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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.
Illustrations in this book were generated with CorelDRAW. Some clip art is courtesy of Corel
Corporation, 1600 Carling Avenue, Ottawa, Ontario, Canada K1Z 8R7.
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-
magnetic system. One abfarad equals 109 farads
problems. Also see ALIGNMENT CHART.
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-
magnetic system. One abhenry equals 10–9 henry
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
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-
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
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
absiemens equals 109 siemens and is the
3. Propagation over a path or in a direction not
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
absolute error • absolute tolerance
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
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-
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.
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.
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
absolute zero The temperature –273.16°C
( 459.7°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
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
propagation) versus frequency. Also called EMIS-
absorption The taking up of one material or me-
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
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
absorption current In a capacitor, the current re-
sulting from absorption of energy by the dielectric
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.
abvolt • accentuation
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 10 7 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
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
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.
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
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-
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.
accw • ac magnetic bias
ac generator 1. A rotating electromagnetic ma-
accw Abbreviation of ALTERNATING-CURRENT
chine that produces alternating current (e.g., a
dynamo or alternator). 2. An oscillator or com-
ac/dc Abbreviation of ALTERNATING CURRENT/
bination of an oscillator and an output ampli-
DIRECT CURRENT. Pertains to equipment that
will operate from either ac utility power or a dc
ac grid voltage Symbol, VG(ac). The ac component
power source. A notebook computer is a good ex-
of control grid voltage in an electron tube. The ac
input signal voltage in a common-cathode ampli-
ac directional overcurrent relay A relay that
fier or cathode follower.
works on a specific value of alternating overcur-
A channel The left channel of a two-channel stereo
rent that is rectified for a desired polarity.
ac drain current Symbol, ID(ac). The ac component
achieved reliability A statement of reliability based
of drain current in a field-effect transistor.
on the performance of mass-produced parts or
ac drain resistance Symbol, RD(ac). The dynamic
systems under similar environmental conditions.
drain resistance in a field-effect transistor; RD(ac)
Also called OPERATIONAL RELIABILITY.
equals dVD/dID for a constant value of gate volt-
achromatic 1. Without color. In a TV image, the
tones from black through gray to white. The term
ac drain voltage Symbol, VD(ac). The ac component
occasionally refers to black-and-white television,
of drain voltage in a field-effect transistor. The ac
although MONOCHROMATIC is more often used
output signal voltage in a common-source FET
in this sense.
achromatic locus Also called achromatic region.
ac dump The removal of all ac power from a system
An area on a chromaticity diagram that contains
all points, representing acceptable reference
ac emitter current Symbol, IE(ac). The ac compo-
nent of emitter current in a bipolar transistor.
achromatic scale A musical scale without acci-
ac emitter resistance Symbol, RE(ac). The dynamic
emitter resistance of a bipolar transistor; RE(ac)
ACIA Abbreviation of asynchronous communica-
equals dVE/dIE for a constant value of base cur-
tions interface adapter.
rent IB (in an emitter-follower circuit) or collector
acicular Pertaining to the shape of magnetic parti-
voltage VCC (in a common-base circuit).
cles on recording tape. Under magnification,
ac emitter voltage Symbol, VE(ac). The ac compo-
these particles look like thin rods.
nent of emitter voltage in a bipolar transistor. The
acid A substance that dissociates in water solution
ac input signal voltage in a common-base ampli-
and forms hydrogen (H) ions (e.g., sulfuric acid).
fier; the ac output signal voltage in an emitter-
Compare BASE, 2.
acid depolarizer Also called acidic depolarizer.
ac equipment An apparatus designed for opera-
An acid, in addition to the electrolyte, used in
tion from an ac power source only. Compare DC
some primary cells to slow the process of polar-
EQUIPMENT and AC/DC.
ac erasing In tape recording, the technique of us-
ac line A power line that delivers alternating cur-
ing an alternating magnetic field to erase material
already recorded on the tape.
ac line filter A filter designed to remove extrane-
ac erasing head Also called ac erase head. In tape
ous signals or electrical noise from an ac power
and wire recording, a head that carries alternat-
line, while causing virtually no reduction of the
ing current to erase material already recorded on
power-line voltage or power.
