. 12
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tire sphere surrounding the transducer, and E2 is (e.g., without recording/reproduction).
the response on the acoustic axis. direct piezoelectricity The production of a piezo-
directivity of antenna For a beam antenna, the electric voltage by mechanically stressing a suit-
ratio Emax/Eavg, where Emax is the maximum field able crystal.
intensity at a selected distance from the antenna direct playback In audio or video recording, the
and Eavg is the average field intensity at the same reproduction of a recording without additional
distance. processing (e.g., the playing of an original
directivity of directional coupler The ratio, in recorded tape, rather than a tape that has been
decibels, of P1 to P2, where P1 is the power at the mass produced).
forward wave-sampling terminals (measured with direct-point repeater A relay-operated telegraph
a forward wave in the transmission line) and P2 is repeater. The received signals actuate the relay,
the power at the terminals when the wave is re- which switches the second line.
versed in direction. direct-radiator loudspeaker A loudspeaker whose
directivity pattern The calculated or measured ra- cone or diaphragm is directly coupled to the air.
diation or response pattern (transmission or re- direct ray An electromagnetic ray (wave) that
ception) of an antenna, microphone, loudspeaker, reaches a receiver without reflection or refraction,
or similar device, with particular attention to the and without encountering obstructions.
directional features of the pattern. direct recording 1. A record produced by a
directivity signal A spurious output signal result- graphic recorder. 2. The technique of producing
ing from finite directivity in a coupler. such a record.
direct light Light rays traveling directly from a direct-recording instrument A device, such as a
source to a receptor or target without reflection. graphic recorder, that directly produces a perma-
directly grounded Connected to earth or to the nent record (such as an inked trace) of the varia-
lowest-potential point in a circuit, without any in- tions of a quantity.
tervening resistance or reactance. direct resistance coupling A form of coupling in
directly heated cathode A vacuum-tube filament. which the output of the first amplifying device is
It is so called because, when heated, it becomes connected through a resistor directly to the input
the cathode of the tube (i.e., the emitter of elec- of the second device. The resistance value can
trons). vary; sometimes the connection is a short circuit.
directly heated thermistor A thermistor whose directrix A fixed line to which a curve is referred
temperature changes with the surrounding tem- (e.g., the axis of a parabola).
perature, and also as a result of power dissipa-
tion in the device itself. Compare INDIRECTLY
directly heated thermocouple A meter thermo-
couple heated directly by signal currents passing
through it. Compare INDIRECTLY HEATED
direct measurement Immediate measurement of
a quantity, rather than determining the value of
the quantity through adjustments of a measuring
device (e.g., measuring capacitance with a capac-
itance meter, rather than with a bridge). Compare
direct memory access Abbreviation, DMA. The
transfer of data from a computer memory to some
other location, without the intervention of the
central processing unit (CPU).
direct numerical control In a computer or data
system, the capability for distributing informa-
tion among numerically controlled machines
whenever desired.
director In a multielement directional antenna, an
element that is usually mounted in front of the
radiator element, and that is phased and spaced
to direct the radiation forward. The director func- direct resistance coupling
direct scanning • discrete capacitor

direct scanning In television, the sequential view- discharge key See DISCHARGE SWITCH.
ing of parts of a scene by the camera”even discharge lamp A gas-filled tube or globe in which
though the entire scene is continuously illumi- light is produced by ionization of the gas between
nated. electrodes. Familiar examples are the neon bulb
direct serial file organization A technique of or- and fluorescent tube.
ganizing files stored in a direct access device, in discharge phenomena The effects associated with
which a record can be chosen by number and electrical discharges in gases, such as luminous
amended where it is without altering other mem- glow.
bers of the file. discharge potential See IONIZATION POTENTIAL.
direct sound wave A sound wave arriving directly discharger 1. A short-circuiting tool for discharg-
from its source”especially a wave within an en- ing capacitors. 2. A spark gap or other device for
closure that is not affected by reflection. automatically discharging an overcharged capac-
direct substitution 1. An exact component re- itor.
