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  • 1. Front 4/9/01 4:38 PM Page i The Illustrated Dictionary of Electronics
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  • 3. Front 4/9/01 4:38 PM Page iii The Illustrated Dictionary of Electronics Eighth Edition Stan Gibilisco Editor-in-Chief McGraw-Hill New York Chicago San Francisco Lisbon London Madrid Mexico City Milan New Delhi San Juan Seoul Singapore Sydney Toronto
  • 4. Front 4/12/01 4:38 PM Page iv Cataloging-in-Publication Data is on file with the Library of Congress McGraw-Hill abc Copyright © 2001 by The McGraw-Hill Companies, Inc. All rights reserved. Printed in the United States of America. Except as permitted under the United States Copyright Act of 1976, no part of this publication may be reproduced or distributed in any form or by any means, or stored in a data base or retrieval system, without the prior written permission of the publisher. 1234567890 AGM/AGM 0987654321 P/N 0-07-137237-7 ISBN 0-07-137236-9 The sponsoring editor for this book was Scott Grillo, and the production supervisor was Pamela Pelton. It was set in Bookman by Techbooks. Printed and bound by Quebecor/Martinsburg. McGraw-Hill books are available at special quantity discounts to use as premiums and sales promotions, or for use in corporate training programs. For more information, please write to the Director of Special Sales, McGraw-Hill, Two Penn Plaza, New York, NY 10121-2298. Or contact your local bookstore Information in this book has been obtained by the publisher from sources believed to be reliable. However, neither the publisher nor the authors guarantee the accuracy or complete- ness of any information published herein. Neither the publisher nor the authors shall be responsible for any errors, omissions, or damages arising out of use of this information. This work is pub- lished with the understanding that the publisher and authors are supplying information but are not attempting to render pro- fessional services in any way, shape or form. If such services are required, the assistance of an appropriate professional should be sought. This book is printed on recycled, acid-free paper containing a minimum of 50 percent recycled de-inked fiber.
  • 5. Front 4/9/01 4:38 PM Page v To Tony, Tim, and Samuel from Uncle Stan
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  • 7. Front 4/9/01 4:38 PM Page vii Contents Preface ix Acknowledgments xi Dictionary 1 Appendix A Schematic Symbols 773 Appendix B Tables and Data 787 Copyright 2001 The McGraw-Hill Companies, Inc. Click Here for Terms of Use
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  • 9. Front 4/9/01 4:38 PM Page ix Preface The Illustrated Dictionary of Electronics—8th Edition has been revised, clarified, and up- dated, reflecting technological advances of recent years. New definitions have been added in the fields of wireless technology, robotics, and artificial intelligence. Every effort has been made to be concise and accurate, without “talking down” to the reader. Many definitions contain cross references (indicated in ALL CAPITALS); these provide recommended additional information or allow comparison with related terms. Expressions of special significance are printed in italics. Electronics abbreviations are included in the text; the full terms are stated as definitions. While an effort has been made to avoid superfluous mathematics, equations are some- times necessary to completely and effectively define a term. Mathematics beyond the high- school level has not been used. Appendix A contains the standard symbols used in electrical and electronic diagrams. These symbols are used in illustrations throughout this dictionary. Appendix B contains the following data tables: 1. Conversion between electrical systems 2. Greek alphabet 3. Mathematical functions and operations 4. Prefix multipliers 5. Resistor color code Suggestions for future editions are welcome. Stan Gibilisco Editor-in-Chief Copyright 2001 The McGraw-Hill Companies, Inc. Click Here for Terms of Use
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  • 11. Front 4/9/01 4:38 PM Page xi Acknowledgments Illustrations in this book were generated with CorelDRAW. Some clip art is courtesy of Corel Corporation, 1600 Carling Avenue, Ottawa, Ontario, Canada K1Z 8R7. Copyright 2001 The McGraw-Hill Companies, Inc. Click Here for Terms of Use
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  • 13. Front 4/9/01 4:38 PM Page xiii The Illustrated Dictionary of Electronics
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  • 15. 5059F-pA_1-55 4/9/01 4:41 PM Page 1 A 1. Symbol for GAIN. 2. Symbol for AREA. 3. Sym- Abbe condenser 1. In microscopy, a special two- bol for AMPERE (SI unit for current). piece lens that has enhanced light-gathering A؊ Symbol for negative terminal of filament-voltage power. 2. A similar focusing device in an electro- source in a vacuum-tube circuit. magnetic antenna. A؉ Symbol for positive terminal of filament-voltage abbreviated dialing In telephone systems, special source in a vacuum-tube circuit. circuits requiring fewer-than-normal dialing op- a 1. Abbreviation of ATTO- (prefix). 2. Abbreviation erations to connect subscribers. of AREA. 3. Abbreviation of ACCELERATION. abc 1. Abbreviation of AUTOMATIC BASS COM- 4. Abbreviation of ANODE. 5. Obsolete abbrevia- PENSATION, a system for boosting the volume of tion of cgs prefix AB-. bass sounds at low amplifier gain. 2. Abbrevi- aA 1. Abbreviation of attoampere. 2. Obsolete for ation of AUTOMATIC BIAS CONTROL. 3. Abbrevi- ABAMPERE. ation of AUTOMATIC BRIGHTNESS CONTROL. AAAS Abbreviation for American Association for the 4. Abbreviation of AUTOMATIC BRIGHTNESS Advancement of Science. COMPENSATION. AAC Abbreviation of automatic aperture control abcoulomb The unit of electrical quantity in the (NASA). cgs electromagnetic system. One abcoulomb AAS Abbreviation of advanced antenna system equals 10 coulombs and is the quantity of elec- (NASA). tricity that flows past any point in a circuit in one AASR Abbreviation of airport and airways surveil- second when the current is one abampere. lance radar. aberration 1. Distortion from perfect shape in a AB Abbreviation of acquisition beacon (NASA). lens or reflecting mirror or antenna dish. 2. A A-B In sound and acoustics, the direct comparison small error in the determination of the direction of two sources of sound by alternately turning on of a source of electromagnetic energy, on account one and the other. of the motion of the source and/or the detecting ab- 1. Prefix that transforms the name of a practi- apparatus. 3. A small displacement in the appar- cal electrical unit to that of the equivalent electro- ent positions of the stars from month to month on magnetic cgs unit (e.g., ABAMPERE, ABOHM, account of the earth’s orbital motion. ABVOLT). See individual entries of such cgs ABETS Acronym for airborne beacon electronic test units. 2. Abbreviation for ABSOLUTE. set (NASA). abac A graphic device for the solution of electronics abfarad The unit of capacitance in the cgs electro- problems. Also see ALIGNMENT CHART. magnetic system. One abfarad equals 109 farads abampere The unit of current in the cgs electro- and is the capacitance across which a charge of magnetic system. One abampere equals 10 1 abcoulomb produces a potential of 1 abvolt. amperes and corresponds to 1 abcoulomb per abhenry The unit of inductance in the cgs electro- second. magnetic system. One abhenry equals 10–9 henry Copyright 2001 The McGraw-Hill Companies, Inc. Click Here for Terms of Use
  • 16. 5059F-pA_1-55 4/9/01 4:41 PM Page 2 2 abhenry • absolute error and is the inductance across which a current that changes at the rate of 1 abampere per sec- ond induces a potential of 1 abvolt. ABL Abbreviation of Automated Biology Laboratory (NASA). abmho The obsolete unit of conductance and of conductivity in the cgs electromagnetic system. Replaced with ABSIEMENS. abnormal dissipation Power dissipation higher or lower than the customary level, usually an over- load. abnormal oscillation 1. Oscillation where none is desired or expected, as in an amplifier. 2. Oscilla- tion at two or more frequencies simultaneously when single-frequency operation is expected. 3. Oscillation at an incorrect frequency. 4. Parasitic oscillation. abnormal propagation 1. The chance shifting of absence-of-ground searching selector A rotary the normal path of a radio wave, as by displace- switch that searches for an ungrounded contact ments in the ionosphere, so that reception is de- in a dial telephone system. graded. 2. Unintentional radiation of energy from absiemens The unit of conductance or conductiv- some point other than the transmitting antenna. ity in the cgs electromagnetic system. One 3. Propagation over a path or in a direction not absiemens equals 109 siemens and is the expected. conductance through which a potential of 1 ab- abnormal reflections Sharp, intense reflections at volt forces a current of 1 abampere. frequencies higher than the critical frequency of absolute 1. A temperature scale in which zero repre- the ionosphere’s ionized layer. sents the complete absence of heat. Units of mea- abnormal termination The shutdown of a running sure are same as units on Celsius and Fahrenheit computer program or other process. Caused by scales. See ABSOLUTE SCALE. 2. Independent of the detection of an error by the associated hard- any arbitrarily assigned units of measure or value. ware that indicates that some ongoing series of absolute accuracy The full-scale accuracy of a me- actions cannot be executed correctly. ter with respect to a primary (absolute) standard. abnormal triggering The false triggering or switch- absolute address In a digital computer program, ing of a circuit or device, such as a flip-flop, by the location of a word in memory, as opposed to some undesirable source instead of the true trigger location of the word in the program. signal. Electrical noise pulses often cause abnor- absolute code A computer code in which the exact mal triggering. address is given for storing or locating the refer- abohm The unit of resistance and of resistivity in ence operand. the cgs electromagnetic system. One abohm absolute coding In computer practice, coding that equals 10–9 ohms and is the resistance across uses absolute addresses. which a steady current of 1 abampere produces a absolute constant A mathematical constant that potential difference of 1 abvolt. has the same value wherever it is used. abort To deliberately terminate an operation, ex- absolute delay The time elapsing between the periment, process, or project before it has run its transmission of two synchronized signals from normal course. the same station or from different stations, as in AB power pack 1. A portable dry-cell or wet-cell radio, radar, or loran. By extension, the time in- array containing both A and B batteries in one terval between two such signals from any source, package. 2. An ac-operated unit in one package as from a generator. for supplying A and B voltages to equipment nor- absolute digital position transducer A digital po- mally operated from batteries. sition transducer whose output signal indicates abrasion machine An instrument for determining absolute position. (See ENCODER.) the abrasive resistance of a wire or cable. absolute efficiency The ratio Xx/Xs, where Xx is abrasion resistance A measure of the ability of a the output of a given device, and Xs is the output wire or wire covering to resist mechanical dam- of an ideal device of the same kind under the age. same operating conditions. ABS A basic programming abbreviation for the ab- absolute encoder system A system that permits solute value (of a number, variable, or expres- the encoding of any function (linear, nonlinear, sion). continuous, step, and so on) and supplies a non- abscissa 1. The independent variable in a function. ambiguous output. 2. The axis (usually horizontal) on the graph of a absolute error The difference indicated by the ap- function that indicates the independent variable. proximate value of a quantity minus the actual
  • 17. 5059F-pA_1-55 4/9/01 4:41 PM Page 3 absolute error • absolute tolerance 3 value. This difference is positive when the ap- proximate value is higher than the exact value, and it is negative when the approximate value is lower than the exact value. Compare RELATIVE ERROR. absolute gain Antenna gain for a given orientation when the reference antenna is isolated in space and has no main axis of propagation. absolute humidity The mass of water vapor per unit volume of air. Compare RELATIVE HUMID- ITY. absolute instruction A computer instruction that absolute Peltier coefficient The product of the states explicitly and causes the execution of a absolute Seebeck coefficient and absolute tem- specific operation. perature of a material. absolute magnitude For a complex number quan- absolute pitch A tone in a standard scale, deter- tity, the vector sum of the real and imaginary mined according to the rate of vibration, indepen- components (i.e., the square root of the sum of dent of other tones in the range of pitch. the squares of those components). Also see AB- absolute pressure Pressure (force per unit area) of SOLUTE VALUE and IMPEDANCE. a gas or liquid determined with respect to that of absolute maximum rating The highest value a a vacuum (taken as zero). quantity can have before malfunction or damage absolute-pressure transducer A transducer actu- occurs. ated by pressure from the outputs of two different absolute maximum supply voltage The highest pressure sources, and whose own output is pro- supply voltage that can be applied to a circuit portional to the difference between the two ap- without permanently altering its characteristics. plied pressures. absolute measurement of current Measurement absolute scale 1. A scale in which the zero value of a current directly in terms of defining quan- indicates the lowest physically possible value that tities. 1. TANGENT GALVANOMETER method: a parameter can attain. 2. A standard scale Current is proportional to the tangent of the an- for measurement of a quantity. 3. A universally gle of deflection of the needle of this instrument. agreed-upon scale for the determination of a vari- Deflection depends on torque, resulting from the able quantity. 4. The Kelvin temperature scale. magnetic field produced by current in the gal- 5. The Rankine temperature scale. vanometer coil acting against the horizontal absolute Seebeck coefficient The quotient, as an component of the earth’s magnetic field. integral from absolute zero to the given tempera- 2. ELECTRODYNAMOMETER method: With this ture, of the Thomson coefficient of a material di- 2-coil instrument, current is determined from vided by its absolute temperature. the observed deflection, the torque of the sus- absolute spectral response The frequency output pension fiber of the movable coil, and the coil di- or response of a device in absolute power units mensions. (such as milliwatts) as opposed to relative units absolute measurement of voltage Measurement (such as decibels). of a voltage directly in terms of defining quan- absolute system of units A system of units in tities. 1. CALORIMETRIC method: A current- which the fundamental (ABSOLUTE) units are carrying coil immersed in water raises the those expressing length (l), mass (m), charge (q), temperature of the water. The difference of and time (t). All other physical units, including potential that forces the current through the coil practical ones, are then derived from these abso- then is determined in terms of the equivalent heat lute units. energy. 2. Disk-electrometer method: In this absolute temperature Temperature measured on setup, a metal disk attached to one end of a either the Kelvin or Rankine scales, where zero balance beam is attracted by a stationary disk represents the total absence of heat energy. mounted below it, the voltage being applied to the absolute temperature scale 1. The Kelvin temper- two disks. The other end of the beam carries a ature scale, in which the divisions are equal in pan into which accurate weights are placed. At size to 1° Celsius, and the zero point is absolute balance, the voltage is determined in terms of the zero, the coldest possible temperature, approxi- weight required to restore balance, the upper-disk mately –273.16° Celsius. 2. The Rankine temper- area, and the disk separation. ature scale, in which the divisions are equal in absolute minimum resistance The resistance be- size to 1° Fahrenheit, and the zero point is abso- tween the wiper and the nearer terminal of a po- lute zero or approximately –459.7° Fahrenheit. tentiometer, when the wiper is as close to that absolute tolerance The value of a component as it terminal as physically possible. All potentiome- deviates from the specified or nominal value. It is ters have two such specifications, one for each usually expressed as a percentage of the specified end terminal. value.
  • 18. 5059F-pA_1-55 4/9/01 4:41 PM Page 4 4 absolute units • A-B test absolute units Fundamental physical units (see into heat or other forms of energy. 2. Loss of all or ABSOLUTE SYSTEM OF UNITS) from which all part of a skywave because of absorption by the others are derived. See, for example, AMPERE, ionosphere. Also called ionospheric absorption or OHM, VOLT, and WATT. atmospheric absorption. absolute value The magnitude of a quantity with- absorption marker A small blip introduced onto out regard to sign or direction. The absolute value an oscilloscope trace to indicate a frequency of a is written |a|. The absolute value of a posi- point. It is so called because it is produced by the tive number is the number itself; thus, |10| action of a frequency-calibrated tuned trap, simi- equals 10. The absolute value of a negative num- lar to an absorption wavemeter. ber is the number with its sign changed: |-10| absorption modulation Amplitude modulation of a equals 10. transmitter or oscillator by means of an audio- absolute-value circuit A circuit that produces a frequency-actuated absorber circuit. In its simplest unipolar signal in response to a bipolar input and form, the modulator consists of a few turns of wire in proportion to the absolute value of the magni- coupled to the transmitter tank coil and con- tude of the input. nected to a carbon microphone. The arrangement absolute-value computer A computer in which absorbs energy from the transmitter at a varying data is processed in its absolute form; i.e., every rate as the microphone changes its resistance in variable maintains its full value. (Compare to accordance with the sound waves it receives. INCREMENTAL COMPUTER.) absolute-value device In computer practice, a de- vice that delivers a constant-polarity output signal equal in amplitude to that of the input signal. Thus, the output signal always has the same sign. absolute zero The temperature –273.16°C (Ϫ459.7°F and 0 Kelvin). The coldest possible temperature, representing the complete absence of heat energy. absorbed wave A radio wave that dissipates in the ionosphere as a result of molecular agitation. This effect is most pronounced at low and medium frequencies. absorptance The amount of radiant energy ab- absorption spectrum For electromagnetic waves, a sorbed in a material; equal to 1 minus the trans- plot of absorption coefficient (of the medium of mittance. propagation) versus frequency. Also called EMIS- absorption The taking up of one material or me- SION SPECTRUM. dium by another into itself, as by sucking or absorption trap See WAVETRAP. soaking up. Also, the retention of one medium (or absorption wavemeter A resonant-frequency indi- a part of it) by another medium, through which cating instrument that is inductively coupled to the first one attempts to pass. See, for example, the device under test. ABSORBED WAVE, ABSORPTION COEFFI- CIENT, DIELECTRIC ABSORPTION. Compare ADSORPTION. absorption band See ABSORPTION SPECTRUM. absorption circuit A circuit that absorbs energy from another circuit or from a signal source—es- pecially a resonant circuit, such as a wavemeter or wavetrap. absorption current In a capacitor, the current re- sulting from absorption of energy by the dielectric material. absorption dynamometer A power-measuring in- strument in which a brake absorbs energy from a revolving shaft or wheel. absorption fading Fading of a radio wave, result- ing from (usually) slow changes in the absorption of the wave in the line of propagation. absorptivity In audio and microwave technologies, absorption frequency meter See WAVEMETER. a measure of the energy absorbed by a given vol- absorption line See ABSORPTION SPECTRUM. ume of material. absorption loss 1. Transmission loss caused by A-B test Comparison of two sounds by reproduc- dissipation of electrical energy, or conversion of it ing them in alternating succession.
  • 19. 5059F-pA_1-55 4/9/01 4:41 PM Page 5 abvolt • accentuation 5 abvolt The unit of potential difference in the cgs acceleration at stall The angular acceleration of a electromagnetic system. One abvolt equals 10–8 V servomotor at stall, determined from the stall and is the difference of potential between any two torque and the moment of inertia of the motor’s points when 1 erg of work is required to move 1 rotor. abcoulomb of electricity between them. acceleration derivative Acceleration (a) expressed abwatt The unit of power in the cgs electromagnetic as the second derivative of distance (s) with re- system. One abwatt equals 10Ϫ7 W and is the spect to time (t): a equals d 2s/dt 2. power corresponding to 1 erg of work per second. acceleration potential See ACCELERATING ac 1. Abbreviation of ALTERNATING CURRENT. VOLTAGE. 2. Abbreviation of ATTITUDE CONTROL. 3. Ab- acceleration switch A switch that operates auto- breviation of AERODYNAMIC CENTER. 4. A suf- matically when the acceleration of a body to fix meaning AUTOMATIC CALCULATOR or which it is attached exceeds a predetermined rate AUTOMATIC COMPUTER. in a given direction. a/c 1. Abbreviation of AIRCRAFT. 2. Abbreviation acceleration time The time required by a com- of AIR CONDITIONING. puter to take in or deliver information after inter- Ac Symbol for ACTINIUM. preting instructions. Compare ACCESS TIME. ACA Abbreviation of automatic circuit analyzer. acceleration torque During the accelerating pe- ac base current Symbol, IB(ac). The ac component of riod of a motor, the difference between the torque base current in a bipolar transistor. demanded and the torque actually produced by ac base resistance Symbol, RB (ac). The dynamic the motor. base resistance in a bipolar transistor. acceleration voltage The potential between accel- ac base voltage Symbol, VB(ac). The ac component erating elements in a vacuum tube, the value of of base voltage in a bipolar transistor. It is the ac which determines average electron velocity. input signal voltage in a common-emitter ampli- accelerometer A transducer whose output voltage fier or emitter-follower amplifier. is proportional to the acceleration of the moving ac bias In a tape recorder, the high-frequency cur- body to which it is attached. rent that passes through the recording head to accentuation The emphasis of a desired band of linearize operation. frequencies, usually in the audio-frequency spec- acc 1. Abbreviation of AUTOMATIC CHROMI- trum. NANCE CONTROL. 2. Abbreviation of AUTO- MATIC COLOR COMPENSATION. 3. Abbreviation of ACCELERATION. ac cathode current Symbol, IK(ac). The ac compo- nent of cathode current in an electron tube. ac cathode resistance Symbol, RK(ac). The dynamic cathode resistance in an electron tube. RK(ac) equals dVK/dIK for a constant value of VG. ac cathode voltage Symbol, VK(ac). The ac compo- nent of cathode voltage in an electron tube. It is the ac output signal voltage in cathode-follower and grounded-grid amplifiers. accelerated life test A test program that simu- lates the effects of time on devices or apparatus, by artificially speeding up the aging process. accelerated service test A service or bench test in which equipment or a circuit is subjected to an extreme condition in an attempt to simulate the effects of average use over a long time. accelerating conductor or relay A conductor or relay that prompts the operation of a succeeding device in a starting mode according to established conditions. accelerating electrode In a cathode-ray tube or klystron, the electrode to which the accelerating voltage is applied. accelerating time The elapsed time that starts when voltage is applied to a motor, and ends when the motor shaft reaches maximum speed. accelerating voltage A positive high voltage applied to the accelerating electrode of a cathode-ray tube to increase the velocity of electrons in the beam.
