIRECTIVE FEED.) DIRECTIONAL FILTERS. In some carrier systems a particular range of frequency is used for east to west paths, and a certain other range for west to east paths. The filters provided to separate these two frequency ranges are known as directional filters, or direc¬ tional separation filters. Directional filters may be conventional low-pass, high-pass, or band-pass filters, the "directional” appellation indicating only the usage. DIRECTIONAL FLOODLIGHT SYSTEM. Landing-area floodlight system so operated that aircraft land essentially parallel with the direc¬ tion of the rays. DIRECTIONAL HOMING. Procedure of following a path in which the ob¬ jective is maintained at a constant relative bear¬ ing. DIRECTIONAL MICROPHONE. Microphone with a response designed to vary with the direction of sound incidence. DIRECTIONAL OVERCURRENT PROTECTION. Effect of a device, operative on a current in ex¬ cess of a predetermined amount and in a prede¬ termined direction, to cause and maintain an in¬ terruption of power in the circuit. DIRECTIONAL PATTERN (RADIATION PATTERN). Graphical representation of the radiation intensi¬ ty or reception gain of an antenna as a function of direction. Cross sections, in which directional patterns are frequently given, are the vertical and horizontal planes, or the principal electric and magnetic polarization planes. DIRECTIONAL RECEPTION. Method of reception capable of accepting or re¬ jecting signals received from a given direction or directions. DIRECTIONAL RELAY. Relay which functions in conformance with the direction of power, voltage, current, pulse, rota¬ tion, etc. DIRECTIONAL SEPARATION FILTERS. In many carrier systems, a certain range of fre¬ quency is used for east to west paths, and a cer¬ tain other range for west to east paths. The filters provided to separate these two frequency ranges are known as directional filters, or direc¬ tional separation filters. DIRECTIVE. 1. Military communication in which a policy is established or a specific action is ordered. 2. Plan issued with a view to placing it in effect when so directed, or in the event that a stated contingency arises. 39-217 AFM 100-39 DIR 1 APRIL 1959 3. Broadly speaking, any communication which initiates or governs action, conduct, or procedure. DIRECTIVE FEED. Device used to extract a portion of the RF energy moving in a given direction in a transmission line. Energy moving in the opposite direction is rejected. (Reference: DIRECTIONAL COU¬ PLER.) DIRECTIVE GAIN. The ratio of the radiation intensity in a given direction to the power radiated in the same direc¬ tion by a standard antenna with the input power kept constant. In a given direction, it is A times the ratio of the radiation intensity in that direc¬ tion to the total power radiated by the antenna. DIRECTIVITY. 1. Characteristic of an antenna which makes it radiate or receive more energy in some directions than in others. 2. Value of the directive gain of an antenna in the direction of its maximum value. DIRECTIVITY ANGLE. Elevation angle of the optimum radius vector of a directive diagram. DIRECTIVE FACTOR. Directivity factor of a directional transducer in any direction is the ratio of the power received or delivered by the transducer in that direction, to the power in the direction of maximum re¬ sponse. DIRECTIVITY INDEX. Defined as 10 log D, where D is the directivity factor. DIRECTLY HEATED CATHODE. Filament cathode which carries its own heating current for electron emission, as distinguished from an indirectly heated cathode. DIRECTOR. 1. Parasitic antenna element located in the gen¬ eral direction of the major lobe of radiation for the purpose of increasing radiation in that direc¬ tion. 2. Telephone switch which translates the digits dialed into the directing digits actually used to switch the call. FIGHTER. Officer on the staff of a tactical air director responsible for direction of such air warning facilities and aircraft as may be allo¬ cated to him for the defense of his area. (Ref¬ erence: AIR CONTROLLER.) SENIOR. Officer who is responsible for the op¬ eration of an air defense direction center, and for the conduct of air defense within a sub¬ sector. TRAFFIC. Radar controller proficient in the identification and directing of aircraft in a de¬ sired traffic pattern, and proficient in main¬ taining suitable separation between aircraft and aircraft tracks so as to allow an expeditious flow of air at all times. DIRECTOR ELEMENT. Undriven element on an antenna so situated with respect to its associated driven element that the direction of maximum radiation from the radiat¬ ing element is toward the director element. DIRECTOR (DEPUTY) OPERATIONS. Member of the battle staff responsible for super¬ vision of air-defense operations within the organ¬ ization area of responsibility. DIRECTORY NUMBER. Full complement of digits required to designate a subscriber in the directory. In a 5, 6, or 7-digit exchange area, the directory number consists of office code followed by four numerals. In some areas a station letter, to control selective ringing, follows the four numerals and is considered part of the number. DirPacALDocks (DIRECTOR PACIFIC AND ALASKAN DIVISION, BUREAU OF YARDS AND DOCKS). DISCERNIBLE DIFFERENCE OF CONVERGENCE ANGLES. Differences in the angles of view from the two eyes to objects or parts of objects. 39-218 1 APRIL 1959 AFM 100-39 DIS DISCHARGE. Release of stored-up electricity. In a storage bat¬ tery, the conversion of the chemical energy of the battery into electric energy. DISCHARGE CIRCUIT OF SURGE GENERATOR. Portion of a surge generator connection in which exists the current and voltage variations consti¬ tuting the generated surge. DISCHARGE CURRENT OF LIGHTNING ARRESTOR. Surge current which flows through the arrestor upon application of a lightning or test surge to its terminals. DISCHARGE KEY. Device for switching a capacitor suddenly from a charging circuit to a load through which it can discharge. DISCHARGE LAMP. Lamp in which light is produced by the lumines¬ cence of a gas or vapor at low pressure, through which an electric discharge is passed between suitable electrodes. Fluorescent materials are sometimes used on the inner surface of the glass envelope to increase the illumination, as in ordi¬ nary fluorescent lamps. DISCHARGE TUBE. Evacuated inclosure containing a gas at low pres¬ sure which permits the passage of electricity through the gas upon application of sufficient voltages. The tube is usually provided with metal electrodes, but one form permits an electrodeless discharge with induced voltage. DISCHARGING CURRENT. 1. Correct rate at which a particular battery should be discharged. 2. Current provided by a battery during dis¬ charge. 3. Current obtained by discharging a capacitor. DISCONNECT SIGNAL. Signal transmitted from one end of a subscriber line or trunk to indicate at the other end that the established connection should be released. DISCONNECTING SWITCH. Form of air switch used for changing connections in a circuit or system, or for isolating purposes. DISCONNECTOR RELEASE. Disengage apparatus used in a telephone connec¬ tion to restore it to its condition when not in use. DISCONTINUITY. Abrupt change at a point in the physical rela¬ tions of electric supply and communication cir¬ cuits or in electrical constants of either circuit which would materially affect the coupling. DISCREET ADDRESS SYSTEM. Ground/air data link under development by the Navy. DISCRETE SENTENCE INTELLIGIBILITY. Percentage of the total number of spoken sen¬ tences which is correctly understood, when each sentence conveys a simple idea and is of a form to test the observer’s acuteness of perception rather than his intelligence. DISCRETE WORD INTELLIGIBILITY. Percentage of the total number of spoken words which is correctly understood when the words are spoken so as to have no contextual relation between them. DISCRIMINATE. Undisguised system indicator. DISCRIMINATION. Difference between the losses, system or trans¬ ducer, in db at specified frequencies with the sys¬ tem or transducer terminated in specified imped¬ ances. # DISCRIMINATOR. 1. Device in which amplitude variations are de¬ rived in response to frequency or phase varia¬ tions. 2. Part of a receiver circuit which removes the desired signal from an incoming FM carrier wave by changing modulations in terms of frequency variation into amplitude variation. AFM 100-39 DIS 1 APRIL 1959 3. Facsimile auxiliary device between the radio receiver and the recorder which converts an audio frequency shift facsimile signal to an am¬ plitude modulated facsimile signal. 4. Circuit, the output voltage of which varies in amplitude and polarity in accordance with the frequency of the applied signal. It is used as a detector in an FM receiver. DISPENSING RATE. Rate at which chaff is dispensed, measured in units per minute, or per second. DISPERSION. 1. Separation of a wave into its component fre¬ quencies. 2. Scattering of a microwave beam caused by an obstruction. DISH. Reflector the surface of which is concave, as, for example, a part of a sphere or of a paraboloid of revolution. Primarily used as a microwave antenna. DISINTEGRATION. Emission of alpha and beta particles by a radio¬ active atom. DISINTEGRATION OF FILAMENT. Burning out of a filament due to normal end of life or to bombardment by heavy ions. DISINTEGRATION PRODUCT. Changed substance that remains after loss of al¬ pha particles due to radioactivity. DISK. Complete phonograph record or the blank used in a sound recorder. DISK RECORDING. Recording made from the reproduction of a re¬ cording. (Reference: RERECORDING DUB¬ BING.) DISPATCH. Message, usually an official communications, sent from one person to another. DISPATCHER. One who dispatches something, as an aircraft dis¬ patcher. DISPENSER. Machine which automatically dispenses units of chaff from an aircraft. DISPENSING. Act of ejecting chaff. 3. Separation of white light into its component colors. 4. Variation of the refractive index of a sub¬ stance with the frequency of the light passing through it. DISPLAY. Visual presentation of a received signal. OFF-CENTER PPI. Modified type of PPI pre¬ sentation in which the sweep origin can be dis¬ placed to one side or moved off the face of the cathode-ray tube as a means of expanding the presentation. This action provides better reso¬ lution and reduces the area under observation. OPEN-CENTER. PPI display on which zero range corresponds to a ring around the cen¬ ter of the display. TYPE B. Type of presentation on a radar indi¬ cator in which the signal appears as a bright spot, with bearing as the horizontal coordinate and range as the vertical coordinate. (Refer¬ ence: RANGE-BEARING DISPLAY.) TYPE C. Type of presentation on a radar indi¬ cator in which the signal appears as a bright spot, with bearing as the horizontal coordinate and elevation angle as the vertical coordinate. TYPE D. Type of presentation on a radar indi¬ cator which combines type B and C displays. The signal appears as a bright spot, with bear¬ ing plotted horizontally and elevation and range plotted vertically. TYPE E. Modification of type B display. The signal appears as a bright spot, with range plotted horizontally and elevation plotted ver¬ tically . 39-220 1 APRIL 1959 AFM 100-39 DIS TYPE EPI. Expanded position indicator. Dis¬ plays an expanded sector from PPI presenta¬ tion. TYPE F. Type of presentation on an indicator in which a single signal appears as a bright spot. Bearing angle is plotted horizontally and elevation angle is plotted vertically. TYPE G. Similar to type F display. A single signal appears as a bright spot with wings that grow as distance to the target is dimi¬ nished. Bearing angle is plotted horizontally and elevation angle is plotted vertically. TYPE H. Modification of the type B display. The signal appears as a bright line, the slope of which is proportional to the line of the angle of elevation. Bearing is plotted hori¬ zontally and range is plotted vertically. TYPE I Type of presentation on a radar indi¬ cator used to indicate range and direction with a conically scanning antenna. The signal ap¬ pears as a circular segment with radius pro¬ portional to range. Brightest part of the circle indicates direction from axis of cone to the target. TYPE J. Modification of the type A display. The sweep provides a circular range scale near the circumference of the cathode-ray tube. Sig¬ nals appear as radial deflections of the sweep. No bearing indication is given. TYPE K. Modification of the type A display. Employs a double trace with the second trace superimposed and offset for use with lobe¬ switching radar. Gives range and either bear¬ ing or elevation. TYPE L. Modification of the type A display. Employs a double trace back-to-back for aim¬ ing a lobe-switching radar. Gives range and either bearing or elevation. TYPE M. Modified type A display with a mov¬ able step or ditch for accurate range measure¬ ment. TYPE N. Modified type A display. Employs a double trace with a movable step or ditch for accurate range measurement. TYPE PPI. Type of presentation on a radar in¬ dicator in which the signal appears as a bright spot, with range indicated by distance from the center of the screen and bearing by its radial angle. DISPLAY WINDOW. Width of the portion of the frequency spectrum presented on panoramic type presentation. Ex¬ pressed in frequency units, usually megacycles. DISRUPTIVE DISCHARGE. Sudden and large increase in current through an insulating medium due to complete failure of the medium under electrostatic stress. DISSEMINATION. Classified definition. (Reference: AFM 100-50.) DISSIPATION. Waste of energy, as by the production of unde¬ sired heat in a circuit. DISSIPATIVE SYSTEM. System that does not conserve energy. DISSOCIATION THEORY. Theory by which eleotrolytic conduction is ex¬ plained by assuming that substances in solution are dissociated into positive and negative ions that travel in opposite directions carrying their respective charges. DISSONANCE. 1. Formation of maxima and minima by the super¬ position of two sets of interference fringes from light of two different wave lengths, i.e., what may be called stationary beats or secondary inter¬ ference. 2. Musical discord. DISSYMMETRICAL TRANSDUCER. Transducer, the input and output image imped¬ ances of which are unequal in magnitude or phase or both. DISTANCE. Range. 39-221 AFM 100-39 DIS 1 APRIL 1959 DISTANCE MARKING LIGHTS. Lights indicating distances on the approach path from the threshold lights. DISTANCE MEASURING EQUIPMENT. Radio-navigation aid in the aeronautical radio¬ navigation service that determines the distance of the interrogator from a transponder by meas¬ uring the time of transmission to and from the transponder. DISTANCE OR RANGE MARK. Mark on a cathode-ray screen which indicates the distance from the radar set to a target. DISTANCE PROTECTION. Effect of a device operative within a predeter¬ mined electrical distance on the protected circuit to cause and maintain an interruption of power in a faulty circuit. DISTANCE RELAY. Protective relay, the operation of which is a func¬ tion of the distance between the relay and the point of fault. DISTANT LINE. Trace of the apparent, or visible, horizon on an oblique photograph used as an approximation to the terrestrial horizon trace when the latter is not identifiable. (Reference: HORIZON.) DISTILLATION. Separation of the more volatile parts of a petro¬ leum oil from those less volatile by vaporization and, subsequently, condensation. DISTORTION. 1. Undesired change in wave form. The princi¬ pal sources of distortion are: (a) a nonlinear re¬ lation between input and output at a given fre¬ quency, (b) non-uniform transmission at differ¬ ent frequencies, and (c) phase shift not propor¬ tional to frequency. In certain types of electronic equipment wave form distortion is sought to sat¬ isfy a desired need, as for instance to produce one frequency from another. 2. Facsimile condition which causes the recorded copy to be other than a perfect reproduction of the transmitted copy. AMPLITUDE. Distortion occurring in an ampli¬ fier or other device when the amplitude of the output is not a linear function of the input amplitude. AMPLITUDE VS. FREQUENCY. Distortion caused by the nonuniform attenuation or gain of the system, with respect to frequency under specified terminal conditions. ATTENUATION. Departure, in a circuit or sys¬ tem, from uniform amplification or attenua¬ tion over the frequency range required for transmission; the effect of such departure on a transmittal signal. BIAS. Teletypewriter transmission system uni¬ form lengthening or shortening of the mark or space elements, one at the expense of the other. CHARACTERISTIC. 1. Displacement of signal transitions resulting from the persistence of transients caused by preceding transitions. 2. Teletypewriter transmission system repeti¬ tive displacement or disruption peculiar to spe¬ cific portions of a signal. There are two types of characteristic distortion; line characteristic distortion and equipment characteristic distor¬ tion. DELAY. Distortion which occurs when the en¬ velope delay of a circuit or system is not con¬ stant over the frequency range required for transmission. DEVIATION. Distortion in an FM receiver due to inadequate bandwidth and inadequate am¬ plitude-modulation rejection or inadequate dis¬ criminator linearity. END. 1. Start-stop teletypewriter shifting of the end of all marking pulses from their proper positions in relation to the beginning of the start pulse. 39-222 1 APRIL 1959 AFM 100-39 DIS 2. Special type of telegraph signal distortion created for testing purposes. It has the effect of advancing or delaying the end of each mark¬ ing selecting impulse with respect to the be¬ ginning of the character cycles or the initial M-S transition. EQUIPMENT CHARACTERISTIC. C Teletype¬ writer transmission repetitive displacement or disruption peculiar to specific portions of a signal; it is normally caused by maladjusted or dirty contacts of the sending or receiving equipment. FORTUITOUS. Teletypewriter transmission ran¬ dom displacement, splitting, and/or breaking up of the mark and space elements. FREQUENCY. 1. Distortion which occurs as a result of failure to amplify or attenuate equally all frequencies present in a complex wave. 2. Impairment of fidelity introduced by a transducer as a result of the unequal transfer of frequencies. GEOMETRIC. Television abberation which caus¬ es the reproduced picture to be geometrically dissimilar to the perspective-plane projection of the original scene. HARMONIC. Production of harmonic frequen¬ cies by the non-linearity of a transducer when a sinusoidal voltage is applied to the input. The amplitude of distortion is usually a func¬ tion of the amplitude of the input signal. INTERMODULATION. Distortion which re¬ sults from intermodulation. KEYSTONE. Distortion produced by scanning in a rectilinear manner, with constant ampli¬ tude sawtooth waves, a plane target area which is not normal to the average direction of the beam. LINE CHARACTERISTIC. Teletypewriter trans¬ mission distortion caused when the lengths of the received signal impulses are affected by the presence of changing current transitions in wire circuits. NON-LINEAR. Distortion which occurs in a sys¬ tem when the ratio of instantaneous voltage to current therein is a function of the magnitude of either. PHASE. Lack of direct proportionality of phase shift to frequency over the frequency range re¬ quired for transmission; the effect of such de¬ parture on a transmitted signal. PHASE COEFFICIENT. Difference between the maximum transit time and the minimum trans¬ it time for frequencies within a specified band. QUANTIZATION. Inherent distortion intro¬ duced in the process of quantization. RADIO. Output wave form which is not a true reproduction of the input wave form. Distor¬ tion may consist of irregularities in amplitude, frequency, or phase. SINGLE-HARMONIC. Ratio of the power of the fundamental frequency, measured at the output of the transmission system considered, to the power of any single harmonic observed at the output of the system because of its non¬ linearity, when a single-frequency signal of specified power is applied to the input of the system; expressed in db. SYSTEMATIC. Term used to denote the period¬ ic or constant distortion, such as bias or char¬ acteristic distortion, and is the direct opposite of fortuitous distortion. TELETYPEWRITER SIGNAL. Shifting of the transition points of a signal teletypewriter pulses from their proper positions relative to the beginning of the start pulse. The magni¬ tude of the distortion is expressed in percent of a perfect unit pulse length. TOTAL. Total of all forms of signal distortion is cumulative and is known as the total distor¬ tion for that signal. TOTAL HARMONIC. Ratio of the power at the fundamental frequency, measured at the out¬ put of the transmission system considered, to 39-223 AFM 100-39 DIS 1 APRIL 1959 the power of all harmonics observed at the output of the system because of its non-linear¬ ity, when a single-frequency signal of specified power is applied to the input of the system; expressed in db. DISTORTION FACTOR OF A WAVE. Ratio of the effective value of the residue after the elimination of the fundamental to the effec¬ tive value of the original wave. DISTORTION TRANSMISSION IMPAIRMENT. Condition where the bandwidth is less than the 2,750 cycles resulting in poorer transmission of intelligence. The degree is expressed in db DTI. DISTRESS FREQUENCY. Frequency allotted to distress calls, generally by international agreement. For ships at sea and aircraft over the sea, it is 500 kc. DISTRIBUTED. Spread out over an electrically significant length of area. DISTRIBUTED AREA JAMMING SYSTEM. Method of dispensing ground-based jammers so that major loads of the airborne radar always point toward a jammer. DISTRIBUTED CAPACITANCE. Capacitance that exists between the turns in a coil or choke, or between adjacent conductors or circuits, as distinguished from the capacitance which is concentrated in a capacitor. DISTRIBUTED CONSTANTS. Constants such as resistance, inductance, or capa¬ citance that exist along the entire length or area of a circuit, as distinguished from constants con¬ centrated in circuit components. DISTRIBUTED FLOODLIGHT SYSTEM. Landing-area floodlight system so operated that the flux from floodlights located a material distance apart is combined to illuminate the area. DISTRIBUTED INDUCTANCE. Inductance that exists along the entire length of a conductor, as distinguished from the induct¬ ance which is concentrated in a coil. DISTRIBUTING AMPLIFIER. Amplifier, either RF or AF, having one input and two or more isolated outputs. DISTRIBUTING BLOCK. Set of punchings, set in hard rubber or other insulating material, mounted on a piece of wood. This assembly is rigidly fastened as to a frame and usually wired permanently on one side, per¬ mitting wires to be connected and changed on the other. (Reference: TERMINAL BLOCK.) DISTRIBUTING FRAME. Structure for terminating permanent wires of a central office, private branch exchange, or private exchange, and for permitting the easy change of connections between them by means of cross-con¬ necting wires. COMBINED. Frame which vertically mounts the protectors for terminating the outside cable plant and horizontally mounts the terminal blocks for terminating the connector and line- finder banks. INTERMEDIATE. Frame which mounts termi¬ nal blocks on both vertical and horizontal sides for terminating such miscellaneous interoffice cables as those from the relay racks, the at¬ tendant’s switchboard jacks, and the selector banks. INTERMEDIATE TRUNK. Frame which mounts the terminal blocks from the line pri¬ mary switches to the local first selector relays. DISTRIBUTING TERMING. ASSEMBLY, SELECTOR. Frame situated between each pair of selector bays, to provide terminal facilities for the selector bank wiring and facilities for crossconnection to trunks running to succeeding switches. DISTRIBUTION CABLE. Cable extending from a feeder cable into a spe¬ cific area for the purpose of providing service to that area. DISTRIBUTION CENTER. 