placement. 2. Installing an exact component re- discharge rate 1. The current that can be supplied
placement. by an electrochemical cell or battery reliably dur-
direct synthesizer A device for producing random, ing its discharging cycle. Usually expressed in
rapidly changing frequencies for security pur- milliamperes or amperes. 2. An expression of the
poses. A reference oscillator provides a compari- speed with which a battery is being discharged at
son frequency; the output frequency is a a specific point in time. It is usually specified in
rational-number multiple of this reference fre- amperes or milliamperes.
quency. discharge switch A switch for connecting a
direct voltage See DC VOLTAGE. charged capacitor to a resistor or other load,
direct wave A wave that travels from a transmitter through which the capacitor discharges. In some
to a receiver without being reflected by the iono- circuits, when the switch is in its resting position,
sphere or the ground. Compare SKYWAVE. it connects the capacitor to the charging source.
direct Wiedemann effect Twisting force (torque) discharge voltage See IONIZATION POTENTIAL.
in a wire carrying current in a longitudinal mag- discharging 1. The conversion of chemical energy
netic field. Occurs because of interaction between to electrical energy by an electrochemical cell or
the longitudinal field and the circular magnetic battery. 2. The release of stored electrical energy
field around the wire. from a capacitor, or from a network containing
direct-wire circuit A communications or control capacitors.
line of wires connecting a transmitter (or control discharging tongs See DISCHARGER, 1.
point) and a receiver (or controlled point) without discone antenna An antenna consisting of a hori-
an intermediary, such as a switchboard. zontal metal or wire-mesh disk above a metal or
direct-writing recorder See GRAPHIC RE- wire-mesh cone. The antenna has an omnidirec-
CORDER. tional radiation pattern in the horizontal plane,
direct-writing telegraph 1. See PRINTING TELE- and provides a good match to a coaxial transmis-
GRAPH. 2. See TELAUTOGRAPH. sion line over a frequency range of several oc-
dis- A prefix meaning “deprived of.” For the forma- taves. Commonly used at very-high frequencies
tion of electronic terms, the prefix must be distin- (VHF) and ultra-high frequencies (UHF).
guished from un-, meaning “not.” For example, a disconnect 1. To separate leads or connections,
discharged body is one that was charged, but has thereby interrupting a circuit. 2. A type of con-
been emptied of its charge. An uncharged body is nector whose halves can be pulled apart to open
one that ordinarily or presently is not charged. a cable or other circuit quickly. 3. To open a
disable 1. To deliberately render a circuit, device, switch or relay.
or system inoperative. 2. In digital computer disconnector See DISCONNECT, 2 and DISCON-
operations, to defeat a software or hardware NECT SWITCH.
function. disconnect signal A signal sent over a telephone
disc See DISK. line, ending the connection.
disc engraving 1. Recording sound by cutting a disconnect switch A switch whose main function
groove in a record disc. 2. The groove resulting is to open a circuit quickly (either manually or
from such a process. automatically) in the event of an overload.
discharge The emptying or draining of electricity discontinuity 1. A break in a conductor. 2. A
from a source, such as a battery or capacitor. The point at which the impedance in a transmission
term also denotes a sudden, heavy flow of cur- line abruptly changes.
rent, as in DISRUPTIVE DISCHARGE. Compare discontinuous wave trains See DAMPED WAVES.
CHARGE. discrete 1. Complete and self-contained, as op-
discharge current 1. Current flowing out of a ca- posed to a part of something else. 2. Composed of
pacitor. 2. Current flowing out of a cell”espe- individual, separate members.
cially a storage cell. Compare CHARGING discrete capacitor Capacitance that is entirely
CURRENT. self-contained, rather than being electrically dis-
200 discrete capacitor • disk capacitor

tributed. Also called LUMPED CAPACITOR. Com- C2
discrete circuit A circuit comprised of discrete
components, such as resistors, capacitors, R1 C5
diodes, and transistors, not fabricated into an in- C3
From C6
C1 amp
tegrated circuit. limiter
discrete component A self-contained device that T1 D2
offers one particular electrical property in lumped
form (i.e., concentrated at one place in a circuit,
rather than being distributed). A discrete compo-
nent is built especially to have a specific electrical
property, and exists independently, not in combi-
nation with other components. Examples: disk discriminator tuner A device that tunes a dis-
capacitor, toroidal inductor, and carbon-compo- criminator to a selected subcarrier.