  • 20. 5059F-pA_1-55 4/9/01 4:41 PM Page 6 6 accentuator • accuracy rating accentuator A circuit or device, such as a filter, RC(ac) equals dVC/dIC for a constant value of base tone control, or equalizer, used to emphasize a current IB (in a common-emitter circuit) or emit- band of frequencies, usually in the audio- ter current IE (in a common-base circuit). frequency spectrum. Also see ACCENTUATION. ac collector voltage Symbol, VC(ac). The ac compo- acceptable-environmental-range test A test to nent of collector voltage in a bipolar transistor. disclose the environmental conditions that equip- The ac output signal voltage in a common-emitter ment can endure while maintaining at least the or common-base amplifier. minimum desired reliability. accompanying audio channel The RF signal that acceptable quality level Abbreviation, AQL. A per- supplies television sound. Also called Cochannnel centage that represents an acceptable average of sound frequency. defective components allowable for a process, or ac component In a complex wave (i.e., one con- the lowest quality that a supplier is permitted to taining both ac and dc), the alternating, fluctu- regularly present for acceptance. ating, or pulsating part of the combination. acceptance sampling plan A probabilistic method Compare DC COMPONENT. of sampling a quantity of units from a lot, and de- accordion A printed-circuit connector contact with termining from the sample whether to accept the a Z-shaped spring that allows high deflection lot, reject the lot, or perform another sampling. with low fatigue. acceptance test A test performed on incoming ac-coupled flip-flop A flip-flop that is operated by equipment or on submitted samples to determine the rise or fall of a clock pulse. if they meet tester’s or supplier’s specifications. ac coupling Transformer coupling or capacitive acceptor 1. Any device or circuit, such as a series- coupling, which transmit ac, but not dc. Compare resonant circuit, that provides relatively easy DIRECT COUPLING. transmission of a signal, in effect accepting the signal. 2. A hole-rich impurity added to a semi- conductor to make the latter p-type. It is so called because its holes can accept electrons. Compare DONOR. acceptor circuit See ACCEPTOR, 1. acceptor impurity See ACCEPTOR, 2. access 1. To gain entrance to something, such as the interior of the cabinet of a high-fidelity ampli- fier. 2. In a computer, the action of going to a spe- cific memory location for the purpose of data retrieval. 3. A port or opening into a piece of equipment, placed there to make the equipment easy to maintain and repair. access arm A mechanical device that positions the read/write mechanism in a computer storage unit. access control register A register that is part of a computer protection system that prevents inter- ference between different software modules. access method A method of transferring informa- tion or data from main storage to an input/out- put unit. access right The access status given to computer system users that indicates the method of access permitted (e.g., read a file only or write to a file). access time The time required by a computer to begin delivering information after the memory or accumulator 1. In a digital computer, a circuit or storage has been interrogated. register device that receives numbers, totals accidental error An unintentional error commit- them, and stores them. 2. Storage battery. ted by a person making measurements and accuracy 1. Precision in the measurement of recording data. quantities and in the statement of physical char- accidental triggering The undesired chance- acteristics. 2. Degree of precision. Usually ex- operation of a flip-flop or other switching circuit pressed, in terms of error, as a percentage of the caused by a noise pulse or other extraneous sig- specified value (e.g., 10 V plus or minus 1%), as a nal. percentage of a range (e.g., 2% of full scale), or as ac collector current Symbol, IC(ac). The ac compo- parts (e.g., 100 parts per million). nent of collector current in a bipolar transistor. accuracy rating The maximum error in an instru- ac collector resistance Symbol, RC(ac). The dy- ment, given as a percentage of the full-scale namic collector resistance of a bipolar transistor. value.
  • 21. 5059F-pA_1-55 4/9/01 4:41 PM Page 7 accw • ac magnetic bias 7 accw Abbreviation of ALTERNATING-CURRENT ac generator 1. A rotating electromagnetic ma- CONTINUOUS WAVE. chine that produces alternating current (e.g., a ac/dc Abbreviation of ALTERNATING CURRENT/ dynamo or alternator). 2. An oscillator or com- DIRECT CURRENT. Pertains to equipment that bination of an oscillator and an output ampli- will operate from either ac utility power or a dc fier. power source. A notebook computer is a good ex- ac grid voltage Symbol, VG(ac). The ac component ample. of control grid voltage in an electron tube. The ac ac directional overcurrent relay A relay that input signal voltage in a common-cathode ampli- works on a specific value of alternating overcur- fier or cathode follower. rent that is rectified for a desired polarity. A channel The left channel of a two-channel stereo ac drain current Symbol, ID(ac). The ac component system. of drain current in a field-effect transistor. achieved reliability A statement of reliability based ac drain resistance Symbol, RD(ac). The dynamic on the performance of mass-produced parts or drain resistance in a field-effect transistor; RD(ac) systems under similar environmental conditions. equals dVD/dID for a constant value of gate volt- Also called OPERATIONAL RELIABILITY. age VG. achromatic 1. Without color. In a TV image, the ac drain voltage Symbol, VD(ac). The ac component tones from black through gray to white. The term of drain voltage in a field-effect transistor. The ac occasionally refers to black-and-white television, output signal voltage in a common-source FET although MONOCHROMATIC is more often used amplifier. in this sense. ac dump The removal of all ac power from a system achromatic locus Also called achromatic region. or component. An area on a chromaticity diagram that contains ac emitter current Symbol, IE(ac). The ac compo- all points, representing acceptable reference nent of emitter current in a bipolar transistor. white standards. ac emitter resistance Symbol, RE(ac). The dynamic achromatic scale A musical scale without acci- emitter resistance of a bipolar transistor; RE(ac) dentals. equals dVE/dIE for a constant value of base cur- ACIA Abbreviation of asynchronous communica- rent IB (in an emitter-follower circuit) or collector tions interface adapter. voltage VCC (in a common-base circuit). acicular Pertaining to the shape of magnetic parti- ac emitter voltage Symbol, VE(ac). The ac compo- cles on recording tape. Under magnification, nent of emitter voltage in a bipolar transistor. The these particles look like thin rods. ac input signal voltage in a common-base ampli- acid A substance that dissociates in water solution fier; the ac output signal voltage in an emitter- and forms hydrogen (H) ions (e.g., sulfuric acid). follower amplifier. Compare BASE, 2. ac equipment An apparatus designed for opera- acid depolarizer Also called acidic depolarizer. tion from an ac power source only. Compare DC An acid, in addition to the electrolyte, used in EQUIPMENT and AC/DC. some primary cells to slow the process of polar- ac erasing In tape recording, the technique of us- ization. ing an alternating magnetic field to erase material ac line A power line that delivers alternating cur- already recorded on the tape. rent only. ac erasing head Also called ac erase head. In tape ac line filter A filter designed to remove extrane- and wire recording, a head that carries alternat- ous signals or electrical noise from an ac power ing current to erase material already recorded on line, while causing virtually no reduction of the the tape or wire. Also see AC ERASING. power-line voltage or power. acetate Cellulose acetate, a tough thermoplastic ac line voltage The voltage commonly delivered material that is an acetic acid ester of cellulose. It by the commercial power line to consumers. In is used as a dielectric and in the manufacture of the United States, the two standards are 117 V photographic films. and 234 V (~ about 5 percent). The lower voltage acetate base 1. The cellulose acetate film that is used by most appliances; the higher voltage is served as the base for the magnetic oxide coating intended for appliances and equipment that in early recording tape. Most such tapes today draws high power, such as electric ovens, cook- are of polyester base. 2. The cellulose acetate ing ranges, clothes dryers, and amateur-radio substrate onto which certain photosensitive ma- amplifiers. In Europe, 220 V is the common terials are deposited for lithographic reproduc- standard. tion. Also see ACETATE and ANCHORAGE. aclinic line Also called magnetic equator. An imag- acetate tape Recording tape consisting of a mag- inary line drawn on a map of the world or of an netic oxide coating on a cellulose acetate film. area that connects points of zero inclination (dip) Also see ACETATE BASE. of the needle of a magnetic compass. ac gate voltage Symbol, VG(ac). The ac component ACM Abbreviation for Association for Computing of gate voltage in a field-effect transistor. The ac Machinery. input signal voltage. ac magnetic bias See AC BIAS.
  • 22. 5059F-pA_1-55 4/9/01 4:41 PM Page 8 8 ac meter • acoustic feedback ac meter A meter that is intended to work only on quencies. If one fork is struck and then brought alternating current or voltage. Such meters in- near the other, the second fork will begin vibrating. clude iron-vane and rectifier types. If the second fork has a fundamental frequency that is a harmonic of the frequency of the first fork, the second fork will vibrate at its own resonant frequency. See HARMONIC, RESONANCE. acoustic coupling Data transfer via a sound link between a telephone and a pickup/reproducer. Was once common in computer terminals and facsimile machines. This scheme has been largely replaced by hard wiring and optical coupling. acoustic damping The deadening or reduction of the vibration of a body to eliminate (or cause to die out quickly) sound waves arising from it. acoustic delay line Any equivalent of a special transmission line that introduces a useful time delay between input and output signals. In one ac noise 1. Electromagnetic interference originat- form, it consists of a crystal block or bar with an ing in the ac power lines. 2. Electrical noise of a input transducer at one end and an output trans- rapidly alternating or pulsating nature. ducer at the other. An electrical input signal in ac noise immunity In computer practice, the abil- the first transducer sets up sound waves that ity of a logic circuit to maintain its state, despite travel through the interior of the crystal; the excitation by ac noise. piezoelectric reaction of the crystal to sound vi- acous Abbreviation for ACOUSTIC. brations sets up an output voltage in the second acoustic Pertaining to audible sound distur- transducer. The delay is caused by the time re- bances, usually in air (versus audio-frequency quired for the acoustic energy to travel the length currents or voltages). of the crystal bar. acoustic absorption The assimilation of energy from sound waves passing through or reflected by a given medium. acoustic absorption loss That portion of sound energy lost (as by dissipation in the form of heat) because of ACOUSTIC ABSORPTION. acoustic absorptivity The ratio of sound energy absorbed by a material to sound energy striking the surface of the material. acoustic attenuation constant The real-number component of the complex acoustical propagation constant, expressed in nepers per unit distance. acoustic burglar alarm An alarm that receives the noise made by an intruder. The alarm device re- acoustic depth finder A direct-reading device for sponds to the impulses from concealed micro- determining the depth of a body of water, or for phones. locating underwater objects via sonic or ultra- acoustic capacitance The acoustic equivalent of sonic waves transmitted downward and reflected electrical capacitance. back to the instrument. acoustic clarifier In a loudspeaker system, a set of acoustic dispersion Variation of the velocity of cones attached to the baffle that vibrate to absorb sound waves, depending on their frequency. and suppress sound energy during loud bursts. acoustic elasticity 1. In a loudspeaker enclosure, acoustic communication Communications by the compressibility of air behind the vibrating means of sound waves. This can be through the cone of the speaker. 2. In general, the compress- atmosphere, or it can be through solids or liq- ibility of any medium through which sound uids, such as a taut wire, a body of water, or the passes. earth. acoustic electric transducer A transducer, such acoustic compliance COMPLIANCE in acoustic as a microphone or hydrophone, that converts transducers, especially loudspeakers. It is equiv- sound energy into electrical energy. Compare alent to electrical capacitive reactance. ELECTRICAL/ACOUSTIC TRANSDUCER. Also acoustic consonance An effect that occurs when see ACOUSTIC TRANSDUCER. two objects are near each other but not in physical acoustic feedback A usually undesirable effect contact, and both have identical or harmonically that occurs when sound waves from a loud- related resonant frequencies. An example is shown speaker (or other reproducer) reach a microphone by two tuning forks with identical fundamental fre- (or other input transducer) in the same system.
  • 23. 5059F-pA_1-55 4/9/01 4:41 PM Page 9 acoustic feedback • acoustic radiator 9 This can cause an amplifier to oscillate, with a re- sultant rumbling, howling, or whistling. acoustic filter Any sound-absorbing or transmit- ting arrangement, or combination of the two, that transmits sound waves of desired frequency while attenuating or eliminating others. acoustic frequency response The sound- frequency range as a function of sound intensity. A means of describing the performance of an acoustic device. acoustic generator A device that produces sound waves of a desired frequency and/or intensity. Examples are electrical devices (headphones or acoustic line Baffles or other such structures loudspeakers operated from a suitable oscillator, within a speaker that act as the mechanical equiv- buzzer, bell, or flame) and mechanical devices alent of an electrical transmission line to enhance (tuning forks, bells, string, or whistles). the reproduction of very low bass frequencies. acoustic grating A set of bars or slits that are par- acoustic load A device that serves simultaneously allel to one another and arranged a fixed distance as the output load of an amplifier and as a trans- apart so that an interference pattern forms as ducer of electrical energy into acoustic energy sound passes through. Used to determine the (e.g., headphones or a loudspeaker). wavelength of acoustic waves. acoustic memory In a computer, a volatile mem- acoustic homing system 1. A system that uses a ory element employing an acoustic delay line, of- sound signal for guidance purposes. 2. A guid- ten incorporating quartz or mercury as the ance method in which a missile homes in on transmission and delay element. noise generated by a target. acoustic mirage A type of sound distortion in acoustic horn A tapered tube (round or rectangu- which the listener experiences the illusion of two lar, but generally funnel-shaped) that directs sound sources when there is only one. The phe- sound and, to some extent, amplifies it. So called nomenon is caused by the effect of a large tem- to distinguish it from a microwave horn. perature gradient in the air or water through acoustic howl See ACOUSTIC FEEDBACK. which the sound passes. acoustician 1. A person skilled in acoustics (an acoustic mode Crystal-lattice vibration without acoustics technician). 2. An AUDIOLOGIST. producing an oscillating dipole. acoustic impedance Unit, ACOUSTIC OHM. The acoustic noise Interferential (usually disagreeable) acoustic equivalent of electrical impedance. Like sounds carried by the air (or other propagation the latter, acoustic impedance is the total opposi- medium) to the ear or to an acoustic transducer. tion encountered by acoustic force. Also like elec- This is in contrast to electrical noise, which con- trical impedance, acoustic impedance has sists of extraneous current or voltage impulses resistive and reactive components: ACOUSTIC and is inaudible until converted into sound. RESISTANCE and ACOUSTIC REACTANCE. acoustic ohm The unit of acoustic resistance, re- acoustic inductance Also called inertance. The actance, or impedance. One acoustic ohm equals acoustic equivalent of electrical inductance. the volume velocity of 1 cm/s produced by a acoustic inertance See ACOUSTIC INDUCTANCE. sound pressure of 1 microbar (0.1 Pa). Also called acoustic inhibition See AUDITORY INHIBITION. acoustical ohm. acoustic intensity See SOUND INTENSITY. acoustic phase constant The imaginary-number acoustic interferometer An instrument that eval- component of the complex acoustic propagation uates the frequency and velocity of sound waves constant expressed in radians per second or radi- in a liquid or gas, in terms of a standing wave set ans per unit distance. up by a transducer and reflector as the frequency acoustic phase inverter A bass reflex loudspeaker or transducer-to-reflector distance varies. enclosure. acoustic labyrinth A loudspeaker enclosure acoustic pressure 1. The acoustic equivalent of whose internal partitions form a maze-like path electromotive force, expressed in dynes per or “tube” lined with sound-absorbing material. square centimeter; also called acoustical pres- The tube effectively runs from the back of the sure. 2. Sound pressure level. speaker down to where it terminates in a MOUTH acoustic propagation The transmission of sound or PORT that opens at the front of the enclosure. waves, or subaudible or ultrasonic waves, as a The labyrinth provides an extremely efficient re- disturbance in a medium, rather than as an elec- production system because of its excellent acous- tric current or electromagnetic field. tic impedance-matching capability. acoustic radiator A device that emits sound acoustic lens A system of barriers that refracts waves. Examples are the cone of a loudspeaker, sound waves the way that an optical lens does the diaphragm of a headphone, and the vibrating with light waves. reed of a buzzer.
  • 24. 5059F-pA_1-55 4/9/01 4:41 PM Page 10 10 acoustic radiometer • ac plate resistance acoustic radiometer An instrument for measuring acoustic scattering The spreading of a sound the intensity of a sound wave (see SOUND IN- wave in many directions as a result of diffraction, TENSITY) in terms of the unidirectional steady- reflection, or refraction. state pressure exerted at a boundary as a result acoustic suspension A loudspeaker design that of absorption or reflection of the wave. allows exceptional low-frequency reproduction acoustic reactance Unit, ACOUSTIC OHM. The for a fairly small physical size. An airtight enclo- imaginary-number component of ACOUSTIC sure is used to increase the tension on the IMPEDANCE. It can take the form of ACOUSTIC speaker cone. CAPACITANCE or ACOUSTIC INDUCTANCE. acoustic system 1. A coordinated array of acous- acoustic reflectivity The ratio Fr/Fi, where Fr is tic components (e.g., acoustic filters, resonators, the rate of flow of sound energy reflected from a etc.) that responds to sound energy in a predeter- surface and Fi is the rate of flow of sound energy mined manner. 2. An audio-frequency system in incident to the surface. which sound energy is converted into electrical acoustic refraction The deflection of sound waves energy, processed, and then reconverted into being transferred obliquely between media that sound energy for a clearly defined purpose. transmit sound at different speeds. acoustic telegraph A telegraph that gives audible acoustic regeneration See ACOUSTIC FEEDBACK. signals, as opposed to visual signals or printed acoustic resistance Unit, ACOUSTIC OHM. The messages. real-number component of ACOUSTIC IMPE- acoustic transducer 1. Any device, such as head- DANCE. The opposing force that causes acoustic phones or a loudspeaker, for converting audio- energy to be dissipated in the form of heat. It is frequency electrical signals into sound waves. 2. attributed to molecular friction in the medium Any device, such as a microphone, for converting through which sound passes. See ACOUSTIC sound waves into alternating, pulsating, or fluc- OHM. tuating currents. acoustic resonance In an enclosed chamber with acoustic transmission The direct transmission of walls that reflect sound waves, resonance that oc- sound energy without the intermediary of electric curs at certain wavelengths because the echoes currents. combine in and out of phase. Speaker enclosures acoustic transmission system A set of compo- almost always have resonance at certain frequen- nents designed to generate acoustic waves. cies. This effect can be used to an advantage when acoustic transmissivity Also called acoustic it is necessary to get good bass (low-frequency) transmitivity. The ratio et/ei, where et is the response from a relatively small speaker. sound energy transmitted by a medium, and ei is acoustic resonator 1. A chamber, such as a box, the incident sound energy reaching the surface of cylinder, or pipe, in which an air column resonates the medium. Acoustic transmissivity is propor- at a particular frequency. 2. A piezoelectric, mag- tional to the angle of incidence. netostrictive, or electrostrictive body that vibrates acoustic treatment Application of sound-absorb- at a resonant audio frequency that is governed by ing materials to the interior of an enclosure or the mechanical dimensions of the body when an room to control reverberation. audio voltage at that frequency is applied. acoustic wave The traveling vibration, consisting of molecular motion, via which sound is trans- mitted through a gas, liquid or solid. Usually refers to sound waves in air. acoustic wave filter See ACOUSTIC FILTER. acoustoelectric effect The generation of a voltage across the faces of a crystal by sound waves trav- eling longitudinally through the crystal. acoustoelectronics A branch of electronics con- cerned with the interaction of sound energy and electrical energy in devices, such as surface-wave filters and amplifiers. In such devices, electrically induced acoustic waves travel along the surface of a piezoelectric chip and generate electrical en- ergy. Also called praetersonics and microwave acoustics. ac plate current Symbol, IP(ac). The ac component of plate current in a vacuum tube. acoustics 1. The physics of sound. The study and ac plate resistance Symbol, RP(ac). The dynamic applications of acoustic phenomena. 2. The qual- plate resistance of an electron tube. RP(ac) equals ities of an enclosure or sound chamber (room, dEP/dIP, where EP is the plate voltage and IP is the auditorium, or box) that describe how sound plate current, for a constant value for grid volt- waves behave in it. age EG.