1. Agency of the adjutant general for routing correspondence and messages within a large headquarters and the comcenter of the head¬ quarters of echelon. 39-224 1 APRIL 1959 AFM 100-39 DIS 2. Point at which is located equipment consisting generally of automatic overload protective de¬ vices connected to busses, the principal functions of which are subdivision of supply, and control and protection of feeders, subfeeders or branch circuits, or any combination thereof. DISTRIBUTION SWITCHBOARD. Power switchboard used for the distribution of electrical energy at the voltage common for each distribution within a building. DISTRIBUTOR. Rotating switch used in automotive ignition sys¬ tems to apply the high voltage of the ignition coil to the spark plugs at correct times and in correct sequence. TEST AND VERIFICATION. Enables the test desk or attendant operator to seize a line through the test switch train instead of through the regular switch train. DISTRIBUTOR BOX. Box or pit through which cables are inserted or removed in a draw-in system of mains. It con¬ tains no links, fuses or switches and its usual function is to facilitate tieing into a customer s peremises. DISTRIBUTOR DUCT. Duct installed for use with distribution mains. DISTURBANCE. 1. Irregular phenomenon associated with trans¬ mission which tends to limit or interfere with the interchange of intelligence. 2. Unwanted current which degrades communi¬ cations by producing noise in the telephone, false signaling, or otherwise interferes with the normal operation of the system. IONOSPHERIC. Variation in the state of ion¬ ization of the ionosphere beyond the normally observed random day-to-day variation from average values for the location, date, and time of day under consideration. SUDDEN IONOSPHERIC. Sudden decrease in the ion intensity in the lower parts of the iono¬ sphere caused by bright solar eruptions. These cause a sudden increase in the absorption of radio waves propagated throughout the lower parts of the ionosphere. The change usually takes place within a few minutes and generally returns to normal within a few hours. DIURNAL VARIATION. Very small variation that occurs daily in the di¬ rection of the magnetic north pole. DIVERGENT BEAM. Beam consisting of rays that spread out (diverge from a point.) DIVERSIONARY COUNTERMEASURES. Classified definition. (Reference: AFM 100-50.) DIVERSITY. Method of radio transmission and/or reception whereby, in order to reduce the effects of fading, a single received signal is derived from a com¬ bination of, or selection from, a plurality of sig¬ nals. FREQUENCY. Method of transmission and/ot reception used to minimize the effects of fre¬ quency selective fading. POLARIZATION. Method of transmission and /or reception used to minimize the effects of selective fading of the horizontal and vertical components of a radio signal. It is usually accomplished by the use of separate vertically and horizontally polarized receiving antenna. SPACE. Method of transmission and/or recep¬ tion used to minimize the effects of flat fad¬ ing. It is usually accomplished by multiple antennas physically separated. DIVERSITY FACTOR. Ratio of the sum of the individual maximum de¬ mands of the various subdivisions of a system or part of a system, to the maximum demand of the whole system, or part under consideration. DIVERSITY GAIN. Gain in reception as a result of the use of two or more receiving antennas. Signals induced in 39-225 AFM 100-39 DIV 1 APRIL 1959 antennas separated by five wavelengths or more fade independently, and better reception is ob¬ tainable in the presence of fading by the use of more than one antenna. DIVERSITY RECEIVER. Radio receiver which overcomes the effects of fading by automatically selecting the strongest signal impulse from two or more antennas usu¬ ally separated a considerable distance. DIVERSITY RECEPTION. Method of radio reception whereby, in order to minimize the effects of fading, a resultant signal is obtained by combination or selection, or both, of two or more sources of received-signal energy which carry the same modulation or intelligence but which may differ in strength or signal-to- noise ratio at any given instant. DIVERSITY SYSTEM. System of radio communication in which a single received signal is derived from a combination of, or selection from, a plurality of transmission channels or paths. The system employed may in¬ clude space diversity, polarization diversity, or frequency diversity. The diversity principle takes advantage of the fact that fading characteristics of a given signal generally vary widely, at any given instant, at different receiving antenna lo¬ cations, and with different frequencies. DIVIDING NETWORK. Coupling system so arranged that at low audio frequencies, power is delivered to a low-frequen¬ cy loudspeaker, while at high frequencies it is delivered to a high-frequency loudspeaker. The frequency at which the power delivered to two loudspeakers is equal is termed the crossover frequency. DIVISION. 1. Army and Marine Corps major administra¬ tive and tactical unit which combines in itself the necessary arms and services required for sus¬ tained combat, larger than a regiment and smal¬ ler than a corps. 2. Number of naval vessels of similar type grouped together for operational and adminis¬ trative command, or a tactical unit of a naval aircraft squadron, consisting of two or more sec¬ tions. 3. Air combat organization normally consisting of two or more wings with appropriate service units. The combat wings of an air division will normally contain similar type units. In air de¬ fense a geographical subdivision of a region de¬ signated as the area of responsibility of a NORAD division under a SAGE division com¬ mander. Its operational facility is a SAGE com¬ bat center. 4. Branch or section of the Headquarters or higher unit, that handles military matters of a particular nature, such as personnel, intelli¬ gence, plans and training, or supply and evacua¬ tion. 5. Number of personnel of a ship’s complement grouped together for operational and administra¬ tive command. DME (DISTANCE MEASURING EQUIPMENT). Radio aid to navigation that determines the dis¬ tance from a transponder beacon by measuring the time of transmission to and from the beacon. DO (DEFENSE ORDER). DOCKS (YARDS AND DOCKS). DOG HOUSE. 1. Structure placed at the base of a transmitting antenna to house the antenna-tuning equipment. 2. Slang for the protuberance on the outside of a rocket which houses instruments. DOHERTY AMPLIFIER. Amplifier circuit in which one vacuum tube sup¬ plies the unmodulated carrier current, with its output being reduced to supply negative peaks of modulation, and a second vacuum tube sup¬ plies approximately half the positive peaks of modulation and lowers the load impedance of the first vacuum tube so it will supply the other half of the positive peaks. This arrangement gives increased power output and increased effi¬ ciency. 39-226 1 APRIL 1959 AFM 100-39 DOL DOLLY. Wheeled truck upon which a television camera is mounted to permit gradual controlled move¬ ment of the camera in any desired direction. DOMESTIC AIR DEFENSE IDENTIFICATION Z °NE. Air defense identification zone within the ConUS. DOMESTIC COUNT. Method used for counting the number of words in a domestic telegram. It includes only the words in the text except when the sender makes the address or signature abnormally long. DOMINANT MODE. Waveguide transmission mode with the lowest cutoff frequency. Designations for this mode are TE,, o, and TE X , T for rectangular and circular waveguides, respectively. (Reference: FUNDA¬ MENTAL MODE.) DOMINANT STATION. Standard class I broadcast station operation on a clear channel. DOMINANT WAVE. Guided wave which has the lowest cutoff fre¬ quency. It is the only wave which will carry en¬ ergy when the excitation frequency is between the lowest cutoff and the next higher. DOOR CONTACT. Electric contacting device attached to a vault door frame operated by opening or closing the door. DOORKNOB. Button or acorn-shaped vacuum tube for ultra high frequency application. Tube has no base, the electrodes being brought out through the glass envelope at the sides, top and bottom. DOORKNOB TUBE. Doorknob-shaped vacuum tube designed for UHF transmitter circuits, having low electron- transit time and low interelectrode capacitance, because of the close spacing and small size, re¬ spectively, of electrodes. DOPPLER EFFECT. 1. Phenomenon evidenced by the change in the observed frequency of a wave in a transmission system caused by a time rate of change in the effective length of the path of travel between the source and the point of observation. 2. Change, or apparent change, in a wave length of sound, light, or other radiation when the source and the observer are in motion relative to one another. DOPPLER RADAR. Form of radar which detects motion of a distant object by means of the change in radio frequency of the echo signal due to motion. DOPPLER SHIFT. Magnitude, in cycles per second, of the change in the observed frequency of a wave caused by the Doppler effect. DOSAGE. Term used in radiology; equal to the product of the intensity of the X-rays and the duration of the exposure. DOSAGE METER. Instrument designed to estimate the quantity of radiation, so as to determine the duration of ex¬ posure when using Roentgen rays for therapy. (Reference: INTENSIMETER.) DOSE. Number of units required to achieve a given ef¬ fect. DOSIMETER. Dosage meter. DOSIMETRY. Technique of measurement, evaluation, and inter¬ pretation of data relative to radiation exposure. DOT. ' Term used in radio telegraphy and is one unit length of signal. When transmitted, a dot will automatically be followed by one unit length of silence. DOT CYCLE. Term used in radiotelegraphy and is defined as two unit lengths (one unit length of signal and one unit length of silence). 39-227 AFM 100-39 DOU 1 APRIL 1959 DOUBLE BOUNCE CALIBRATION. Method of calibration which is used to determine the zero set error by using round-trip echoes. The correct range is the difference between the first and second echoes. DOUBLE REFRACTION. Phenomenon observed in certain crystals, in which light passing through is separated into two components that are polarized at right an¬ gles to each other, have different velocities with¬ in the crystal, and generally take different direc¬ tions. These components are termed ordinary and extraordinary rays. DOUBLE SCREEN. Three layer screen consisting of a two layer screen with the addition of a second long per¬ sistence coating having a different color and dif¬ ferent persistence from the first. DOUBLE SIDEBAND. Amplitude modulated intelligence which is trans¬ mitted at frequencies both above and below the carrier frequency by the audio frequency value of the intelligence. DOUBLE TRANSPOSITION. Transposition in which the characters of a first or primary transposition are subjected to a sec¬ ond transposition. DOUBLE TRIODE. Vacuum tube having two triodes in the same en¬ velope. (Reference: DUOTRIODE.) DOUBLE-BREAK SWITCH. Switch which opens the connected circuit at two points. DOUBLE-BUTTON CARBON MICROPHONE. One having two buttons or containers for carbon granules, one on each side of the diaphragm, so as to give twice the resistance change obtainable with a single button. DOUBLE-CONCAVE LENS. Lens with two concave surfaces. DOUBLE-CONVEX LENS. Lens with two convex surfaces. DOUBLE-CURRENT GENERATOR. Machine which supplies both direct and alter¬ nating currents from the same armature winding. DOUBLE-DIODE. Vacuum tube (or semiconductor) having two diodes in the same envelope. (Reference: DUO- DIODE.) DOUBLE-DIODE LIMITER. Type of limiter which is used to remove all posi¬ tive signals from a combination of positive and negative pulses, or to remove all the negative signals from such a combination of positive and negative pulses. DOUBLE-ENDED WIPER. Wiper arm (contacting arm) of a 25-point rotary stepping switch, which has a wiper at either end. When one wiper end rests on the bank, the other wiper end is off the bank. When one wiper end moves off the bank, the other wiper end moves onto the bank. DOUBLE-GRID TUBE. Vacuum tube having two grids. DOUBLE-LAYER PHOSPHOR. Phosphor compound consisting of two layers. DOUBLE-LENGTH NUMBER. Electronic computer number having twice as many digits as are ordinarily used in a given computer. DOUBLE-MODING. Frequency jumping; changing abruptly from one frequency to another at irregular intervals. DOUBLE-MODULATION. Method of modulation in which a carrier wave is first modulated with the desired intelligence, and the resulting modulated wave is then used to modulate a second carrier having a higher frequency. DOUBLE-POLE, DOUBLE-THROW. Applying to a switch having six terminals and used to connect one pair of terminals to either of two other pairs of terminals. 1 APRIL 1959 AFM 100-39 DOU DOUBLE-POLE, SINGLE-THROW. Applying to a switch having four terminals and used to connect or disconnect two pairs of term¬ inals simultaneously. DOUBLE-POLE SWITCH. Switch that simultaneously changes connections in two separate circuits or in both sides of the same circuit. DOUBLE-PRECISION NUMBER. Synonym for double-length number. DOUBLE-PULSING STATION. Loran station that receives two pairs and emits pulses at two pulse rates. DOUBLE-RING STRAPPING. Use of two ring straps, one being connected to alternate segments and the other to the remain¬ ing set of alternate segments of a magnetron. DOUBLE-SIDEBAND TRANSMISSION. Method of communication in which all the fre¬ quencies produced by the process of modulation, that are symmetrically spaced both above and be¬ low the carrier frequency, are transmitted. DOUBLE-SIDEBAND TRANSMITTER. Transmitter whose output contains both of the sidebands which result from the modulation of the carrier by the modulating signal. In most instances it also contains a large carrier compo¬ nent. DOUBLE-SPOT TUNING. Superheterodyne reception of a given station at two different local oscillator frequency values: (1) With the local oscillator adjusted above the incoming signal frequency by the intermediate- frequency value. (2) With the local oscillator ad¬ justed below the incoming signal frequency by the intermediate-frequency value. (Reference: REPEAT POINT.) DOUBLE-STUB TUNER. . Impedance-matching device for a transmission line, consisting of two adjustable length stubs spaced a fixed distance apart. DOUBLE-SUPERHETERODYNE RECEPTION. Method of reception in which two frequency con¬ verters are employed before final detection. DOUBLE-THROW CIRCUIT BREAKER. Circuit breaker by means of which a change in the circuit connections can be obtained by clos¬ ing either of two sets of contacts. DOUBLE-THROW SWITCH. Switch by means of which a change in circuit connections can be obtained by closing the switch blade into either of two sets of contacts. DOUBLE-TUNED AMPLIFIER. Amplifier of one or more stages in which each stage utilizes coupled circuits having two tuned circuits. DOUBLE-TUNED CIRCUIT. Circuit which has two resonant circuits with sep arate controls. DOUBLE-VOLTAGE RATING OF A TRANSFORMER. Rating applied to a transformer which has two separate windings (primary and secondary) with two voltage ratings assigned to each, the turn ratio being the same for both ratings. DOUBLE-WINDING SYNCHRONOUS GENERATOR. Synchronous generator which has two similar windings in phase with one another, mounted on the same magnetic structure but not connected electrically, designed to supply power to two in¬ dependent external circuits. DOUBLER. Electronic circuit in which the output is tuned to twice the frequency of the input. DOUBLET ANTENNA. Antenna consisting of two elevated conductors substantially in the same straight line and of substantially equal length, with the power de¬ livered at the center. DOUBLET TRIGGER. Trigger signal consisting of two pulses spaced by a fixed amount for coding. 39-229 AFM 100-39 DOV 1 APRIL 1959 DOVE. Air-to-surface missile developed for the Navy. Nomenclature is XASM-N-4. DOW OSCILLATOR. Electron-coupled oscillator circuit. DOWN LEAD. Wire that connects an antenna with a transmitter or receiver. (Reference: LEAD-IN.) DOWNGRADE. Reduce the security classification of a classified document or an item of classified matter or ma¬ terial. DOWNWARD MODULATION. Modulation in which the instantaneous ampli¬ tude of a carrier is always less than the unmod¬ ulated carrier amplitude. DN (DEPARTMENT OF THE NAVY). Executive part of the Navy establishment of the seat of government, including Secretary of the Navy and the supporting staffs. DP (BY DIRECTION OF THE PRESIDENT). dpdt (DOUBLE-POLE, DOUBLE-THROW). Applying to a switch having six terminals and used to connect one pair of terminals to either of two other pairs of terminals. dpst (DOUBLE-POLE, SINGLE-THROW). Applying to a switch having four terminals and used to connect or disconnect two pairs of termi¬ nals simultaneously. DR. ITU designation for directive antenna provided with a reflector. DR (DEAD RECKON). Computer action resulting from a manually in¬ serted instruction on a track; this action projects a track for six frames. This is accomplished by logical conclusions based on the assumption of continuity of previously known data. It tempor¬ arily prevents a track from being dropped. DRAFTER. Person who actually composes a message for re¬ lease by the originator or the releasing officer. (Reference: ORIGINATOR.) DRAG ANGLE. Stylus cutting angle such that the point drags during recording instead of being at 90 degrees to the record surface. It is the opposite of dig¬ in angle. DRAG-CUT MOTOR. Small high-speed two-phase alternating-current electric motor having a two-pole two-phase sta¬ tor. The rotating element consists only of an extremely light metal cup attached to a shaft ro¬ tating on bail bearings. Reversal is accomplished by reversing the connections to one phase. Used in applications requiring quick starting, stop¬ ping, and reversal characteristics. DRAIN, CURRENT. Current passing through a battery when in use. DRAIN UNIT. Battery unit drain per link. DRAWINGS AND LISTS. Pictures, sketches, etc., and entrances in the form of catalogues, registers, and the like. CIRCUIT DRAWING. Representation of the ele¬ ments of an electrical circuit and its connec¬ tions by lines and symbols. CABLE - AND - TRUNK SCHEMATIC. Provides a record of the general trunking scheme and circuitry of the central office’s distributing frame, automatic-switching, relay-rack, atten¬ dant’s switchboard, and local test-desk equip¬ ment. CABLE RACK ASSEMBLY DRAWING. Indicates the layout of the central office cable rack in relation to equipment units and building de¬ tails. CABLE RUNNING LIST. Indicates the origin and destination of all central office cable runs, the route of each cable, and the method of form¬ ing at each end. CENTRAL OFFICE KEYSHEET. Tabular listing of all the job drawings and all the manufacturer’s drawings applicable to the office involved. 39-230 1 APRIL 1959 AFM 100-39 ORA DISTRIBUTING FRAME DRAWING. Indicates the frame assembly of the CDF, the termination of all cable runs on the individual terminal strips, and details of terminating and strip¬ ping. distributing terminal assembly draw¬ ing. Indicates details of the grading scheme and cross-connections to outgoing trunks. FLOOR PLAN. Definitive guide to the location of all central office equipment. INSTALLATION PROCEDURES CHART. Provides a guide for determining the sequence and pro¬ gress of the installation from the preliminary survey of the entire job to the final installation of the last unit. JOB SCHEDULE. Chart indicating the order of installation procedures in a coordinated man¬ ner. LINEFINDER-TO-FIRST-SELECTOR-CROSS- CON¬ NECTION DRAWING. Indicates the cross-con¬ nection scheme between these two equipments and guides the installation team when making cross-connections. MANUAL FRONT-EQUIPMENT DRAWING. Indicates the jack panels, as well as the posi¬ tions of the attendant’s switchboard. MANUAL KEYSHEET. Lists all manual equip¬ ment circuits by name; also lists manufactur¬ er’s circuit wiring diagram, and associated relay equipment assembly drawing numbers and options. POWER SCHEMATIC. Wiring record of the central office’s ac service circuit, charging cir¬ cuit, battery and control circuit, and dis¬ charge circuit. RELAY-RACK DRAWING. Indicates the equip¬ ment mounted on each relay rack and the posi¬ tion in which the equipment is mounted. RINGING SCHEMATIC. General layout of the central-office tone-and-interrupter, test and control circuits associated with the ringing ma¬ chines. SWITCHING-EQUIPMENT-AND-CIRCUIT LIST. Provides a reference to all manufacturer s drawings associated with the central office switching equipment. DRDTO. Classified definition. (Reference: AFM 100-50.) DRESSER CABLE. Shaped hardwood block with a handle for beat¬ ing the ends of sleeves into shape for wiping. DRIFT. 1. Relative motion between plane and target at right angles to the desired course, caused either by wind or target velocity. 2. Undesired change of frequency in time usu¬ ally due to charges of circuit constants with tem¬ perature. 3. Resultant motion of a group of electrons in some general direction. 4. Measure of the change of an oscillator fre¬ quency from its desired frequency. DRIFT ANGLE. Horizontal angle between the longitudinal axis of an aircraft and its path relative to the ground. DRIFT CORRECTION ANGLE. Angular difference between the desired course and the heading. DRIFT SPACE. Distance between the buncher and catcher in a velocity-modulated vacuum tube. drift speed. Average, speed at which electrons or ions pro¬ gress through a medium. DRIP-PROOF MACHINE. Machine in which the ventilating openings are so constructed that drops of liquid or solid parti¬ cles falling on the machine at any angle not greater than 15 degrees from the vertical, cannot enter the machine directly or by striking and run¬ ning along a horizontal or inwardly inclined sur¬ face. 39-231 AFM 100-39 DRI 1 APRIL 1959 DRIVE BELT. Belt used to transmit power from a driving motor to a turntable in a recorder, phonograph, or other machine. DRIVE HOLES. Holes spaced around the center hold of a re¬ cording disk to engage a drive pin in the turn¬ table, preventing the disk from slipping during recording. DRIVE PIN. Projecting rod positioned near the center pin of a phonograph, used with a two hole phonograph disk to prevent the record from slipping on the turntable during recording. DRIVE-PIN HOLE. Hole in the record which fits over the turntable drive pin. DRIVEN ELEMENT. Antenna array element that receives power di¬ rectly from the transmitter. DRIVEN SWEEP. Sweep triggered only by incoming signal or trigger. DRIVER. 1. Electronic circuit which supplies input to another electronic circuit. 2. Stage of amplification which precedes the power output stage. 3. Circuit in a radar transmitter which produces a pulse to be delivered to the control grid of the modulator tube. 4. Unit (or stage) driving another unit (or stage), as PPI driver, etc. (Reference: EXCITA¬ TION.) driver stage. Amplifier stage just ahead of a high-power stage. driver tube. Tube used in a driver stage. driving point impedance. Pair of terminals of a network, the ratio of an applied potential difference to the resultant current at these terminals, all terminals being terminated in any specified manner. 2. Complex quotient at any driving point of the force (or sound pressure) by the velocity (linear or volume) of vibration at that point. DRIVING SIGNALS. Television signals that time the scanning at the pick-up point. DROLLER. Circuit which distorts a square pulse by reduc¬ ing the sharpness of leading and trailing edges, and tending to round the top of the pulse. DRONE. Remotely controlled aircraft. DROP. 1. Action which causes a track to be dropped from the system, either automatically or as the result of a manually inserted instruction. 