sition resistor. Compare DISTRIBUTED COMPO- discriminator tuning device See DISCRIMINA-
discrete device Any component or device that op- dish See DISH ANTENNA.
erates as a self-contained unit. dish antenna A transmitting and/or receiving an-
discrete element A discrete device that forms part tenna consisting of a driven element and a large
of a larger system. reflector. The reflector has the shape of a shallow,
discrete inductor An inductive component that is circular section of a paraboloid or sphere. The
entirely self-contained, rather than being electri- feed point is at the focus of the reflector. This an-
cally spread out. Also called lumped inductor. tenna, noted for its high directivity and gain, is
Compare DISTRIBUTED INDUCTANCE. used mainly at ultra-high and microwave fre-
discrete information source A source of data con- quencies for communications and satellite televi-
taining a finite number of individual elements, sion. Large antennas of this type are used in
rather than a continuously variable parameter. some radio telescopes.
discrete part See DISCRETE COMPONENT. dish-type construction A type of panel-and-chas-
discrete resistor A resistive component that is en- sis construction in which the chassis is fastened
tirely self-contained, rather than being electri- vertically to the back of the panel.
cally spread out. Also called lumped resistor. disintegration 1. The destructive breakdown of a
Compare DISTRIBUTED RESISTANCE. material. 2. The stripping of a vacuum-tube cath-
discrete sampling Sampling of individual bits or ode of its emissive coating (see DISINTEGRATION
characters, one or more at a time. VOLTAGE). 3. The decay of a radioactive mate-
discrete thin-film component A discrete compo- rial.
nent produced by the thin-film process (e.g., thin- disintegration voltage The anode voltage at which
film capacitor, thin-film potentiometer, etc.). the cathode of a gas tube begins to be stripped of
discretionary wiring A method of interconnecting its electron-emitting material. For safety and rea-
the components and circuits on a semiconductor sonable tube life, the anode working voltage must
wafer for optimum performance. This requires a be between the ionization and disintegration val-
separate analysis and wiring pattern for every ues.
chip. disintegrator An ultrasonic device for reducing
discrimination 1. Sharp distinction between elec- crystals or particles to fine suspensions.
trical quantities of different value. 2. The detection disjunction The logical inclusive-OR operation.
of a frequency-modulated (FM) signal (i.e., the de- disk 1. A flat, circular plate (e.g., rectifier disk). 2.
livery of an audio signal corresponding to the fre- See DISKETTE. 3. See HARD DISK. 4. See COM-
quency or phase variations in the FM carrier). PACT DISC. 5. See CD-ROM. 6. A phonograph
discriminator A second detector for frequency- record or the equivalent unrecorded blank.
modulated (FM) signals, in which two diodes are disk capacitor A fixed (usually two-plate) capaci-
operated from the center-tapped secondary of a tor consisting of a disk of dielectric material on
special intermediate-frequency (IF) transformer. whose faces are deposited metal-film plates.
The circuit is balanced for zero output when the
instantaneous received signal frequency is at the
unmodulated carrier frequency; the circuit deliv-
ers output when the instantaneous received
signal frequency swings above or below the
unmodulated carrier frequency. Also see FOS-
discriminator transformer The special input
transformer in a DISCRIMINATOR. disk capacitor
disk coil • display loss

disk coil See DISK WINDING. of a wave into its various component frequencies
disk dynamo A rudimentary direct-current (dc) (as when white light is broken up into the color
generator, in which a copper disk rotates between spectrum by a prism). 3. The scattering of a mi-
the poles of a permanent magnet. The outer edge crowave beam when it strikes an obstruction. 4.
of the disk becomes positively charged; the center The scattering of sound or ultrasound as it em-
of the disk becomes negatively charged. anates from an acoustic transducer. 5. A suspen-
diskette A magnetic recording disk used for micro- sion of finely divided particles within another
computer data storage. Housed in a square, flat substance.
case. In personal computing, there are two sizes: dispersive medium A medium that disperses a
5.25 inches square and 3.5 inches square. The wave passing through it.