  • 25. 5059F-pA_1-55 4/9/01 4:41 PM Page 11 ac plate voltage • active chord mechanism 11 ac plate voltage Symbol, EP(ac). The ac component ac source voltage Symbol, VS(ac). The ac compo- of plate voltage in an electron tube. The ac out- nent of source voltage in a field-effect transistor. put-signal voltage in a common-cathode ampli- The ac output-signal voltage in a source-follower fier. (grounded-drain) FET amplifier. ac power Symbol, Pac. Unit, watt (W). The power acss Abbreviation of analog computer subsystem. acting in an ac circuit, Pac equals EI cos q, where ac time overcurrent relay A device with a certain E is in volts, I in amperes, and q is the phase an- time characteristic, which breaks a circuit when gle. Compare DC POWER. Also see POWER. the current exceeds a certain level. ac power supply A power unit that supplies ac actinic rays Short-wavelength light rays in the vi- only (e.g., ac generator, vibrator-transformer, os- olet and ultraviolet portion of the spectrum that cillator, or inverter). Compare DC POWER give conspicuous photochemical action. SUPPLY. actinism The property whereby radiant energy acquisition 1. The gathering of data from trans- (such as visible and ultraviolet light, X-rays, etc.) ducers or a computer. 2. Locating the path of an causes chemical reactions. orbiting body for purposes of collecting teleme- actinium Symbol, Ac. A radioactive metallic ele- tered data. 3. Orienting an antenna for optimum ment. Atomic number, 89. Atomic weight, 227. pickup of telemetered data. actinodielectric Exhibiting a temporary rise in acquisition and tracking radar An airborne or electrical conductivity during exposure to light. ground radar, which locks in on a strong signal actinoelectric effect The property whereby cer- and tracks the body that reflects (or transmits) tain materials (such as selenium, cadmium sul- the signal. fide, germanium, and silicon) change their acquisition radar A radar that spots an oncoming electrical resistance or generate a voltage on ex- target and supplies position data regarding the posure to light. Also see ACTINODIELECTRIC. target to a fire-control or missile-guidance radar, actinometer An instrument for measuring the di- which then tracks the target. rect heating power of the sun’s rays or the actinic acr 1. Abbreviation of AUDIO CASSETTE RE- power of a light source. CORDER. 2. Abbreviation of AUDIO CASSETTE action current A small transient current that RECORDING SYSTEM. flows in a nerve in the human body as a result of ac reclosing relay The controlling component in stimulation. an alternating-current circuit breaker. It causes activate To start an operation, usually by applying the breaker to reset after a specified period of an appropriate enabling signal. time. activation 1. Supplying electrolyte to a battery cell ac relay A relay designed to operate on alternating to prepare the cell for operation. 2. Causing the current without chattering or vibrating. acceleration of a chemical reaction. ac resistance Pure resistance in an ac circuit. Un- activation time In the activation of a battery cell like reactance and impedance, which are also (see ACTIVATION, 1), the interval between addi- forms of opposition to the flow of current, ac re- tion of the electrolyte and attainment of full cell sistance introduces no phase shift. voltage. acronym A word formed from letters or syllables activator A substance added to an accelerator (see taken from other applicable words of a multiword ACCELERATOR, 3) to speed the action of the ac- term. Acronyms are convenient for naming new celerator. devices and processes in electronics. Usually, a active Pertaining to a circuit or device that re- term is considered an acronym only when it is quires a power supply for its operation. This dif- spelled in all-capital letters; once the term is ac- fers from a passive circuit or device, which cepted and popularized, it is written as a conven- operates with no external source of power. tional word and is no longer thought of as an active antenna An antenna that uses a small acronym. For example, LASER was once an whip, loop, or ferrite loopstick with a high-gain acronym for light amplification by the stimulated amplifier for receiving at very-low, low, medium, emission of radiation. By the popularization pro- and high radio frequencies (approximately 9 kHz cess, the acronym became a conventional word to 30 MHz). from which other terms (such as the verb “lase”) active area The forward-current-carrying portion were derived. of the rectifying junction of a metallic rectifier. acrylic resin A synthetic resin used as a dielectric active arm See ACTIVE LEG. and in electronic encapsulations. It is made from active balance In telephone repeater operation, the acrylic acid or one of its derivatives. sum of return currents at a terminal network bal- ACS Abbreviation of automatic control system. anced against the local circuit or drop resistance. ac source current Symbol, IS(ac). The ac component active chord mechanism Abbreviation, ACM. In of source current in a field-effect transistor. robots, an electromechanical gripper capable of ac source resistance Symbol, RS(ac). The dynamic conforming to irregular objects. It has a structure source resistance in a field-effect transistor; RS(ac) similar to the human spine, with numerous equals dVS/dIS for a constant value of VG. small, rigid links connected by hinges.
  • 26. 5059F-pA_1-55 4/9/01 4:41 PM Page 12 12 active communications satellite • active repair time active communications satellite A satellite con- active file A computer file in use (i.e., one that is taining receivers (which pick up beamed electro- being updated or referred to). magnetic signals from a ground point and amplify active filter A bandpass, bandstop, highpass or them) and transmitters (which send signals back lowpass filter, consisting of resistors, capacitors, to the surface of the earth). Also called active and operational amplifiers, arranged to pass a de- comsat. Compare PASSIVE COMMUNICATIONS sired frequency response. Commonly used at au- SATELLITE. dio frequencies. active component 1. A device capable of some dy- active infrared detection Detection of infrared namic function (such as amplification, oscilla- rays reflected from a target to which they were tion, or signal control) that usually requires a beamed. power supply for its operation. Examples include active jamming Transmission or retransmission bipolar transistors, field-effect transistors, and of signals for the purpose of disrupting communi- integrated circuits. Compare PASSIVE COMPO- cations. NENT. 2. In an ac circuit, a quantity that con- active junction A pn junction in a semiconductor tains no reactance so that the current is in phase device that has been created by a diffusion pro- with the voltage. cess. active component of current See ACTIVE CUR- active leg An element within a transducer that RENT. changes one or more of its electrical characteris- active computer A computer in an installation or tics in response to the input signal of the trans- network that is processing data. ducer. Also called active arm. active comsat See ACTIVE COMMUNICATIONS active lines In a U.S. television picture, the lines SATELLITE. (approximately 488) that make up the picture. active control system A device or circuit that The remaining 37 of the 525 available lines are compensates for irregularities in the operating blanked and are called INACTIVE LINES. environment. active material 1. In a storage cell, the chemical active current In an ac circuit, the current compo- material in the plates that provides the electrical nent that is in phase with the voltage. This is in action of the cell, as distinguished from the sup- contrast to reactive current, which is not in phase porting material of the plates themselves. 2. A ra- with the voltage, and is “inactive,” with respect to dioactive substance. 3. The phosphor coating of a power in the circuit. The active current is equal to cathode-ray tube screen. 4. The material used to the average power divided by the effective voltage. coat an electron-tube cathode. active decoder An automatic ground-station de- active mixer A signal mixer using one or more ac- vice that gives the number or letter designation of tive components, such as transistors or in- a received radio beacon reply code. tegrated circuits. An active circuit provides active device 1. An electronic component, such as a amplification, input-output isolation, and high transistor that needs a power supply, and/or that input impedance, in addition to the mixing ac- is capable of amplifying. 2. Broadly, any device (in- tion. Compare PASSIVE MIXER. cluding electromechanical relays) that can switch active modulator A modulator using one or more (or amplify) by application of low-level signals. active components, such as transistors or inte- active electric network A network containing one grated circuits. An active circuit provides gain, or more active devices or components, usually input-output isolation, and high input impe- amplifiers or generators, in addition to passive dance, in addition to modulation. Compare PAS- devices or components. SIVE MODULATOR. active element The driven or RF-excited element active network See ACTIVE ELECTRIC NET- in a multielement antenna or antenna array. WORK. active pressure The electromotive pressure that produces a current in an ac circuit. active pull-up An arrangement using a transistor as a pull-up resistor replacement in an integrated circuit, providing low output impedance and low power consumption. active RC network 1. A resistance-capacitance (RC) circuit that contains active components (transistors or integrated circuits), as well as pas- sive components (capacitors and resistors). 2. An RC network in which some or all of the resistors and capacitors are simulated by the action of ac- tive components. active repair time The time during which mainte- nance is done on a system and the system is out of operation.
  • 27. 5059F-pA_1-55 4/9/01 4:41 PM Page 13 active satellite • adapter 13 ily in the same physical location as the true ground surface (i.e., the earth itself ). An actual ground can be an artificial ground plane, such as that provided in some antenna structures. Actual ground can also be modified by nearby rooftops, buildings, guy wiring, and utility wiring. actual height The highest altitude where radio wave refraction actually occurs. actual power Also called active or AVERAGE POWER. Symbol, Pavg. In a resistive circuit under sine-wave conditions, average power is the prod- uct of the rms voltage and the rms current. It is also equal to half the product of the maximum current and maximum voltage. actuating device A device or component that oper- ates electrical contacts to affect signal transmis- sion. active satellite See ACTIVE COMMUNICATIONS actuating system 1. An automatic or manually SATELLITE. operated system that starts, modifies, or stops an active sensor In an electronic security system, a operation. 2. A system that supplies energy for transducer that generates an electromagnetic ACTUATION. field or acoustic-wave field, and detects changes actuating time Also called actuation time. The in the field resulting from the presence or move- time interval between generation of a control sig- ment of objects in the vicinity. nal, or the mechanical operation of a control de- active substrate In an integrated circuit, a sub- vice, and the resulting ACTUATION. strate consisting of single-crystal semiconductor actuation 1. The starting, modification, or termi- material into which the components are formed; nation of an operation or process. 2. Activation of it acts as some or all of the components. This is in a mechanical or electromechanical switching de- contrast to a substrate consisting of a dielectric, vice. where the components are deposited on the sur- actuator An electromechanical device that uses face. electromagnetism to produce a longitudinal or ro- active system A radio and/or radar system that tary thrust for mechanical work. It is often the requires transmitting equipment to be carried in end (load) device of a servosystem. a vehicle. ACU Abbreviation of automatic calling unit. active tracking system A system in which a ac voltage A voltage, the average value of which is transponder or responder on board a vehicle re- zero, that periodically changes its polarity. In one transmits information to tracking equipment cycle, an ac voltage starts at zero, rises to a max- (e.g., azusa, secor). imum positive value, returns to zero, rises to a active transducer 1. A transducer that contains maximum negative value, and finally returns to an active device, such as a transistor or inte- zero. The number of such cycles per second is grated circuit, for immediate amplification of the termed the ac frequency. sensed quantity. 2. A transducer that is itself an ac voltmeter See AC METER. active device. acyclic machine Also called ACYCLIC GENERA- active wire In the armature of a generator, a wire TOR. A dc generator in which voltage induced in experiencing induction and, therefore, is deliver- the active wires of the armature is always of the ing voltage. same polarity. activity 1. Intensity of, as well as readiness for, os- A/D Abbreviation for ANALOG-TO-DIGITAL. See cillation in a piezoelectric crystal. 2. Radioactive ANALOG-TO-DIGITAL CONVERSION. intensity. 3. Intensity of thermal agitation. 4. Ada A microcomputer language designed primarily Thermionic emission of electrons. for use in multi-computer systems, where each activity ratio The ratio of active to inactive records small computer communicates with the others, in a computer file. providing some of the advantages of a larger com- ac transducer A transducer that either requires an puter. ac supply voltage or delivers an ac output sig- Adam A communications code word sometimes nal—even when operated from a dc supply. used for phonetic verbalizing of the letter A. More ac transmission The use of an alternating voltage commonly, ALPHA is used. to transfer power from one point to another, usu- adapter 1. A fitting used to change either the ter- ally from generators to a distribution center, and minal scheme or the size of a jack, plug, or socket generally over a considerable distance. to that of another. 2. A fitting used to provide a actual ground The ground as “seen” by an an- transition from one type or style of conductor to tenna. The actual ground surface is not necessar- another (e.g., waveguide to coaxial line). 3. An
  • 28. 5059F-pA_1-55 4/9/01 4:41 PM Page 14 14 adapter • address generation addend In a calculation, any number to be added to another. Compare AUGEND. addend register In a digital computer, the register that stores the addend. adder 1. In a digital computer, the device or circuit that performs binary addition. A HALF ADDER is a two-input circuit that can produce a sum out- put and a carry output, but it cannot accommo- date a carry signal from another adder. A FULL ADDER can accommodate a carry input, as well as two binary signals to be added. Also see ANA- LOG ADDER. 2. A circuit in a color TV receiver auxiliary system or unit used to extend the oper- that amplifies the receiver primary matrix signal. ation of another system (e.g., a citizens-band additive 1. The character or characters added to a adapter for a broadcast receiver). code to encipher it. 2. In a calculation, an item adaptive communication A method of communi- that is to be added. 3. An ingredient, usually in a cation that adjusts itself according to the particu- small quantity, added to another material to im- lar requirements of a given time. prove the latter in quality or performance. adaptive suspension vehicle Abbreviation, ASV. additive color A color formed by combining the A specialized robot that moves on mechanical rays from two or three primary-colored lights legs, rather than on wheels. It generally has six onto a single neutral surface. For example, by legs and resembles an insect. It is designed to projecting a red and a green beam onto a neutral move over extremely irregular or rocky terrain, screen, a yellow additive color results. and to carry a human passenger. additive primaries Primary colors that form other adaptivity The ability of a system to respond to its colors in a mixing of light (see ADDITIVE COLOR), environment by changing its performance char- but are not themselves formed by mixing other acteristics. additive primaries. For example, red, green, and adc Abbreviation of ANALOG-TO-DIGITAL CON- blue are the additive primaries used in color tele- VERTER. vision. Through appropriate mixing, these colors Adcock antenna A directional antenna system can be used to generate an unlimited variety of consisting of two vertical antennas, spaced in other colors. Compare SUBTRACTIVE PRI- such a way that the whole array behaves like a MARIES, which form the color spectrum by mix- loop antenna. Its members are connected and po- ing pigments rather than lights. In additive sitioned so that it discriminates against horizon- systems, each superimposed primary color in- tally polarized waves, and delivers output that is creases the total light output from the reflecting proportional to the vector difference of signal volt- (viewing) surface; in subtractive systems, each su- ages induced in the two vertical arms. perimposed primary decreases the total reflectiv- ity. Thus, equal combination of additive primaries produces gray or white, and equal combination of subtractive primaries produces gray or black. addition record An extra data store created in a computer during processing. address 1. In computer operations, a usually nu- merical expression designating the location of material within the memory or the destination of such material. 2. The accurately stated location of information within a computer; a data point within a grid, matrix, or table; a station within a network. 3. In computer operations, to select the location of stored information. address comparator A device that ensures that Adcock direction finder A radio direction-finding the address being read is correct. system based on the directivity of the ADCOCK address computation In digital computer opera- ANTENNA. tions, the technique of producing or modifying Adcock radio range A radio range system with only the address part of an instruction. four ADCOCK ANTENNAS situated at the corners address field In a computer, the part of the in- of a square, and a fifth antenna at the center of struction that gives the address of a bit of data (or the square. a word) in the memory. add-and-subtract relay A stepping relay that can address generation The programmed generation be switched either uprange (add) or downrange of numbers or symbols used to retrieve records (subtract). from a randomly stored direct-access file.
  • 29. 5059F-pA_1-55 4/9/01 4:41 PM Page 15 address indirect • adjusted decibels 15 address indirect An address that specifies a stor- age location that contains another address. address memory The memory sections in a digital computer that contain each individual register. address modification In computer operations, altering only the address portion of an instruc- tion; if the command or instruction routine is then repeated, the computer will go to the new address. address part In a digital computer instruction, the part of an expression that specifies the location. Also called ADDRESS FIELD. address register In a computer, a register in which an address is stored. add/subtract time In a computer, the time re- quired to perform addition or subtraction, ex- cluding the time required to get the quantities from storage and to enter the sum or difference into storage. from the picture signal in the next higher chan- add time In computer operations, the time re- nel and the sound signal in the next lower quired to perform addition, excluding the time re- channel. quired to get the quantities from storage and to adjacent-channel selectivity The extent to which enter the sum into storage. a receiver or tuned circuit can receive on one a/d converter A device that changes an analog channel and reject signals from the nearest outly- quantity into a digital signal. See ANALOG-TO- ing channels. DIGITAL CONVERSION. adjacent sound channel In television, the radio- ADF Abbreviation of AUTOMATIC DIRECTION frequency (RF) channel containing the sound FINDER. modulation of the next lower channel. ADI Abbreviation of ALTERNATE DIGIT INVER- adjacent video carrier In television, the radio- SION. frequency (RF) carrier containing the picture adiabatic damping In an accelerator (see ACCEL- modulation of the next higher channel. ERATOR, 1), reduction of beam size as beam en- adjustable component Any circuit component ergy is increased. whose main electrical value can be varied at will adiabatic demagnetization A technique using a (e.g., a variable capacitor, inductor, resistor, or magnetic field to keep a substance at a low tem- load). perature, sometimes within a fraction of a degree adjustable instrument 1. An instrument whose of absolute zero. sensitivity, range, or response can be varied at adjacency A character-recognition condition in will (e.g., multirange meter or wideband genera- which the spacing reference lines of two charac- tor). 2. An instrument that requires adjustment ters printed consecutively in line are closer than or manipulation to measure a quantity (e.g., specified. bridge, potentiometer, or attenuator). adjacent- and alternate-channel selectivity The adjustable motor tuning An arrangement that al- selectivity of a receiver or radio-frequency (RF) lows the motor tuning of a receiver to be confined amplifier, with respect to adjacent-channel and to a portion of the frequency spectrum. alternate-channel signals. That is, the extent to adjustable resistor A wirewound resistor in which which a desired signal is passed, and nearby un- the resistance wire is partially exposed to allow wanted signals are rejected. varying the component’s value. adjacent audio channel See ADJACENT SOUND adjustable voltage divider A wirewound resistor CHANNEL. with terminals that slide on exposed resistance adjacent channel The channel (frequency band) wire to produce various voltage values. immediately above or below the channel of in- adjusted circuit A circuit in which leads that are terest. normally connected to a circuit breaker are adjacent-channel attenuation The reciprocal of shunted so that current can be measured under the selectivity ratio of a radio receiver. The selec- short-circuit conditions without breaker trip- tivity ratio is the ratio of the sensitivity of a re- ping. ceiver (tuned to a given channel) to its sensitivity adjusted decibels Noise level (in decibels) above a in an adjacent channel or on a specified number reference noise level (designated arbitrarily as of channels removed from the original. zero decibels) measured at any point in a system adjacent-channel interference In television or with a noise meter that has previously been ad- radio reception, the interference from stations justed for zero (at reference), according to specifi- on adjacent channels. A common form arises cations.