2. Visual shutter device consisting of an elec¬ tromagnet and a visual target either moved or tripped magnetically to a position indicating the condition supervised. (Reference: DROP SIG¬ NAL.) POTENTIAL. Difference in potential between the two ends of a resistance with a current flowing through it. RELAY. Relay actuated by a ringing current and used to call an operator’s attention to a sub¬ scriber’s line. SUBSCRIBER’S. Line from a cable termination to a subscriber’s location. SWITCHBOARD. Entire switchboard circuit which terminates a line circuit. DROP BAR. Protective device used to ground a high-voltage capacitor when opening a door. DROP BRACKET TRANSPOSITION. Reversal of the relative positions of two parallel wire conductors while depressing one, so that the cross-over is in a vertical plane. 39-232 1 APRIL 1959 AFM 100-39 DRO DROP CYCLE. Track status indicating that a particular track is about to be dropped from the system. DROP MESSAGE. Message dropped from an aircraft to a ground or surface unit. DROP REPEATER. Microwave repeater that is provided with the nec¬ essary equipment for local termination of one or more circuits. DROP SIGNAL. Visual shutter device consisting of an electromag¬ net and visual target either moved or tripped magnetically to a position indicating the condi¬ tion supervised. (Reference: DROP.) DROP WIRE. Wire suitable for extending an open wire or ca¬ ble pair from a pole or cable terminal to a build¬ ing. DROP ZONE. Specified area upon which airborne troops, equip¬ ment, and supplies are dropped by parachute, or on which supplies and equipment may be de¬ livered by free fall. DROPOUT. Dropout value of a relay is the maximum cur¬ rent, voltage, power, etc., at which it will release from its energized position. For example, an overcurrent relay which closes its contacts on pick-up will just open the contacts on dropout. DROPOUT CURRENT. Value to which relay coil current must be reduc¬ ed after the relay is closed in order to release the armature and open the relay contacts. DROPOUT VOLTAGE OR CURRENT. Voltage or current at which a magnetically op¬ erated device will release to its deenergized posi¬ tion. DROPPING INTERVAL. Interval of time in seconds between each ejection of chaff. dropping resistor. Resistor used to decrease a given voltage to a lower value. DRUM. Hollow cylinder on which is secured facsimile copy to be transmitted or the paper or film for recording received copy. DRUM SHIELD, MANHOLE. Adjustable shield, made of sheet iron and placed around the ring of a manhole opening. DRUM ARMATURE. Ordinary type of armature used in rotating ma¬ chines, having axial active wires rotating through a magnetic field in which the lines of force are chiefly radial. DRUM CONTROLLER. Electrical controller which untilizes a drum switch as the main switching element. A drum controller usually consists of a drum switch and a resistor. DRUM RECORDER. Facsimile recorder in which the record sheet is mounted on a rotating drum or cylinder. DRUM SPEED. 1. Number of revolutions per minute made by the transmitting or receiving drum of the facsimile transmitter or recorder. 2. Number of scanning lines per minute. (Ref¬ erence: STROKE.) DRUM SWITCH. Switch in which the electrical contacts are made on segments or surfaces on the periphery of a rotating cylinder or drum by the operation of a rotating cam. Used for complex band switching or circuit changes. DRUM TRANSMITTER. Facsimile transmitter in which the subject copy is mounted on a rotating drum or cylinder. DRY BATTERY. Series, parallel, or series-parallel arrangement of dry cells in a single housing to provide desired voltage and current values. AFM 100-39 DRY 1 APRIL 1959 DRY BULB. Thermometer used to determine the tempera¬ ture of the air. DRY CELL. Source of electrical energy depending on the re¬ action of a chemical paste on carbon and metal or two metals for its supply. DRY CONTACT. Contact through which no direct current flows. DRY FLASHOVER VOLTAGE. Voltage at which the air surrounding a clean dry insulator or shell completely breaks down be- ween electrodes. DRY-DISK RECTIFIER. Rectifier consiting of disks of metal and other material in contact under pressure, such as a copper-oxide rectifier or selenium rectifier. DRY-ELECTROLYTIC CAPACITOR. Electrolytic capacitor in which the electrolyte is in paste, rather than liquid form. (Reference: ELECTROLYTIC CAPACITOR.) dsc (DOUBLE-SILK-COVERED WIRE). DSMA (DEFENSE SUPPLY MANAGEMENT AGENCY). dspch (DISPATCH, DISPATCHER). 1. Dispatch; a message, usually an official com¬ munications, sent from one person to another. 2. Dispatcher; one who dispatches something, as an aircraft dispatcher. dt (DATE). 1. Point of time at which a transaction or event takes place. 2. Point or period of time to which anything is referred as present, as to usage, style, know¬ ledge, etc. DT CUT CRYSTAL. Crystal plate of specified dimensions with an edge parallel to the X-axis and making an an¬ gle of 53 degrees with the Z-axis. DTA (DISTRIBUTING TERMINAL ASSEMBLY). Frame situated between each pair of selector bays, to provide terminal facilities for the selector bank wiring and facilities for cross-connection to trunks running to succeeding switches. dta wire (DOUBLE-WIRE ARMORED). DTG (DATE-TIME GROUP). DTI (DISTORTION TRANSMISSION IMPAIRMENT). Reduction of effective transmission due to the presence of distortion. DUAL-AUTOMATIC RADIO COMPASS. Arrangement of two automatic radio compasses feeding into a dual azimuth indicator having two pointers, each indicating the direction to a dif- erent radio station. The complete bearing is thus visible to the pilot at all times, eliminating the need for tuning to one station after Another to obtain a radio fix. DUAL BEAM CRT (CATHODE-RAY TUBE). Cathode-ray tube having either two separate elec¬ tron guns producing two electron beams or a method of splitting the beam from one gun into two separate beams before deflection. DUAL CAPACITATOR. Two capacitors in a single housing. DUAL CHANNEL AMPLIFIER. Instrument designed to amplify an audio signal. DUAL DIVERSITY RECEIVER. Radio receiver that receives signals from two dif¬ ferent receiving antennas and uses whichever signal is the stronger at each instant, in order to offset facing. In one arrangement, two iden¬ tical RF systems, each with its own antenna, feed a common audio-frequency channel. In another arrangement, a single receiver is changed over from one antenna to the other by elec¬ tronic switching at a rate fast enough to prevent loss of intelligibility. DUAL METER. With reference to pulse analyzer presentations, two D’Arsonval meters are used, one calibrated in PRF and one calibrated in PD. 39-234 1 APRIL 1959 AFM 100-39 DUA DUAL MODULATION. Process of modulating a common carrier wave, or subcarrier, by two different types of modula- ion each conveying separate intelligence. dubbing. 1. Recording from one or more records. 2. In a cutting stylus, same as burnishing sur¬ face. 3. Copying a recording by playing it and feed¬ ing the resulting af signal into a sound re¬ corder. DUCT. , . Underground tube or pipe used as a path tor a cable. ARTIFICIAL LINE. Balancing network, simu¬ lating the impedance of the real line and dis¬ tant terminal apparatus, which is employed in a duplex circuit for the purpose of making the receiving device unresponsive to outgoing sig¬ nal currents. MULTIPLE TILE. Tile member arranged to hold several cables in separate channels. DUCT BANK. Arrangement of conduit providing one or more continuous ducts between two points. (Refer¬ ence: CONDUIT RUN.) DUCT EDGE SHIELD. Collar or thimble, usually flared, inserted at the duct entrance in a manhole to protect the cable sheath or insulation from being worn away by the duct edge. (Reference: CABLE SHIELD.) DUCT ENTRANCE. Opening of a duct at a manhole, distributor box, or other accessible space. DUCT RODDING. Tnreading of a duct by means of a jointed rod of suitable design for pulling in the cable-pul- ling rope, mandrel, or the cable itself. DUCT RUN. System of underground cuts. DUCT SEALING. Closing of the duct entrance to exclude water, gas, or other undesirable substances. DUCTILITY. Property of a material which permits deforma¬ tion to occur without fracture. DUDDEI ARC. DC electric arc that generates an AF current and corresponding sound waves when a coil and ca¬ pacitor are connected in parallel with the arc. This gives a musical tone. (Reference: SING¬ ING ARC.) DUE-IN. Quantity of unsupplied items on requisitions sub¬ mitted by unit supply officers to higher supply echelons. DUE-OUT. Obligation assumed and recorded by any supply echelon to issue at a subsequent date. A re¬ quested item which was not immediately availa¬ ble for supply but one for which source of sup¬ ply has been established. DULLING. Forming the burnishing surface of the cutting stylus. DUMBBELL WAVEGUIDE. Waveguide section shaped like a dumbbell. DUMMY. 1. Simulating device with no operating feat¬ ures as, a dummy heat coil. 2. Telegraphy network simulating a customers loop for adjusting a telegraph repeater. The dummy side of the repeater is that toward the customer. DUMMY ANTENNA. Resistor network or other device that duplicates the electrical characteristics of a particular anten¬ na but does not radiate an appreciable amount of energy. Used chiefly for testing and adjust¬ ing transmitters. DUMMY GROUP. Group of dummy letters and/or figures. 39-235 AFM 100-39 DUM DUMMY LETTERS. Letters with no plain text significance inserted within a cryptogram (a) with the intent to delay or prevent its solution, or (b) to complete the last enciphered group for transmission pur¬ poses; a null. DUMMY LOAD. Device in which the output power can be ab¬ sorbed, used for simulating conditions of opera¬ tion for test purposes. Usually a load to simu¬ late an antenna. DUMMY MESSAGE. Message sent for some purpose other than its content. DUMMY PLUG. Plug which makes no electrical contact but which holds jack springs in an operated position or which blocks the jack from use. DUMP. Temporary stock of supplies or a place of storage established in the field or afloat where military supplies are held temporarily. When supplies are issued from dumps, they become distributing points. DUODIODE. Vacuum tube (or semiconductor) having two diodes in the same envelope. (Reference: DOU¬ BLE-DIODE.) DUODIODE-PENTODE. Vacuum tube having two diodes and a pentode in the same envelope. DUOLATERAL COIL. Coil having a special cris-cross or honeycomb, winding to reduce distributed capacitance. DUOTRIODE. Vacuum tube having two triodes in the same en¬ velope. (Reference: DOUBLE TRIODE.) dupe (DUPLICATE, DUPLICATION). 1. Duplicate; that which exactly resembles or corresponds to something else; hence, a copy; counterpart. 2. Duplication; act of duplicating, or state of be¬ ing duplicated; especially a doubling; a fold. 1 APRIL 1959 DUPLEX. 1. Method of operation of a communication cir¬ cuit where each end can simultaneously trans¬ mit and receive. Ordinary telephone are duplex. When used on a radio circuit duplex operation required two frequencies. 2. Two-in-one as, two conductors with a com¬ mon over-all insulation or two telegraph trans¬ mission channels over one wire. DUPLEX CIRCUIT. 1. Method of operation in which all electrical communications between stations take place in both directions simultaneously. 2. Denotes a circuit which permits electrical communication between stations in both direc¬ tions simultaneously. DUPLEX OPERATION. Operation of associated transmitting and receiv- ing apparatus in which the processes of transmis¬ sion and reception are concurrent. DUPLEX SYSTEM. Telegraph system which affords simultaneous in¬ dependent operation in oppostie directions over the same channel. DUPLEX TUBE. Combination of two vacuum tubes in one enve¬ lope. DUPLEXER. 1. Radar device which utilizes the finite delay between the transmission of a pulse and the echo thereof so as to permit the connection of the transmitter and receiver to a common antenna. 2. Device which permits the use of the same antenna for both transmitting and receiving. DUPLICATE. That which exactly resembles or corresponds to something else; hence, a copy counterpart. DUPLICATE LINES. Lines of substantially the same characteristics, normally operated in parallel, connecting the same supply point with the same distribution point. 39-236 1 APRIL 1959 DUPLICATION. Act of duplicating, or state of being duplicated; especially a doubling; a fold. DURAL SHANK. Duraluminum shank commonly used on a sap¬ phire or satellite cutting stylus. DURALUMINUM. Alloy containing approximately 95.5 parts alu¬ minum, 3 parts copper, 1 part manganese, and 0.5 part magnesium. It is comparable in strength to soft steel. DURATION CONTROL. Control for adjusting the time duration of re¬ duced gain in a sensitivity-time control circuit. AFM 100-39 DUP occur at regular intervals in the product of the pulse duration and the pulse repetition frequency. The ratio of pulse interval to pulse length. Re¬ ciprocal of duty cycle. OVER (DEFENSE VISUAL FLIGHT RULES). Rules applicable to visual rules (VFR) which originate within or penetrate an air defense identification zone. DW. Type of wire designation for drop wire. DW (DOUBLE WEIGHT). DWA (DOUBLE-WIRE ARMOR). Designation used for wire cable. DUST CORE. Pulverized iron core, consisting of extremely fine iron particles mixed with a binding material, for use in RF coils. DUST COUNTER. Instrument for determining approximately the number of dust particles or condensation nuclei per unit volume in a sample of air. DUTY. Requirement of service which defines the degree of regularity of the load. DUTY CLASSIFICATION OF A RELAY. Expression of the frequency with which the relay may be required to operate without exceeding prescribed limitations. DUTY CYCLE. 1. Cycle of starting, running, and stopping opera¬ tions that a motor or other equipment of inter¬ mittent duty performs. 2. Ratio of pulse duration time to pulse repeti¬ tion time, which is the same as the ratio of aver¬ age power to peak power in a pulse. DUTY CYCLEMETER. Test meter which gives direct reading of duty cycle. DUTY FACTOR. Duty factor of a wave composed of pulses that DWG (DRAWING). Picture or sketch. DX. ,. 1. Reception of stations located at a distance from the receiver. 2. Teletypewriter designation for duplex repeater. DYN (DYNAMOTOR). Combination motor and generator on a single shaft. dynameter. Device for measuring magnifying power. DYNAMIC CHARACTERISTICS. Relation between the instantaneous plate volt¬ age and plate current of a vacuum tube as the voltage applied to the grid is moved; thus, the characteristics of a vacuum tube during operation. DYNAMIC LOUDSPEAKER. Loudspeaker in which the coil carrying the AF current is attached to the moving diaphragm or cone (Reference; MOVING COIL LOUD- SPEAKER.) DYNAMIC MICROPHONE. Microphone having a diaphragm with a coil that moves in a magnetic field. (Reference; MOV- ING COIL MICROPHONE.) 39-237 AFM 100-39 DYN DYNAMIC PICK-UP. Phonograph pick-up in which the electrical out¬ put results from the motion of a conductor in a magnetic field. DYNAMIC PLATE IMPEDANCE. Internal resistance to the flow of alternating current between the cathode and plate of a tube. It is equal to small change in plate voltage divid¬ ed by the corresponding change in plate voltage divided by the corresponding change in plate current, and is expressed in ohms. It is also called ac resistance, internal impedance, plate impedance, and dynamic plate impedance, its symbol is rp. DYNAMIC PLATE RESISTANCE. Opposition that the plate circuit of a vacuum tube offers to a small increment of plate voltage. It is the ratio of a small change in plate voltage to the resulting change in the plate current, other voltages remaining constant. Dynamic plate resis¬ tance is usually designated by rp and is expressed in ohms. (Reference: ALTERNATING-CUR¬ RENT PLATE RESISTANCE.) DYNAMIC RANGE. 1. Range over which the input signal amplitude may vary and yet maintain an undistorted output. 2. Transmission system difference in decibels between the noise level of the system and its over¬ load level. DYNAMIC REGULATOR. Transmission regulator in which the adjusting mechanism is in self-equilibrium at only one or a few settings and requires control power to main¬ tain it at any other setting. DYNAMIC SENSITIVITY. Photo tube quotient of the alternating component of anode current by the alternating component of incident radiant flux. This is variational and not a total sensitivy. As most precisely used, the term refers to infinitesimal amplitudes. DYNAMIC SPEAKER. Loudspeaker in which the diaphragm motion is generated by means of alternating current in a I APRIL 1959 moving coil mounted on the diaphragm with the coil in a magnetic field. DYNAMICS. Branch of physics which deals with forces and their action upon material bodies. DYNAMO. Machine for converting mechanical energy into electrical energy generally called a generator. The term dynamo more often applies to a dc generator, while alternator applies to an ac generator. DYNAMOELECTRIC. Pertaining to the relation between mechanical force and electrical energy, or vice versa. DYNAMOELECTRIC MACHINE. Rotating device that converts mechanical energy into electrical energy, or vice versa, as a dynamo, alternator, or electric motor. DYNAMOMETER-TYPE INSTRUMENT. Instrument in which current, voltage, or power is measured by the force between a fixed coil and moving coil. DYNAMOTOR. Combination electric motor and dc generator hav¬ ing two or more separate armature windings and a common set of field poles. One armature wind¬ ing receiving direct current, operates as a motor, producing rotation, while the others operate as a dynamo or generator, generating voltage. More simply a rotating device used to change one dc voltage to a different dc voltage. DYNATROL OSCILLATOR. Negative-resistance oscillator in which negative resistance is derived between plate and cathode of a screen-grid tube operating so that secondary electrons produced at the plate are attached to the higher potential screen grid. DYNATRON. Four-electrode vacuum tube so designed that secondary emission of electrons from the plate causes the plate current to decrease as plate volt¬ age is increased, giving a negative resistance char¬ acteristic. Used in oscillator circuits. 39-238 1 APRIL 1959 AFM 100-39 DYN DYNATRON OSCILLATION. Oscillation occurring in a vacuum-tube circuit due to secondary emission of electrons from the plate giving a negative resistance characteristic. DYNATRON OSCILLATOR. Negative-resistance oscillator in which the nega¬ tive resistance is devised between plate and cath¬ ode circuits. Maintains oscillations in a resonant circuit connected in parallel with the plate and cathode. DYNE. Unit of force in the centimeter-gram-second system. It is that force which will give an acceler¬ ation of one centimeter per second during each second to a free mass of one gram. DYNE PER SQUARE CENTIMETER. Unit of sound pressure. The term bar or barve was originally applied to a pressure of 10« dynes per square centimeter, and in all other fields except acoustics it is used with this meaning, in acoustics it is used to mean one dyne per square centimeter. DYNODE. One of the reflecting electron mirrors in a multi¬ plier-type phototube. It is coated with a material capable of high secondary emission. DZ (DROP ZONE). Area on the ground designated as the place where troops are to be dropped from aircraft. 39-239 AFM 100-39 E 1 APRIL 1959 E E. Symbol for voltage. E/A (ENEMY AIRCRAFT). Hostile aircraft. e 9- Symbol for the grid voltage. E P- Symbol for plate voltage. Es g- Symbol for screen grid voltage. E-BEND. Smooth change in the direction of the axis of a waveguide, throughout which the axis remains in a plane parallel to the direction of polariza¬ tion. E-INDICATOR. Modification of type B radar indicator. The sig¬ nal appears as a bright spot with range as the horizontal coordinate and elevation as the ver¬ tical coordinate. E-LAYER. One of the regular ionospheric layers with an average height of about 100 kilometers. This layer occurs during daylight hours and its ionization is dependent on the sun's angle. The principal ayer corresponds roughly to what was for¬ merly called the Kennelly-Heaviside layer. In addition, areas of abnormally intense ioniza¬ tion frequently occur, which are called "spor¬ adic B.” “ e-mode, transverse magnetic. Type mode in which the longitudinal component of the magnetic field is zero and the longitudinal component of the electric field is not zero. E-PLANT BEND. Waveguide E-bend is a smooth change in the direction of the axis of a waveguide, throughout which the axis remains in a plane parallel to the direction of polarization. E-PLANT T-JUNCTION. Waveguide T-junction in which a change in struc¬ ture occurs in the plane of the electric field. E-REGION. Region in the ionosphere, between about 55 and 85 miles (90 to 160 kilometers) above the sur¬ face of the earth, that contains ionized layers cap¬ able of bending (refracting or reflecting) radio waves. E-SCAN. Modification of B-scan. Signal appears as a bright spot with range as the horizontal coordinate and elevation as the vertical coordinate. E-SCOPE. (Reference: E-SCAN.) E-UNITS. Radar signal-noise ratio. E-units Ratio E-l 1 to 1 E-2 2 to 1 £-3 4 to 1 E-4 8 to 1 E-5 16 to 1 Description Barely Perceptible Weak Good Strong Very strong or Saturating. E-VECTOR. Vector representing the electric field of an elec¬ tromagnetic wave. In free space it is perpen¬ dicular to the direction of propagation. E-WAVE. Designation for TM (transverse magnetic) wave. One of the two classes of electromagnetic waves that can be sent through wave guides. E-ZONE. One of the three zones into which the earth is divided to show the variations of the F2 layer in respect to longitude when making freqeuncy predictions. This zone roughly covers what is known as the eastern hemisphere: Asia, Austra¬ lia, Philippines and Japan. EADF (EASTERN AIR DEFENSE FORCE) Major component of the Air Defense Command, providing air defense for the eastern United States, covering nineteen states and the District of Columbia. EAM (ELECTRICAL ACCOUNTING MACHINE). 39-240 ( 1 APRIL 1959 AFM 100-39 EAR EARLY WARNING. Warning system near the outer boundaries of a defended area to warn of approaching airborne objects. EARLY WARNING RADAR. System that sweeps the skies in all directions and at all elevations to detect the approach of enemy planes and/or missiles e*rly enough for fighter planes to be in the air ready to meet their ap¬ proach or for other adequate defense measures to be taken. EARLY WARNING STATION. Essential element of this type of installation is surveillance and the absence of air-intercept con¬ trol capability. In isolated instances, it may be organized and manned to provide for the exten¬ sion of some function delegated by the ADDC or ADCC to which it is operationally respon¬ sible. EARTH. , • , Term used in Great Britain for a ground which acts as a large conductor and a return path for both radio and electrical systems. EARTH BORER. Motor-driven auger mounted on a construc¬ tion vehicle and used to drill holes for poles. EARTH CURRENTS. 1. Currents flowing through the ground due to natural causes, affecting the magnetic field of the earth and sometimes causing magnetic storms. 2. Return, fault, leakage, or stray currents pas¬ sing through the earth from electrical equip¬ ment. that serves in place of the earth. A British term, corresponding to grounded. EAST. (EAST, EASTERN). 1. Direction of sunrise; accurately, that point on the sensible horizon where the center of the sun is seen to rise at the equinox. 2. Direction toward the right hand of one fac¬ ing north. 