5.25-inch version is flexible and is sometimes displacement 1. A change in the position of a
called a floppy disk. point, particle, figure, or body. 2. The vector rep-
disk files An information-storage system in which resenting a change in the position of a point, par-
data are recorded on rotating magnetic disks. ticle, figure, or body. 3. Movement of a member
disk generator 1. See DISK DYNAMO. 2. A disk- through a specified distance.
type electrostatic generator. displacement current 1. An alternating current
disk memory A common misnomer for DISK proportional to the rate of change of an electric
STORAGE. field, and existing in addition to usual conduction
Disk Operating System Abbreviation, DOS. Any of current. 2. The current flowing into a capacitor
several command-driven operating systems com- immediately after application of a voltage. This
monly used in IBM-compatible personal comput- current continues to flow, although continually
ers. diminishing in value, until the capacitor becomes
disk pack In disk files, a set of disks that can be fully charged.
handled as a single unit. displacement of porches In a television signal,
disk recorder A device for recording (and usually the amplitude difference between the front porch
also playing back) sound or other signals on and back porch of a horizontal sync pulse.
record disks. displacement of vectors Vector rotation through
disk recording 1. Recording sound or other sig- a specified number of angular degrees or radians.
nals on disks. 2. A disk resulting from such a displacement transducer A transducer in which
recording. See DISK. movement (displacement) of a rod, armature,
disk rectifier A semiconductor rectifier (such as core, reed, or other object converts mechanical
copper-oxide, selenium, magnesium-copper- energy into proportionate electrical energy.
sulfide, or germanium type) in which the active display 1. Visually observable presentation of in-
material is deposited on a metal disk. formation, such as data entered into a computer,
disk resistor A resistor consisting of a resistive an answer to a problem solved by a computer, the
material deposited on a metal disk; or a disk of value of a measured quantity, or a graph of a
resistive material. In the latter, electrodes are function. 2. The screen in a computer system or
plated on the faces of the disk, one or more of terminal that visually portrays text and graphical
which are held between clips or screws for con- data. In laptop, notebook, and portable comput-
nections. ers, this is usually a liquid-crystal display (LCD);
disk storage In digital computer systems, an on- in desktop computers and terminals, it is usually
line or offline data storage scheme, in which in- a cathode-ray tube (CRT ). 3. To portray informa-
formation is recorded on the magnetic coating of tion in a visual manner (e.g., as text, numerals,
a rotating disk or set of disks. See DISKETTE, symbols, or graphic images).
and HARD DISK. display blanking See DISPLAY INHIBIT.
disk system A sound-motion-picture system using display console In a computer system, a periph-
audio disks synchronized with the film. eral that is used to access and display data being
disk thermistor A thermistor having the general processed or stored; often, it is a unit with a
shape of a disk. cathode-ray tube (CRT), keyboard, and light pen.
disk-type storage See DISK STORAGE. display control An interface device between a cen-
disk varistor A varistor having the general shape tral processor and several visual display units
of a disk. (terminals).
disk winding An armature or coil winding that is display dimming See DISPLAY INHIBIT.
flat, rather than cylindrical. Also called disk coil, display inhibit In a digital meter, the blanking or
pancake coil, and spiral coil. dimming of the display when the instrument is
dislocation A crystal region in which the arrange- not being used. It is used to conserve battery en-
ment of atoms does not have the perfect lattice ergy.
structure of the crystal. display loss The ratio P1/P2, where P1 is the mini-
dispersion 1. The property of a material that mum input-signal power that can be detected by
causes energy at different wavelengths to pass an ideal output device at the output of a receiver,
through it at different speeds. 2. The separation and P2 is the minimum input-signal power value
202 display loss • distance-double law

seen by an operator using an output device with Aperture
the same receiver. Also called visibility factor. Photocathode
display mode 1. A particular method of presenting Optics
a display. For example, a character display on a
video unit might consist of bright characters on a
dark background, or dark characters on a light Object
background. 2. An operating mode for a particu-
lar device, in which a display is used.
display module A self-contained unit with cir-
cuitry and readouts for indicating a numerical
dc dc
display primaries Also called primary colors. In a Input Input
color television receiver, the colors red, green,
and blue. When mixed correctly, these three col-
ors can produce any visible hue.
display-storage tube A special cathode-ray tube in
which patterns and other information can be dissector tube
stored for later viewing. The tube has two electron
guns: a writing gun and a reading (viewing) gun.