  • 30. 5059F-pA_1-55 4/9/01 4:41 PM Page 16 16 admittance • affirmative admittance Symbol, Y. Unit, siemens (formerly aeronautical fixed service station A station that mho). The property denoting the comparative operates in the aeronautical fixed service. ease with which an alternating current flows aeronautical ground station A land station that through a circuit or device. Admittance is the re- provides communication between aircraft and ciprocal of impedance (Z ): Y = 1/Z. ground stations. adp 1. Abbreviation of AMMONIUM DIHYDROGEN aeronautical marker-beacon signal A distinctive PHOSPHATE, a piezoelectric compound used for signal that designates a small area above a beacon sonar crystals. 2. Abbreviation of AUTOMATIC transmitting station for aircraft navigation. DATA PROCESSING. aeronautical marker-beacon station A land sta- adsorption Adhesion of a thin layer of molecules of tion that transmits an aeronautical marker- one substance to the surface of another without beacon signal. absorption. An example is adsorption of water to aeronautical mobile service A radio service con- the surface of a dielectric. This term is often con- sisting of communications between aircraft, and fused with ABSORPTION because the spellings of between aircraft and ground stations. the two words are almost identical. Compare AB- aeronautical radio-beacon station An aeronauti- SORPTION. cal radio-navigation land station that transmits adu Abbreviation of automatic dialing unit. signals used by aircraft and other vehicles to de- advanced-class license An amateur-radio license termine their position. conveying all operating privileges, except for a few aeronautical radionavigation services Services small bands that are allocated to extra-class li- provided by stations transmitting signals used in censees. The second-highest class of amateur li- the navigation of aircraft. cense. aeronautical radio service A service that encom- advance information Data published prior to the passes aircraft-to-aircraft, aircraft-to-ground, actual production or availability of a manufac- and ground-to-aircraft communications impor- tured component, circuit, or system. Advance in- tant to the operation of aircraft. formation is often only an approximate reflection aeronautical station A station on land, and occa- of the expected characteristics of a device. sionally aboard ship, operating in the aeronauti- advance wire A resistance wire used in thermo- cal mobile service. couples and precision applications. It is an alloy of Aeronautical Telecommunication Agency The copper and nickel, which has high resistivity and agency that administers the operation of stations a negligible temperature coefficient of resistance. in the aeronautical radio service. aeolight A glow lamp using a cold cathode and a aeronautical telecommunications Collectively, mixture of inert gases. Because its illumination all of the electronic and nonelectronic communi- can be regulated with an applied signal voltage, it cations used in the aeronautical service. is sometimes used as a modulation indicator for aeronautical utility land station A ground sta- motion-picture sound recording. tion in an airport control tower that provides aerial See ANTENNA. communications having to do with the control of aerial cable A wire or cable run through the air, us- aircraft and other vehicles on the ground. ing support structures, such as towers or poles. aeronautical utility mobile station At an airport, aerodiscone antenna A miniature discone an- a mobile station that communicates with aero- tenna designed for use on aircraft. nautical utility land stations and with aircraft aerodynamics The science dealing with forces ex- and other vehicles on the ground. erted by air and other gases in motion—especially aerophare See RADIO BEACON. upon bodies (such as aircraft) moving through aerospace 1. The region encompassing the earth’s these gases. atmosphere and extraterrestrial space. 2. Per- aerogram See RADIOGRAM. taining to transport and travel in the earth’s at- aeromagnetic Pertaining to terrestrial magnetism, mosphere and in outer space. This includes as surveyed from a flying aircraft. aircraft, orbiting space vessels, and interplane- aeronautical advisory station A civil defense and tary spacecraft. advisory communications station in service for AES Abbreviation for Audio Engineering Society. the use of private aircraft stations. AEW Abbreviation of airborne (or aircraft) early aeronautical broadcasting service The special warning. service that broadcasts information regarding air aF Abbreviation of ATTOFARAD. navigation and meteorological data pertinent to AF Abbreviation of AUDIO FREQUENCY. aircraft operation. AFC 1. Abbreviation of AUTOMATIC FREQUENCY aeronautical broadcast station A station of the CONTROL. 2. Abbreviation of AUDIO-FRE- aeronautical broadcasting service. QUENCY CHOKE. aeronautical fixed service A fixed radio service affirmative In voice communications, a word often that transmits information regarding air naviga- used for “yes”—especially when interference is tion and flight safety. present or signals are weak.
  • 31. 5059F-pA_1-55 4/9/01 4:41 PM Page 17 AFIPS • aircraft bonding 17 AFIPS Acronym for American Federation of Infor- airborne intercept radar A type of short-range mation Processing Societies. radar used aboard fighter and interceptor aircraft afpc Abbreviation of automatic frequency/phase for tracking their targets. control. airborne long-range input Equipment aboard air- AFSK Abbreviation of AUDIO-FREQUENCY-SHIFT craft, for the purpose of facilitating the use of KEYING. long-range missiles. afterglow The tendency of the phosphor of a cath- airborne noise See ACOUSTIC NOISE. ode-ray-tube screen to glow for a certain time af- airborne radar platform Surveillance and alti- ter the cathode-ray beam has passed. Also see tude-finding radar used aboard aircraft. PERSISTENCE. air capacitor A capacitor in which air is the dielec- afterpulse An extraneous pulse in a multiplier tric between two sets of conductive plates. Also phototube (photomultiplier), induced by a pre- called air-dielectric capacitor. ceding pulse. aircarrier aircraft station On an aircraft, a radio AF transformer See AUDIO-FREQUENCY TRANS- station that is involved in carrying people for hire FORMER. or in transporting cargo. a/g Abbreviation of AIR-TO-GROUND. air cell A primary electrochemical cell in which the AGC Abbreviation of AUTOMATIC GAIN CONTROL. positive electrode is depolarized by reduced oxy- AGE Abbreviation of AEROSPACE GROUND gen in the air. EQUIPMENT. air cleaner See DUST PRECIPITATOR. agent An active force, condition, mechanism, or air column The open space inside an acoustic substance that produces or sustains an effect. chamber, pipe, or horn. Thus, a sudden voltage rise is a triggering agent air-cooled component A component, such as a in certain bistable circuits; arsenic is a doping power transistor, that is cooled by circulating air, agent in semiconductor processing; the slow cool- compared with one cooled by a circulating liquid, ing of a heated metal to improve ductility is an such as water or oil. ANNEALING AGENT. air-cooled transistor A transistor (particularly a aging 1. An initial run of a component or circuit power transistor) from which the heat of opera- over a certain period of time shortly after manu- tion is drawn away, through radiation and con- facture to stabilize its characteristics and per- vection, into the surrounding air. The transistor formance. 2. The changing of electrical is usually mounted on a heatsink or fitted with characteristics or of chemical properties over a fins. protracted period of time. air-cooled tube An electron tube from which heat agonic line An imaginary line connecting points on is drawn away, mainly via convection, into the the earth’s surface at which a magnetic needle surrounding air. A device called a chimney can be shows zero declination (i.e., points to true geo- placed around the tube, through which air is graphic north). blown by a fan. Cool air enters through the bot- AGREE Acronym for Advisory Group on Reliability tom of the assembly, and hot air escapes from the of Electronics Equipment. top. Ah Abbreviation of AMPERE-HOUR. Depending on air-core inductor A coil of wire wound around a the standard used, the abbreviation can be amp- hollow cylindrical form or in a loop, designed to hr, a-h, a-hr, or A-h. introduce inductive reactance into a circuit or aH Abbreviation of ATTOHENRY. system. In practice, the maximum attainable in- aided tracking In radar and fire control, a system ductance is approximately 1 mH. This type of in- in which manual correction of target tracking er- ductor is used in some wireless transmitters, ror automatically corrects the rate of movement receivers, and antenna networks. The component of the tracking mechanism. can be designed for high current-carrying capac- AIEE Abbreviation for American Institute of Electri- ity by using heavy-gauge wire and a large winding cal Engineers, now consolidated with the IRE, radius. The magnetic lines of flux extend consid- forming the IEEE. erably beyond the interior of the coil, especially AIP Abbreviation for American Institute of Physics. along the winding axis. This increases the likeli- air The mixture of gases that constitutes the hood of mutual inductance between the coil and earth’s atmosphere and figures prominently in surrounding electrical components, devices, or the manufacture and operation of numerous circuits. electronic devices. By volume, air contains about air-core transformer A transformer without a fer- 21 percent oxygen, 78 percent nitrogen, and romagnetic core, so called because air is the only lesser amounts of argon, carbon dioxide, helium, material at the center of (and immediately sur- hydrogen, krypton, neon, and xenon. It also con- rounding) the transformer coils. tains varying amounts of water vapor, and in aircraft bonding The practice of solidly connect- smoggy areas, carbon monoxide and the oxides of ing, for electrical purposes, the metal parts of an sulfur and nitrogen. aircraft, including the engine.
  • 32. 5059F-pA_1-55 4/9/01 4:41 PM Page 18 18 aircraft flutter • airwaves aircraft flutter Rapid, repetitive fading and inten- sifying of a received radio or television signal, re- sulting from reflections of the signal by passing aircraft. aircraft station A nonautomatic radio communi- cations station installed on an aircraft. air-dielectric coax A special type of COAXIAL CA- BLE designed to have minimum loss. The space between inner and outer conductors is mostly empty (i.e., air-filled). Some such cables are sealed and filled with an inert gas. The inner con- ductor is held away from the inner wall of the outer conductor by beads, washers, or a spiral- wound filament of high-grade dielectric material, such as polyethylene. airport beacon A radio or light beacon that marks the location of an airport. airport control station A station that provides communications between an airport control air environment Pertaining to communications tower and aircraft in the vicinity. equipment aboard aircraft. airport surveillance radar An air-traffic-control airflow The path or movement of air in, through, or radar that scans the airspace within about 60 around an electronic device or piece of equip- miles (approximately 100 kilometers) of an air- ment—especially pertaining to an AIR-COOLED port, and displays in the control tower the loca- COMPONENT. tion of all aircraft below a certain altitude and all air gap 1. A narrow space between two parts of a obstructions in the vicinity. magnetic circuit (e.g., the gap in the core of a fil- air-position indicator An airborne computer sys- ter choke). Often, this gap is filled with a non- tem that, using airspeed, aircraft heading, and magnetic material, such as plastic, for elapsed time, furnishes a continuous indication mechanical support. 2. The space between two or of the position of the aircraft. The indication is more magnetically coupled or electrostatically affected by high-altitude winds. Compare coupled components. 3. A device that gets its GROUND-POSITION INDICATOR. name from the narrow gap between two small air-to-air communication Radio transmission metal balls, needle points, or blunt rod tips from one aircraft to another in flight. Com- therein. When an applied voltage is sufficiently pare AIR-TO-GROUND COMMUNICATION and high, a spark discharges across the gap. GROUND-TO-AIR COMMUNICATION. air/ground control radio station A station for air-to-ground communication Radio transmis- aeronautical telecommunications related to the sion from an aircraft in flight to a station located operation and control of local aircraft. on the ground. Compare AIR-TO-AIR COMMUNI- air-insulated line 1. An open-wire feeder or trans- CATION and GROUND-TO-AIR COMMUNICA- mission line. Typically, the line consists of two TION. parallel wires held apart by separators (bars or air-to-ground radio frequency The carrier fre- rods of high-grade dielectric material) situated at quency, or band of such frequencies, allocated for wide intervals. 2. AIR-DIELECTRIC COAX. transmissions from an aircraft to a ground sta- air-moving device A mechanical device, such as a tion. specially designed fan or blower, used to facilitate airwaves 1. Radio waves. The term is slang, but is air cooling of electronic components. widely used. It probably came from the public’s
  • 33. 5059F-pA_1-55 4/9/01 4:41 PM Page 19 airwaves • aliasing noise 19 mistaken notion that radio signals are propa- gated by the air. 2. Skywaves. Al Symbol for ALUMINUM. alabamine See ASTATINE. alacratized switch A mercury switch in which the tendency of the mercury to stick to the parts has been reduced. alarm 1. An electronic security system. 2. A silent and/or audible alert signal transmitted by an electronic security system when an intrusion oc- curs. 3. A silent and/or audible signal that in- forms personnel of the occurrence of an equipment malfunction. alarm circuit A circuit that alerts personnel to a system malfunction, a detected condition, or an intruder. alarm condition 1. An intrusion or equipment malfunction that triggers an alarm circuit. 2. The operation of an alarm circuit that occurs in re- sponse to an intrusion or equipment malfunc- tion. alarm hold A device that keeps an alarm sounding once it has been actuated. alarm output The signal sent from an alarm cir- cuit to a siren, buzzer, computer, or other exter- nal device to alert personnel to an ALARM CONDITION. alarm relay A relay that is actuated by an alarm device. A-law A form of companding law frequently used in European electronics (the mu-law is more often used in North America). A nonlinear transfer algebraic adder In computer operations, an adder characteristic in companding circuits. It can be that provides the algebraic sum, rather than the continuous, or can be a piecewise linear approxi- arithmetic sum, of the entered quantities. mation of a continuous function. algebraic operation A form of electronic calculator A-law companded Companding by means of an 8- operation, in which the keystrokes proceed in an bit binary code following the A-LAW, a specific intuitive sequence, following the way in which the companding function. calculation is written down. Compare REVERSE albedo For an unpolished surface, the ratio of re- POLISH NOTATION. flected light to incident light. It can vary from 0.0 algebraic sum The sum of two or more quantities to 1.0, or from 0 to 100 percent. with consideration of their signs. Compare albedograph An instrument for measuring the ARITHMETIC SUM. albedo of planets. algorithm A step-by-step procedure for solving a ALC Abbreviation of AUTOMATIC LEVEL CON- problem, (e.g., the procedure for finding the TROL. square root of a number). It can be expressed in a alerting device An audible alarm that includes a line-by-line instruction set or as a flowchart. self-contained solid-state audio oscillator. Pow- algorithmic language A computer language used ered from the ac line or a battery, the device pro- to describe a numeral or algebraic process. duces a raucous noise when actuated. alias A label that is an alternate term for items of Alexanderson antenna A very-low-frequency the same type; a label and several aliases can (VLF) and low-frequency (LF) vertically polarized identify the same data element in a computer antenna, designed to minimize ground losses in program. structures of manageable height. It usually con- aliasing 1. In analog-to-digital (A/D) conversion, a sists of several wires, each quarter-wave reso- false output signal that results from a sampling nant with a loading coil, and all connected rate that is too slow. Ideally, the sampling rate is at together at the apex of a tower. The antenna is least twice the highest input signal frequency. 2. fed between the ground and the base of one of Sawtooth-like irregularities, also called jaggies, the wires. which are sometimes introduced into a bit-mapped Alford antenna A loop antenna, in a square config- computer image when it is changed in size. uration, with the corners bent toward the center aliasing noise A form of signal distortion caused to lower the impedance at the current nodes. by a signal with an excessive bandwidth.
  • 34. 5059F-pA_1-55 4/9/01 4:41 PM Page 20 20 align • alloy diode align 1. To adjust (i.e., to preset) the circuits of an Allen wrench A tool used to tighten or loosen an electronic system, such as a receiver, transmit- Allen screw. It is a hexagonal rod and is available ter, or test instrument, for predetermined re- in various sizes. sponse. 2. To arrange elements in a certain precise orientation and spacing, relative to each other, as in a Yagi antenna. 3. To orient antennas so that they are in line of sight, with respect to each other. alignment The process of ensuring that equip- ment, components, or systems are adjusted, both physically and electronically, for the most effi- cient possible performance. alignment chart A line chart for the simple solu- tion of electronic problems. It is so called because its use involves aligning numerical values on var- ious scales, the lines intersecting at the solution on another scale. Also called nomograph. alligator clip A spring-loaded clip with jagged alignment pin A pin or protruding key, usually in teeth, designed to be used for temporary electri- the base of a removable or plug-in component, to cal connections. ensure that the latter will be inserted correctly allocate 1. To assign (especially through legisla- into a circuit. Often, the pin mates with a keyway, tion) operating frequencies or other facilities or notch, or slot. conditions needed for scientific or technical activ- alignment tool A specialized screwdriver or ity; see, for example, ALLOCATION OF FRE- wrench (usually nonmagnetic) used to adjust QUENCIES. 2. In computer practice, to assign padder or trimmer capacitors or inductor cores. locations in the memory or registers for routines alive See LIVE. and subroutines. alkali See BASE, 2. allocated channel A frequency channel assigned alkali metals Metals whose hydroxides are bases to an individual or group. (alkalis). The group includes cesium, francium, allocated-use circuit 1. A circuit in which one or lithium, potassium, rubidium, and sodium. more channels have been authorized for the ex- alkaline battery 1. A battery composed of alkaline clusive use of one or more services. 2. A commu- cells and characterized by a relatively flat dis- nications link assigned to users needing it. charge curve under load. allocation of frequencies See RADIO SPECTRUM. alkaline cell A common non-rechargeable electro- allocator A telephone system distributor associ- chemical cell that employs granular zinc for ated with the finder control group relay assembly. the negative electrode, potassium hydroxide as It reserves an inactive line-finder for another call. the electrolyte, and a device called a polarizer as allophone A variation in the sound of a phoneme, the positive electrode. Produces approximately depending on what comes before and/or after the 1.5 volts under no-load conditions. The geometry phoneme in the course of speech. Important in of construction is similar to that of the zinc– speech recognition and synthesis. There are 128 carbon cell, but it can deliver current effectively different phoneme variations in the English lan- at lower temperatures. Cells of this type have guage. See PHONEME. shelf lives longer than zinc–carbon cells; they also alloter relay A telephone system line-finder relay have greater energy-storage capacity per unit that reserves an inactive line-finder for the next volume, but they are more expensive than zinc– incoming call from the line. carbon cells. They are used in calculators, tran- allotropic Pertaining to a substance existing in sistor radios, and cassette tape and compact-disc two forms. players. Compare ZINC–CARBON CELL. alloy A metal that is a mixture of several other met- alkaline-earth metals The elemental metals bar- als (e.g., brass from copper and zinc), or of a ium, calcium, strontium, and sometimes beryl- metal and a nonmetal. lium, magnesium, and radium, some of which are alloy deposition In semiconductor manufacture, used in vacuum tubes. depositing an alloy on a substrate. alkaline earths Substances that are oxides of the alloy-diffused transistor A transistor in which the alkaline-earth metals. Some of these materials base is diffused and the emitter is alloyed. The are used in vacuum tubes. collector is provided by the semiconductor sub- all-diffused A type of INTEGRATED CIRCUIT in strate into which alloying and diffusion are which both active and passive elements have affected. Compare ALLOY TRANSISTOR and been fabricated by diffusion and related pro- DIFFUSE TRANSISTOR. cesses. alloy diode A junction-type semiconductor diode Allen screw A screw fitted with a six-sided (hexag- in which a suitable substance (such as p-type) is onal) hole. alloyed into a chip of the opposite type (such as
  • 35. 5059F-pA_1-55 4/9/01 4:41 PM Page 21 alloy diode • alternating-charge characteristic 21 n-type) to form the junction. Also called alloy- alphabetic-numeric Also called alphabetical- junction diode. numerical and alphanumeric. In computer opera- alloy junction In a semiconductor device, a posi- tions, pertaining to letters of the alphabet and tive/negative (pn) junction formed by alloying a special characters, and to numerical digits. suitable material (such as indium) with the semi- alpha cutoff frequency Also called alpha cutoff. In conductor (silicon or germanium). a bipolar transistor circuit, the frequency at alloy transistor A transistor whose junctions are which the alpha (current gain) becomes 0.707 created by alloying. Also see ALLOY JUNCTION. (70.7 percent) of its value at 1 kHz. A bipolar transistor can have considerable gain at its alpha cutoff. This specification denotes how rapidly a transistor loses gain as the frequency increases, an important consideration in the design of radio- frequency (RF) amplifiers. See ALPHA. Compare GAIN BANDWIDTH PRODUCT. alpha decay The decay of a substance in which the nuclei of the atoms emit alpha particles, resulting in a change of the atomic number and atomic weight of the substance over a period of time. alphanumeric See ALPHABETIC-NUMERIC. all-pass filter Also called all-pass network. A filter alphanumeric code In computer operations or in that (ideally) introduces a desired phase shift or communications, a code composed of, or using, time delay, but has zero attenuation at all fre- both letters and numbers. quencies. alphanumeric readout A type of digital readout all-relay central office In telephone service, an that displays both letters and numerals. automatic central-office switchboard that uses alpha particle A nuclear particle bearing a positive relay circuits to make line interconnections. charge. Consisting of two protons and two neu- all-wave Pertaining to a wide operating-frequency trons, it is given off by certain radioactive sub- range. Few systems are literally all-wave. For ex- stances. Compare BETA RAYS and GAMMA RAYS. ample, a so-called “all-wave radio receiver” might alpha system An alphabetic code-signaling sys- cover 500 kHz to 30 MHz only. tem. all-wave antenna An antenna that can be operated alphatron An ionizing device in which the radia- over a wide frequency range with reasonable effi- tion source is an emitter of alpha particles. ciency and preferably without needing readjust- alteration An inclusive-OR operation. ment. Examples are the DISCONE ANTENNA and alternate channel In communications, a channel the LOG-PERIODIC ANTENNA. situated two channels higher or lower than a all-wave generator A signal generator that will given channel. Compare ADJACENT CHANNEL. supply output over a wide range of frequencies. alternate-channel interference Interference all-wave receiver A radio receiver that can be caused by a transmitter operating in the chan- tuned over a very wide range of frequencies, such nel beyond an adjacent channel. Compare as 10 kHz to 70 MHz. ADJACENT-CHANNEL INTERFERENCE. allyl plastics Plastics, sometimes used as dielectrics alternate digit inversion In multiplex equipment, or for other purposes in electronics, based on a method of switching the binary signals to the resins made by polymerization of monomers (such opposite state, in accordance with A-law com- as diallyl phthalate) that contain allyl groups. panding. alnico Coined from the words aluminum, nickel, alternate frequency A frequency allocated as an and cobalt. An alloy used in strong permanent alternative to a main assigned frequency and magnets, it contains the constituents noted plus used under certain specified conditions. (sometimes) copper or titanium. alternate-mark inversion signal A signal that alpha 1. Symbol, α. The current gain of a common- conveys bits in which the successive signals are base-connected bipolar transistor. It is the ratio of of opposite polarity (positive, then negative, then the differential of collector current to the differen- positive, etc.). They are equal in absolute value tial of emitter current; α = dIC/dIE. For a junction amplitude. transistor, alpha is always less than unity, but alternate mode The technique of displaying sev- very close to it. 2. In voice communications, the eral signals on an oscilloscope screen by rapidly phonetic representation of the letter A. switching the signals in sequence at the end of alphabet The set of all characters in a natural lan- each sweep. guage. alternate routing A secondary, or backup, com- alphabetic coding In computer practice, an abbre- munications path, used when primary (normal) viation system for coding information to be fed routing is impossible. into the computer. The coding contains letters, alternating-charge characteristic In a nonlinear words, and numbers. capacitor, the relationship between the instanta-
  • 36. 5059F-pA_1-55 4/9/01 4:41 PM Page 22 22 alternating-charge characteristic • amateur extra-class license neous charge and the instantaneous value of an above the earth’s surface. 3. The angle, measured alternating voltage. in degrees, with respect to the horizon, at which a alternating current Abbreviation, ac. A current that highly directional antenna is pointed. periodically reverses its direction of flow. In one cy- altitude delay In a plan-position-indicating type of cle, an alternation starts at zero, rises to a maxi- radar, the sync delay introduced between trans- mum positive level, returns to zero, rises to a mission of the pulse and start of the trace on the maximum negative level, and again returns to zero. indicator screen to eliminate the altitude circle in The number of such cycles completed per second is the display. termed the ac frequency. Also see CURRENT. ALU Abbreviation of ARITHMETIC AND LOGIC alternating-current continuous wave An ampli- UNIT. tude-modulated signal resulting from the opera- alumel An alloy used in the construction of one tion of an oscillator or RF amplifier with raw ac type of THERMOCOUPLE. It is composed of voltage. nickel (three parts) and aluminum (one part). alternating current/direct current See AC/DC. alumina An aluminum-oxide ceramic used in elec- alternating-current erasing head See AC ERAS- tron tube insulators and as a substrate in the ING HEAD. fabrication of thin-film circuits. alternating-current pulse A short-duration ac aluminum Symbol, Al. An elemental metal. Atomic wave. number, 13. Atomic weight, 26.98. Aluminum is alternating-current transmission 1. The propa- widely used in electronics, familiar instances be- gation of alternating currents along a length of ing chassis, wire, shields, semiconductor doping, conductor—especially for power-transfer pur- and electrolytic-capacitor plates. poses. 2. A means of picture transmission in aluminum antimonide Formula, AlSb. A crystalline which a given signal strength produces a con- compound useful as a semiconductor dopant. stant value of brightness for a very short time. aluminized screen A television picture-tube alternating voltage Also called alternating-current screen with a thin layer of aluminum deposited voltage. See AC VOLTAGE. on its back to brighten the image and reduce ion- alternation In ac practice, a half cycle. In a complete spot formation. cycle, there are two alternations, one in the positive Am Symbol for AMERICIUM. direction and one in the negative direction. A/m Abbreviation of ampere per meter: the SI unit of magnetic field strength. AM 1. Abbreviation of amplitude modulator. 2. Ab- breviation of AMPLITUDE MODULATION. amalgam An alloy of a metal and mercury. Loosely, any combination of metals. amateur 1. A nonprofessional, usually noncom- mercial devotee of any technology (i.e., a hobby- ist). 2. A licensed radio operator legally authorized to operate a station in the AMATEUR SERVICE. amateur band Any band of radio frequencies as- signed for noncommercial use by licensed radio amateurs (see AMATEUR, 2). In the United States, numerous such bands are above 1.8 MHz (160 meters). Also see AMATEUR SERVICE and AMATEUR STATION. amateur call letters Call letters assigned by a gov- ernment licensing authority—especially to ama- teur stations. Call-letter combinations consist of a letter prefix denoting the country in which the station is situated, plus a number designating alternative denial A NOT-AND operation. the location within the country, and two or more alternator Any mechanically driven machine for letters identifying the particular station. For ex- generating ac power. Sometimes specifically one ample: W6ABC: W (or K) = United States, 6 = Cal- having a permanent-magnet rotor, such as a ifornia, and ABC = identification of individual magneto. licensee (issued alphabetically, except under spe- altimeter station An airborne transmitter whose cial circumstances). signals are used to determine the altitude of air- amateur callsign See AMATEUR CALL LETTERS. craft. amateur extra-class license The highest class of altitude 1. The vertical distance of an object above amateur-radio operator license in the United sea level. 2. The vertical distance of an object States. It conveys all operating privileges.