3. Eastern; belonging to or characteristic of the East. EAST TERMINAL. Conventions (rules) for directions of transmis¬ sion of various frequency ranges have been estab¬ lished in order to minimize interference between operating systems. For this reason, the East terminal of a microwave or carrier system must be so arranged that the frequency allocation of both the outgoing and incoming channels cor¬ responds to the established pattern. It is impor¬ tant that such conventions be respected, if only to guard against possible future conflict. Geo¬ graphically, and "East” terminal is usually lo¬ cated at the east or north end of a circuit. EASTERN AIR DEFENSE FORCE. Major component of the Air Defense Command, providing air defense for the eastern United States, covering nineteen states and the District of Columbia. EASTERN STANDARD TIME. Mean time based on the 75th meridian, west longitude. ECA (ECONOMIC COOPERATION a rMAIKIICTDATIONJl EARTH INDUCTOR. Coil arranged to permit rotation in the earth s magnetic field. EARTH INDUCTOR COMPASS. Compass whose indications depend on the cur¬ rent generated in a coil revolving in the magnetic field of the earth. (Reference: INDUCTION COMPASS.) EARTHED. Connected to earth or to some conducting body ECC (EUROPEAN COORDINATING COMMITTEE). Consists of United States Representative to Coun¬ cil of Deputies as Chairman, United States Mili¬ tary Representatives for Europe. ECCENTRIC. 1. Circle not having the same center as another within it. 2. Device mounted off center for converting ro¬ tary motion into reciprocating motion. 39-241 AFM 100-39 ECC 1 APRIL 1959 ECCENTRIC MOUNTING. Type lens mounting that consists of eccentric rings that may be rotated to shift the axis of the lens to a prescribed position. ECCLES-JORDAN TRIGGER CIRCUIT. Multivibrator circuit in which the output and input portions of two electronic amplifiers are direct coupled. It has two conditions of stability, either one of which endures until some action causes the nonconducting tube to conduct, then the functions of the electronic amplifiers reverse. (Reference: FLIP-FLOP CIRCUIT.) ECCM (ELECTRONIC COUNTER - COUNTERMEASURES). Various tactics used to reduce the effectiveness of electronic countermeasures. ECH (ECHELON). 1. Subdivision of a headquarters. 2. Separate level of command. As compared to a regiment, a division is a higher echelon, a battalion is a lower echelon. 3. Fraction of a command in the direction of depth, to which a principal combat mission is assigned. 4. Formation in which the subdivisions are placed one behind another, extending beyond and unmasking one another wholly or in part. FIFTH. Operations performed in fixed installa¬ tions designated as base shops or depots. It has equipment for the complete rebuilding of material. It manufactures items when no other source of supply is available. FIRST. Operations performed by the user, wearer, or operator of the equipment. Includes care, use, operation, cleaning, preservation, and lubrication. FOURTH. Operations usually performed by an established pool, of variable numbers and types, of heavy maintenance and supply units, formed as a semimobile shop, serving an area. Its main function is the rebuilding of items, usually from serviceable parts on hand. SECOND. Operations performed by a mainten¬ ance platoon, or section, of the combat com¬ pany, battalion, or regiment. This maintenance unit carries a predetermined stock of parts called the organizational spare parts set, and has skilled mechanics, capable of the mainte¬ nance of equipment in forward areas. STRAPPING. Connecting the end of each mag¬ netron segment by a single strap to the next segment. The straps are all alike and are ar¬ ranged similarly to a set of blades in a radial- flow turbine. THIRD. Operations that are usually performed by mobile maintenance organizations attached to, designated for, or an organic part of troop units. ECHO. 1. Wave which has been reflected or otherwise returned with sufficient magnitude and delay to be perceived, in some manner, as a wave dis¬ tinct from that directly transmitted. 2. Signal reflected by a distant target to a radar set. 3. Deflection or indication on the screen of a cathode-ray tube representing a target. 4. Facsimile multiple reproduction on the re¬ cord sheet due to the same original facsimile sig¬ nal arriving at different times from transmis¬ sion paths of different lengths. This may be caused by multipath transmission on radio circuits or reflections on wire circuits. 3. Electronic condition in a simple or integrated radio system which causes a signal such as a voice signal to be reflected from some point or points in the circuit back to the point of origina¬ tion of the signal. ARTIFICIAL. 1. Received reflections of a trans¬ mitted pulse from an artificial target, such as an echo box, corner reflector, or other metallic reflecting surface. 2. Delayed signal from a pulsed RF signal generator. 39-242 1 APRIL 1959 AFM 100-39 ECH FRADULENT. False echo produced by use of deceptive devices. PERMANENT. Signal received by a ground-based radar as a result of reflections from fixed objects. RADAR. 1. Radio frequency energy received after reflection from an object. 2. Term is also used to describe the deflec¬ tion or change of intensity on a cathode-ray tube display produced by a radar echo. ECHO AREA. Equivalent echoing area of a target. This quan¬ tity indicates the relative amount of radar energy which the target will reflect. ECHO BOX. High Q resonant cavity that receives RF en¬ ergy through a pick-up antenna or a directional coupler during the transmitted pulse and re¬ turns this energy to the radar set immediately after the pulse through the same antenna or coupler. The echo box may be used to test the overall performance of the radar set or it may be used to demonstrate graphically, on a PPI scope, the form of the antenna pattern. ECHO BOX ANTENNA. Small dipole supported on a bracket near t e radar antenna, used to pick up the radar pulse and to feed the echo box oscillations back to the radar antenna. ECHO CHAMBER. Reverberant room or inclosure used in a radio studio to add hollow effects or actual echoes to radio programs. ECHO DEPTH SOUNDING. System of determining ocean depth by measuring the time interval between production of a soun just below the surface of the water and arrival of the echo refelected from the ocean bottom. ECHO HOMING. Classified definition. (Reference: AFM 100-50.) ECHO MATCHING. Turning the antenna or array until the two echoes that correspond with the two directions of the beam are equal. ECHO RANGING. Determination of both direction and distance of an underwater object from a vessel. ECHO SOUNDER. Sounding device used by ships to determine the depth of water. ECHO SPLITTING. In certain radar equipment, the echo return is split and appears as a double indication on the screen of the radar indicator. This splitting is accomplished by special electronic circuits associ¬ ated with the antenna lobe-switching mechanism. When the two echo indications are of equal height, the target bearing is read from a calibra¬ ted scale. ECHO SUPPRESSION. IFF (identification, friend or foe) control use to disable the responser for a short time to pre¬ vent reception of echoes from nearby targets that are produced by the interrogator pulse. ECHO SUPPRESSOR. Voice-operated device for connection to a two- way telephone circuit to attenuate echo currents in one direction caused by telephone currents in the other direction. Reflected radar signal received from an object by a radar receiver. ECL (EQUIPMENT COMPONENT LIST). Publication prescribing the kits and sets of too s or equipment needed by an individual, activity, or organization to perform a specific duty or function. ECLIPTIC. , . ( Term msed in reference to the annual path of the earth around the sun. ECM (ELECTRONIC COUNTERMEASURES). Any of the various offensive or defensive tactics which use electronic and reflecting devices to reduce the effectiveness of enemy equipment or of tactics employing electromagnetic radiations. ECM HOMING. Act of approaching an enemy source of electro¬ magnetic radiation guided by a receiver wit 39-243 1 APRIL 1959 directional antennas. ECM TACTICS. General term which applies to those methods employed to nullify or reduce the effectiveness of a defense system. ECMP (ELECTRONIC COUNTERMEASURES PROGRAM). ECO (ELECTRON-COUPLED OSCILLATOR). Oscillator which employs electron coupling be¬ tween the oscillator and the output or load, using a vacuum tube as the medium for coupling. ECP (ENGINEERING CHANGE PROPOSED). ECSA (EUROPEAN COMMUNICATIONS SECURITY AGENCY). EDDY CURRENT. Current induced in a metal by a changing electro¬ magnetic field. EDGE GRINDING. Hand lapping the edges of a crystal oscillator- plate to increase the activity. EDISON BASE. Standard screw-thread base used for ordinary electric lamps. EDISON DISTRIBUTION SYSTEM. Three wire dc distribution system, usually 120- 240 volts for combined light and power service from a single set of mains. EDISON EFFECT. Phenomena wherein electrons, emitted from a heated element within a vacuum tube, will flow •to a second element that is connected to a posi¬ tive potential with respect to the emitter but will not flow to an element that is connected to a negative pontential. EDISON STORAGE CELL. Storage cell having negative plates of iron oxide and positive plates of nickel oxide immersed in an alkaline solution and producing an open- circuit voltage of 1.2 volts per cell. EDP (ELECTRONIC DATA-PROCESSING) CENTER. Automatically operated equipment engineered to simplify the use and interpretation of the mass of data gathered by modern instrument installa¬ tions. Can automatically handle information fed to it from thousands of widely scattered points. EDPE (ELECTRONIC DATA PROCESSING EQUIPMENT). Equipment used to process the Punch Card Accounting Machine Cards used in the AMC LOGCOM SYSTEM. The electronic data pro¬ cessing equipment is located at specified cen¬ ters to process other Air Material Area or Air Force Depot records. EEI (ESSENTIAL ELEMENTS OF INFORMATION). Statement of the additional data regarding the enemy, terrain not under our control, or me¬ teorological or hydrographic conditions, which must be collected and processed in order to en¬ able a commander to make a sound decision as to course of action, conduct a maneuver, avoid surprise, or formulate details of a plan of op¬ erations. The essential elements are usually enunciated in the form of questions posed for the purpose of focusing the attention and activi¬ ties of all collecting agencies on the high-priority information which is needed at a particular time. EFFECTIVE ANTENNA LENGTH. Length which, when multiplied by the current at the point of maximum current, will give the same product as the length and uniform cur¬ rent of an elementary electric dipole at the same location, giving the same radio field intensity in the direction of maximum radiation. EFFECTIVE APERTURE OR OBJECTIVE. (Reference: APERTURE.) EFFECTIVE AREA. Square of the wavelength multiplied by the power gain (or directive gain) in that direction, and divided by 4 tt. Note. When power gain is used, the effective area is that for power reception; when directive gain is used, the effective area is that for directivity. 39-244 1 APRIL 1959 AFM 100-39 EFF EFFECTIVE CONDUCTIVITY. Conductance between the opposite parallel faces of a portion of material having unit length and unit cross section. EFFECTIVE CONFUSION AREA. Amount of chaff whose radar cross-sectional area equals the radar cross-sectional area of the partt- cular aircraft at a particular frequency. EFFECTIVE CONFUSION QUANTITY. Number of units necessary to hide a given target in the same resolving radar cell. EFFECTIVE CURRENT. Value of alternating current which will give the same heating effect as the corresponding value of direct current. The effective value is 0.707 times the peak value in the case of sine-wave alternating currents. EFFECTIVE CUTOFF FREQUENCY. Frequency at which its insertion loss between specified terminating impedances exceeds y some specified amount the loss at some reference point in the transmission band. EFFECTIVE FIELD INTENSITY. Root-mean-square value of the inverse distance fields at a distance of one mile from the trans¬ mitting antenna in all directions in the horizontal plane. FFECTIVE HEIGHT. . 1 Quantity used to define the transmission char¬ acteristics of an antenna. For a receiving antenna the effective height defines the voltage induced in the antenna when mulitplied by the inci ent field intensity. 2 In low frequency applications the term effec¬ tive height” is applied to loaded or nonloaded vertical antennas and is equal to the movement of the current distribution in the vertical section divided by the input current. : FFECTIVE PERCENTAGE MODULATION. ‘ Ratio of the peak value of the fundamental com¬ ponent of the envelope of the dc component in the modulated conditions, expressed in per EFFECTIVE P<5WER. Product of the antenna input power in kilowatts and the antenna gain. EFFECTIVE RADIUS OF THE EARTH. Effective value for this radius of the earth, whic is used in place of the geometrical radius to cor¬ rect for atmospheric refraction when the index or refraction in the atmosphere changes linearly with height. Note. Under conditions of standard refraction, the effective radius of the earth is 8.5 x 10 ,; meters, or 4/3 the geometrical radius. EFFECTIVE RESISTANCE. Quotient of the average rate of dissipation of electric energy during a cycle divided by the square of the effective current. EFFECTIVE SIGNAL RADIATED. Basis for licensing radio transmitters, equal to the product of the square root of the effective radiated power, times the antenna height in feet above the ground level. EFFECTIVE SOUND PRESSURE. Root-mean-square value of the instantaneous sound pressure, at a point, over a complete eye e. The unit is the dyne per square centimeter. FFECTIVE VALUE. Alternating-current value that will produce the same amount of heat in a resistance as the cor¬ responding direct-current value. The effective value is also called the RMS (root-mean- square) value. It is 0.707 times the peak value. EFFICIENCY. . Efficiency of an electroacoustic transducer is the ratio of the useful power output to the signa power input. MECHANICAL. Ratio between the brake horse¬ power (BHP) and the indicated or total horse- power (IHP). RATIFICATION. Ratio of the dc power output to the ac input of a rectifier. VOLUMETRIC. Ratio of the volume of air or fuel mixture actually taken into the cylinder to the cent. 39-245 AFM 100-39 EHF 1 APRIL 1959 EHF (EXTREMELY HIGH FREQUENCY). 1. Frequency; 30,000 to 300,000 megacycles (Millimetric waves). 2. Wave length: 0.1 to 1 centimeter. EINSTEIN SHIFT. Shift toward the red in the spectral lines of light which, according to the relativity theory, has its frequencies slightly reduced upon emerg¬ ing from a strong gravitational field, such as that of a dense star. EINTHOVEN STRING GALVANOMETER. Moving coil type of galvanometer where the coil is a single wire suspended between the poles of a powerful electromagnet. ELASTANCE. Measure of the difficulty with which an electric displacement can be produced in a capacitor. It is measured in drafts, and is the reciprocal of capacitance. ELASTICITY. Ability of a material to return to its original shape after being stretched, bent, or otherwise deformed. ELCO. Classified definition. (Reference: AFM 100-50.) ELEC (ELECTRIC, ELECTRICAL, ELECTRICIAN). 1. Electric; a nonconductor of electricity, as am¬ ber, glass, resin, etc., used to excite or store electricity. 2. Electrical; pertaining to, consisting of, con¬ taining, producing, derived from, produced, or operated by, electricity. 3. Electrician; one who designs, makes or re¬ pairs electric instruments, machinery, etc., or sets up electrical installations. ELECOM (ELECTRONIC COMPUTING SYSTEM). ELECT. (ELECTRONICS). General term used to describe that branch of elec¬ trical science and technology that treats the be¬ havior of electronics in vacuous and gaseous space. Lately extended to include transistors and other semiconductor devices. ELECTRA. Radio navigational system developed by Germany for wartime bombing and navigational uses. Es¬ sentially, it is a multiple radio range, providing a large number (frequency 24) of equisignal zones. Deviations from the equisignal zones were detected by hearing dots on one side of the zone and dashes (interlocked) on the other. Other methods, such as direction finding on the trans¬ mitter station, had to be employed to solve the ambiguity problem. A simple three-tower antenna system was used. The azimuths of several equi¬ signal lanes could be adjusted together so that one of them would extend along any chosen great circle from the transmitter. Thus area bombing was carried out during instrument conditions by adjusting two ELEKTRA stations so that two of their lanes intersected over the target. ELEKTRA becomes SONNE when the equisig¬ nal zones are periodically rotated in bearing. ELECTRIC. Nonconductor of electricity, as amber, glass, re¬ sin, etc; used to excite or store electricity. ELECTRIC ANGLE. % Means of specifying a particular instant in an ac cycle. One cycle is considered equal to 360 de¬ grees, hence a half cycle is 180 degrees and a quarter cycle is 90 degrees. If one voltage reaches a peak value a quarter of a cycle after another, the electrical angle between the voltages (the phase difference) is 90 degrees. ELECTRIC BRAZING. Brazing process in which the heat is obtained from an electric current. ELECTRIC BREAKDOWN. Electric discharge taking place through an in¬ sulating material. ELECTRIC CHARGE. Electric energy stored on the surface of an in¬ sulated object. ELECTRIC CHRONOGRAPH. Apparatus for measuring and recording intervals of time with a high degree of accuracy. By closing contacts, current impulses are sent 39-246 APRIL 1959 AFM 100-39 ELE through electromagnets that act on a recording pen to produce indications on a paper strip trav¬ eling at a known speed. ELECTRIC CIRCUIT. Path or circuit consisting of wires or group interconnected paths and circuit elements so connected as to allow the flow of electric cur- rents. ELECTRIC CONTROLLER. Device which serves to govern, in some pre e- termined manner, the electric power delivered to the apparatus to which it is connecte . ELECTRIC DETONATOR. . . Cap filled with an explosive mixture in which is embedded a fine resistance wire connected to external terminals. When a current is sent through the wire, it heats and detonates the mix- ture. ELECTRIC DIPOLE OR DOUBLET. , Simple antenna comprising a pair of cond tors which is capable of radiating an electromag¬ netic wave in response to a displacement of elect- trie charge from one conductor to t e o ELECTRIC DISCHARGE LAMP. Sealed glass inclosure in which light is produce by the passage of electricity through a meta ic vapor or inert gas. ELE l CT populM E name for a photoelectric cell of any type. 2. Cathode-ray tuning indicator tube used in some radio receivers. ELEC ™gion E around an electrically charged body wherein lines of electric stress exist. 2 Space in which an electric charge will experi¬ ence a force exerted upon it. electric field intensity 1. Measure of the force that would be exerted at a point by a unit charge placed at that point. 2 Property of electromagnetic radiation measured in terms of the EMF it produces (Referenc e : electric field strength, electric FORCE.) ELECTRIC FIELD STRENGTH. Magnitude of the electric field in an electromag¬ netic wave, usually in volts per meter. ELECTRIC FILAMENT LAMP. Glass bulb either evacuated or filled with an in¬ ert gas havng a resistance element electrically heated to (and maintained at) incandescence. ELECTRIC FILTER. Electronic filter. ELECTRIC FORCE. Electric field intensity. ELECTRIC FURNACE. Furnace in which an electrical current is source of heat. ELECTRIC GENERATOR. . Machine that transforms mechanical power into electrical power. ELECTRIC HYSTERESIS. Internal friction occurring in a dielectric n erial like paper or mica when subjected to a varying electric field as in a capacitor in an ac circuit. It is accompanied by generation of heat in the dielectric and this can eventually cause breakdown of th.e capacitor. ELECTRIC IMAGE. Electrical counterpart of an object, comprising a fictitious distribution of electricity that is mathe¬ matically equivalent to the actual distribution on a nearby real object. ELECTRIC- INTENSITY. Electric field intensity. ELECTRIC LIGHT. Light produced by an electric lamp. This light may be produced by using an electric current to heat a resistance material to incandesence, to ionize a gas and produce a luminous glow dis¬ charge, or to ionize a gas and thereby activa e a fluorescent material. 39-247 1 APRIL 1959 AFM 100-39 ELE ELECTRIC MOMENT. Electrical moment of two charges having equal magnitude and opposite sign is a vector whose magnitude is equal to the product of the magni¬ tude of each charge by the distance between the centers of the charges. The direction of the vec¬ tor is from the negative to the positive charge. ELECTRIC MOTOR. Machine that transforms electrical energy into mechanical energy. ELECTRIC NETWORK. Combination of any number of electric elements, the impedances of which may be either lumped or distributed, or both. The elements may be con¬ nected in any manner. It is assumed to be a passive electric network (containing no source of energy) unless otherwise stated. An active electric network contains one or more sources of energy. ELECTRIC OSCILLATIONS. Oscillatons set up whenever a circuit containing inductance and capacitance is electrically dis¬ turbed. ELECTRIC POTENTIAL. Potential of a point is the potential difference be¬ tween that point and some equipotential surface (usually the earth which is arbitrarily chosen as having zero potential). ELECTRIC POTENTIAL DIFFERENCE. Potential difference between two points is equal to the work associated with the transfer of unit quantity of positive electricity from one point to the other. If outside energy is required to trans¬ fer unit positive quantity from a to b, b is at a higher potential than a. ELECTRIC PRECIPITATION. Collecting of dust or other finely divided part¬ icles of matter by charging the particles induc¬ tively with an electric field, then attracting them to highly charged collector plates. ELECTRIC SHIELD. Housing or metal usually aluminum or copper, placed around a circuit. The housing prevents interaction between circuits by providing a low resistance and reflecting path to ground for high- frequency radiations. ELECTRIC STRAIN GAGE. Strain gage in which the change in the shape of the structural member under load causes a corres¬ ponding variation in the current flowing through the gage. ELECTRIC STRENGTH. Maximum potential gradient that dielectric mat¬ erial can withstand without rupture. ELECTRIC SUPPLY LINES. Conductors and their necessary supporting or containing structures which are located entirely outside of buildings and are used for conveying electric energy. ELECTRIC TELEMETER. Complete measuring, transmitting, and receiving apparatus for indicating, recording, or integrat¬ ing at a distance, by electric translating means, the value of a quantity. ELECTRIC TELEMETERING. Measurements at a distance by the use of electric circuits. ELECTRIC TRANSDUCER. Transducer designed to be actuated by, or to de¬ liver, electric waves. ELECTRIC VECTOR. Component of the electromagnetic field associ¬ ated with electromagnetic radiation which is of the nature of an electric field. The electric vector is supposed to coexist with, but act at right angles to, the magnetic vector. ELECTRIC WAVE. Another name for an electromagnetic wave produced by oscillations of electricity in a con¬ ductor. ELECTRIC WAVE FILTER. Wave filter designed to separate electric waves of different frequencies. ELECTRIC-CAPACITY ALTIMETER. Altimeter, the indications of which depend on the variation of electric capacity with distance from the earth’s surface. 