display unit A device that presents information for amplifier, the difference between the collector,
visual reading. Included are analog and digital drain, or plate input power and the usable output
meters, cathode-ray tubes, data printers, graphic power.
recorders, etc. Also see DISPLAY CONSOLE. dissipation constant For a thermistor, the ratio of
display visibility The ease with which a display the change in power dissipation to a correspond-
can be read by an operator. ing change in body temperature.
display window 1. In a panoramic display, the dissipation factor 1. For a dielectric material, the
width of the presented frequency band in hertz. tangent of the dielectric loss angle. Also called
2. The panel opening through which the indica- loss tangent. 2. Symbol, D. For an impedance
tion of a display unit appears. (such as a capacitor), the ratio of resistance to re-
displayed part That portion of a number displayed actance; D = R/X. It is the reciprocal of the figure
in the readout of a calculator or computer. There of merit (Q).
might be digits that are not displayed, but which dissipation line A resistive section of transmission
the machine might take into consideration line, used for dissipating power at a certain
when making calculations. For example, in a impedance. Two parallel lengths of resistance
10-digit calculator display, the number wire are terminated by a large, noninductive re-
245.789378214895 would be displayed as sistor that has a value equal to the characteristic
245.7893782. Depending on the calculator de- impedance of the line.
sign, the machine might truncate (disregard) the dissipator 1. A device used primarily to consume
undisplayed digits (14895), or take the undis- power (i.e., a power sink). 2. A device for remov-
played digits into account when making calcula- ing heat generated by a device™s operation (e.g., a
tions. heatsink attached to a power transistor).
disposable component A circuit component or dissociation The condition that characterizes elec-
machine part that is so inexpensive that it is trolytes (certain acids, bases, or salts in water so-
more cost-effective to discard it than to repair it lution) in which the molecules of the material
when it fails. break up into positive and negative ions.
disruptive discharge Sudden, heavy current flow dissonance The unpleasant effect (especially in
through a dielectric material when it fails com- music) produced by nonharmonious combina-
pletely under electric stress. tions of sounds.
dissector A transducer that samples an illumi- dissymmetrical network A network having un-
nated image point by point. equal input and output image impedances.
dissector tube A camera tube using a flat photo- dissymmetrical transducer A transducer having
cathode, upon which the image is focused by the unequal input and output image impedances.
lens system. Electromagnetic deflection from distance-double law A theoretical rule for deter-
external coils provides scanning. Electrons pass mining the rate at which sound intensity de-
sequentially from the image cathode to a scan- creases as distance increases. Under ideal
ning tube at the opposite end of the camera tube. conditions, when the distance from a sound
Also called Farnsworth dissector tube and or- source is doubled, the sound pressure is re-
thiconoscope. duced to one-fourth of its original level, a reduc-
dissipation 1. The consumption of power, often tion of 6 decibels. This is analogous to the
without contributing to a useful end, and usually inverse-square law for visible light and other ra-
accompanied by the generation of heat. 2. In an diant energy.
distance mark • distributed component

distance mark On a radar screen, a mark indicat-
ing the distance from the radar set to the target. Voltmeter
distance measurement Also called ranging. A
method or system that allows a robot to navigate
in its environment. It also allows a central com-
puter to track the locations of robots under its
control. Can use radar, sonar, visible light, or in-
distance-measuring equipment In radionaviga-
tion, a system that measures the distance of the
interrogator to a transponder beacon in terms of
the transmission time to and from the beacon.
distance protection The use of a protective device
within a specified electrical distance along a cir-
distance relay In circuit protection, a relay that distortion meter
operates to remove power when a fault occurs
within a predetermined distance along the cir-
distortion tolerance The maximum amount of
distortion that can be present in a signal without
distance resolution 1. Qualitatively, the ability of
making it useless. This varies over wide limits.
a ranging system to differentiate between two ob-
The maximum harmonic distortion that might be
jects or beacons that are almost, but not quite,
acceptable in a high-fidelity sound system could
the same distance away. See RANGING. 2.
be less than 0.1% total, whereas in some applica-
Quantitatively, the minimum radial separation of
tions of ac power, 10% would be acceptable.