  • 37. 5059F-pA_1-55 4/9/01 4:41 PM Page 23 amateur radio • AM/FM tuner 23 amateur radio 1. A general term, referring to the will cause no malfunction of, or damage to, a cir- practice of operation, experimentation, and other cuit or device. work in and related to the amateur service. 2. The ambiguity 1. Any unclear, illogical, or incorrect in- hardware that comprises an amateur radio sta- dication or result. 2. The seeking of a false null by tion. 3. A radio receiver, transmitter, or transceiver a servo. 3. In digital computer operations, an er- that is specifically designed for operation in the ror resulting from improper design of logic. amateur bands. ambiguous count In digital counters, a clearly in- amateur radio operator Also called radio ham or correct count. See ACCIDENTAL TRIGGERING. ham radio operator. An individual licensed to ambisonic reproduction A close approximation of transmit radio signals in the amateur service. the actual directional characteristics of a sound in amateur service A two-way radio service, existing a given environment. The reproduced sound al- purely for hobby purposes (i.e., without pecu- most exactly duplicates the sound in the actual niary interest). environment in which it was recorded. amateur station A radio station licensed in the American Morse code (Samuel F. B. Morse, 1791– AMATEUR SERVICE. 1872). Also called Railroad Morse. A telegraph amauroscope An electronic aid to the blind, in code, at one time used on wire telegraph lines in which photocells in a pair of goggles receive light the United States. It differs from the Continental images. Electric pulses proportional to the light code, also called the International Morse Code, are impressed upon the visual receptors of the which is used in radiotelegraphy. Compare CON- brain through electrodes in contact with nerves TINENTAL CODE. above each eye. American National Standards Institute Ac- amber A yellow or brown fossil resin that is histor- ronym, ANSI. An industrial group in the United ically important in electronics. It is the first mate- States that encourages companies to manufac- rial reported to be capable of electrification by ture devices and equipment in accordance with rubbing (Thales, 600 BC). Also, the words elec- certain standards. The objective is to minimize tricity, electron, and electronics are derived from hardware incompatibility problems. the Greek name for amber, elektron. American Radio Relay League A worldwide orga- ambience The acoustic characteristic of a room, in nization of amateur radio operators, headquar- terms of the total amount of sound reaching a lis- tered in Newington, Connecticut. The official tener from all directions. publications are the monthly magazines, QST ambient An adjective meaning “surrounding.” Often and QEX. They also publish numerous books and used as a noun in place of the adjective-noun com- other educational materials. bination (thus, “10 degrees above ambient,” in- American Standards Association Abbreviation, stead of “10 degrees above ambient temperature”). ASA. At one time, the name of the national associ- ambient humidity The amount of moisture in the ation in the U.S. devoted to the formation and dis- air at the time of measurement or operations in semination of voluntary standards of dimensions, which dampness must be accounted for. performance, terminology, etc. See ANSI. ambient level The amplitude of all interference American wire gauge Abbreviation, AWG. Also (acoustic noise, electrical noise, illumination, called Brown and Sharpe gauge or B & S gauge. etc.) emitted from sources other than that of a The standard American method of designating signal of interest. wire sizes. Wire is listed according to gauge num- ambient light Also called ambient illumination. ber from 0000 (460 mils diameter) to 40 (3.145 Room light or outdoor light incident to a location mils diameter). at the time of measurement or operations. americium Symbol, Am. A radioactive elemental ambient-light filter In a television receiver, a filter metal first produced artificially in the 1940s. mounted in front of a picture-tube screen to min- Atomic number, 95. Atomic weight, 243. imize the amount of ambient light reaching the AM/FM receiver A radio set that can receive either screen. amplitude-modulated or frequency-modulated ambient noise 1. In electrical measurements and signals. Usually, a band switch incorporates the operation, background electrical noise. 2. In demodulation-selection circuitry so that as the acoustical measurements and operations, audi- frequency range is changed, the appropriate de- ble background noise. tector is accessed. ambient pressure Surrounding atmospheric pres- AM/FM transmitter A radio transmitter whose sure. output signal can be frequency- or amplitude- ambient temperature The temperature surround- modulated by a panel selector switch. ing apparatus and equipment (e.g., room temper- AM/FM tuner A compact radio receiver unit that ature). can handle either amplitude- or frequency- ambient-temperature range 1. The range over modulated signals, and delivers low-amplitude which ambient temperature varies at a given lo- output to a high-fidelity audio power amplifier. cation. 2. The range of ambient temperature that Compare AM TUNER and FM TUNER.
  • 38. 5059F-pA_1-55 4/9/01 4:41 PM Page 24 24 AMI • Amperian whirl Character Symbol Character Symbol ammeter-voltmeter method The determination of A .— U ..— resistance or power values from the measure- B —... V ...— ment of voltage (E) and current (I ). For resistance, C .. . W .—— R = E/I; for power, P = EI. D —.. X .—.. ammonium chloride Formula, NH4Cl. The elec- E . Y .. .. trolyte in the carbon-zinc type of primary cell. F .—. Z ... . Also called SAL AMMONIAC. G ——. 1 .——. AMNL Abbreviation of AMPLITUDE-MODULATION H . ... 2 ..—.. NOISE LEVEL. I .. 3 ...—. amortisseur winding 1. A winding that acts against pulsation of the magnetic field in an elec- J —.—. 4 ....— tric motor. 2. A winding that acts to prevent os- K —.— 5 ——— cillation in a synchronous motor. L —— 6 ...... amorphous substance A noncrystalline material. M —— 7 ——.. amp 1. Slang for AMPERE. 2. Slang for AMPLIFIER— N —. 8 —.... especially in audio high-fidelity applications. O .. 9 —..— ampacity Current-carrying capacity expressed in P ..... 0 —— amperes. Q ..—. period ..——.. amperage The strength of an electric current (i.e., R . .. comma .—.— the number of amperes). S ... question —..—. ampere (Andre Marie Ampere, 1775-1836). Abbrevi- T — mark ations, A (preferred), a, amp. The SI base unit of current intensity (I ). The ampere is the constant current that, if maintained in two straight parallel conductors of infinite length and of negligible cir- cular cross section and placed 1 meter apart in a American Wire Gauge (AWG) Diameters vacuum, would produce between the conductors a force of 2 × 10 –7 newton per meter. One ampere AWG Millimeters Inches AWG Millimeters Inches flows through a 1-ohm resistance when a potential 1 7.35 0.289 21 0.723 0.0285 of 1 volt is applied; thus I = E/R. Also see MI- 2 6.54 0.257 22 0.644 0.0254 CROAMPERE, MILLIAMPERE, NANOAMPERE, 3 5.83 0.230 23 0.573 0.0226 and PICOAMPERE. 4 5.19 0.204 24 0.511 0.0201 ampere balance A device consisting of two con- 5 4.62 0.182 25 0.455 0.0179 ductors in which the force between them (caused by current) is balanced against the gravitational 6 4.12 0.163 26 0.405 0.0159 force exerted on an object in the gravitational 7 3.67 0.144 27 0.361 0.0142 field of the earth. Used for the precise determina- 8 3.26 0.128 28 0.321 0.0126 tion of current of large dimension, or of the size of 9 2.91 0.115 29 0.286 0.0113 the ampere. 10 2.59 0.102 30 0.255 0.0100 ampere-hour Abbreviations: Ah, amp-hr. The 11 2.31 0.0909 31 0.227 0.00894 quantity of electricity that passes through a cir- 12 2.05 0.0807 32 0.202 0.00795 cuit in one hour when the rate of flow is one am- pere. Also see BATTERY CAPACITY. 13 1.83 0.0720 33 0.180 0.00709 ampere-hour meter An instrument for measuring 14 1.63 0.0642 34 0.160 0.00630 ampere-hours. It contains a small motor driven by 15 1.45 0.0571 35 0.143 0.00563 the current being measured and which moves a 16 1.29 0.0508 36 0.127 0.00500 point on an ampere-hour scale. The motor speed is 17 1.15 0.0453 37 0.113 0.00445 proportional to the current. The position of the 18 1.02 0.0402 38 0.101 0.00398 pointer is proportional to current and elapsed time. 19 0.912 0.0359 39 0.090 0.00354 Ampere’s law Current flowing in a wire generates 20 0.812 0.0320 40 0.080 0.00315 a magnetic flux that encircles the wire in the clockwise direction when the current is moving AMI See ALTERNATE-MARK INVERSION SIGNAL. away from the observer. A-minus Also, A-. The negative terminal of an A ampere-turn Symbol, NI. A unit of magnetomotive battery, or pertaining to the part of a circuit con- force equal to 1 ampere flowing in a single-turn nected to that terminal. coil. The ampere-turns value for any coil is ob- ammeter An instrument used to measure the tained by multiplying the current (in amperes) by amount of current (in amperes) flowing in a circuit. the number of turns in the coil. ammeter shunt A resistor connected in parallel with Amperian whirl The stream of electrons in a an ammeter to increase its current range. Also see single-turn, current-conducting wire loop acting AYRTON-MATHER GALVANOMETER SHUNT. as an elementary electromagnet.
  • 39. 5059F-pA_1-55 4/9/01 4:41 PM Page 25 amp-hr • amplify 25 Direction of tical. 2. The number of decibels by which an AM- PLIFIER circuit increases the amplitude of a sig- flux flow nal. For voltage or current, this figure has meaning only when the input and output impedances are identical. See DECIBEL. 3. The Wire axis ALPHA or BETA of a bipolar transistor. 4. In the operation of an electron tube, the ratio of the derivative (instantaneous rate of change) of the plate voltage to the derivative of the grid volt- age, for zero change in plate current. amplified ALC Abbreviation, AALC. An automatic- level-control (ALC) system that uses the amplifi- cation of the fed-back control signal. It is used in RF power amplifiers, particularly single-sideband Direction (SSB) linear amplifiers, to prevent overmodula- of current tion and nonlinearity. amplified back bias A declining voltage developed across a fast-time-constant circuit in an amplifier Ampere’s Law stage and fed back into a preceding stage. amplifier Any device that increases the magni- tude of an applied signal. It receives an input signal and delivers a larger output signal that, in amp-hr One style of abbreviating AMPERE-HOUR. addition to its increased amplitude, is a replica Also, Ah. of the input signal. Also see CURRENT AMPLI- amplidyne A dynamo-like rotating dc machine FIER, POWER AMPLIFIER, and VOLTAGE AM- that can act as a power amplifier because the re- PLIFIER. sponse of the output voltage to changes in field amplifier diode Any semiconductor that can pro- excitation is quite rapid. Used in servo systems. vide amplification in a suitable circuit or mi- crowave system. See DIODE AMPLIFIER. amplifier distortion A change in the waveform of a signal, arising within an amplifier that is oper- ated in compliance with specified conditions. amplifier input 1. The terminals and section of an amplifier that receive the signal to be amplified. 2. The signal to be amplified. amplifier noise Collectively, all extraneous signals present in the output of an amplifier when no working signal is applied to the amplifier input terminals. amplifier nonlinearity A condition in which the amplifier output signal does not exhibit a linear relationship to the corresponding input signal. Some amplifiers are designed to operate in a lin- ear manner at all times, but many amplifier types amplification 1. The process of increasing the need not function in this manner to be effective. magnitude of a signal. This entails an input sig- Also see AMPLIFIER DISTORTION and LINEAR nal controlling a local power supply to produce a AMPLIFIER. larger output signal. Depending on the kind of in- amplifier output 1. The terminals and section of put and output signals, amplification can be cat- an amplifier that deliver the amplified signal for egorized as CURRENT, VOLTAGE, POWER, or external use. 2. The amplified signal. some combination of these. 2. The qualitative sig- amplifier power The power level of the output sig- nal increase resulting from the process in 1. 3. nal delivered by an amplifier (also called OUTPUT The quantitative signal increase (resulting from POWER), or the extent to which the amplifier in- the process in 1), expressed as a factor (such as creases the power of the input signal (also called 100) or in terms of decibels (dB). See AMPLIFICA- POWER AMPLIFICATION). TION FACTOR and DECIBEL. amplifier response The performance of an ampli- amplification factor 1. The ratio of the output fier throughout a specified frequency band. Fac- voltage, current, or power to the input voltage, tors usually included are gain, distortion, current, or power of an AMPLIFIER circuit. For amplitude versus frequency, and power output. voltage or current, this ratio has meaning only amplify To perform the functions of amplification when the input and output impedances are iden- (see AMPLIFICATION, 1).
  • 40. 5059F-pA_1-55 4/9/01 4:41 PM Page 26 26 amplifying delay line • amplitude selection amplifying delay line A delay line that causes am- munications and broadcasting. The modulating- plification of signals in a circuit intended for signal energy appears at sideband frequencies pulse compression. above and below, and very close to, the carrier amplistat A self-saturating magnetic amplifier. frequency. These sideband signals carry all the amplitron A backward-wave amplifier used in mi- information. The extent of modulation is ex- crowave circuits. pressed as a percentage, from 0, which represents amplitude The extent to which an alternating or an unmodulated carrier, to 100, which repre- pulsating current or voltage swings, positively sents full modulation. In a signal modulated 100 and negatively, from zero or from a mean value. percent, one-third of the power is used to convey amplitude-controlled rectifier A thyratron- or the data; the other two-thirds is consumed by the thyristor-based rectifier circuit. carrier. This form of modulation is essentially amplitude density distribution A mathematical outmoded, although it is still used in the stan- function giving the probability that, at a given in- dard broadcast band from 535 to 1605 kHz. See stant in time, a fluctuating voltage has a certain FREQUENCY MODULATION, PHASE MODU- value. LATION, SINGLE SIDEBAND. amplitude distortion In an amplifier or network, the condition in which the output-signal ampli- tude exhibits a nonlinear relationship to the in- put-signal amplitude. amplitude error 1. The error in measuring the am- plitude of a signal, normally expressed as a per- centage of signal amplitude or as a percentage of full scale. 2. The frequency at which the output amplitude of a signal is in error by 1% with am- plitude at 10% of full scale. amplitude factor For an ac wave, the ratio of the peak value to the rms value. The amplitude factor of a sine wave is equal to the square root of 2 = 1.4142136. amplitude fading In the propagation of electro- magnetic waves, a condition in which the ampli- tudes of all components of the signal (i.e., carrier and sidebands) increase and decrease uniformly. Compare SELECTIVE FADING. amplitude/frequency response Performance of an amplifier throughout a specified range, as ex- hibited by a plot of output-signal amplitude ver- sus frequency for a constant-amplitude input signal. amplitude gate A transducer that transmits only those portions of an input wave that lie within two close-spaced amplitude boundaries; also called slicer. amplitude-modulation noise Spurious amplitude amplitude limiter A circuit, usually with auto- modulation of a carrier wave by extraneous sig- matic gain control (AGC), that keeps an amplifier nals and random impulses, rather than by the in- output signal from exceeding a certain level, de- tended data-containing signal. spite large variations in input-signal amplitude. A amplitude noise In radar, amplitude fluctuations dc-biased diode performs passive limiting action of an echo returned by a target. This noise limits via clipping. the precision of the system. amplitude-modulated generator A signal genera- amplitude of noise The level of random noise in a tor whose output is amplitude modulated. Usu- system. The amplitude of noise is measured in ally, this instrument is an RF generator that is the same way that signal amplitude is measured. modulated at an audio frequency. amplitude range The maximum-to-minimum am- amplitude-modulated transmitter A radio- plitude variation of a signal. It can be expressed frequency transmitter whose carrier is varied in as a direct numerical ratio or in decibels. amplitude, according to the rate of change of amplitude response The maximum output obtain- some data-containing signal (such as voice, mu- able at various frequencies over the range of an sic, facsimile, television pictures, control signals, instrument operating under rated conditions. or instrument readings). amplitude selection The selection of a signal, ac- amplitude modulation Abbreviation, AM. A cording to its correspondence to a predetermined method of conveying intelligence in wireless com- amplitude or amplitude range.