the tape or wire. Also see AC ERASING.
ac line voltage The voltage commonly delivered
acetate Cellulose acetate, a tough thermoplastic
by the commercial power line to consumers. In
material that is an acetic acid ester of cellulose. It
the United States, the two standards are 117 V
is used as a dielectric and in the manufacture of
and 234 V (~ about 5 percent). The lower voltage
is used by most appliances; the higher voltage is
acetate base 1. The cellulose acetate film that
intended for appliances and equipment that
served as the base for the magnetic oxide coating
draws high power, such as electric ovens, cook-
in early recording tape. Most such tapes today
ing ranges, clothes dryers, and amateur-radio
are of polyester base. 2. The cellulose acetate
amplifiers. In Europe, 220 V is the common
substrate onto which certain photosensitive ma-
terials are deposited for lithographic reproduc-
aclinic line Also called magnetic equator. An imag-
tion. Also see ACETATE and ANCHORAGE.
inary line drawn on a map of the world or of an
acetate tape Recording tape consisting of a mag-
area that connects points of zero inclination (dip)
netic oxide coating on a cellulose acetate film.
of the needle of a magnetic compass.
Also see ACETATE BASE.
ACM Abbreviation for Association for Computing
ac gate voltage Symbol, VG(ac). The ac component
of gate voltage in a field-effect transistor. The ac
ac magnetic bias See AC BIAS.
input signal voltage.
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
form, it consists of a crystal block or bar with an
ac noise 1. Electromagnetic interference originat-
input transducer at one end and an output trans-
ing in the ac power lines. 2. Electrical noise of a
ducer at the other. An electrical input signal in
rapidly alternating or pulsating nature.
the first transducer sets up sound waves that
ac noise immunity In computer practice, the abil-
travel through the interior of the crystal; the
ity of a logic circuit to maintain its state, despite
piezoelectric reaction of the crystal to sound vi-
excitation by ac noise.
brations sets up an output voltage in the second
acous Abbreviation for ACOUSTIC.
transducer. The delay is caused by the time re-
acoustic Pertaining to audible sound distur-
quired for the acoustic energy to travel the length
bances, usually in air (versus audio-frequency
of the crystal bar.
currents or voltages).
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
acoustic depth finder A direct-reading device for
noise made by an intruder. The alarm device re-
determining the depth of a body of water, or for
sponds to the impulses from concealed micro-
locating underwater objects via sonic or ultra-
sonic waves transmitted downward and reflected
acoustic capacitance The acoustic equivalent of
back to the instrument.
acoustic dispersion Variation of the velocity of
acoustic clarifier In a loudspeaker system, a set of
sound waves, depending on their frequency.
cones attached to the baffle that vibrate to absorb
acoustic elasticity 1. In a loudspeaker enclosure,
and suppress sound energy during loud bursts.
the compressibility of air behind the vibrating
acoustic communication Communications by
cone of the speaker. 2. In general, the compress-
means of sound waves. This can be through the
ibility of any medium through which sound
atmosphere, or it can be through solids or liq-
uids, such as a taut wire, a body of water, or the
acoustic electric transducer A transducer, such
as a microphone or hydrophone, that converts
acoustic compliance COMPLIANCE in acoustic
sound energy into electrical energy. Compare
transducers, especially loudspeakers. It is equiv-
ELECTRICAL/ACOUSTIC TRANSDUCER. Also
alent to electrical capacitive reactance.
see ACOUSTIC TRANSDUCER.
acoustic consonance An effect that occurs when
acoustic feedback A usually undesirable effect
two objects are near each other but not in physical
that occurs when sound waves from a loud-
contact, and both have identical or harmonically
speaker (or other reproducer) reach a microphone
related resonant frequencies. An example is shown
(or other input transducer) in the same system.
by two tuning forks with identical fundamental fre-
acoustic feedback • acoustic radiator
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 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.
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
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.
ac plate voltage • active chord mechanism
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.
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
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-
active repair time The time during which mainte-
nance is done on a system and the system is out
active satellite • adapter
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-
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
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.
address indirect • adjusted decibels
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 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.
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.
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