objects or beacons necessary for a ranging
distress frequency A radio frequency on which an
system to tell them apart. 3. For two targets
emergency signal is transmitted. Ships at sea and
having the same azimuth bearing, the minimum
aircraft over the sea use 500 kHz (by interna-
difference in range for which a radar display
tional agreement). In Citizen Band communica-
renders them as distinct blips.
tions, channel 9 has been set aside for emergency
distant control See REMOTE CONTROL.
distorted-drive multiplier A frequency multiplier
distress signal A signal indicating that trouble ex-
whose excitation signal is a peaked wave that has
ists at the transmitting station and imploring aid
been predistorted to decrease the angle of flow in
from the recipient. The international radiotele-
the device, thus increasing its efficiency.
graph distress signal is the three-letter combina-
distorted nonsinusoidal wave A nonsinusoidal
tion SOS; the international radiotelephone
wave whose ideal shape (square, rectangular,
distress signal is the word mayday, the phonetic
sawtooth, etc.) has been altered.
equivalent of the French m™aidez (help me).
distorted sine wave A wave that is approximately
distributed Existing over a measurable interval,
of sinusoidal shape (i.e., it is not an exact plot of a
area, or volume; not concentrated in a single
sine wave because of the presence of harmonics).
place or places.
distortion 1. Deformation of a signal waveform. 2.
distributed amplifier A wideband, untuned am-
The additional deformation of a signal exhibiting
plifier whose active devices are spaced (dis-
a less-than-ideal waveshape when it passes
tributed) along parallel, artificial delay lines
through a circuit. Some distortion originates
consisting of coils that act in combination with
within the signal generator itself; other forms re-
the input and output capacitances of the active
sult from circuits and devices transmitting the
devices. Adding active devices to the lineup in-
signal. 3. Any degradation in the quality of a
creases the gain. Commonly used as preampli-
high-fidelity audio signal. 4. See TOTAL HAR-
fiers for television receivers.
distributed capacitance Symbol, Cd. Capacitance
distortionless 1. Having no distortion. 2. Having a
that is dispersed throughout a component or sys-
propagation velocity that does not depend on fre-
tem, rather than being lumped in one place. An
example is the distributed capacitance of a coil.
distortion meter An instrument for measuring
distributed component An electrical property that
harmonic distortion. It consists of a highly selec-
is spread throughout a circuit or device, rather
tive band-rejection filter (notch filter) that re-
than being concentrated at one point, as in a dis-
moves the fundamental frequency of the signal
crete component. For example, DISTRIBUTED
under test, and a sensitive voltmeter that can be
switched between the filter input and the filter
TANCE are spread along the length of a transmis-
output. The distortion percentage is determined
sion line. Another example is the DISTRIBUTED
from the ratio between filter-output and filter-
RESISTANCE of a wire coil. Distributed compo-
input voltages.
204 distributed component • diversity gain

nents are often unintended, but they can be use- mined in terms of the coil voltage VC and the
ful. Compare DISCRETE COMPONENT and number of coils n: VT = nVC. Distribution factor
kd = (sin(sd/2))/(s — sin(d/2)), where s is the
distributed constant See DISTRIBUTED COMPO- number of slots per phase per pole, and d is the
NENT. angle between adjacent slots.
distributed-constant delay line A delay line distribution function In statistical analysis, the
whose capacitance and inductance are dis- function F(x) expressing the probability that F
tributed throughout the line. Compare LUMPED- takes on a value equal to or less than x.
CONSTANT DELAY LINE. distribution switchboard 1. A switchboard
distributed inductance Symbol, L d. Inductance through which signals can be routed to or among
that is dispersed throughout a system or compo- various points. 2. A switchboard for routing elec-
nent, rather than being lumped in one place, tric power to points of use.
such as in a coil (e.g., the inductance of an an- distribution transformer A step-down trans-
tenna or capacitor). former used to supply low-voltage alternating-
distributed network 1. A network in which electri- current (ac) utility power to one or more
cal properties (such as resistance, inductance, consumers from a high-voltage line.