  • 41. 5059F-pA_1-55 4/9/01 4:41 PM Page 27 amplitude separator • analog integrator 27 amplitude separator In a television receiver, a cir- an output equal to their sum or difference (in any cuit that separates the control pulses from the combination), as desired. composite video signal. analog channel In an ANALOG COMPUTER, an in- amplitude suppression ratio The ratio of an un- formation channel in which the extreme limits of desired output of a frequency-modulated (FM) re- data magnitude are fixed, and the data can have ceiver to the desired output, when the test signal any value between the limits. is amplitude modulated and frequency modu- analog communications Any form of communica- lated simultaneously. tions in which a carrier, generally an electromag- amplitude-versus-frequency distortion Distortion netic wave or high-frequency current, is varied in resulting from varying gain or attenuation of an a continuous and controlled way by a data- amplifier or network, with respect to signal fre- containing signal. See ANALOG, 2. quency. analog computer A computer in which input and AMTOR A form of amateur-radio data communica- output quantities are represented as points on tions, in which the accuracy of a group of charac- continuous (or small-increment) scales. To repre- ters in a message is checked periodically by the sent these quantities, the computer uses voltages receiving station. If an error appears likely, then or resistances that are proportional to the num- the receiving station sends an instruction to the bers to be worked on. When the quantities are transmitting station to retransmit that particular nonelectrical (such as pressure or velocity), they group of characters. Characters are sent in are made analogous by proportional voltages or bunches with pauses for possible inquiries from resistances. the receiving station. analog data 1. Data represented in a quantita- AM tuner A compact radio receiver unit that han- tively analogous way. Examples are the deflection dles amplitude-modulated signals and delivers of a movable-coil meter, the positioning of a slider low-amplitude audio output to a high-fidelity am- on a slide rule, and the setting of a variable resis- plifier. Compare AM/FM TUNER and FM TUNER. tor to represent the value of a nonelectrical quan- amu Abbreviation of atomic mass unit. tity. Also see ANALOG. 2. Data displayed along a amusement robot An electromechanical robot, of- smooth scale of continuous values (as by a ten computer-controlled, that is intended for use movable-coil meter), rather than in discrete steps as a toy. (as by a digital meter). AN- A prefix designator used by American military analog differentiator An analog circuit or device services to indicate commonality. whose output waveform is the derivative of the anacoustic Pertaining to the lack of sound or ab- input-signal waveform, with respect to time. sence of reverberation or transmission of sonic waves. analog 1. A quantity that corresponds, point for point or value for value, to an otherwise unrelated quantity. Thus, voltage is the analog of water pressure, and current is the analog of water flow. 2. Varying over a continuous range and, there- fore, capable of attaining an infinite number of values or levels. Compare DIGITAL. analog adder An analog circuit or device that re- ceives two or more inputs and delivers an output equal to their sum. analog adder/subtracter An analog circuit or de- vice that receives two or more inputs and delivers analog divider An analog circuit or device that re- ceives two inputs and delivers an output equal to their quotient. analog electronics Electronic techniques and equipment that is based on uniformly changing signals, such as sine waves, and often having continuous-scale indicators, such as D’Arsonval meters. Compare DIGITAL ELECTRONICS. analog information Approximate numerical infor- mation, as opposed to digital information, which is assumed to be exact. analog integrator An analog circuit or device whose output waveform is the integral of the in- put signal waveform, with respect to time.
  • 42. 5059F-pA_1-55 4/9/01 4:41 PM Page 28 28 analog inverting adder • AND circuit that produces an analog record. The counterpart is a digital recorder, which produces a readout in discrete numbers (printed or visually displayed). analog representation Representation of informa- tion within a smooth, continuous range, rather than as separate (discrete) steps or points. analog signal A signal that attains an infinite number of different amplitude levels, as opposed to one that can attain only a finite number of lev- els as a function of time. analog subtracter An analog circuit or device that receives two inputs and delivers an output equal to their difference. analog summer See ANALOG ADDER. analog inverting adder An analog adder that de- analog switch A switching device that will only livers a sum with the opposite sign to that of the pass signals that are faithful analogs of trans- input quantities. ducer parameters. analog meter An indicating instrument that uses analog-to-digital conversion 1. A process in a movable-coil arrangement or the equivalent, which an analog signal (such as a voice wave- causing a rotating pointer to indicate a particular form) is changed into a digital or binary signal value on a graduated printed scale. Compare that conveys the same information. This process DIGITAL METER. is commonly used in digital computers to encode sounds and images. It is also used in communi- cations systems to improve efficiency, minimize the necessary bandwidth, and optimize the sig- nal-to-noise ratio. 2. A process in which continu- ous mechanical motion is encoded into a digital or binary electronic signal. analog-to-digital converter Any circuit or device that performs ANALOG-TO-DIGITAL CONVER- SION. analysis 1. The rigorous determination of the con- stants and modes of operation for electronic equipment. Compare SYNTHESIS. 2. A branch of mathematics dealing with point sets, relations, and functions. analytical engine A primitive mechanical calculat- ing machine, invented in 1833 by Charles Bab- analog multiplexer 1. A multiplexer used with bage. analog signals (see MULTIPLEXER). 2. An analog analyzer 1. Any instrument that permits analysis time-sharing circuit. through close measurements and tests (e.g., dis- analog multiplier An analog circuit or device that tortion analyzer, WAVE ANALYZER, or gas ana- receives two or more inputs and delivers an out- lyzer). 2. A computer program used for debugging put equal to their product. purposes; it analyzes other programs and sum- analog network A circuit that permits mathemati- marizes references to storage locations. 3. An cal relationships to be shown directly by electric analysis interface to an oscilloscope. or electronic means. anastigmatic yoke Also called full-focus yoke. In a analogous pole In a PYROELECTRIC MATERIAL, television (TV) receiver, a deflection yoke with a the end or face having the positive electric charge. cosine winding for better focus at the edges of the analog output An output quantity that varies picture. smoothly over a continuous range of values, anchorage In plastic recording tape, the adhesion rather than in discrete steps. of the magnetic oxide coating to the surface of the analog record Also called analog recording. A tape. record or recording method in which some prop- ancillary equipment Equipment that does not di- erty of the recorded material, such as displace- rectly enter into the operation of a central system. ment or magnetization, varies over a continuous Examples are input/output components of a com- range that is relative to time and/or physical po- puter and test instruments attached to a system. sition. AND circuit In digital systems and other switching analog recorder Any recorder, such as a recording circuits, a logic gate whose output is high (logic 1) oscillograph, potentiometric recorder, electroen- only when all input signals are high. Otherwise cephalograph, electrocardiograph, or lie detector, the output is low (logic 0). Compare OR CIRCUIT.
  • 43. 5059F-pA_1-55 4/9/01 4:41 PM Page 29 Anderson bridge • angle of beam 29 anechoic chamber An enclosure that does not re- Anderson bridge An ac bridge circuit with six flect sound waves that approach its walls. Such a impedances, permitting the value of an unknown chamber is used to test certain audio devices. inductance to be determined in terms of a stan- anemograph An electromechanical device that dard capacitance. produces a recording of wind speed versus time. Generally, it consists of an ANEMOMETER con- nected to a PEN-AND-INK RECORDER via a suit- able electronic interface. anemometer An instrument that measures or indicates wind speed, or speed and direction (ve- locity). angel 1. An extraneous image, usually of short du- ration, on a cathode-ray-tube (CRT) display. The term applies particularly to anomalies in a radar image caused by low-atmospheric reflection, birds, or other mobile objects. 2. Air-deployed metallic debris, also known as chaff, designed to create radar echoes as a decoy or diversion tactic. angle jamming A radar jamming technique in which the return echo is jammed with a signal containing improper azimuth or elevation angle components. angle modulation Variation of the angle of a sine- wave carrier in response to the modulating source, as in FREQUENCY MODULATION and PHASE MODULATION. angle noise In radar reception, the interference re- AND gate 1. AND circuit. 2. In a TV receiver, an sulting from variations in the angle at which an AND circuit that holds the keyed-AGC signal off echo arrives from the target. until a positive horizontal flyback pulse and a angle of arrival The angle which the line of propa- horizontal sync pulse appear simultaneously at gation of an incoming radio wave makes with the the input. surface of the earth. Compare ANGLE OF DE- android A sophisticated robot built in humanoid PARTURE. form. Usually, it propels itself by rolling on angle of azimuth The horizontal angle between wheels or on a track drive. A rotatable head con- the viewer and object or target, usually measured tains position sensors, a machine vision system, clockwise from north. and/or a machine hearing system. Mechanical angle of beam The angle enclosing most of the arms are equipped with end effectors to perform transmitted energy in the radiation from a direc- various tasks. The most advanced androids have tional antenna. It is usually measured between self-contained computer control systems. the half-power points in the main lobe of the di- anechoic Pertaining to the absence of echoes. Ex- rectional pattern. This angle can be measured in amples: ANECHOIC CHAMBER, anechoic enclo- the horizontal (azimuth) plane or in the vertical sure, or anechoic room. (elevation) plane.
  • 44. 5059F-pA_1-55 4/9/01 4:41 PM Page 30 30 angle of conduction • anhysteresis angle of conduction 1. Also called angle of flow. frequency. Compare ANGLE OF LAG. Also see The number of degrees of an excitation-signal cy- PHASE ANGLE. cle during which output (drain, collector or plate) angle of radiation 1. The angle, measured with re- current flows in an amplifier circuit. 2. The num- spect to the horizon, at which the principal lobe of ber of degrees of any sine wave at which conduc- an electromagnetic wave leaves a transmitting tion of a device (e.g., a diode) begins. antenna. 2. The angle, measured relative to the angle of convergence 1. In any graphical repre- horizon, of a receiving or transmitting antenna’s sentation, the angle formed by any two lines or optimum sensitivity. plots that come together at a point. 2. The angle angle of reflection The angle, measured relative to formed by the light paths of two photocells fo- the perpendicular (orthogonal) to a surface, sub- cused on the same object. tended by a ray leaving the surface after having angle of declination The angle between the hori- been reflected from it. Compare ANGLE OF INCI- zon and a descending line. Compare ANGLE OF DENCE. ELEVATION. angle of refraction The angle, measured relative angle of deflection In a cathode-ray tube, the an- to the perpendicular (orthogonal) to a boundary gle between the electron beam at rest and a new between two different media, subtended by a ray position resulting from deflection. leaving the boundary after having been refracted angle of departure The angle, relative to the thereat. Compare ANGLE OF INCIDENCE. horizon, made by the line of propagation of a angle tracking noise Noise in a servo system that transmitted radio wave. Compare ANGLE OF results in a tracking error. ARRIVAL. angstrom (Anders J. Angstrom, 1814 –1874). A unit of length used to describe certain extremely short waves and microscopic dimensions; 1 angstrom equals 10–4 microns (10–10 meters). angular deviation loss The ratio of microphone or loudspeaker response on the principal axis of re- sponse to the response at a designated angle from that axis. Expressed in decibels. angular difference See PHASE ANGLE. angular displacement In an ac circuit, the separa- tion, in degrees, between two waves. See PHASE ANGLE. angular frequency The frequency of an ac signal, expressed in radians per second (rad/sec) and ap- proximately equal to 6.28f, where f is the fre- quency in Hertz. angular length Length, as along the horizontal axis of an ac wave or along the standing-wave angle of depression See ANGLE OF DECLINA- pattern on an antenna, expressed as the product TION. of radians and wavelength. angle of divergence In a cathode-ray tube, the an- angular-mode keys On a calculator or computer, gle formed by the spreading of an undeflected the DEG, RAD, and GRAD keys for expressing or electron beam as it extends from the gun to the converting angles in DEGREES, RADIANS, and screen. GRADS, respectively. angle of elevation The angle that an ascending angular phase difference For two sinusoidal line subtends, with respect to the horizon. Com- waves, the phase difference, expressed in degrees pare ANGLE OF DECLINATION. or radians. angle of flow See ANGLE OF CONDUCTION. angular rate In navigation, the rate of bearing angle of incidence The angle, measured relative to change, expressed in degrees or radians. the perpendicular (orthogonal) to a surface or angular resolution The ability of a radar to distin- boundary, subtended by an approaching ray. guish between two targets by angular measure- Compare ANGLE OF REFLECTION and ANGLE ment. OF REFRACTION. angus pen recorder An instrument that makes a angle of lag The phase difference (in degrees or ra- permanent record of the time whenever a channel dians) whereby one component follows another in is used. time, both components being of the same fre- anharmonic oscillator An oscillating device in quency. Compare ANGLE OF LEAD. Also see which the force toward the balance point is not PHASE ANGLE. linear, with respect to displacement. angle of lead The phase difference (in degrees or anhysteresis The magnetization of a material by a radians) whereby one component precedes an- unidirectional field containing an alternating field other in time, both components being of the same component of gradually decreasing amplitude.
  • 45. 5059F-pA_1-55 4/9/01 4:41 PM Page 31 anhysteretic state • anomalous propagation 31 anhysteretic state The condition of a substance anode efficiency Also called plate efficiency. In a after it has been subjected to a strong magnetic power amplifier using an electron tube, the ratio field, the intensity of which alternates in direction Po/Pi, where Po is the output power in watts and Pi and diminishes gradually to zero. is the dc anode power input in volt-amperes. animism A belief or philosophy, held especially in anode power input Symbol, PA(input). The product of Eastern civilizations, such as Japan, that all anode current and anode voltage. things contain an essence of life. This theory ren- anode power supply The ac or positive dc power ders irrelevant the question of whether or not ma- supply unit that delivers current and voltage to chines, such as computers and robots can be the anode of a device. “alive.” anode saturation The point beyond which a fur- anion A negative ion. Also see ION. ther increase in anode voltage does not produce anisotropic Pertaining to the tendency of some an increase in anode current. materials to display different magnetic and other physical properties along different axes. ANL Abbreviation of AUTOMATIC NOISE LIMITER. anneal To heat a metal to a predetermined temper- ature and let it cool slowly. The operation pre- vents brittleness and often stabilizes electrical characteristics. annealed laminations Core laminations for trans- formers or choke coils that have been annealed. annealed shield A magnetic shield for cathode-ray tubes, that has been processed by annealing. annealed wire Soft-drawn wire that has been sub- jected to annealing. annotations 1. Marking on copies of original engi- neering-installation documents to show changes made during the installation. 2. Any set of com- ments or notes accompanying a program, an equipment or system, or a process. annular 1. Pertaining to the region between two concentric circles that lie in the same plane; ring- shaped. 2. Pertaining to two or more concentric circles that lie in a common plane. annular conductor A number of wires stranded in three concentric layers of alternating twists around a hemp core. annular transistor A mesa transistor in which the base and collector take the form of concentric anode strap In a multicavity magnetron, a metal rings around a central emitter. strap connecting the anodes. annulling network A subcircuit that shunts a fil- anode terminal 1. In a diode, the terminal to ter to cancel reactive impedance at the extreme which a positive dc voltage must be applied for ends of the pass band of the filter. forward bias. Compare CATHODE TERMINAL. 2. annunciation relay A relay that indicates whether In a diode, the terminal at which a negative dc or not a circuit is carrying current. voltage appears when the device is used as an ac annunciator A device that produces loud sound rectifier. Compare CATHODE TERMINAL. 3. The and/or conspicuous light to attract attention terminal that is connected internally to the an- (e.g., the electronic siren in an automotive secu- odic element of any device. rity system). anode voltage Symbol, EA or VA. The difference in po- anode 1. The positive electrode of a vacuum tube tential between the anode and cathode of a device. or solid-state device (i.e., the electrode toward anodic Pertaining to the anode of a device, or to which electrons move during current flow). 2. In anode-like effects. an electrochemical cell, the electrode that loses anodizing An electrolytic process in which a pro- electrons by oxidation. This is usually the nega- tective oxide film is deposited on the surface of a tive electrode. metallic body acting temporarily as the anode of anode balancing coil Mutually coupled windings the electrolytic cell. used to maintain equal currents in parallel an- anomalous dispersion Dispersion of electromag- odes operating from a common transformer ter- netic radiation that is characterized by a decrease minal. in refractive index with increase in frequency. anode current Current flowing in the anode circuit anomalous propagation 1. The low-attenuation of a device. propagation of UHF or microwave signals through
  • 46. 5059F-pA_1-55 4/9/01 4:41 PM Page 32 32 anomalous propagation • antenna current atmospheric layers. 2. Unusual, bizarre, or unex- antenna amplifier 1. A radio-frequency amplifier, plainable electromagnetic-wave propagation (e.g., often installed at the antenna, used to boost sig- apparent F-layer ionospheric effects in the FM nals before they reach a receiver (also called an broadcast band). 3. Rapid fluctuation of a sonar RF preamplifier). 2. Occasionally, the first RF am- echo because of variations in propagation. plifier stage of a receiver, also known as the front anoxemia toximeter An electronic instrument for end. measuring or alerting against the onset of anox- antenna array See ARRAY. emia (deficiency of oxygen in the blood)—espe- antenna bandwidth The frequency range through- cially in airplane pilots. out which an antenna will operate at a specified AN radio range A navigational facility entailing four efficiency without needing alteration or adjust- zones of equal signal strength. When the aircraft ment. deviates from course, an aural Morse-code signal, antenna beamwidth A measure of the extent to A (DIT DAH) or N (DAH DIT) is heard; but when the which a directional antenna focuses a transmit- aircraft is on course, a continuous tone is heard. ted electromagnetic field, or focuses its response ANSI Acronym for American National Standards In- to incoming electromagnetic fields. Expressed as stitute. the angle in degrees between opposite half-power AN signal The signal provided by an AN radio range points in the main lobe of the directional pattern. to apprise aircraft pilots of course deviation. Usually determined in the horizontal plane, but answerback The automatic response of a terminal occasionally in the vertical plane. station to a remote-control signal. antenna coil The primary coil of the input RF answer cord In a telephone system, the cord used transformer of a receiver, or the secondary coil of for answering subscribers’ calls and incoming the output RF transformer of a transmitter. trunk calls. answering machine A device that automatically answers a telephone and records an audio mes- sage from the caller. answer lamp A telephone switchboard lamp that lights when an answer cord is plugged into a line jack; it switches off when the telephone answers and lights when the call is completed. ant Abbreviation of ANTENNA. antenna In a communications system, a special- ized transducer that converts incoming electro- magnetic fields into alternating electric currents having the same frequencies (receiving antenna), or converts an alternating current at a specific frequency into an outgoing electromagnetic field at the same frequency (transmitting antenna). An antenna coincidence The condition in which two antenna can be a simple wire or rod, or a compli- directional antennas are pointed directly toward cated structure. Thousands of geometries and each other. specifications are possible. The optimum antenna antenna-conducted interference Extraneous sig- type for a given situation depends on the commu- nals generated in a transmitter or receiver and nications frequency, the distance to be covered, presented to the antenna, from which they are ra- and various other factors. diated. antenna ammeter An RF ammeter, usually of the antenna core A ferrite rod or slab around which a thermocouple type, employed to measure current coil of wire is wound to act as a self-contained an- flowing to a transmitting antenna. tenna, usually in a miniature receiver. antenna coupler A device consisting of an induc- tor, RF transformer, or a combination of induc- tor(s) and capacitor(s), used to match the impedance of an antenna to that of a transmitter or receiver. Also known as a transmatch or an- tenna tuner. antenna coupling Inductive and/or capacitive coupling used to optimize the transfer of energy from an antenna to a receiver, or from a trans- mitter to an antenna. antenna current 1. Radio-frequency current flow- ing from a transmitter into an antenna. 2. Radio- frequency current flowing from a receiving antenna into a receiver.