39-248 1 APRIL 1959 AFM 100-39 ELE ELECTRICAL. . . Pertaining to, consisting of, containing, pro¬ ducing, derived from, or produced or operatec by, electricity. ELECTRICAL AXIS. X-axis of a crystal. ELECTRICAL BANDSPREAD. Use of a small variable capacitor in parallel with each tuning capacitor section in a short-wave re¬ ceiver to spread the stations in a single band over the entire range of a dial and thereby obtain more accurate tuning. ELECTRICAL CENTER. Point approximately midway between the ends of an inductor or resistor that divides the indue tor or resistor into two equal electrical values. ELECTRICAL CONTROL. Control of a machine, device, or action by swit¬ ches, relays, rheostats, or other equipment not employing vacuum tubes. ELECTRICAL DEGREE. . 1. One 360th part of the angle subtended, at the center of the armature shaft of a rotating machine, by two consecutive filed poles of i e polarity. 2. One 360th of a cycle of an alternating current. EL Dltl A e L m D el^d C in a unit based on the velocity of light. ELECTRICAL INTERFERENCES. Interference or electrical disturbance caused by the operation of electrical apparatus other tha radio stations. It may be either selective inter ference (a narrow band of frequencies) or noise (random frequency distribution), usua y latter. ELECTRICAL INERTIA. Inductance that opposes any change in current flow through an inductor. E T“ o L f EN an T anten„a length in free space which will give the same radiation characteris dcs as a given antenna in a normal location near the ground. For a 1/2 wave antenna the electrical length is about 5 percent less than the actual physical length, because of capacitance ef ects (end effects) at the ends of the antenna wire. 2. Length expressed in wavelengths, or an gular units. When expressed in angular units, it is the distance in wavelengths multiplied by 3„ to give radians or by 360 degrees to give degrees. ELECTRICAL LOAD. Device or circuit component into which power is intended to be delivered by an amplifier, gen¬ erator, etc.; comprises resistive and/or reactive components. ELECTRICAL MEASUREMENTS. Electromotive force, measured in volts. Current, measured in amperes. Resistance, measured in ohms. Inductance, measured in henries. Impedance, measured in ohms. Capacitance, measured in farads. ELECTRICAL MODULATION. Method in which the carrier is introduced into an electrical modulator, together with the signal currents directly produced by the density changes of the subject facsimile copy. ELECTRICAL PHONOGRAPH RECORDER. Electromechanical transducer actuated by power in an electrical system and supplying power to a recording mechanical system, the recorded waves produced by the mechanical system having re- quency components corresponding to those in the electrical system. ELECTRICAL QUARTZ. Synonymous with oscillator quartz. ELECTRICAL RESOLVER. . ,. Special type of synchro in which a single winding r P u< on the stator and two windings whose axes are 90 degrees apart on the rotor. ELECTRICAL SCANNING. Scanning by variation of the elecmcal phases 39-249 AFM 100-39 ELE 1 APRIL 1959 amplitudes existing at the primary radiating ele¬ ments. ELECTRICAL TRANSCRIPTION. Recording made in advance of a radio program for broadcast purposes. ELECTRICAL TWINNING. Defect occurring in natural quartz crystals, in which adjacent regions of quartz have their elec¬ trical axes oppositely poled. Each type of axis is usable but not both in the same plate. During manufacture, the dividing line is marked on the crystal and the regions subsequently separated. (Reference: ORIENTATIONAL TWINNING.) ELECTRICALLY CONNECTED. Connected by means of a conducting path or through a resistor, as distinguished from connec¬ tion merely through electro-magnetic induction. ELECTRICALLY-POWERED TELEPHONE. Telephone in which the operating power is ob¬ tained either from batteries located at the tele¬ phone (local battery) or from a telephone cen¬ tral office (common battery). ELECTRICIAN. One who designs, makes, or repairs, electric in¬ struments, machinery etc.; or sets up electrical installations. ELECTRICITY. Fundamental quantity in nature consisting of ele¬ mentary particles: electrons (negative), and positrons (positive). ELECTRIFICATION. Process of establishing an excess of positive elec¬ tricity or negative electricity in a body with re¬ spect to a given point. ELECTROACOUSTIC TRANSDUCER. Transducer which is actuated by power from an electrical system and supplies power to an acous¬ tical system or vice versa. Loudspeakers and mic¬ rophones are examples. ELECTROANALYSIS. Process of depositing an element or compound upon an electrode by electrolysis for the purpose of determining its quantity in the electrolyte so¬ lution. ELECTROBALLISTICS. Measurement of the speed of projectiles by elec¬ trical or electronic methods. ELECTROBIOLOGY. Science dealing with electrical phenomena of living creatures. ELECTROBIOSCOP Y. Application of a voltage to an animal body to detect signs of life by the production of muscular contractions. ELECTROCARDIOGRAM. Photographic or other graphic trace of the man¬ ner in which the electric current or voltage as¬ sociated with the action of heart muscles varies with time. This record is obtained with an elec¬ trocardiograph. ELECTROCARDIOGRAPH. Instrument for recording the changes in voltage occurring in the human body in synchron¬ ism with heart-beats. ELECTROCAUTERY. Apparatus for cauterizing tissue. ELECTROCHEMICAL EQUIVALENT. Weight of an element, compound, radical, or ion involved in a specified electrochemical reaction during the passage of a specified quantity of elec¬ tricity as a farad, ampere-hour, or coulomb. ELECTROCHEMICAL RECORDING. Facsimile recording by means of a chemical reac¬ tion brought about by the passage of signal-con- trolled current through the sensitized portion of the record sheet. ELECTROCHEMISTRY. Branch of science and technology which deals with reciprocal transformations of chemical and elec¬ tric energy. This includes batteries, electrolysis, electroplating, etc. ELECTROCOAGULATION. Coagulation of tissue by means of a high- frequency electrical current. 1 APRIL 1959 AFM 100-39 ELE ELE StImuladln of growth, flowering, or seeding by electrical means. ELECT T°m!nal at which electricity passes from one medium into another. 2 In a vacuum tube, the conducting element that performs one or more of the functions of emit¬ ting, collecting, or controlling electrons. Elec trodes include cathodes, grids and plates. ELECTRODE ADMITTANCE. Quotient of dividing the alternating componen of the electrode current by the alternating com¬ ponent of the electrode voltage, all other e trode voltages being maintained constant. ELECTRODE CAPACITANCE. Capacitance between one electrode and all the other electrodes connected together. “SIX , 1 SW • «■* an electrode voltage and current. electrode conductance. Quotient of the in-phase .te¬ trode alternating current by the elec . • nating voltage, all other electrode voltage be g maintained constant. This is a variational and a total conductance. El p C rM°s D of S< dteolving a substance from an elec- trode by electrolysis. ELECTRODYNAMIC INSTRUMENT. instrument which depends for its operation on the reaction between the current in one or more moving coils and the current in one or more fixe coils. ELECTRODYNAMIC LOUDSPEAKER. Dynamic loudspeaker in which the magnetic fte ‘STS— them. ■ .»«»■ £ rween two parts of the samel circuit are t*^ detecting or measuring an elect ■ss?rs.— tage developed in the brain. EL E C x T tr°tiono^ metals or compounds from ores and intermediate compounds by electrochemica pro cesses. ELE Curr°nt passing to or from an electrode. ELE p C i° D d Jpi'dinT form of heat by an elec- trode as a 'result of electron and/or ion bomb- ardment. fiectrode voltage or potential vJuage between an electrode and the cathode. EL p7oce° DE o P f"ng a substance on an elec¬ trode by electrolysis, as in electroplating, e ec trofornting, electro-refining, or electrow.nn.ng, electrodiagnosis. condidon of Determination of the tunc their various organs and tissues Dy st y s response to electric stimulation. electrodeposition. "srrs-. -* a- - - motion. ELE F C x"lf“e„ce by the application of "rtca. potential to a crystalline phospho or the suspension of such a crystal in a chang. g electric field. ELECT p R °duc.mn of chemical changes by means of current through an electrolyte. AFM 100-39 ELE 1 APRIL 1959 2. Destruction of underground structure by chem¬ ical action caused by straying electrical currents. ELECTROLYTE. Chemical compound either liquid or pastelike, the chemical action of which causes a current flow, or in which a chemical reaction is caused by the flow of a current. Examples of electrolytes are the liquid solution used in storage cells and pastelike compound used in dry cells or in dry electrolytic capacitors. ELECTROLYTIC CAPACITOR. Capacitor which is comprised of two plates sep¬ arated by electrolyte. Under the action of the applied dc voltage, a film of hydrogen gas is formed on one plate, and it is this film which acts as the dielectric. This type of construction makes it possible to concentrate large values of capacitance in a relatively small space. ELECTROLYTIC CELL. Unit of a battery which includes the container, two electrodes, and the electrolyte. ELECTROLYTIC CONDENSER. Capacitor, usually of large capacity, employing a set of plates immersed in an electrolytic solu¬ tion. Chemical action forms a very thin dielectric film on the anode plates, insulating them from the electrolyte, which then becomes the other electrode of the capacitor. ELECTROLYTIC CONDUCTION. Current flow due to movement of ions in an electrolyte when a voltage is applied between electrodes immersed in an electrolyte. ELECTROLYTIC COPPER. Copper obtained by an electrolytic process. ELECTROLYTIC DEPOSITION. Electroplating. ELECTROLYTIC DISSOCIATION. Process in a solution whereby the molecules are separated into their ions. ELECTROLYTIC INTERRUPTER. Device for regularly interrupting an electric cur¬ rent. ELECTROLYTIC IRON. Iron obtained by an electrolytic process. ELECTROLYTIC OXIDATION. Electrolytic process by which electrons are re¬ moved from, or positive charges are added to, an atom or ion. Occurs only at an anode. ELECTROLYTIC PICKLING. Removal of oxides or other compounds from a metal surface by passing a current through the metal in an acid solution. ELECTROLYTIC RECORDING. Form of electrochemical facsimile recording in which the chemical change is made possible prin¬ cipally by ionization. This is usually done on a chemically moistened paper. ELECTROLYTIC RECTIFIER. Rectifier in which rectification of an alternating current is accompanied by electrolytic action. ELECTROLYTIC REDUCTION. Electrolytic process by which electrons are ad¬ ded to, or positive charges are removed from an atom or ion. It occurs only at a cathode. ELECTROLYTIC REFINING. Refining or purifying metals by electrolytic pro¬ cesses. ELECTROLYZER. 1. Electrolytic cell for the production of alkali, chlorine, or other allied products. ELECTROMAGNET. Core of magnetic material, such as soft iron, that becomes temporarily magnetized by the passage of electric current through a coil of wire wound around the core. Current passing through the coil magnetizes the metal and gives it properties of attracting other magnetizable metal masses. ELECTROMAGNETIC CRACK DETECTOR. Instrument for detecting the presence of cracks in iron or steel objects. 2. Device used in electrotherapy for reducing urethral stricture with the aid of electricity. 39-252 1 APRIL 1959 AFM 100-39 ELE ELECTROMAGNETIC COUPLING. Mutual relationship between two wire pairs when the magnetic field of one pair induces a voltage in an adjacent pair. ELECTROMAGNETIC ENERGY. Forms of radiant energy, such as radio waves, heat waves, light waves, X-rays, gamma rays, and cosmic rays. ELECTROMAGNETIC FIELD. 1. Field of influence which an electric current produces around the conductor through which it flows. 2. Rapidly moving electric field and its associated magnetic field located at right angles to both the electric lines of force and to their direction of motion. 3. Magnetic field resulting from the flow of elec¬ tricity. ELECTROMAGNETIC HORN. Florn-shaped structure used for highly directive radiation of radio waves at frequencies of the order of 100 megacycles or higher. ELECTROMAGNETIC INDUCTION. Production of a voltage in a coil due to a change in the number of magnetic lines of force (flux linkages) passing through the coil. ELECTROMAGNETIC LENS. Electron lens in which focusing is produced electromagnetically. ELECTROMAGNETIC MIRROR. Surface or region capable of reflecting radio waves, such as one of the ionized layers in the upper atmospheres. ELECTROMAGNETIC RADIATION. Emission of energy in the form of electro¬ magnetic waves. The term is also used to des¬ cribe the radiated energy. ELECTROMAGNETIC RELAY. Electromagnetically operated switch, ordinarily composed of one or more coils which control one or more armatures, each of which actuates elec¬ tric contacts. ELECTROMAGNETIC SPECTRUM. Chart or graph showing the relation of all known electromagnetic wave forms classified by wavelength. ELECTROMAGNETIC THEORY OF LIGHT. Recognition of the identical nature of electro¬ magnetic waves and light. ELECTROMAGNETIC UNIT. Electric unit based primarily on the magnetic ef¬ fect of electric current. The fundamental centi¬ meter-gram-second unit in this system is the a- bampere. ELECTROMAGNETIC WAVE. 1. Transverse wave associated with the trans¬ mission of electromagnetic energy. 2. Wave produced by the oscillation of an elec¬ tric charge. 3. Wave iri which there are both electric and mag¬ netic displacements. Electromagnetic waves are known as radio waves, heat rays, light rays, X- rays, etc., depending on the frequency. ELECTROMAGNETICS. Branch of physics which deals with the mutual relationships existing between electric currents and the attendant magnetic fields. ELECTROMECHANICAL BELL. Bell having a prewound spring-driver mechan¬ ism, the operation of which is initiated by actua¬ tion of an electrical tripping mechanism. ELECTROMECHANICAL RECORDING. Facsimile recording by means of a mechanical de¬ vice, such as a stylus, which is actuated by the signal. ELECTROMECHANICAL TRANSDUCER. Transducer for receiving waves from an electric system and delivering waves to a mechanical sys¬ tem, or vice versa. ELECTROMECHANICS. Branch of electrical engineering which deals with machines producing or operated by electric cur¬ rents. ELECTROMETALLURGY. Branch of science and technology which deals with the application of electrochemistry to the ex¬ traction or treatment of metals. 39-253 AFM 100-39 ELE 1 APRIL 1959 ELECTROMETER. Electrical measuring instrument for measuring potential difference; it depends for its action on the force of attraction or repulsion between charged plates or needles. Used to determine the position and polarity of the X-axes in crystal blanks, etc. ELECTROMETER TUBE. Vacuum tube designed to amplify extremely small currents. ELECTROMOTIVE FORCE. Property which tends to alter the motion of elec¬ tricity or to maintain its motion against resistance. Difference of electrical potential, or pressure is measured in volts. ELECTROMOTIVE SERIES. Arrangement of the metal elements in the order of the amount of electromotive force (voltage) set up between metal and solution when the metal is placed in a normal solution of any of its salts. Each metal is negative to those preceding it in the list, and positive to those succeeding it. ELECTRON. 1. According to classical theory, an elementary negative charge that revolves around the nucleus of an atom. 2. Elementary unit of a negative electrical charge. 3. Negatively charged particles of matter. 4. Smallest particle of matter. Electrons are e- mitted by the cathode of an electron tube ELECTRON AVALANCHE. Process by which one electron produces many additional electrons by collision. ELECTRON COUPLING Coupling of two circuits inside a vacuum tube; used principally with multigrid tubes. The elec¬ tron stream between electrodes in one circuit transfers energy to electrodes in the other circuit. ELECTRON DRIFT. Actual movement of electrons in a definite direc¬ tion through a conductor during current flow, as contrasted with transfer of energy from one electron to another by collision. ELECTRON EMISSION. 1. Liberation of electrons from the surface of a body into space under the influence of heat, light, impact, chemical disintegration, or a po¬ tential difference. 2. Release of electrons from a material, as from the cathode of an electron tube. ELECTRON GUN. 1. Group of electrodes which produce and focus an electron beam of controllable intensity. 2. Portion of a cathode-ray tube or camera tube which emits a beam of controlled electrons. In a kinescope picture tube, these electrons form the scanning beam which produces the visible picture on the luminescent screen. ELECTRON IMAGE TUBE. Cathode-ray tube having a photoemissive mosaic, upon which an optical image is projected, and an electron gun to scan the mosaic and convert the optical image into corresponding electronic current. ELECTRON LENS. Arrangement of electrodes and/or magnets ar¬ ranged to produce a predetermined configuration of electrical and magnetic fields so as to focus, deflect, etc., a beam of electrons in much the same manner as a glass lens controls a beam of light. ELECTRON MICROSCOPE. Instrument that sends a beam of electrons through a thin sample of the material being ex¬ amined, magnifies the resulting shadow caused by denser portions of the sample, and makes this shadow visible on a fluorescent screen or records it on photographic film. ELECTRON MIRROR. Reflecting electrode in a multiplier-type photo¬ tube. (Reference: DYNODE.) ELECTRON MULTIPLIER. Vacuum tube in which electrons liberated from a photosensitive cathode are attracted successively to a series of electrodes, called dynodes. Each 39-254 1 APRIL 1959 AFM 100-39 ELE electron liberates others (by secondary emission) as it strikes each dynode, causing a great increase, or multiplication, in the number of electrons flow¬ ing in the tube. ELECTRON OPTICS. Branch of electronics that deals with the control of electron beams by means of electric or mag¬ netic fields. ELECTRON TELESCOPE. Apparatus for seeing through fraze an d fog, j n which an infrared image is formed optically on the photoemissive mosaic of an electron image tube and then rendered visible by the tube. ELECTRON TRANSIT TIME. Time required for electrons to travel between two electrodes in a vacuum tube. This time is ex¬ tremely important in tubes designed for ultra- high frequencies. ELECTRON TUBE. Vacuum tube in which the motion of electrons is especially important, such as a thermionic, pho¬ toelectric, or X-ray tube. ELECTRON VOLT. Amount of energy gained by an electron in pas¬ sing from one point to another that is one volt higher in potential. One electron volt is equal to 1.592 x 10 12 ergs. ELECTRON-BEAM GENERATOR. Velocity modulated generator, such as a klys¬ tron tube, used to generate extremely high fre¬ quencies. ELECTRON-COUPLED OSCILLATOR. Oscillation which employs electron coupling be¬ tween the oscillator and the output or load, using a vacuum tube as the medium for coupling. ELECTRON-RAY TUBE. Cathode-ray tuning indicator tube. ELECTRONIC. Pertaining to an electron or electronics. ELECTRONIC AUTOPILOT. Arrangement of gyroscopes combined with electronic amplifiers and servo motors to detect deviations in the flight of aircraft and apply the required corrections directly to the control cables of the aircraft. ELECTRONIC CAMOUFLAGE. Use of radar absorbent materials to reduce the radar echoing properties of any surface. ELECTRONIC COMPUTING GUNSIGHT. Electrical computing device used in connection with an electronic servo system on an aircraft gunsight to provide, automatically, the required offset between the line of sight and the gun. This compensates for such factors as gun elevation and direction, target range, bomber air speed, bomber altitude, relative velocity between bomber and target, and correction for windage and gravity. ELECTRONIC CONFUSION. Classified definition. (Reference: AFM 100-50.) ELECTRONIC CONTROL. Control of a machine or condition by apparatus using electron tubes. Electronic safety devices are examples of electronic control. ELECTRONIC COUNTER COUNTERMEASURES. 1. Various tactics used to reduce the effective¬ ness of electronic countermeasures. 2. Classified definition. (Reference: AFM 100- 50.) ELECTRONIC COUNTERMEASURES. Major subdivision of the use of electronics in¬ volving actions taken to reduce the effectiveness of enemy equipment and/or tactics employing or affected by electromagnetic radiations. (Re¬ ference: AFM 100-50.) ELECTRONIC COUNTERMEASURES OFFICER. USAF officer who plans airborne electronic in¬ tercept operations, determines tactical use of ac¬ tive airborne and ground electronic countermea¬ sures, operates countermeasure equipment, and serves as electronic countermeasures staff officer. ELECTRONIC COUPLING. Method of coupling electrical energy from one 39-255 AFM 100-39 ELE 1 APRIL 1959 circuit to another through the electron stream in a vacuum tube. ELECTRONIC COVER AND DECEPTION. Classified definition (Reference: AFM 100-50.) ELECTRONIC DATA PROCESSING EQUIPMENT. Equipment used to process the punch card ac¬ counting machine cards used in the AMC LOG- COM SYSTEM. The electronic data processing equipment is located at specified centers to pro¬ cess either Air Material Area or Air Force Depot records. ELECTRONIC DECEPTION. 1. Radiation or reradiation of electromagnetic waves in a manner intended to mislead the enemy in the interpretation of data received by his elec¬ tronic equipment. 2. Classified definition. (Reference: AFM 100- 50.) ELECTRONIC (ELECTRIC) FILTER. Selective circuit network designed to pass cur¬ rents within a continuous band or bands of fre¬ quencies, and substantially reduce the amplitude of undesired frequencies. It is composed of an arrangement of electronic parts such as resistors, inductors, capacitors, and quartz crystals. ELECTRONIC INTELLIGENCE. Search for, and analysis of, transmitted signals to determine the location or the technical char¬ acteristics of a transmitting device. Electronic in¬ telligence is divided into a search or electronic reconnaissance phase and a reduction and dis¬ semination of intelligence phase. ELECTRONIC JAMMING. 1. Action involved in electronic countermeasures, being the radiation or reradiation of electromag¬ netic waves to impair the use of a specified seg¬ ment of the radio spectrum. 2. Classified definition. (Reference: BARRAGE JAMMING, AFM 100-50.) ELECTRONIC KEYING. Method of keying in which the keyed circuit is controlled by electron tubes. ELECTRONIC LINE SCANNING. Scanning in which the spot moves across the copy by electronic movement of a spot on a cathode- ray tube while the record sheet or subject copy is being moved in a perpendicular direction by me¬ chanical means. ELECTRONIC PHOTOMETER. Electronic instrument designed to measure in¬ tensity of light, brightness of paints, turbidity of solutions, etc. It comprises a phototube, an electronic direct-current amplifier, and an indi¬ cating instrument. ELECTRONIC PROFILOMETER. Electronic instrument for measuring surface roughness. The diamond-point stylus of a per¬ manent magnet dynamic pick-up is moved over the surface to be examined, and the resulting varying voltage is amplified, rectified, and mea¬ sured with a meter calibrated to read directly in microinches of deviation from smoothness. ELECTRONIC RASTER SCANNING. Method of scanning, whereby the spot is moved across and also perpendicular to the scanning line by cathode-ray tube sweep circuits. This method is the same as used in television trans¬ mission. ELECTRONIC RECOGNITION AND IDENTIFICATION. Determination, by electronic means, of the friend¬ ly or enemy character, or of the individuality of another, and the identification by electronic means of your own friendly character or own indivi¬ duality. ELECTRONIC RECONNAISSANCE. Search for electromagnetic radiations to determine existance, source and pertinent characteristics for electronics warfare purposes. ELECTRONIC RECTIFIER. Rectifier in which rectification of an alternating current is accompanied by the passage of electrons only at the boundary of an electrochemical valve metal and a compound of that metal (as in a copper oxide rectifier of a selenium rectifier) or in an electron tube. 39-256 1 APRIL 1959 AFM 100-39 ELE ELECTRONIC SCANNING. Scanning with an electronic beam as in a cathode- ray tube, as contrasted with mechanical scanning with a rotating disk, prismatic disk, or mirror drum. ELECTRONIC SEARCH OR RECONNAISSANCE. Determination of existence, source, and pertin¬ ent characteristics of electromagnetic radia¬ tions; a passive countermeasure. (Reference: COUNTERMEASURES.) ELECTRONIC SUPPLY SUPPORT BASE. Base supplying electronic equipment to radar sites. The major air commands will designate elec¬ tronic supply support bases as required, and will inform Headquarters, AMC, of the bases so de¬ signated. ELECTRONIC SWITCH. 