  • 47. 5059F-pA_1-55 4/9/01 4:41 PM Page 33 antenna detector • antenna pattern 33 antenna detector A circuit that warns aircraft jects in the vicinity of an antenna which, taken personnel that they are being observed by radar. together, form the radio-frequency (RF) ground It picks up the radar pulses and actuates a warn- system against which the antenna operates. ing light or other device. Some antennas require an extensive ground sys- antenna diplexer A coupling device that permits tem to function efficiently; others need no ground several transmitters to share one antenna with- system. out troublesome interaction. Compare ANTENNA antenna/ground system An arrangement em- DUPLEXER. bodying both an antenna and a low-resistance antenna directivity The directional characteris- connection to the earth, as opposed to an an- tics of a transmitting or receiving antenna, usu- tenna system that involves no connection to ally expressed qualitatively (e.g., omnidirectional, earth. bidirectional, or unidirectional ). A more precise antenna height 1. The height of an antenna above expression is ANTENNA BEAMWIDTH. the surface of the earth immediately beneath the antenna director In a directional antenna, a PAR- driven element(s). 2. The height of an antenna ASITIC ELEMENT situated in front of the radiator above the effective radio-frequency (RF) ground and separated from it by an appropriate fraction immediately beneath the driven element(s). 3. of a wavelength. Its function is to intensify radia- The height of an antenna above average terrain, tion in the direction of transmission. Compare determined against the mean altitude of a num- ANTENNA RADIATOR and ANTENNA REFLEC- ber of points on the earth’s surface that lie within TOR. a certain radius of the antenna structure. Also antenna duplexer A circuit or device permitting called height above average terrain (HAAT). one antenna to be shared by two transmitters antenna impedance The complex-number im- without undesirable interaction. pedance that an antenna presents to a transmis- antenna effect The tendency of wires or metallic sion line. It can vary over a tremendous range, bodies to act as antennas (i.e., to radiate or re- and depends on the antenna type, antenna size, ceive radio waves). antenna height, operating frequency, and various antenna efficiency The ratio of radio-frequency other factors. energy supplied to a wireless transmitting an- antenna-induced potential Also called antenna- tenna, to the energy radiated into space. Electri- induced microvolts. The voltage across the open- cally, the radiation resistance of the antenna (RR) circuited terminals of an antenna. appears in series with loss resistance (RL). The ef- antenna lens Also called lens antenna. A radiator ficiency Eff of the antenna can be determined by designed to focus microwave energy in much the the following formula: same manner that an optical lens focuses light Eff = RR/(RR + RL) rays. Lens antennas are made from dielectric ma- terials and/or metals. As a percentage, antenna loading 1. The insertion of inductance in Eff % = 100 (RR/(RR + RL) antenna elements to lower the resonant fre- The efficiency is always less than 1 (100 percent) quency of the system without necessarily making because, in practice, the loss resistance can the system physically larger or the elements never be reduced to zero. longer. 2. The insertion of capacitance in antenna antenna factor A factor (in decibels) added to an elements to raise the resonant frequency of the RF voltmeter reading to find the true open-circuit system without necessarily making the system voltage induced in an antenna. physically smaller or the elements shorter. antenna field The electromagnetic field immedi- antenna lobe A well-defined region in the radiation ately surrounding an antenna. pattern of an antenna in which radiation is most antennafier Low-profile antenna/amplifier device, intense, or in which reception is strongest. Also sometimes used with portable communications see ANTENNA PATTERN. systems. Also called an active antenna. antenna matching The technique of establishing a antenna front-to-back ratio For a directional an- satisfactory relationship between the antenna tenna, the ratio of field strength in front of the an- impedance and the transmission-line or trans- tenna (i.e., directly forward in the line of mitter-output impedance, for maximum transfer maximum directivity) to field strength in back of of power into the antenna. Also, the matching the antenna (i.e., 180 degrees from the front), as of antenna impedance to receiver-input im- measured at a fixed distance from the radiator. It pedance, for delivery of maximum energy to the is usually specified in decibels. receiver. antenna gain For a given antenna, the ratio of sig- antennamitter An antenna/oscillator combina- nal strength (received or transmitted) to that ob- tion that serves as a low-power transmitter. tained with a comparison antenna, such as a antenna pattern A polar plot of antenna perfor- simple dipole. Generally specified in decibels. mance that shows field strength versus angle of antenna ground system The earth, counterpoise, azimuth, with the antenna at the center. It is guy wires, radials, and/or various conducting ob- usually specified in the horizontal plane.
  • 48. 5059F-pA_1-55 4/9/01 4:41 PM Page 34 34 antenna polarization • anthropomorphism antenna range 1. The frequency band, communi- cation distance characteristically covered, or other continuum of values that specify the oper- ating limits of an antenna. 2. The region immedi- ately surrounding an antenna in which tests and measurements usually are made. Sometimes called ANTENNA FIELD. antenna reflector In a directional antenna, a PAR- ASITIC ELEMENT situated behind the radiator and separated from the latter by an appropriate fraction of a wavelength. Its function is to inten- sify radiation in the direction of transmission. Compare ANTENNA DIRECTOR and ANTENNA RADIATOR. antenna relay In a radio station, a low-loss, heavy- duty relay that enables the antenna to be switched between transmitter and receiver. antenna polarization The orientation of electric antenna resistance The resistive component of lines of flux, with respect to the surface of the ANTENNA IMPEDANCE. earth, for which an antenna is most efficient. A antenna resonant frequency The frequency, or vertical antenna radiates and receives vertically narrow band of frequencies, at which an an- polarized waves. A horizontal antenna radiates tenna’s impedance appears resistive. and receives horizontally polarized waves broad- antenna stage 1. The first RF amplifier stage of a side to itself, and vertically polarized waves at receiver. 2. Occasionally, the final RF amplifier of high elevation angles off its ends. In other direc- a transmitter. tions, the polarization is slanted at various an- antenna switch In a radio station, a low-loss, gles. heavy-duty switch that enables the antenna to be antenna power Symbol, Pant. The RF power devel- connected to transmitter, receiver, or safety oped in an antenna by a transmitter; Pant equals ground. I 2R, where I is the antenna current and R is the antenna resistance at point I is measured. antenna power gain The ratio of the maximum ef- fective radiated power (ERP) from a wireless transmitting antenna to the ERP from a reference antenna, expressed in decibels (dB). If the ERP from an antenna under test is PT watts and the ERP from the reference antenna is PR watts, then the gain GdB is: GdB = 10 log10 (PT/PR) Power gain is always measured in the direction in which the test antenna performs the best. The reference antenna, usually a dipole, is chosen antenna system Collectively, an antenna and all of with a gain assumed to be unity, or 0 dB. Gain the auxiliary electrical and mechanical devices relative to a dipole is expressed in dBd (decibels needed for its efficient operation, including cou- relative to a dipole). Alternatively, the reference plers, tuners, transmission lines, supports, insu- antenna can be an isotropic radiator, in which lators, and rotator. case the gain is expressed in dBi (decibels relative antenna terminals 1. The points at which a trans- to an isotropic radiator). Gain figures in dBd and mission line is attached to an antenna. 2. The sig- dBi differ by a constant amount as follows: nal input terminals of a receiver. 3. The signal output terminals of a transmitter. GdBi = 2.15 + GdBd antennaverter An antenna and converter com- antenna preamplifier A highly sensitive amplifier bined into a single circuit, intended for connec- used to enhance the gain of a receiver. It is usu- tion to the antenna terminals of a receiver to ally used at the very high frequencies and above. allow operation on frequencies outside the band antenna radiation The propagation of radio waves for which the receiver has been designed. by a transmitting antenna. antenna wire 1. The radiator element of a wire- antenna radiator The element of an antenna that type antenna. 2. A strong solid or stranded wire receives RF energy from the transmitter and radi- (e.g., hard-drawn copper, copper-clad steel, or ates waves into space. Also known as the driven phosphor-bronze) used for antennas. element. Compare ANTENNA DIRECTOR and AN- anthropomorphism The perception, by people, of TENNA REFLECTOR. machines as having human qualities. This can
  • 49. 5059F-pA_1-55 4/9/01 4:41 PM Page 35 anthropomorphism • antiparticle 35 lead to emotional attachment to hardware, such example, log 10,000 = log 104 = 4, and thus an- as computers and robots. The more sophisticated tilog 4 = 104 = 10,000. the apparatus, in general, the more powerful this antilogous pole In a PYROELECTRIC MATERIAL, perception can become. the end that becomes negatively charged as the antialiasing filter A low-pass or bandpass filter temperature rises. that limits the bandwidth of an input signal to antimagnetic Pertaining to materials having ex- prevent aliasing and its effects. See ALIASING, 1. tremely low RETENTIVITY. anticapacitance switch A switch whose members antimatter Pertaining to particles that are the are thin blades and stiff wires widely separated to counterparts of conventional particles (i.e., minimize capacitance between them. positrons instead of electrons, antineutrons in- anticathode The target electrode of an X-ray tube. stead of neutrons, and antiprotons instead of Anticipatory Sciences A group of futurists, people protons). When a particle meets its antiparticle, who attempt to predict the course of technology. the two annihilate, releasing energy. Also see AN- Some futurists believe that progress will continue TIPARTICLE. until, for example, homes become fully automated antimicrophonic See NONMICROPHONIC. and artificial intelligence reaches a level compara- antimony Symbol, Sb. A metalloidal element. ble to human intelligence. Other futurists believe Atomic number, 51. Atomic weight, 121.76. Often that such things are highly improbable. used as n-type dopant in semiconductor manu- anticlutter circuit A supplementary circuit in a facture. radar receiver that minimizes the effect of extra- antineutrino The antiparticle of the NEUTRINO, neous reflections that would obscure the image of emitted as a result of radioactive decay. the target. antineutron An uncharged particle with a mass anticlutter gain control In a radar receiver, a cir- equal to that of the neutron, but with a magnetic cuit that automatically raises the gain of the re- moment in the direction opposite that of the neu- ceiver slowly to maximum after each transmitter tron. pulse to reduce the effect of clutter-producing antinode A point of maximum amplitude in a echoes. standing wave. anticoincidence Noncoincidental occurrence of two or more signals. Compare COINCIDENCE. anticoincidence circuit In computers and control systems, a circuit that delivers an output signal only when two or more input signals are not re- ceived simultaneously. Compare COINCIDENCE CIRCUIT. Also see NAND CIRCUIT. anticoincidence operation An exclusive-OR oper- ation. anticollision radar A vehicular radar system that is used to minimize the probability of a collision with another vehicle, whether or not that other vehicle has a similar system. antinoise carrier-operated circuit A circuit that antiferroelectric 1. Pertaining to the property cuts off the audio output of a receiver while the wherein the polarization curve of certain crys- station transmitter is in use. This can be accom- talline materials shows two regions of symmetry. plished in the automatic-gain-control (AGC) cir- 2. A material that exhibits the aforementioned cuit of the receiver, or in the speaker or audio property. line. The circuit is actuated by energy from the antiferromagnetic Pertaining to the behavior of transmitted signal. materials in which, at low temperatures, the antinoise microphone Any microphone that dis- magnetic moments of adjacent atoms point in op- criminates against acoustic noise (e.g., a lip mi- posite directions. crophone or throat microphone). antihunt The condition in which hunting is coun- antinucleon A particle with the mass of a nucleon, teracted, usually by removing overcorrection in but with the opposite electrical charge and direc- automatic control or compensation systems. tion of magnetic moment. Compare NUCLEON. antihunt circuit 1. A circuit that minimizes or antioxidant A material, such as a lacquer coat or eliminates hunting. Also see ANTIHUNT. 2. In a an inactive oxide layer, that prevents or slows ox- television (TV) receiver, a circuit that stabilizes an idation of a material exposed to air. automatic frequency control (afc) system. antiparticle A subatomic particle opposite in char- antijamming Pertaining to communications sys- acter to conventional particles, such as electrons, tems that are resistant to, or that counteract, the neutrons, protons. Antiparticles constitute effects of jamming. antimatter. Also see ANTINEUTRINO, ANTI- antilogarithm Abbreviated, antilog or log–1. The NEUTRON, ANTINUCLEON, ANTIPROTON, and number corresponding to a given logarithm. For POSITRON.
  • 50. 5059F-pA_1-55 4/9/01 4:41 PM Page 36 36 antiphase • A plus antiphase The property of being in phase opposi- aperture 1. The larger, normally open end of a tion (180 degrees out of phase). horn antenna or horn loudspeaker. 2. An opening antipincushioning magnets In some television in an opaque disk or mask that passes a prede- (TV) receivers, a pair of corrective magnets in the termined amount of light or other radiant energy. deflection assembly on the picture tube that elim- 3. The portion of a directional antenna through inate pincushion distortion (disfigurement of the which most of the radiated energy passes. raster so that it resembles a pincushion—a rect- aperture angle For an antenna or telescope or mi- angle with its sides bowed in). croscope, the half angle formed by the radius of antiproton A subatomic particle with a mass equal the detecting instrument, as viewed from the to that of the proton, but with opposite electrical source. charge. antiquark An ANTIPARTICLE of a QUARK. antirad substance A material that protects against damage caused by atomic radiation. antiresonance 1. Parallel resonance. 2. The con- dition of being detuned from a resonant fre- quency. antiresonant circuit See PARALLEL-RESONANT CIRCUIT. antiresonant frequency 1. The resonant fre- quency of a parallel-resonant circuit. 2. In a piezoelectric crystal, the frequency at which impedance is maximum (as in a parallel-resonant aperture antenna An antenna whose beamwidth circuit). depends on the size of a horn, reflector, or lens. antisidetone Pertaining to the elimination in tele- aperture compensation In a television (TV) cam- phone circuits of interference between the micro- era, the minimizing of APERTURE DISTORTION phone and earphone of the same telephone. by widening the video-amplifier passband. antistickoff voltage The low voltage applied to the aperture distortion In a television (TV) camera coarse synchro control transformer rotor winding tube, a form of distortion that occurs when the in a dual-speed servo system to eliminate am- scanning beam covers several mosaic elements biguous behavior in the system. simultaneously. This condition, caused by exces- antitransmit/receive switch Abbreviated ATR. In sive beam thickness, results in poor image reso- a radar installation, an automatic device to pre- lution. vent interaction between transmitter and re- aperture mask In a three-gun color picture tube, a ceiver. thin, perforated sheet mounted behind the view- antivirus program A computer program or utility ing screen to ensure that a particular color phos- designed to detect and eliminate viruses and Tro- phor will be excited only by the beam for that jan horses in a computer system. color. Also called shadow mask. antivoice-operated transmission Radio commu- aperture synthesis In telescopes, a method of ob- nications that use a voice-activated circuit as a taining high resolution using several small anten- transmitter interlock during reception on the nas separated by great distances. The small companion receiver. antennas are moved around to simulate the re- apc 1. Abbreviation of automatic picture control. 2. solving power of a much larger antenna that Abbreviation of AUTOMATIC PHASE CONTROL. would, in practice, be impossible or impractical to aperiodic Characterized by a lack of predictable construct. repetitive behavior. For example, the sferics or aphelion 1. The point at which a solar-orbiting “static” electromagnetic interference caused by satellite attains its highest altitude. It occurs lightning. once for every complete orbit. At this point, the aperiodic current The unidirectional current that satellite travels slower than at any other point in follows an electromagnetic disturbance in an LCR the orbit. 2. The altitude, measured from the circuit, in which R is equal to or higher than the sun’s surface or the sun’s center, of a solar- critical circuit resistance. orbiting satellite at its most distant point. aperiodic damping Damping of such a high degree APL Abbreviation for A Programming Language. A that the damped system, after disturbance, high-level computer language designed for ease of comes to rest without oscillation or hunting. use, and characterized by the requirement for a aperiodic discharge A discharge in which current special character set. flowing in an LCR circuit is unidirectional, rather apl 1. Abbreviation of average picture level. 2. Ab- than oscillatory. For this condition, 1/LC is less breviation of automatic phase lock. than or equal to R2/4L2. A plus Also, A+. The positive terminal of an A bat- aperiodic function A nonrepetitive function (e.g., tery. Also, pertaining to the part of a circuit con- a hyperbolic trigonometric function). nected to that terminal.