1. Vacuum tube (or transistor) used as an on and off switching device. 2. Test instrument that is used to present two wave shapes on a single gun cathode-ray tube. ELECTRONIC TELEVISION. Television system utilizing cathode-ray tubes to scan the scene at the transmitter and to recon¬ struct it at the receiver. The process is electrical, with no moving mechanical parts. ELECTRONIC TIMER. 1. Synchronizer, pulse generator, modulator, or keyer originates a continuous series of identical control pulses, which occur at an exact and un¬ varying rate of repetition, known as the pulse recurrence frequency. 2. Interval timer using an electronic circuit. ELECTRONIC TUBE. Glass or metal envelope, usually highly eva¬ cuated, wherein the flow of electrons emitted by a cathode are collected by a positive anode. The flow of electrons may be controlled by one or more grids. ELECTRONIC TUBES. Controls the amount, direction, and speed of elec¬ trical current. Changes alternating current to direct current or direct current to alternating cur¬ rent; amplifies it into greater power, and changes it into radio or X-rays. ELECTRONIC VOLTMETER. Voltage measuring instrument utilizing the char¬ acteristics of a vacuum tube (or transistor) for measuring voltages with minimum effect on the circuit to which the instrument is connected. (Re¬ ference: VACUUM-TUBE VOLTMETER.) ELECTRONIC WARFARE. Electronic warfare is that division of the military use of electronics involving actions taken to prevent or reduce an enemy’s effective use of radiated electromagnetic energy, and actions taken to insure our own effective use of radiated electromagnetic energy. ELECTRONICS. General term used to describe that branch of electrical science and technology that treats the behavior of electrons in vacuous or gaseous space. Lately extended to include transistors and other semiconductor devices. ELECTROPHORUS. Early type of static electricity generator. ELECTROPLANE CAMERA. Optical lens system in which one or more of the lens elements are electronically oscillated back and forth to provide greater depth of field than can be obtained by optical means alone. De¬ veloped primarily for standard motion picture cameras. ELECTROPLATE. Coating of metal placed on a surface by means of electrolysis. ELECTROPLATING. Electrodeposition of an adherent coating upon an electrode for the purpose of securing a sur¬ face with .properties or dimensions different from those of the base metal. ELECTROREFINING. Process of dissolving a metal from an impure anode by means of electrodeposition and depos¬ iting it in a purer state. ELECTROSCOPE. Instrument used for detecting small charges of electricity. 39-257 AFM 100-39 ELE 1 APRIL 1959 ELECTROSENSITIVE RECORDING, Type of recording where the record image is pro¬ duced by passage of electric current into the re¬ cord sheet. ELECTROSTATIC. Pertaining to electricity at rest, such as charges on an object (static electricity). ELECTROSTATIC CHARGE. Electric charge stored in a capacitor or on the surface of an insulated object. ELECTROSTATIC COUPLING. Coupling by means of capacitance, so that charges on one circuit influence the other circuit through the capacitance. ELECTROSTATIC DEFLECTION. Deflecting an electron beam by applying a volt¬ age between plates mounted inside a cathode- ray tube. ELECTROSTATIC ENERGY STORAGE SPOT WELDER. Welder, consisting essentially of a capacitor bank that is charged slowly to a predetermined volt¬ age, then discharged suddenly through the mat¬ erial to be welded. ELECTROSTATIC FIELD. Field of force (influence) between two elec¬ trically charged bodies. ELECTROSTATIC FOCUS. Production of a focused electron beam in a cat¬ hode-ray tube by the application of an electric field. ELECTROSTATIC FOCUSING. Method of focusing an electron stream in which focus is produced through the action of an elec¬ tric field. ELECTROSTATIC GENERATOR. Device for the production of electric charges by electrostatic action. ELECTROSTATIC INDUCTION. Process of charging an object electrically by bring¬ ing it into the electric field of a charged object. ELECTROSTATIC MICROPHONE. Microphone which depends for its operation upon variations of its electrostatic capacitance. ELECTROSTATIC PRECIPITATOR. Electronic apparatus for collecting or removing small particles from air by electrostatic means, as in the Precipitron. ELECTROSTATIC SEPARATOR. Apparatus in which a finely pulverized mix¬ ture of the materials to be separated is allowed to fall in a stream through a powerful electro¬ static field produced between two electrodes. ELECTROSTATIC SHIELD. Shield used to prevent electrostatic coupling be¬ tween circuits but which permits electromagnetic coupling. ELECTROSTATIC UNIT. Electric unit based primarily on the dynamic in¬ teraction of the electric charges. The electro¬ static unit charge which, if concentrated upon a small sphere, would repel a similar charge one centimeter distant in a vacuum with a force of one dyne. ELECTROSTATIC VOLTMETER. Voltmeter, depending for its action upon electro¬ static forces. ELECTROSTATICS. Branch of physics which deals with the proper¬ ties of electricity, which does not depend upon its motion. ELECT ROSTRICTION. Contraction or expansion of a quartz or other crystal along an electric axis when subjected to an electric field in that direction. (Reference: INVERSE PIEZOELECTRIC EFFECT.) ELECTROTHERMAL RECORDING. Type of electrochemical recording, used in facsimile equipment, wherein the chemical change is produced principally by thermal action. ELECTROTHERMIC INSTRUMENT. Instrument which depends for its operation on the heating effect of a current. 39-258 1 APRIL 1959 AFM 100-39 ELE ELECTROTHERMICS. Branch of science and technology which deals with the direct transformations of electric energy and heat. ELECTROTYPE. Printing plate made by electrolytically depositing copper or nickel in a wax or soft lead impression of the desired printing surface and backing this shell with molten metal. The wax mold is made conductive for electroplating by coating it with graphite. Electrotypes are usually made to secure duplicates of more costly original engravings. ELECTROTYPING. Production or reproduction of printing plates by electroforming. ELECTROWINNING. Extraction of a metal from its salts by causing a current to flow through a solution of its salts. Often used to separate a metal from its ore. ELECTRUM. 1. Natural alloy of gold and silver. 2. Plating of German silver. ELEKTRA. Radio navigation aid that provides a number of equisignal zones. Elektra becomes Sonne when the equisignal zones are periodically rotated in bearing. ELEMENT. 1. Substance, in chemistry, that cannot be di¬ vided into simpler substances by any means or¬ dinarily available. 2. Radiator, active or parasitic, that helps make up an antenna. 3. Element or finished element is sometimes ap¬ plied as a synonym of oscillator plate. 4. Element is a component part of an Interna¬ tional Morse Character, either a dot or a dash. MESSAGE KEYING. Part of the key which changes with every message. PARASITIC. Radiating element, not coupled dir¬ ectly to the feed line of the antenna, which materially affects the pattern of the antenna. PICTURE. Segment of a scanning line, the di¬ mension of which along the line is exactly eq¬ ual to the nominal line width. PIEZOELECTRIC CRYSTAL. Piece of piezoelec¬ tric material, cut and finished to a speci¬ fied geometrical shape and orientation with respect to the crystallographic axes of the material. RADIATING. Basic subdivision of an antenna which in itself is capable of radiating or re¬ ceiving radio frequency energy. (Reference: RADIATOR.) SIGNAL. Part of a signal which occupies the shortest interval of the signaling code. It is considered to be of unit duration building up signal combinations. ELEMENT OF A FIX. Specific values of the navigation coordinates necessary to define a position. ELEMENTAL AREA. Smallest segment scanned at any given instant in a television or facsimile system. It can be con¬ sidered a square area having dimensions equal to the width of the scanning line. (Reference: CRITICAL AREA, SCANNING SPOT.) ELEMENTARY CHARGE. Natural unit or quantum into which both posi¬ tive and negative changes appear to be subdivided. It is the charge on a single electron, and its value is about 4.77 x 10 -10 electro-static units. ELEMENTARY LENS EQUATION. Law giving the quantitative relation between the distance of the object, the image, and the princi¬ pal focus of the lens. ELEVATION. Angular position in a plane prependicular to the earth’s surface. The horizon is usually minimum elevation and the zenith is maximum elevation. It is usually expressed in degrees. This is, the horizon is 0 degrees and the zenith is 90 de¬ grees. It is ocassionally expressed in mils, 0 de¬ grees being equal to 0 mils and 90 degrees be¬ ing equal to 1,600 mils. 39-259 AFM 100-39 ELE 1 APRIL 1959 ELEVATION ANGLE. Angle that a radio wave makes with the horizon¬ tal. ELEVATION RESOLUTION. Minimum angular separation in a vertical plane between two targets at the same range and bear¬ ing that will allow an operator to obtain data on either individual target. ELEVATION ROD. Vertical position of a conductor in an air terminal by means of which it is elevated above the object that is to be protected. ELEVATION-POSITION INDICATOR. Radar display which shows simultaneously an¬ gular elevation and slant range of objects de¬ tected in the vertical sight plane. ELIMINATOR. Device that takes the place of batteries in a radio receiver. It generally consists of a rectifier oper¬ ating from alternating current. ELINT (ELECTRONIC INTELLIGENCE). Information obtained from the analysis of in¬ tercepted foreign electronic signals. ELONGATION. Extension or elongation of the envelope of a signal due to the delayed arrival of certain of the multipath components. ELLA. Airborne propeller-modulation detector and in¬ dicator, AN/APX-15. It is used with the AN/ APG-15 airborne radar gunsight. Its purpose is to provide an indication to the gunner, when tracking a target with the AN/APG-15 system, as to whether the target is a B-29 or some other aircraft. The basis of identification is the fre¬ quency of the propeller modulation of the B-29. The set weighs 15 pounds and requires 75 watts of power. Maximum operating altitude is 40, 000 feet. It will give reliable identification up to 200 yards except of aircraft with a 10-second lag in the true identification of a new target after switching from a friendly target. Indication is by means of two paralleled dimmer-type dial lights which are on if the target being tracked is a B-29. ELLIPTICAL POLARIZATION. Wave, polarized in such a manner that both the transverse electric and magnetic fields have unequal components, at right angles to each other, that are not in time phase. The electric vec¬ tor at right angles to the direction of propa¬ gation rotates, with its magnitude changing, while in rotation. ELLIPTICALLY POLARIZED WAVE. Wave for which the electric intensity vector at a point describes an ellipse. ELSEC. Classified definition. (Reference: AFM 100-50.) EMANATION. Gaseous radioactive products formed by the ex¬ pulsion of an alpha particle from radium thor¬ ium X, or actinium X. Now known as radon, thoron, and actinon, respectively. emb (EMBASSY). Residence or office of an ambassador. EMBARKATION AREA. Area ashore, including a group of embarkation points, in which final preparations for embarka¬ tion are completed and through which assigned loads for craft and ships are called forward to embark. EMBASSY. Residence or office of an ambassador. EMBOSSED GROOVE RECORDING. Method of recording vocal sounds on disks or film strips by embossing sound grooves with a relatively blunt stylus, rather than by cutting grooves with a sharp stylus. Embossing throws the material up in furrows on each side of the sound groove, without removing any material. EMC (ENGINEERED MILITARY CIRCUIT). Leased long lines established in the ConUS for which only the station equipment, local loops, and reserved portions of interexchange channels are continuously paid for. The unreserved por¬ tions of leased long line or interexchange chan¬ nels are placed on a standby status by the com¬ mercial communications company, and they are 39-260 1 APRIL 1959 AFM 100-39 EMC placed in an actual operational status and paid for only when required by the command con¬ cerned. EMCCC (EUROPEAN MILITARY COMMUNICATIONS COORDINATING COMMITTEE). EMERGENCY. Message precedence designation. (Reference: PRECEDENCE DESIGNATIONS.) EMERGENCY COMMUNICATION. Transmission or reception of distress, alarm, ur¬ gent, or safety signals, or messages relating there¬ to or any matter relating to the safety of life or property, or occasional operation of equip¬ ment for determining whether or not the radio installation is in good working condition. EMERGENCY DESTRUCTION. Destruction of classified documents and mater¬ ial under emergency conditions, in accordance with standing instructions from proper author¬ ity, to prevent them from falling into unauthor¬ ized hands. The usual occasion for emergency destruction is when capture is imminent. EMERGENCY-OFF. Control not normally intended to turn off sys¬ tem power. EMERGENCY RADIO CHANNEL. Radio frequency reserved for emergency use, particularly for distress signals. EMERGENCY RECEIVER. Receiver immediately available in a ship station for emergency communication and capable of be¬ ing energized solely by a self-contained or emer¬ gency power supply. EMERGENCY SERVICE. Radio communication service carrier for emer¬ gency purposes. EMERGENCY SWITCH. Switch located ahead of meters in some buildings for the purpose of cutting off all electrical power in case of a fire or other emergency. EMERGENT NODAL POINT. Node, usually assumed to be a voltage node, having zero potential with respect to ground. (Re¬ ference: NODAL POINT.) EMERGENT RAY. Term applied to a ray of light, in optics, leaving a dense medium as contrasted with the entering or incident ray. EMF (ELECTROMOTIVE FORCE). Force causing a flow of current. Measured in volts. EMISSION. 1. Radio waves radiated into space by a radio transmitter. 2. Process of ejecting electrons from the sur¬ face of a material under the influence of heat, radiation, or other causes. ELECTRON. Liberation of electrons from the surface of a body, under the influence of heat, light, impact, chemical disintegration, or po¬ tential difference. PHOTOELECTRIC. Emission of electrons from certain materials when exposed to light. SECONDARY. 1. Electron emission which is the direct result of the impact of electrons against a surface. 2. Liberation Of electrons from an element within the tube other than the cathode, due to impact of electrons traveling from the cathode to some other element at a higher potential. THERMIONIC. 1. Electron emission from a solid body as a result of its elevated temperature. 2. Liberation of electrons due to the temper¬ ature rise of a cathode alone, independent of any bther electrodes within the tube. EMISSION CHARACTERISTIC. Relation, usually shown by a graph between the emission and a factor controlling the emission (as temperature, voltage, or current of the fila¬ ment.) EMISSION CURRENT. Current produced in the plate circuit of a tube 39-261 AFM 100-39 EMI 1 APRIL 1959 when all of the electrons emitted by the cathode pass to the plate. (Reference: SATURATION CURRENT.) EMISSOIN SPECTRUM. Spectrum showing the radiation emitted by a sub¬ stance, such as the spectrum of light emitted when a metal is placed in an electric arc or of light emitted by an incandescent filament. EMISSIVE POWER. Line rate of emission of radiant energy in all directions per unit surface area of a radiating body at a given temperature. (Reference: RAD¬ IATING POWER.) EML (EQUIPMENT MODIFICATION LIST). List of changes by addition, deletion, or substi¬ tution in the equipment section of a table of organization and equipment. EMPHASIZER. Circuit or device that intentionally increases sig¬ nal strength at certain audio frequencies. EMPIRE CLOTH. Cotton or linen cloth coated with linseed oil, used for insulating coils and other parts of elec¬ trical equipment. EMPIRICAL. Based on actual measurement, observation, or ex¬ perience as opposed to theoretical determina¬ tions. EMULSION. Suspension of a light-sensitive silver slat, es¬ pecially silver chloride or silver bromide, in a co¬ lloidal medium, usually gelatin, used for coating photographic films, plates, or papers. ENCA (EUROPEAN NAVAL COMMUNICATIONS AGENCY). EN ROUTE RADAR CONTROL. Portion of the long-range radar operation that applies to the positive fixing and/or control of aircraft operating between two terminal areas. ENABLING PULSE. Pulse which opens a normally closed electrical gate, or otherwise permits an operation for which it is necessary but not sufficient condition. ENAMELED WISE. Wire coated with an insulating layer of baked enamel. ENANTIOMORPHIC. Term applied to certain classes of crystals that occur in two forms, in one of which the external faces on all internal properties are the mirror image of those in the other. Quartz and Rochelle salts are examples. For quartz, the two forms are called right-quartz and left-quartz. ENCHANCED MULTISPOT NOISE. Classified definition. (Reference: AFM 100-50.) ENCIPHER. Convert a plain text message into unintelligible language by means of a cipher system. ENCIPHERED FACSIMILE COMMUNICATIONS. Communications in which security is accomplished by mixing pulses of key, produced by a key generator with the output of the facsimile con¬ verter. Plain text is recovered by subtracting the identical key at the receive terminal. Unauthor¬ ized listeners are unable to reconstruct the plain text unless they have an identical key generator and the daily key setting. ENCLOSED VENTILATED APPARATUS. Apparatus totally enclosed except that openings are provided for the admission and discharge of cooling air. ENCODE. 1. Convert a plain text message into its coded form. 2. Section of a code book in which the plain text equivalents of the code groups are in alpha¬ betical, numerical or other systematic order. EMMETROPIA. Normal refractive condition of the eyes. EMMETROPIC. Normal eye. EMN (EQUIPMENT MANUFACTURERS NUMBERS). r be regarded as a measure of the degree in w ic the energy of the system is unavailable. ENVELOPE. 1. Glass or metal housing of a vacuum tube. 2. Curve drawn to pass through the peaks of a graph showing the wave form of a modulated radio-frequency carrier signal. ENVELOPE DELAY. Time, which elapses betw een the instants at whic any designated point of a transmitted wave passes any two points of a transmission circuit between which the delay is measured or specified. Sue delay is primarily determined by the constants o has upwardly projecting diversion horns of thick wire, up which the arc travels as soon as it is formed. When the arc reaches the widest part of the gap, it extinguishes. HORN GAP. Type of spark gap which is provided with diver¬ gent electrodes. HORN MOUTH. End of the horn with the larger-cross-sectional area. HORN RADIATOR. Open-ended, metallic device for concentrating energy from a waveguide and directing this en¬ ergy into space. HORN THROAT. End of the horn with the smaller cross-sectional area. HORN-GAP SWITCH. Form of air switch provided with arcing horns. HORSEPOWER. Unit of power equal to 550 foot-pounds per second, and electrically equivalent to nearly 746 watts. HORSESHOE MAGNET. Permanent magnet or electromagnet bent into the shape of a horseshoe or having parallel sides like a U, to bring the two poles near each other. HOSTILE. Air defense expression, which is the classifica¬ tion of a track based upon established criteria, indicating the airborne object to be that of an enemy. It may also be an identification, if such action is taken. HOT. 1. Connected, alive, energized; pertains to ter¬ minal, or any ungrounded conductor. 2. Not grounded. HOT CATHODE. Cathode in which electron emission is produced by heat. HOT-CATHODE, X-RAY TUBE. High-vacuum, X-ray tube in which the cathode is heated in order to produce the emission of electrons. HOT-WIRE AMMETER. Instrument in which current is measured by send¬ ing it through a fine wire, which is thereby heated. The resulting expansion or sag of the wire is used to deflect the meter pointer. It can 39-350 1 APRIL 1959 AFM 100-39 HOT be used to measure either alternating current or direct current, since both having the same heat¬ ing effect, but is used chiefly at radio frequen¬ cies. HOT-WIRE ANEMOMETER. Instrument for measuring the velocity of wind or a moving gas by means of its cooling effect on an electrically heated wire. HOT-WIRE INSTRUMENT. Instrument which depends for its operation on the expansion by heat of a wire carrying a current. HOT-WIRE MICROPHONE. Microphone which depends for its operation on the change in resistance of a hot-wire, due to the change in temperature caused by the cooling ef¬ fect produced by a sound wave. HOT-WIRE VOLTMETER. Hot-wire ammeter which has a suitable series resistance for voltage measurements. HOUSE CABLE. Distribution cable within the confines of a sin¬ gle building or a series of related buildings, but excluding cable run from the point of entrance to a cross-connecting box, terminal frame, or point of connection to a block cable. HOUSEKEEPING EQUIPMENT. Items listed in Tables of Allowances which are required for the shelter, health, welfare, and administration of personnel and which are issued on memorandum receipt to users with property responsibility remaining with the base supply of¬ ficer. HOUSING. Covering over apparatus, usually removable. HOW (HOWITZER). HOWL. An undesirable prolonged sound produced by a radio receiver or audio-frequency amplifier system because of either electric or acoustic feedback. HOWL REPEATER. Condition in telephone repeater operation where more energy is returned than sent, resulting in an oscillation being set up in the circuit. HOWLER. 1. Electromechanical device which produces an audio-frequency tone. 2. (Telephone) An associated unit by which the test desk operator may connect a high tone of varying loudness to a subscriber’s line, to call the subscriber’s attention to the fact that his re¬ ceiver is off the hook. HP (HORSEPOWER). Unit of power equal to 550 foot-pounds. per sec¬ ond, and electrically equivalent to nearly 746 watts. HPDS (HOSPITAL PROGRAM DISTRIBUTION SYSTEM). HPF (HIGHEST PROBABLE FREQUENCY). Arbitrarily chosen frequency value 15 percent a- bove the F2 layer MUF for the circuit. For the E layer the highest probable frequency (HPF) is equal to the MUF. HP HR (HORSEPOWER HOUR). HQ (HEADQUARTERS). (Reference: HED (HEADQUARTERS) .) HR (HOUR, HEIGHT RANGE). HRI (HEIGHT-RANGE INDICATOR). Cathode-ray tube from which altitude and range measurements of .airborne objects may be viewed. HRI (HEIGHT-RANGE INDICATOR SCOPE). HRIOp (HEIGHT-RANGE INDICATOR OPERATOR). In air defense, an airman at a long-range-radar site who uses a height finder to obtain altitude information on airborne objects. HS (HERMETICALLY SEALED, HIGH STRENGTH). HS (HEIGHT SUPERVISOR). In air defense, a noncommissioned officer res¬ ponsible to the .direction center air surveillance officer for operation of the height-finding sec¬ tion. HT. HF carrier telegraph channel. 39-351 AFM 100-39 HT 1 APRIL 1959 HT (HEIGHT TECHNICIAN). In air defense, an airman in the direction center air surveillance branch who is responsible for obtaining altitude data from height finders on specified airborne targets by semiautomatic meth¬ ods or from height-range indicator operators by manual method. HUE. Dominant wavelength which distinguishes a co¬ lor as red, yellow, etc. Often synonymous with the term color, but does not include grey. Vary¬ ing saturations may have same hue in color tele¬ vision terminology. HUM. In audio-frequency systems, a low-pitched dron¬ ing noise, usually composed of several harmoni¬ cally related frequencies, resulting from an ac power supply or from ripple from a dc power supply or from induction due to exposure to a power system. By extension, the term is applied in visual systems to interference resulting from similar sources. In facsimile, it is a parttern pro¬ duced on the record sheet due to power-line frequency or harmonics of the power-line fre¬ quency mixing with the facsimile signal or mod¬ ulating the facsimile signal. HUM MODULATION. Hum that is heard in a receiver only when a station is tuned in. HUMMING. Sound produced by transformers having loose laminations or by magnetostriction effects in iron cores. The frequency of the sound is twice the power-line frequency. HUNTING. 1. Mechanical oscillation in a servo system due to improper adjustment of control voltage, servo amplifier, or feedback. 2. Sychronous motor is said to hunt when it tends to drive ahead of syn ronous speed, then fall back several times a second (for small motors). The average speed of the motor is not affected unless the hunting causes the motor to fall out of synchronism. 3. Power - Erratic engine operation, caused by the inability of a governor to respond accurately to changes in engine speed. 4. Radar - Mechanical oscillation in a servo sys¬ tem due to improper adjustment of control volt¬ age, servo amplifier, or feedback. 5. Operation of a selector in moving from ter¬ minal to terminal until one is found which is idle. HUSH UP. Project for airborne secure communications. HV (HEAVY, HIGH VOLTAGE). HVAR (HIGH-VELOCITY AIRCRAFT ROCKET). Any large air-to-ground aircraft rocket specially designed for high velocities, such as a rocket de¬ veloped by the U.S. during World War II, nick¬ named Holy Moses. HWY (HIGHWAY). HX. ITU designation for station having no specific working hours. hy (HENRY). Centimeter-gram-second electromagnetic unit of inductance or mutual inductance. The induc¬ tance of a circuit is one henry when a current variation of one ampere per second induces one volt. It is the basic unit of inductance. In radio, smaller units are used such as the millihenry (mh), which is one thousandth of a henry, and the microhenry (uh) which is one millionth of a henry. HYBRID. Transformer or combination of transformers or resistors affording paths to three branches, circuits A, B and C, so arranged that A can send to C, B can receive from C, but A and B are effectively isolated. A hybrid coil or resistance network, with an associated aritificial line, is the essential functional element of a four-wire, ter¬ minating set and isolates the transmitting branch from the receiving branch. 39-352 1 APRIL 1959 AFM 100-39 HYB HYBRID BALANCE. Loss between two conjugate sides of a hybrid set less the same loss when one of the other sides is open or shorted. It is determined by the degree of balance between impedances connected to the other two sides of the hybrid set and is given by the formula for return loss. HYBRID COIL. Single transformer which has, effectively, three windings, and which is designed to be connected to four branches of a circuit so as to render these branches conjugate in pairs. HYBRID ELECTROMAGNETIC WAVE. Wave which has both transverse and longitu¬ dinal components of displacement. HYBRID SET. Two or more transformers interconnected to form a network having four pairs of accessible termin¬ als to which may be connected four impedances so that the branches containing them may be made conjugate in pairs. HYBRID T. Waveguide interconnector which has four wave¬ guide terminals, and which is designed to be con¬ nected to four branches of a circuit so as to render these branches conjugate in pairs. HYBRID TRANSFORMER. Hybrid coil. HYDROELECTRIC. Pertai nin g to the production of electricity by means of water power. HYDROGEN. Gas which has the simplest known atom, con¬ sisting of only one proton and one electron. HYDROGEN ELECTRODE. Electrode composed of platinum covered with platinum black, around which a stream of hy¬ drogen is bubbled. It furnishes a standard elec¬ trode potential for comparison with other elec¬ trode potentials. HYDROLOGICAL AND METEOROLOGICAL FIXED STATION. Fixed station, the emissions of which are used for the automatic transmission of either hydro- logical or meteorological data, or both. HYDROLOGICAL AND METEOROLOGICAL LAND STATION. Land station, the emissions of which are used for the automatic transmission either hydro- logical or meterorological data, or both. HYDROLOGICAL AND METEOROLOGICAL MOBILE STATION. Mobile station, the emissions of which are used for the automatic transmission of either hydro- logical or meteorological data, or both. HYDROMETER. Graduated float used in measuring specific gra¬ vity of a liquid, such as that of a storage bat¬ tery electrolyte. HYDROPHONE. Electroacoustic transducer which responds to waterborne sound waves and delivers essentially equivalent electric waves. There are many types of hydrophones whose definitions are analagous to those of corresponding microphones, such as crystal hydrophone, magnetic hydrophone, and pressure hydrophone. HYGROSTAT. Device for closing a pair of contacts when the air humidity reaches a prescribed level. HYPERAN. Electronic bombing system. HYPERBOLIC HORN. Horn whose equivalent cross-sectional radius (25/ ) increases according to a hyperbolic law, where S is the cross-sectional area of the horn. HYPERBOLIC NAVIGATION SYSTEM. Certain pulse-type methods of radionavigation, in which two or more properly synchronized ground stations transmit pulses. An aircraft or ship receives the pulses and records the differ¬ ence in their time of arrival, which is a measure of the difference in its distance from the two ground stations and which establishes its loca¬ tion on a particular hyberbolic curve out of the large number of curves drawn on the maps 39-353 AFM 100-39 HYP 1 APRIL 1959 used. A second reading from another pair of stations (or from the same master and a differ¬ ent slave station) establishes its location on a different hyperbolic curve, the intersection of which with the first curve gives the position fix. Systems using this principle are the British GEE and American LORAN. HYPERFREQUENCY WAVES. Microwaves having wavelengths in the range from one centimeter to one meter. HYPERSONIC. Faster than five times the speed of sound. Sound travels at 1078 feet per second in air at sea level, or 735 MPH. HYSTERESIS. Lagging of the magnetic flux in a magnetic material behind the magnetizing force which is producing it. Caused by molecular friction within the material. HYSTERESIS ERROR. Difference between the readings of a measur¬ ing instrument containing iron when the current is brought up to a definite value and when the current is reduced from a larger value to that same definite value. HYSTERESIS LOOP. Hysteresis loop for a magnetic material in a cy- clicly magnetized condition is a curve (usually with rectangular coordinates) showing two values of the magnetic induction for each value of the magnetizing force, one when the magnetizing force is increasing, the other when it is decreasing. HYSTERESIS LOSS. Power loss in an iron-core transformer or other alternating current device due to magnetic hy¬ steresis. HYSTERESIS METER. Instrument for measuring the amount of hy¬ steresis loss in a ferromagnetic material inde¬ pendently of other losses. It usually depends on the torque produced when the test specimen is placed in a rotating magnetic field or is rotated in a stationary magnetic field. HYSTERESIS MOTOR. Synchronous motor without salient poles and without direct-current excitation, which starts by virtue of the hysteresis losses induced in its hard¬ ened steel secondary member by the revolving field. 39-354 1 APRIL 1959 AFM 100-39 I I I (INCEDIARY, INDICATOR). I SCOPE. Type of radar presentation which is related to type C and is produced by a system using conical scanning. The echo signal appears on the indi¬ cator screen as a bright, circular segment whose position on the screen indicates the bearing of the target and whose radius is proportional to its range. The circular length of the segment is proportional to the error in aiming. The scan¬ ning beam; true aim produces a full circle. I SIGNAL. Fine chrominance transmission primary 0-1.5 me wide, which combines with Q signal to convey chrominance information. Comprises sidebands produced by modulating subcarrier 57° from ref¬ erence burst. Called in-phase signal. Color tele¬ vision terminology. I/S. Ratio normally expressed in decibels of the in¬ terference per kilocycle to the signal carrier power of the receiver. The interference is aver¬ aged over the pass band of the receiver or over the interference spectrum, whichever is the smaller. I-R (INTERROGATOR-RESPONDER). Radio transmitter and receiver combined to in¬ terrogate a transponder and display the result¬ ing replies. IAD (INITIATION AREA DISCRIMINATOR). Cathode-ray tube and photoelectric cell combina¬ tion. The photoelectric cell picks up unmapped, uncorrelated long-range data for processing by the automatic-initiation program of the computer. IADS (INTER-AMERICAN DEFENSE BOARD). IAS (INDICATED AIRSPEED). 1. Airspeed shown by an airspeed indicator. 2. In British usage, calibrated airspeed. IAZ (INNER ARTILLERY ZONE). Defined airspace, in an air defense situation, in which all aircraft, friendly, hostile, or otherwise, will be engaged by antiaircraft artillery. IBM (INTERNATIONAL BUSINESS MACHINES). ICA (INTERNATIONAL COOPERATION ADMINISTRATION). ICAF (INDUSTRIAL COLLEGE OF THE ARMED FORCES). ICAO (INTERNATIONAL CIVIL AVIATION ORGANIZATION). Organization established to develop the princi¬ ples and techniques of international air naviga¬ tion, and to foster the planning and development of international air transport. ICAO STANDARDS AND RECOMMENDED PRACTICES. 1. Standard: Any specification for physical char¬ acteristics, configuration, materiel, performance, personnel or procedure, the uniform application of which is recognized as necessary for the safety or regularity of international navigation and to which Contracting States will conform in ac¬ cordance with the Convention; in the event of impossibility of compliance, notification to the Council is compulsory under Article 38; 2. Recommended practice: Any specification for physical characteristics, configuration, materiel, performance, personnel, or procedure, the uni¬ form application of which is recognized as desir¬ able in the interest of safety, regularity, or ef¬ ficiency of international air navigation, and to which Contracting States will endeavor to con¬ form in accordance with the Convention. ICONOSCOPE. Electronic camera tube for television. A picture, focused on a light-sensitive mosaic inside the tube, is converted into electrical charges which, when scanned by a high-speed electron beam, produces a train of electrical signals. ICONOSCOPE CAMERA. Cathode-ray tube used in a television camera to convert an optical image into corresponding elec¬ trical impulses by scanning the image on a mosaic screen with an electron beam. ICS (INTERPHONE CONTROL STATION). ICW (INTERRUPED CONTINOUS WAVE). 39-355 * AFM 100-39 ID 1 APRIL 1959 ID (IDENTIFICATION). Determination of an airborne object’s friendly or hostile character during Warning Red or Yellow. This may be accomplished by flight-plan correla¬ tion, visual observation, or acceptance of an iden¬ tification passed from another unit (if continu¬ ous surveillance has been in effect). ID (INSIDE DIAMETER). IDEAL BUNCHING. Theoretical condition in which the bunching of electrons in a velocity-modulated tube would give a single, infinitely large current peak dur¬ ing each cycle. IDEAL CRYSTAL. Having no mosaic structure and capable of X-ray reflection in accordance with the Darwin-Ewald- Prins law. IDEAL DIELECTRIC. Dielectric in which all the energy required to establish an electric field in the dielectric is re¬ turned to the field is removed. A perfect dielec¬ tric must have zero conductivity. Also, all ab¬ sorption phenomena must be lacking. A vacuum is the only known perfect dielectric. IDEAL TRANSDUCER. Ideal transducer for connecting a specified source to a specified load is a hypothetical linear passive transducer which dissipates no energy and which, when connected to the specified source and load, presents to each its conjugate impedance. Such a transducer transfers the maxi¬ mum theoretically possible power from the source to the load. IDEAL TRANSFORMER. Imaginary transformer which neither stores nor dissipates energy. It is a transformer having self and mutual impedances which are pure induct¬ ance of infinitely great values and one which has a unity coefficient of coupling. IDENTIFICATION. Determination of an airborne object’s friendly or hostile character during Warning Red or Yel¬ low. This may be accomplished by flight-plan correlation, visual observation, or acceptance of an identification passed from another unit (if continuous surveillance has been in effect). IDENTIFICATION BEACON. Code beacon used to identify positively a par¬ ticular point on the surface of the earth. IDENTIFICATION CIRCUIT. Circuit which is established for the purpose of passing identification information relative to the movement of aircraft from CAA air-route traf¬ fic-control centers or military flight service cen¬ ters to air-defense installations. IDENTIFICATION, FRIEND OR FOE. System using radar transmissions to which equip¬ ment carried by friendly forces automatically re¬ sponds, for example, by emitting pulses, thereby distinguishing themselves from enemy forces. It is the primary method of determining the friend¬ ly or unfriendly character of aircraft and ships by other aircraft or ships and by ground forces employing radar detection equipment and as¬ sociated IFF units. IDENTIFICATION OFFICER. Officer responsible to the Senior Director for the classification and/or identification of tracks in accordance with existing regulations and proce¬ dures. IDENTIFICATION PANEL. Specially shaped and/or colored cloth or other material displayed in accordance with a prear¬ ranged code to convey messages. IDENTIFICATION TECHNICIAN. Noncommissioned officer who assists the identi¬ fication officer in the SAGE center. IDF (INTERMEDIATE DISTRIBUTING FRAME). IDIOCHROMATIC. Having photoelectric properties characteristic of the material of the pure crystal itself, and not due to foreign matter. IDLER PULLEY. Pulley used only for tightening a belt or chang¬ ing its direction. The shaft of the pulley does not drive any other part. <( 39-356 1 APRIL 1959 IDO (IDENTIFICATION OFFICER). Officer responsible to the senior director of a SAGE center for the classification and/or iden¬ tification of tracks in accordance with existing, regulations and procedures. IDT (IDENTIFICATION TECHNICIAN). Noncommissioned officer who assists the iden¬ tification officer in a SAGE center. IDTRC (INDOCTRINATION DIVISION AIR TRAINING COMMAND). IF (INTERMEDIATE FREQUENCY). 1. Fixed frequency to which all carrier waves are converted in a superheterodyne receiver. 2. Carrier frequency used in a stage of modula¬ tion intervening between the original signal and the final modulated carrier. 3. Frequency to which a signaling wave is shifted locally as an intermediate step in transmission or reception. 4. Frequency resulting from the combination of the received signal and that of the local oscil¬ lator in a superheterodyne receiver. (Reference. HETERODYNE.) IFF (IDENTIFICATION, FRIEND OR FOE). System using radar transmissions to which equip¬ ment carried by friendly forces automatically re¬ sponds, for example, by emitting pulses, thereby distinguishing themselves from enemy forces. It is the primary method of determining the friend¬ ly or unfriendly character of aircraft and ships by other aircraft or ships and by gound forces employing radar detection equipment and asso¬ ciated IFF units. IFF COORDINATION. Unit for coordination of IFF trigger, range indi¬ cator trigger and radar, and IFF displays on an indicator. IFR (INSTRUMENT FLIGHT RULES). Directives which govern flight procedures under conditions requiring the pilot to fly other than by Visual Flight Rules. IFR (INSTRUMENT FLIGHT RULES) CONDITIONS. Weather conditions below the minimum pre¬ scribed for flights under VFR. AFM 100-39 IDO IFRB (INTERNATIONAL FREQUENCY REGISTRATION BOARD). IGF (IMPRACTICABLE FOR THE GOVERNMENT TO FURNISH). IGN (IGNITION). IGNITION COIL. Iron-core transformer having an open core, a heavy primary winding connected to a battery or other direct-voltage source through a vibrating amature contact, and a secondary winding hav¬ ing many turns of fine wire. It converts a low direct voltage to a value of the order of 20,000 volts, required to produce a spark for ignition purposes in gasoline engines. IGNITION SYSTEM. For internal combustion engines, a method of electrically igniting the Compressed, combusti¬ ble mixture in the engine cylinders. Note. This may be accomplished electrically by the use of spark plugs and a high-ten¬ sion magneto, together with necessary wiring; or by electric energy from a stor¬ age battery together with suitable inter¬ rupting mechanism induction coil, etc. For internal combustion engines of the diesel-type using oil as fuel, the heat of compression ignites the combustible mix¬ ture. IGNITOR. Electrode that is partly immersed in the mercury- pool cathode of an ignitron and used to initiate conduction at the desired points in each cycle. ILAS (INSTRUMENT LOW-APPROACH SYSTEM). Mobile Air Force instrument landing system. ILLUMINOMETER. Portable photometer designed to measure the il¬ lumination on a surface. ILS (INSTRUMENT LANDING SYSTEM). System which provides the horizontal and verti¬ cal guidance and the distance information neces¬ sary for an aircraft landing. Specifically, a radio navigational aid which consists essentially of two transmitters which transmit fixed intersecting 39-357 AFM 100-39 ILS 1 APRIL 1959 vertical and horizontal radio beams, plus radio marker beacons at various distances from the run. The intersection of these beams determines the proper path of the landing aircraft. The transmitter for the vertical or localizer beam op¬ erates in the VHF band. The glide slope beam operates in the UHF band. From a practical standpoint, this system is not in itself adequate for actual landing of the aircraft. The addition of a radar altimeter in the aircraft to effect the flare-out would make possible a true instrument low approach landing. The nomenclature for the new mobile localizer transmitter is the AN/MRN-7. The new glide slope transmitter is designated as the AN/MRN-8. Older ILS equipment is designated SCS-51. IM. VHF boundary marker (CAA). IMAGE. One of two groups of sidebands generated in the process of modulation. The unused group is referred to as the unwanted image. IMAGE ANTENNA. Imaginary counterpart of an actual antenna, as¬ sumed for mathematical purposes to be located below the surface of the ground and symmetri¬ cal with the actual antenna above ground. IMAGE DISSECTOR. Cathode-ray tube developed for television cam¬ eras by P. T. Farnsworth. It converts a scene into corresponding electrical impulses that form a video signal. IMAGE DISTORTION. Failure of the reproduced image in a television receiver to appear the same as that scanned by the television camera. IMAGE EFFECT. Effect produced on the field of an antenna due to the presence of the earth. Electromagnetic waves are reflected from the earth’s surface and these reflections often are accounted for by an image antenna at an equal distance below the earth’s surface. IMAGE FREQUENCY. 1. In heterodyne frequency converters in which one of the two sidebands produced by beating is selected, the image frequency is an undesired input frequency capable of producing the se¬ lected frequency by the same process. The word image implies the mirror-like symmetry of signal and image frequencies about the beating oscil¬ lator frequency or the intermediate frequency, whichever is the higher. 2. Carrier frequency of a undesired signal which is capable of combining with the frequency of the local 'oscillator in a superheterodyne, thus forming the intermediate frequency, and eventu¬ ally being reproduced together with the de¬ sired signal. For example, if the intermediate frequency is 500 kilocycles, a locally generated signal of 5-500 kilocycles combined with sig¬ nals of either 5,000 or 6,000 kilocycles would result in the proper intermediate frequency. If the 5,000 kilocycles signal is the desired one, the 6,000 kilocycle is the image frequency. 3. In superheterodyne reception, the image fre¬ quency is a radio frequency which is as far re¬ moved on one side from the intermediate fre¬ quency as the desired signal is on on the other side. IMAGE IMPEDANCES. Of a transducer, the impedances which will sim¬ ultaneously terminate all of its inputs and out¬ puts; the impedances in both directions are equal. IMAGE INTERFERENCE. In a superheterodyne receiver, the condition in which a station broadcasting on the image fre¬ quency for a particular tuning-dial setting is heard along with the desired station. Both sta¬ tions differ from the oscillator frequency by the intermediate-frequency value and the receiver cir¬ cuits do not have sufficient selectivity to reject the higher frequency undesired signal. IMAGE ORTHICON. Television camera tube of high sensitivity for use in the studio and outdoors. It features a scanning beam of low-velocity electrons and sev¬ eral stages of electron multiplication. Capable of picking up scenes in semi-darkness. 39-358 1 APRIL 1959 AFM 100-39 IMA IMAGE RATIO. Ratio of the field strength at the image frequency to the field strength at the desired frequency, each field being applied in turn, under specified conditions, to produce equal outputs. IMAGE RESPONSE. Response of a superheterodyne receiver to the image frequency, as compared to the response to the desired frequency; usually expressed in decibels. IMAGE-INTERFERENCE RATIO. In a superheterodyne receiver, a rating indicat¬ ing the effectiveness of the preselector in reject¬ ing signals at the image frequency. IMITATIVE COMMUNICATIONS DECEPTION. Classified definition. (Reference: AFM 100-50.) IMITATIVE DECEPTION. Transmission of messages in the enemy’s com¬ munication channels with the intention of deceiv¬ ing the enemy. IMITATIVE RADIO COMMUNICATION DECEPTION. Classified definition. (Reference: AFM 100-50.) IMP (IMPREGNATE). IMPACT EXCITATION. Starting of damped oscillations in a radio circuit by a sudden surge, such as that produced by a spark discharge. IMPAIRMENT. Diminish in quantity, value, or strength. DISTORTION TRANSMISSION. Condition where the band-width is less than the 2,750 cycles between 250 and 3,000 cycles resulting in poorer transmission of intelligence than if the full band were used. The degree is ex¬ pressed in db DTI. NOISE TRANSMISSION. Reduction in useful value of a telephone circuit due to noise; ex¬ pressed db NTI. IMPEDANCE. 1. Ratio of the effective value of the potential difference between the terminals under consider¬ ation to the effective value of the resulting cur¬ rent, where there is no source of power in the portion of the circuit under consideration. 