  • 51. 5059F-pA_1-55 4/9/01 4:41 PM Page 37 apogee • arc cosecant 37 apogee 1. The point at which an earth-orbiting appliance Electrical equipment in general. This satellite attains its highest altitude. It occurs might include any home-operated device. once for every complete orbit. At this point, the application A task or job for which an electronic satellite travels slower than at any other point in device or system is used. It especially pertains to the orbit. 2. The altitude, measured from the personal-computer software that has practical earth’s surface or the earth’s center, of an earth- usefulness. orbiting satellite at its most distant point. application factor A factor involved in determin- A power supply A term sometimes used to denote ing the failure rate of a circuit or system affected the unit that supplies energy to a vacuum-tube by unusual operating conditions. filament. Compare B POWER SUPPLY. application schematic diagram A diagram of pic- apparent bearing In radio-direction finding, the torial symbols and lines that illustrate the inter- uncorrected direction from which a signal ap- relationship of functional circuit blocks in a pears to arrive. specific program mode. apparent power In an ac circuit, the power value applicators 1. In dielectric heating, the electrodes obtained by multiplying the current by voltage (P between which the dielectric body is placed and equals IE), with no consideration of the effects of the electrostatic field developed. 2. In medical phase angle. Compare TRUE POWER. electronics, the electrodes applied to a patient apparent power loss The loss in an ammeter or undergoing diathermy or ultrasonic therapy. voltmeter, caused by the imperfection of the in- applied voltage The voltage presented to a circuit strument. At full scale, the ammeter has a certain point or system input, as opposed to the voltage voltage across its terminals; the apparent power drop resulting from current flow through an ele- loss is the current multiplied by this voltage. A ment. voltmeter carries a small current; the apparent applique circuit A circuit for adapting equipment power loss is the product of the current and the to a specialized job. indicated voltage. approach-control radar A radar installation serv- appearance potential The potential through ing a ground-controlled approach (GCA) system. which an electron must move to produce a cer- approximate data 1. Data obtained through phys- tain ion from the atom with which it is associated. ical measurements. Such data can never be ex- applause meter An instrument consisting essen- act; all measurements are subject to error. 2. tially of a microphone, audio amplifier, and indi- Loosely estimated data or imprecise calculations. cating meter (reading directly in sound level). It is AQL Abbreviation of ACCEPTABLE QUALITY so called because of its familiar use in measuring LEVEL. A statistically defined quality level, de- audience response, as indicated by loudness of fined in terms of percent defective, accepted on applause. an average of 95 percent of the time. Aquadag A tradename for a material that consists of a slurry of fine particles of graphite. Aquadag forms a conductive coating on the inside and out- side walls of some cathode-ray tubes. aqua pura Pure water; in most instances, distilled water. Formula, H2O. Pure water is a nonconduc- tor with a dielectric constant of about 81. Ar Symbol for ARGON. arbitrary function fitter A circuit or device, such as a potentiometer, curve changer, or analog computer element, providing an output current or voltage that is some preselected function of the input current or voltage. arc 1. A luminous sustained discharge between two electrodes. Because it is sustained, rather than intermittent, an arc is distinguished from a spark discharge, the latter being a series of dis- charges (sparks)—even when it appears continu- Applegate diagram For a velocity-modulated tube, ous. 2. In graphical presentations, a section of a plot of the positions of electron bunches in the curved line, as of a circle. drift space versus time. arc angle The angle in degrees traced out by a cir- Appleton layer Collectively, the F1 and F2 layers cular arc if the center point of the circle is con- of the ionosphere, at a height between 150 and sidered to be the vertex of an angle formed by 400 kilometers above the surface of the earth. two rays intersecting the arc at designated apple tube A color picture tube, used in television, points. with the red, blue, and green phosphor in vertical arc cosecant Abbreviated arc csc or csc–1. 1. The strips. inverse of the cosecant function. 2. The angle, in
  • 52. 5059F-pA_1-55 4/9/01 4:41 PM Page 38 38 arc cosecant • area code radians or degrees, corresponding to a given cosecant. arc cosine Abbreviated arc cos or cos–1. 1. The in- arc length The length along a given arc, usually a verse of the cosine function. 2. The angle, in radi- part of the circumference of a circle. If the circle ans or degrees, corresponding to a given cosine. has circumference C and the arc measures x de- arc cotangent Abbreviated arc cot or cot–1. 1. The grees, then the arc length is Cx/360 units. inverse of the cotangent function. 2. The angle, in arc minute See MINUTE. radians or degrees, corresponding to a given arc oscillation Oscillations that can occur when cotangent. opening relay contacts arc. arc failure 1. Damage to, and/or failure of, insula- arcover The occurrence of an electrical ARC be- tion or a dielectric as a result of ARCOVER. 2. tween electrodes, contacts, or capacitive plates. Failure of make-and-break contacts through arcover voltage The voltage at which disruptive damage caused by arcover. discharge occurs, typically accompanied by an arc function An inverse trigonometric function. See arc. ARC COSECANT, ARC COSINE, ARC COTAN- arc resistance The ability of a material, usually a GENT, ARC SECANT, ARC SINE, and ARC TAN- dielectric, to resist damage from arcing. This GENT. property is commonly expressed as the length of arc furnace A high-temperature electric furnace in time between the start of the arc and the estab- which heat is produced by one or more electrical lishment of a conductive path through the mate- arcs. rial. architecture The functional design elements of a arc secant Abbreviated arc sec or sec–1. 1. The in- computer—especially the components of the cen- verse of the secant function. 2. The angle, in ra- tral processing unit (CPU) and the manner in dians or degrees, that corresponds to a given which these elements interact. secant. archived file A computer file stored on some arc second See SECOND. backup medium, such as magnetic tape, disk- arc sensor A device for detecting visible arcs and ette, or CD-ROM (compact disk, read-only mem- excessive reflected power in microwave systems. ory), rather than being held on the hard disk. arc sine Abbreviated arc sin or sin–1. 1. The inverse Such a file will be apart from the operating sys- of the sine function. 2. The angle, in radians or tem’s catalog of current files, but can be reconsti- degrees, that corresponds to a given sine. tuted as needed. arc suppression Extinguishing an arc discharge. archives A complete, periodically updated set of Disruptive arcs in electronic circuits are sup- ARCHIVED FILES. pressed by means of auxiliary diodes or resistor- arcing See ARCOVER. capacitor networks. arcing contacts Make-and-break contacts be- arc-suppressor diode A semiconductor diode used tween which an arc occurs when they are sepa- to prevent arcing between make-and-break con- rated. tacts. arcing ring A metal ring placed around an insula- arc tangent Abbreviated arc tan or tan–1. 1. The tor in a high-voltage electrical system. This keeps inverse of the tangent function. 2. The angle, in an arc from charring or breaking the insulator. radians or degrees, corresponding to a given tan- arcing time The elapsed time between the break- gent. ing of contacts and the end of the arc between the arcthrough The puncturing of a material by an contacts. arc. arc lamp An electric lamp in which a brilliant arc area code In the United States, a three-digit jumps between the tips of two rods (originally car- number that indicates the location, according to bon). specified assigned districts, of a telephone sub-
  • 53. 5059F-pA_1-55 4/9/01 4:41 PM Page 39 area code • arithmetic symmetry 39 scriber. When making a long-distance call, the argon Symbol, Ar. An inert gaseous element. area code of the desired station must be given in Atomic number, 18. Atomic weight, 39.94. Argon, addition to the seven-digit telephone number. present in small amounts in the earth’s atmo- area protection Coverage of a defined region, in sphere, is used in various specialized devices, terms of area or volume, by an alarm system. such as lasers. area redistribution A scheme to determine the ef- argon laser A laser whose tube is filled with argon fective duration of an irregularly shaped pulse. A gas. It generates coherent light at specific wave- rectangle is constructed whose height is equal to lengths that are characteristic of elemental ar- the peak height of the pulse, as displayed on an gon. oscilloscope. The rectangle width is adjusted un- argument 1. The direction angle of a polar vector. til the area of the rectangle is the same as the 2. An independent variable whose value deter- area under the curve representing the pulse. The mines the value of a function. width of the rectangle then represents the effec- arithmetic address An address obtained by per- tive duration of the pulse. forming an arithmetic operation on another ad- area search The scanning of a large group of com- dress. puter records for those of a major category or arithmetic and logic unit Abbreviation, ALU. The class. part of a digital computer containing the circuits area sensor A transducer, used with an alarm sys- that perform calculations and logic operations; tem, that protects a defined region or volume, distinguished from mass storage, input/output, such as an office or bedroom. and peripheral units. Argand diagram Named after Jean Robert Argand, arithmetic circuit Also called arithmetic element. (1768-1822) of Geneva, for his work on the In a digital computer, a circuit that is involved in graphical representation of complex numbers. A the execution of calculations. Included are graphical illustration of a complex number in the adders, storage registers, accumulators, sub- form A + jB, where the real-number (A) axis is tracters, and multipliers. perpendicular to the imaginary-number ( jB) axis. arithmetic mean The average of a group of quan- The value j is the square root of -1, the unit imag- tities, obtained by dividing their sum by the num- inary number. The axes are perpendicular, usu- ber of quantities. ally with the A axis horizontal. The length of the arithmetic operation In digital computer prac- line from the point (0,0) to the point (A,jB) is the tice, a numerical process performed: addition, amplitude of the vector X = A + jB. The direction subtraction, multiplication, division, compari- is specified as the angle, in degrees or radians, of son. the vector measured counterclockwise from the A arithmetic progression A mathematical series in axis. which each term following the first is obtained by adding a constant quantity to the preceding one. For example, S = 1, 2, 3, 4, . . . n. Compare GEO- METRIC PROGRESSION. arithmetic shift In a digital computer, the multi- plication or division of a quantity by a power of the base used in the notation. arithmetic sum The sum of two or more quantities disregarding their signs. Compare ALGEBRAIC SUM. arithmetic symmetry A filter response that is ex- actly symmetrical about the center frequency when the frequency scale is linear.
  • 54. 5059F-pA_1-55 4/9/01 4:41 PM Page 40 40 arm • arsenic arm 1. Any of the distinct branches of a circuit or network. Also called leg. 2. A movable element in a device, usually containing a contact for switching. armature 1. The rotating member of a motor. 2. The rotating member of some types of electro-me- chanical generator. 3. The movable member of a relay, bell, buzzer, or gong. 4. The movable mem- ber of an actuator. 5. The soft-iron keeper placed across the poles of a permanent magnet to con- serve power. armature coil A coil of insulated wire wound on a ferromagnetic core to provide the electromagnetic properties of an armature. In a motor or genera- tor, the armature coil is distinguished from the FIELD COIL. armature core The ferromagnetic core upon which the armature coil of a motor or generator is wound. armature gap 1. In a motor or generator, the space between an armature core and the pole of a field magnet. 2. In a relay, the space between the ar- mature and the relay-coil core. armature hesitation A momentary delay in the movement of a relay. armature-hesitation contact chatter Undesired (usually rapid, repetitive) making and breaking of relay contacts. Generally caused by armature hesitation. armature-impact contact chatter Undesired ARPA Acronym for Advanced Research Projects (usually rapid, repetitive) making and breaking of Agency, a subsidiary of the U.S. Department of relay contacts, caused by contact bounce when Defense. the armature strikes the relay core (closure) or array 1. A directive antenna that consists of an as- backstop (opening). sembly of properly dimensioned and spaced ele- armature relay A relay that uses an electromagnet ments, such as radiators, directors, and to pull a lever toward or away from a set of fixed reflectors. 2. A coordinated group or matrix of contacts. components, such as diodes, resistors, memory armature travel The distance traveled by an arma- cells, etc., often enclosed in one capsule. 3. Sub- ture during relay operation. scripted variables representing data arranged so armor A protective metal cable covering. that a program can examine the array and extract Armstrong FM system (Edwin H. Armstrong, data relevant to a particular subscript. 1890 –1954). A phase-shift method of frequency array device A group of similar or identical compo- modulation. See PHASE MODULATION. nents that are connected together in a certain armature voltage control A means of controlling fashion, to perform a specific task. motor speed by changing the applied armature arrester 1. A device used to protect an installation winding voltage. from lightning. It consists of a varistor or an air armchair copy An amateur radio term for recep- gap connected between an antenna or power line tion of exceptionally clear signals. and an earth ground. The device passes little or arming the oscilloscope sweep Enabling an oscil- no current under ordinary conditions, but passes loscope to trigger on the next pulse by closing a heavy current to ground during a lightning switch. stroke. Also called LIGHTNING ARRESTER. 2. A Armstrong oscillator (Edwin H. Armstrong, self-restoring protective device used to reduce 1890–1954). An oscillator circuit that uses in- voltage surges on power lines. ductive feedback between the output and input. ARRL Abbreviation for American Radio Relay Either the output coil or the input coil can be League. tuned to set the oscillator frequency. The amount arrowhead A wideband, log-periodic antenna with of positive feedback is controlled by varying the linear polarization. coupling between the coils. ARS Abbreviation of Amateur Radio Service. Armstrong superheterodyne circuit See SUPER- arsenic Symbol, As. A metalloidal element. Atomic HETERODYNE CIRCUIT. number, 33. Atomic weight, 74.91. Arsenic is fa- Armstrong superregenerative circuit See SU- miliar as an n-type dopant in semiconductor pro- PERREGENERATIVE CIRCUIT. cessing.
  • 55. 5059F-pA_1-55 4/9/01 4:41 PM Page 41 ARSR • assemble 41 ARSR Abbreviation of air route surveillance radar. those of the more bulky transmission line it re- articulation A measure of the effectiveness of voice places in tests and measurements. It also serves communications, expressed as the percentage of as a time-delay or phase-shift device and as a speech units understood by the listener when the pulse-forming network. effect of context is negligible. artificial voice A device used to test and calibrate artificial antenna See DUMMY ANTENNA. noise-canceling microphones, consisting essen- artificial ear A microphone-type sensor, equiva- tially of a small loudspeaker that has a baffle lent to the human ear, used to measure sound whose acoustical properties simulate those of the pressures. human head. artificial echo 1. In radar practice, the reflections artos stripper A machine that cuts and strips wire of a transmitted pulse returned by an artificial for the fabrication of multiconductor cables. target. 2. A signal from a pulsed radio-frequency artwork 1. In the manufacture of printed circuits, (RF) generator, delayed to simulate an echo. the scaled drawings from which the mask or etch artificial ground The effective ground provided by pattern is obtained photographically. 2. Collec- the radials or disk of a ground-plane antenna, as tively, the illustrations depicting an electronic cir- opposed to actual ground (the earth itself ). Com- cuit, device, or system. pare TRUE GROUND. As Symbol for ARSENIC. artificial horizon In aircraft instrumentation, a ASA Abbreviation of AMERICAN STANDARDS AS- device that displays lines showing the position of SOCIATION. the aircraft in flight, with reference to the hori- asbestos A nonflammable fibrous material consist- zon. ing of calcium and magnesium silicates that is artificial intelligence Abbreviation, AI. 1. A spe- used for high-temperature insulation. cialized field of computer science overlapping A-scan A radar-screen presentation in which the with electronics, biology, physiology, and other horizontal time axis displays distance or range, sciences, concerning attempts to develop ad- and the vertical axis displays the amplitude of vanced computer systems that can emulate the signal pulse and echo pulses. processes of the human mind. 2. The ability of a ascending node For a satellite orbiting the earth or computer to learn from its mistakes, refine its another planet, any point at which the ground- own processes, and perhaps ultimately reason in track crosses the equator as it moves from the a humanlike manner. southern hemisphere into the northern hemi- artificial ionization An artificial reflecting layer sphere. This node generally changes for each that is created in the atmosphere to provide a succeeding orbit, because the earth or planet ro- skip condition. tates underneath the orbit of the satellite. Com- artificial language A language that is not com- pare DESCENDING NODE. monly used, but has been devised for efficiency in ascending pass For a specific point on the earth’s a particular situation—especially in a computer surface, the time during which an artificial com- system. munications satellite is accessible when its lati- artificial life 1. The ultimate endpoint of ARTIFI- tude is moving northward. The duration of CIAL INTELLIGENCE, wherein machines acquire accessibility depends on the altitude of the satel- qualities, such as wisdom and the capability to lite, and on how close its groundtrack comes to feel emotions. The state of the art is currently the earth-based point. Compare DESCENDING nowhere near this point. 2. A hypothetical ma- PASS. chine or set of machines with lifelike qualities, in- ASCII Acronym (pronounced “ask-ee”) for Ameri- cluding human-level intelligence, wisdom, and can Standard Code for Information Interchange. emotion. ASI Abbreviation for American Standards Institute. artificial stimulus An electronic method of robot A-scope A radar system that displays an A-SCAN. guidance and navigation using radar, sonar, vi- Askarel A synthetic, nonflammable liquid dielec- sion systems, edge detection, and/or beacons. tric. artificial transmission line A network of capaci- aspect ratio The width-to-height ratio of a video tors and inductors with characteristics similar to image, generally three units high by four units wide. asperities On the surface of an electrode, tiny points at which the electric field is intensified and from which discharge is highly probable. ASR 1. Abbreviation of AIRBORNE (or AIRPORT) surveillance radar. 2. Abbreviation of AUTO- MATIC SEND/ RECEIVE. ASRA Acronym for automatic stereophonic record- ing amplifier. assemble 1. To gather subprograms into a com- plete digital computer program. 2. To translate a
  • 56. 5059F-pA_1-55 4/9/01 4:41 PM Page 42 42 assemble • astrionics Symbols for ASCII teleprinter code assembly program The program that operates on a symbolic-language program to produce a ma- chine language program in the process of assem- First Last three signals bly. Also called assembler. four assembly robot A form of industrial robot that puts signals 000 001 010 011 100 101 110 111 hardware together. Such a robot is generally a component of an automated integrated manufac- 0000 NUL DLE SPC 0 P / p turing system (AIMS). The robot can do repetitive 0001 SOH DC1 ! 1 A Q a q work at high speed and precision for long periods of time. 0010 STX DC2 " 2 B R b r assign To reserve part of a computing system for a 0011 ETX DC3 # 3 C S c s specific purpose, normally for the duration of a 0100 EOT DC4 $ 4 D T d t program run. 0101 ENQ NAK % 5 E U e u assigned frequency The radio carrier frequency or 0110 ACK SYN & 6 F V f v band of frequencies designated for a transmitting 0111 BEL ETB 7 G W g w station by a licensing authority. Also see RADIO 1000 BS CAN ( 8 H X h x SPECTRUM. 1001 HT EM ) 9 I Y i y associative memory Computer memory in which 1010 LF SUB * : J Z j z locations are identified by content, rather than by specific address. 1011 VT ESC + ; K [ k { assumed decimal point A decimal point that does 1100 FF FS , < L / l / not occupy an actual computer storage space, 1101 CR GS – = M ] m } but is used by the computer to align values for 1110 SO RS . > N n ~ calculation; the decimal point is assumed to be at 1111 SI US | ? O - o DEL the right unless otherwise specified. astable Having two temporary states; BISTABLE. ACK: acknowledge FF: form feed astable circuit A circuit that has two unstable states, and whose operation is characterized by BEL: bell FS: file separator alternation between those states at a frequency BS: back space GS: group separator determined by the circuit constants. CAN: cancel HT: horizontal tab astable multivibrator A free-running multivibra- CR: carriage return LF: line feed tor. The common circuit uses two bipolar or field- DC1: device control no. 1 NAK: do not acknowledge effect transistors, their inputs and outputs being DC2: device control no. 2 NUL: null cross coupled. Conduction switches alternately DC3: device control no. 3 RS: record separator between the two. DC4: device control no. 4 SI: shift in astatic 1. Without fixed position or direction. 2. In DEL: delete SO: shift out a state of neutral equilibrium. astatic galvanometer A galvanometer with a mov- DLE: data link escape SOH: start of heading able element consisting of two identical magne- ENQ: enquiry SPC: space tized needles mounted nonparallel on the same EM: end of medium STX: start of text suspension. Each needle is surrounded by a coil. EOT: end of transmission SUB: substitute The coils are wound in opposite directions, and ESC: escape SYN: synchronous idle are connected in series to the current source. A ETB: end of transmission US: unit separator large permanent magnet provides the field block VT: vertical tab against which the needle assembly rotates. The ETX: end of text instrument functions independently of the geo- magnetic field. astatine Symbol, At. A radioactive elemental halo- gen produced from radioactive decay. Atomic symbolic program language into a machine (bi- number, 85. Atomic weight, 210. Formerly called nary) language program by substituting opera- alabamine. tion codes and addresses. A station One of the two stations in the transmit- assembly 1. A finished unit that can be either a ting system of LORAN (long-range navigation). practical working model or a dummy, a proto- astigmatism A focusing fault in a cathode-ray type, or a final model; an integrated aggregation tube (CRT), in which electrons in different axial of subunits. 2. A low-level computer source-code planes focus at different points. language that uses crude mnemonics that are ASTM Abbreviation for American Society for Testing easier to remember than the machine-language and Materials. equivalents. astrionics The design, production, and application assembly language A source code that uses of electronic devices and systems for use in space mnemonic instructions. (See ASSEMBLY, 2.) vehicles and space navigation.
  • 57. 5059F-pA_1-55 4/9/01 4:41 PM Page 43 astronomical unit • atmospheric absorption noise 43 astronomical unit Abbreviation, AU. A unit of dis- tance equal to 1.496 × 108 kilometers (9.296 × 107 miles). Approximately equal to the mean distance between the earth and the sun. A supply See A POWER SUPPLY. asymmetrical cell A photocell exhibiting ASYM- METRICAL CONDUCTIVITY. asymmetrical communications 1. Two-way com- munications in which the volume of transmitted data is much greater in one direction than in the other. 2. Two-way communications in which the speed of transmitted data is much greater in one direction than in the other. Compare SYMMET- RICAL COMMUNICATIONS. asymmetrical conductivity A condition in which a device conducts well in one direction, but poorly in the other direction. A rectifier diode is a com- mon example of a component that exhibits this effect. asymmetrical distortion In a binary system, lengthening or shortening of one of the states, by comparison to the theoretical or ideal duration. asymmetrical FET A FIELD-EFFECT TRANSIS- asynchronous input In digital circuitry, any flip- TOR in which the source and drain cannot be in- flop input at which a pulse can affect the output terchanged without degrading performance. independently of the clock. asymmetrical multivibrator An unbalanced mul- asychronous motor An ac motor whose speed is tivibrator (i.e., one in which the circuit halves are not proportional to the supply frequency. not identical). If the time constants of the halves asynchronous transmission Data transmission are different, the output pulses will be short and in which each character or symbol begins with a widely separated. start signal and ends with a stop signal. This asymmetrical sideband See VESTIGIAL SIDE- eliminates the need for the data to be sent at a BAND. uniform speed. asymmetrical sideband transmission See VESTI- asynchronous vibrator In a vibrator-type portable GIAL SIDEBAND TRANSMISSION. power supply, a vibrator that only makes and asymmetrical wave A wave whose upper (positive breaks the primary circuit of the step-up trans- half-cycle) and lower (negative half-cycle) por- former. This is in contrast to the synchronous vi- tions have different amplitudes or shapes. Also brator, which also makes and breaks the called asymmetric wave. secondary circuit in synchronism with the pri- asymmetry control An adjustment in a device in- mary. Also called NONSYNCHRONOUS VIBRA- tended for measuring the pH (acidity/alkalinity). TOR. This corrects the inaccuracies that results from AT A quartz crystal cut wherein the angle between the differences between the electrodes. the x-axis and the crystal face is 35 degrees. asymptote In analytical geometry, a fixed straight At Symbol for astatine. line or ray L with a special relationship to a AT-cut crystal A piezoelectric crystal cut at a 35- curve or part of a curve K that recedes to infin- degree angle, with respect to the optical axis of ity. As the distance from the origin (0,0) in- the quartz. The frequency of such a crystal does creases without limit, the separation between K not appreciably change with variations in tem- and L approaches zero, but K and L never actu- perature. ally meet. atmosphere 1. The gas surrounding a planet, par- asymptotic breakdown voltage A voltage that will ticularly the air sheathing the earth. 2. Abbrevia- cause dielectric breakdown if applied continu- tion, atm. A unit of pressure equal to 1.013