2. Total oposition offered to the flow of an al¬ ternating current. It may consist of any combina¬ tion of resistance, inductive reactance, and capaci¬ tive reactance. 3. That property of an electrical circuit which opposes the flow of current. While a resistance is an impedance, the term is usually reserved for the opposition to current flow offered by induc¬ tors, capacitors, or combinations of both. ACOUSTIC. Total acoustic resistance of a medi¬ um to sound waves. Force per unit area on the surface of the medium divided by the flux through that surface. This impedance is ex¬ pressed in lines and is equal to the mechani¬ cal impedance divided by the surface area. Acoustic impedance contains both acoutstic re¬ sistance and acoustic reactance. CHARACTERISTIC. Of a transmission line, the impedance which the line would have if it were of infinite length. CONJUGATE. Impedance having resistance components which are equal and reactance components which are equal in magnitude but opposite in sign. DRIVING-POINT.' At any pair of terminals of a network, the ratio of an applied potential difference to the resultant current at these terminals, all terminals being terminated in any specified manner. FREE. Of a transducer, the impedance at the input of the transducer when the impedance of its load is made zero. IMAGE. Of a transducer, the impedances which will simultaneously terminate all of its inputs and outputs in such a way that at each of its inputs and outputs the impedances in both di¬ rections are equal. INPUT. Impedance presented by a device to the source. 39-359 AFM 100-39 IMP 1 APRIL 1959 ITERATIVE. Of a transducer, that impedance which, when connected to one pair of termi¬ nals, produces a like impedance at the other pair of terminals. LOADED. Of a transducer, the impedance at the input of the transducer when the output is connected to its normal load. MATCHED. Condition which exists when two coupled circuits are adjusted so that the im¬ pedance of one circuit equals the impedance of the other. MOTIONAL. Of a transducer, the complex re¬ mainder after the blocked impedance has been subtracted from the loaded impedance. OPEN-CIRCUIT. Of a line or four-terminal net¬ work, the driving-point impedance when the far-end is open. OUTPUT. Impedance presented by a device to the load. PLATE-LOAD. Impedance in the plate circuit across which the output signal voltage is de¬ veloped by the alternating component of the plate current. REFLECTED. Impedance which appears at the input terminals as a result of the characteris¬ tics of the impedance at the output terminals. SELF. At any pair of terminals of a network the ratio of an applied potential difference to the resultant current at these terminals, all other terminals being open. SENDING-END. Of a line, the ratio of an ap¬ plied potential difference to the resultant cur¬ rent at the point where the potential differ¬ ence is applied. The sending-end impedance of a line is synonymous with the driving-point impedance of the line. For an infinite uniform line the sending-end impedance and the char¬ acteristic impedance are the same; and for an infinite periodic line the sending-end imped¬ ance and the iterative impedance are the same. SHORT-CIRCUIT. Of a line or four-terminal network, the driving-point impedance when the far-end is short-circuited. SOURCE. Impedance presented by a source of energy to the input terminals of a device. SURGE. Characteristic impedance of a transmis¬ sion line. When a transmission line is termi¬ nated in a load equal to its surge impedance, no reflection will occur and no standing waves will appear. TERMINAL. Complex impedance as seen at the unloaded output or input terminals of a transmission equipment or line which is other¬ wise in normal operating condition. TRANSFER. Between any two pairs of termi¬ nals of a network, the ratio of a potential dif¬ ference applied at one pair of terminals to the resultant current at the other pair of termi¬ nals, all terminals being terminated in any spe¬ cified manner. WAVE. Of a transmission line at any specified plane, the complex ratio at every point in that plane, of the transverse component of the elec¬ tric field to the transverse component of the magnetic field. Both incident and reflected waves may be present. IMPEDANCE BRIDGE. Circuit used to measure the combined resistance and inductance of a device. IMPEDANCE CHARACTERISTIC. Graph of the impedance of a circuit plotted against frequency. IMPEDANCE COIL. Used to impede the flow of alternating current by its inductive reactance. (Reference: CHOKE COIL.) IMPEDANCE COMPENSATOR. Electric network designed to be associated with another network or a line for the purpose of giving the impedance of the combination a de¬ sired characteristic with frequency over a de¬ sired frequency range. IMPEDANCE COUPLING. Use of an inductor or an impedance coil as the common coupling element between two circuits. 39-360 1 APRIL 1959 AFM 100-39 IMP IMPEDANCE IRREGULARITIES. Discontinuities or abrupt changes in an imped¬ ance-frequency curve which result from junc¬ tions between unlike sections of a transmission line or irregularities on a line. IMPEDANCE MATCHING. 1. Connection, across a source impedance, of an impedance having the same magnitude and the same angle. 2. Method of minimizing the adverse effects of junctions between dissimilar transmission lines as, for instance, cable and open wire whereby a transformer or auto transformer is used to inter¬ connect the two, or loading coils are used to modify the impedance characteristic of a cable so as to match the open wire. IMPEDANCE TRANSFORMER. Device used to provide a maximum transfer of energy from one circuit to another. IMPEDANCE TRIANGLE. Diagram consisting of a right angle triangle with sides proportional to the resistance and react¬ ance, respectively, of an alternating current and with the hypotenuse representing the impedance of the circuit. The cosine impedance is the power factor of the circuit. IMPEDANCE-MATCHING TRANSFORMER. Transformer used to obtain an impedance match between a source and load. IMPEDOR. Corresponding phraseology to resistor, inductor, and capacitor. It is rarely used. IMPERFECT DIELECTRIC. Dielectric in which a part of the energy required to establish an electric field in the dielectric is not returned to the electric system when the field is removed. The energy not returned is con¬ verted into heat in the dielectric. IMPREGNATED. Impregnated means that a suitable substance re¬ places the air between its fibers, even though this substance does not fill completely the spaces between the insulated conductors. IMPRESSED VOLTAGE. Voltage applied to a circuit or device. IMPULSE. Force acting for a comparatively short period of time, such as a momentary rise in voltage and generally meant to be of unidirectional polarity. IMPULSE COUNTER, MAGNETIC. Relay with two step armatures and their asso¬ ciated contacts whose function is to register dial pulses. IMPULSE EXCITATION. Method of producing oscillatory current in a cir¬ cuit in which the duration of the impressed volt¬ age is relatively short compared with the dura¬ tion of the current produced. IMPULSE FREQUENCY. Number of pulse periods per second generated by the dial pulse springs in opening and closing in rapid succession in response to the dialing of a digit. (Reference: PULSE SPEED.) IMPULSE GENERATOR. 1. Electric apparatus suitable for the production of high-voltage surges used for testing insula¬ tors and for other purposes. (Reference: SURGE GENERATOR, LIGHTING GENERATOR.) 2. Oscillator circuit that generates electric im¬ pulses for synchronizing purposes in a television system. IMPULSE NOISE. 1. Noise due to disturbances having abrupt changes and of short duration. These noise im¬ pulses may or may not have systematic phase re¬ lationships. It is noise characterized by non-over¬ lapping transient disturbance. The same source may produce impulse noise in one system and random noise in a different system. 2. In telephone operations, noise characterized by transient disturbances separated in time by quiescent intervals. The frequency spectrum of these disturbances must be substantially uni¬ form over the useful pass band of the transmis¬ sion system. IMPULSE PERIOD. (Reference: PULSE PERIOD.) 39-361 AFM 100-39 IMP 1 APRIL 1959 IMPULSE RADIATION. Impact fluorescence. IMPULSE SEPERATOR. In a television receiver, the circuit that separates the horizontal synchronizing impulses in the re¬ ceived signal from the vertical synchronizing im¬ pulses. IMPULSE SPEED. Time rate at which a telephone dial mechanism makes and breaks the circuit to transmit pulses. IMPULSE TRANSMISSION. Form of signaling used principally to reduce the effects of low-frequency interference which em¬ ploys impulses of either or both polarities for transmission to indicate the occurrence of transi¬ tions in the signals. The impulses are generally formed by suppressing the low-frequency compo¬ nents, including direct current, of the signals. IMPULSE TRAIN. Group of pulses of similar characteristics. (Ref¬ erence: FULSE TRAIN.) IMPULSE-DRIVEN CLOCK. Electric clock in which the hands are moved for¬ ward at regular intervals by current impulses controlled by a master clock. IMPULSE-TYPE TELEMETER. Employs electric impulses as the translating means. IN-LINE TUNING. Method of tuning the IF strip of a superhetero¬ dyne receiver in which all the IF amplifier stages are made resonant to the same frequency. This type of tuning results in a narrow IF bandwidth. IN-PHASE. Condition that exists when two waves of the same frequency pass through their maximum and minimum values of like polarity at the same instant. IN-PHASE COMPONENT. Component of an alternating voltage or alternat¬ ing current due to resistance alone, independent¬ ly of reactance. IN-STEP. (Reference: IN-PHASE.) INC (INCOMPLETE). INCANDESCENCE. State of a body in which its temperature is so high that it gives off light. Example: The sun, or the filament of an electric lamp. INCANDESCENT LAMP. Electric lamp in which the light is produced by electric current flowing through a filament of resistance material, heating it to incadescence. INCEP (INTERCEPT). 1. Distance from the origin to the point where a line, curve, or surface cuts a particular axis on a graph. 2. To cut off or bound some part of a line or other geometric figure. INCIDENCE ANGLE. Angle between an approaching light ray or emis¬ sion and the perpendicular (normal) to the sur¬ face in the patch of the ray. INCIDENT. Refers to a wave traveling in a direction toward the load. Example: Incident radar wave. INCIDENT FIELD INTENSITY. Field strength of a downcoming sky-wave with¬ out including the effects of earth reflections at the receiving location. INCIDENT WAVE. In a medium of certain propagation characteris¬ tics, a wave which impinges on a discontinuity or medium of different propagation characteris¬ tics. INCLINATION. The angle which a line, surface, or vector makes with the horizontal. Thus magnetic inclination, also called magnetic dip, is the angle that the magnetic field of the earth makes with the horizontal at a particular location. INCLINOMETER. Instrument for measuring inclination. A magnet¬ ic needle pivoted in a vertical plane is used to 1 APRIL 1959 AFM 100-39 INC indicate the magnetic inclination of the earth’s magnetic field. INCOMING TRUNK. Trunk coming into a central office. INCREASED INTELLIGENCE WATCH. Condition of command alertness directed by the Commander in Chief North American Air De¬ fense Command when closer scrutiny and evalua¬ tion of intelligence is required. INCREMENT. Change in the value of a variable. It is usually a small amount added to the given value of the variable. INCREMENT BORER. Tool for taking wood samples from a pole to determine depth of creosote treatment or extent of rot. INCREMENTAL HYSTERESIS LOSS. Losses when a magnetic material is subjected to a pulsating magnetizing force. INCREMENTAL PERMEABILITY. Ratio of the cyclic change in magnetizing force when the mean magnetic induction differs from zero. IND (INDUCTANCE). Property of a circuit which tends to oppose a change in the existing current and is present only when the current is changing. IND (INTERCEPT DIRECTOR). Officer in the Direction Center Weapons Branch responsible for monitor and control of intercep¬ tors in a SAGE center. INDEFINITE CALL SIGN. Sign which does not represent a specific facility, command, authority, activity, or unit, but which may represent any one or any group of these. INDEX OF CO-OPERATION. In facsimile, the product of the scanning drum diameter in inches and the number of scanning lines per inch. INDEX OF MODULATION. Modulation factor. INDEX OF REFRACTION. Ratio of the speeds of a light ray or other radia¬ tion in two different materials. It determines the amount the ray will be refracted or bent when passing from one material to the other, such as from air to water. INDICATING FUSE. Protective device which is placed in a telephone circuit; it consists of a fuse, a pilot lamp, a relay, and a buzzer. When a line fault blows the fuse, the lamp lights and the buzzer sounds, thus pro¬ viding visual and audible indication of the line fault. (Reference: FUSE ALARM.) INDICATING INSTRUMENT. Instrument in which the present value of the quantity measured is indicated by the position of a pointer relative to a scale. INDICATING LAMP. Indicates the position of a device or the condi¬ tion of a circuit. INDICATOR. That component of a set, such as a radar set, by which the data obtained by the set is presented for visual observation. Type of presentation on a cathode-ray indicator in which time is one co¬ ordinate (horizontal) and signals appear as de- flectives in a direction perpendicular to the time scale (vertical). (Reference: A-SCAN.) AZIMUTH STABLILZED PLAN POSITION. Pre¬ sentation of signals on a plan position indi¬ cator arranged so the top of the screen repre¬ sents a fixed direction and not the plane’s tail-nose axis. The fixed direction may be north or may be established by a gyroscope. COURSE LINE DEVIATION. Cross-pointer in¬ strument which indicates deviation from a course line. DIRECTION-FINDER BEARING. Instrument which is used with an airborne radio direc¬ tion finder to indicate the relative, magnetic, or true bearing of a station from an aircraft, or the reciprocal of this bearing. A direction¬ finder bearing indicator of the manual type is 39-363 AFM 100-39 IND 1 APRIL 1959 known as an MDF bearing indicator, and one of the automatic type is known as an ADF bearing indicator. DROP Indicator for signaling, consisting of a hinged flap normally held up by a catch. The catch is released by an electromagnet, allow¬ ing the flap to drop when a signal is made. GROUND POSITION. Dead-reckoning compu¬ ter, similar to an API, with provision for tak¬ ing account of drift. HEIGHT-RANGE. Radar indicator which is cap¬ able of showing the height and range of a target. LOCAL. Radar operator’s indicator as con¬ trasted to the remote indicator for the pilot or navigator. MAGNETIC DIRECTION. Instrument providing compass-indication obtained electrically from a remote gyrostabilized magnetic compass or equivalent. MESSAGE. Element placed within a message to serve as a guide to the selection or derivation and application of the correct key in order to facilitate the prompt decryption of the mes¬ sage. MOVING TARGET. Device which limits the display of radar information primarily to mov¬ ing targets. MULTIPLE CALL. Last entry on line two of a multiple call message which indicates the total number of routing indicators in that line. OMNI-BEARING. Instrument which provides automatic and continuous indication of omni¬ bearing. PILOT DIRECTION. Meter that indicates to the pilot the direction and amount of change in heading that should be applied at any one time. RADAR. Cathode-ray tube which is used to give a visual presentation of the signal re¬ turned from the target. RADIO MAGNETIC. Dual indicator provided with an automatic means for stabilization of the rotatable scale to conform with the head¬ ing of the aircraft. It provides automatic and continuous indication of magnetic bearing, re¬ lative bearing, airplane heading, and drift, us- ing signals from two fixed stations. REMOTE. Radar indicator which is connected in parallel with the radar operator’s indicator, but which is located so as to be visible to the navigator or pilot. ROUTING. Routing indicator is a group of letters, engineered and assigned to identify a station within a teletypewriter network. SYSTEM. Group of symbols indicating which cryptochannel (system) was used to encrypt the message. TERRAIN CLEARANCE. Device for measuring the distance from an aircraft to the suface of the sea c: ground. TO-FORM. Instrument which shows whether the numerical reading of an omni-bearing se¬ lector for an on-course indication of the devia¬ tion indicator represents the bearing toward or away from an omni range. VOLUME. Specially designed high-impedance voltmeter calibrated to indicate speech energy levels in volume units. INDICATOR GATE. Rectangular voltage waveform which is applied to the grid or cathode circuit of an indicator cathode-ray tube so as to sensitize or desensitize it during the desired portion of the operating cycle. INDICATOR LIGHT. Device designed to be used on board an aircraft to illuminate or irradiate an instrument or in¬ struments. INDIRECT PIEZOELECTRICITY. Peizoelectric effect in which a mechanical strain is produced in a crystal by an applied voltage. (Reference: ELECTROSTRICTION.) .39-364 1 APRIL 1959 AFM 100-39 IND INDIRECT WAVE. Wave reaching a given reception point by a path from the transmitting point other than the direct line path between the two. Example: A sky wave received after reflection from the ionosphere layers. INDIRECTLY HEATED CATHODE. Cathode which is brought to the temperature necessary for electron emission by a separated heater element. INDIVIDUAL EQUIPMENT. In Army and Air Force usage, referring to meth¬ od of use, signifies personal clothing and equip¬ ment for the personal use of a soldier or airman. INDIVIDUAL LINE. Subscriber line arranged to serve only one main station although additional stations may be con¬ nected to the line as extensions. An individual line is not arranged for discriminatory ringing with respect to the stations on that line. INDIVIDUAL SOUND ARTICULATION. Articulation analyzed to show the percentage correctly recognized for a particular sound such as e. INDOOR. 1. Not suitable for exposure to the weather. 2. Out of the weather. INDOOR ANTENNA. Reciving antenna located entirely inside a build¬ ing but outside the radio receiver. It may be a wire strung in an attic, between walls, around the walls, under a rug, etc. INDOOR TRANSFORMER. Transformer which, because of its construction, must be protected from the weather. INDUCED. Produced as a result of exposure to the influ¬ ence or variation of an electric or magnetic field. INDUCED CHARGE. Electrostatic charge produced on an object by the electric field that surrounds a near-by object. INDUCED CURRENT. Current due to an induced voltage. INDUCED VOLTAGE. Voltage produced in a circuit by a change in the number of magnetic lines of force passing through a coil in the circuit. INDUCTANCE. Property of a circuit which tends to oppose a change in the existing current and is present only when the current is changing. INDUCTANCE BRIDGE. Instrument similar to a Wheatstone bridge, used to measure an unknown inductance by compar¬ ing it with a known inductance. INDUCTANCE DISTRIBUTED. Inductance which exists along the entire length of a conductor, as distinguished from the self¬ inductance concentrated in a coil. INDUCTANCE-TUBE MODULATION. Method of modulation employed in frequency- modulated transmitters, in which an oscillator control tube acts as a variable inductance in par¬ allel with the tank circuit of the radio-frequency oscillator tube, causing the oscillator frequency to vary in proportion to the audio-frequency voltage applied to the grid of the oscillator control tube. INDUCTION. 1. Phenomenon whereby a body is electrified, magnetized, or given an induced voltage or cur¬ rent by exposure to a field of force. 2. In telephony, a condition where, due to mag¬ netic coupling, a change in current in one circuit causes an equivalent change in an adjacent cir¬ cuit. NOISE. Audible disturbance in a circuit due to electric coupling with another. POWER. Noise interference directly traceable to commercial power line. RINGING. 1. Noise interference directly trace¬ able to a source of ringing supply. 2. Small portion of the ringing current which is returned to the calling subscriber as an in¬ dication that the called party is being rung. 39-365 AFM 100-39 IND 1 APRIL 1959 INDUCTION BRAZING. Electric brazing process in which the heat is ob¬ tained from induced current. INDUCTION COIL. 1. Transformer used in a telephone set for in¬ terconnecting the transmitter, receiver, and line terminals. 2. Transformer for converting interrupted di¬ rect current into high voltage alternating cur¬ rent. 3. Coil in which a voltage is established by the electromagnetic field of another coil through which alternating current is flowing. INDUCTION COMPASS. Compass whose indications depend on the cur¬ rent generated in a coil revolving in the magnet¬ ic field of the earth. INDUCTION FIELD. That portion of the electromagnetic field of a transmitting antenna which acts as if it were permanently associated with the antenna. The field near an antenna into which energy is alter¬ nately stored and removed. Energy of this type is not permanently lost to the antenna. (The ra¬ diation field leaves the transmitting antenna and travels through space as radio waves.) INDUCTION FREQUENCY CONVERTER. Slip-ring induction machine, which is driven by an external source of mechanical power and whose primary circuits are connected to a source of electric energy having a fixed frequency. The secondary circuits deliver energy at a frequency proportional to the relative speed of the primary magnetic field and the secondary member. INDUCTION FURNACE. Transformer of electric energy to heat by elec¬ tromagnetic induction. INDUCTION HEATING. Process of transferring the energy in an alter¬ nating magnetic field into a metal by induction and there converting it into heat. INDUCTION INSTRUMENT. Meter that depends for its operation on the re¬ action between magnetic flux set up by current in fixed windings, and other currents set up by electromagnetic induction in conducting parts of the moving system. INDUCTION LOUDSPEAKER. Moving conductor loudspeaker in which the moving conductor is in the form of a coil induc¬ tively coupled to the source of electrical energy. INDUCTION MOTOR. Alternating-current motor that converts electrical energy into mechanical energy. The rotor rotates due to the reaction between the magnetic fields of the connected primary and the field of the induced voltage in the shorted secondary. Either the rotor or the stator can have the external con¬ nections. INDUCTION NOISE. Audible disturbance in a circuit due to electric coupling with another. When a disturbance can be classified as thump, flutter, crossfire, or cross¬ talk, it is not considered noise. INDUCTION POWER. Noise interference traced directly to commercial power lines. INDUCTION RESISTANCE WELDING. Welding process in which the heating current is caused to flow in the parts to be welded by elec¬ tromagnetic induction, without any electric con¬ tact between the source and the work. INDUCTION SPEAKER. (Reference: INDUCTION LOUDSPEAKER.) INDUCTIVE. Pertaining to inductance, to the inducing of a voltage through mutual inductance, or to the in¬ ducing of an electrical charge by electrostatic in¬ duction. INDUCTIVE CIRCUIT. Circuit containing a higher value of inductive re¬ actance than capacitive reactance. INDUCTIVE COORDINATION. Location, design construction, operation, and maintenance of electric supply and communica¬ tion systems in conformity with harmoniously ad¬ justed methods which will prevent inductive in¬ terference. ■■ -i >