and capacitance) are distributed over a measur- distributor 1. See COMMUTATOR. 2. A switching
able interval, area, or volume. 2. A network device consisting of a rotating blade and a num-
whose characteristics do not depend on fre- ber of contacts arranged in a circle. Accomplishes
quency within a given range. sequential switching of a voltage to a number of
distributed-parameter network A network com- points in a circuit. A common example is the dis-
posed of distributed components, rather than tributor in the ignition system of an automotive
lumped components. engine.
distributed pole In a motor or generator, a pole disturbance An undesired variation in, or interfer-
having a DISTRIBUTED WINDING. ence with, an electrical or physical quantity.
distributed resistance Symbol, Rd. Resistance disturbed-one output In digital computers, the
that is dispersed throughout a component or cir- one output of a magnetic cell that has received
cuit, rather than being lumped in one place, such only a partial write pulse train because it was last
as in a resistor. An example is the high-frequency written into. Compare UNDISTURBED-ONE
resistance of an antenna system. OUTPUT.
distributed-shell transformer A transformer hav- disturbed-zero output In digital computers, the
ing two complete closed cores that are perpendic- zero output of a magnetic cell that has received
ular to each other. only a partial write pulse train since it was last
distributed winding In a motor or generator, a read from. Compare UNDISTURBED-ZERO OUT-
winding that is placed in several slots (rather PUT.
than in one slot) under a pole piece. dither 1. Vibrate; quiver. 2. The condition of vibra-
distributing amplifier An amplifier having a single tion or quivering (e.g., the dither of a meter
input and two or more outputs that are isolated pointer). 3. To blend pixels in a digitized image to
from each other; it distributes signals to various obtain various shades and colors.
points. divergence 1. The tendency of a collimated beam
distributing cable 1. In cable television, the cable of energy to spread out. 2. The extent to which a
connecting the receiver to the transmission cable. collimated beam of energy spreads out, generally
2. In power service, the cable running between a measured in seconds of arc, minutes of arc, an-
feeder and a consumer™s house. gular degrees, or angular radians.
distribution 1. The selective delivery of a quantity divergence loss Loss of transmitted sound energy,
(e.g., power distribution). 2. In statistical analy- resulting from spreading.
sis, the number of times particular values of a diverging lens A lens having a virtual focus for
variable appear. Also called frequency distribu- parallel rays; generally a concave lens.
tion. diversity 1. The property of consisting of two or
distribution amplifier A low-output-impedance more independent components or media. 2. See
power amplifier that distributes a radio, televi- DIVERSITY RECEPTION. 3. See DIVERSITY
sion, or audio signal to a number of receivers or TRANSMISSION.
speakers. diversity factor 1. A measure of the degree to
distribution cable See DISTRIBUTING CABLE. which a system exhibits unity among its con-
distribution center 1. The central point from stituents. 2. The sum of the requirements of each
which a signal is routed to various points of use. constituent of a system, divided by the total re-
2. In electric power operations, the point at which quirement of the system.
generation, conversion, and control equipment is diversity gain 1. Signal gain achieved by using
operated to route power to points of use. two or more receiving antennas. 2. Signal gain
distribution factor For a polyphase alternator, the achieved by using two or more transmitting an-
factor by which the total voltage VT can be deter- tennas.
diversity reception • DNL

diversity reception Also called dual-diversity re- 6
ception. A method of minimizing the effects of fad-
ing in ionospheric communication at high
frequencies (HF). Accomplished using two re- 5 5
ceivers whose antennas are 5 to 10 wavelengths Input Output
apart. Each receiver, tuned to the same signal,
4 7 7
feeds a common audio amplifier. The timing of
the fading is different at the two antennas be-
cause of phasing effects. The composite signal,
therefore, fades less than either of the component
signals. Some diversity systems use three or more
divide-by-seven circuit
antennas and receivers to reduce the effects of
fading even further; this is sometimes called
multiple-diversity reception.
divided-carrier modulation Modulation obtained
by adding two identical frequency carriers that
5 to 10 are 90 degrees out of phase.
divided circuit A parallel circuit.
divided equipment A system of modular elec-
tronic components interconnected with cables. A
simple example is a radio receiver having an ex-
stages stages
ternal power supply and external loudspeaker.
divider 1. See VOLTAGE DIVIDER. 2. See FRE-
Mixer and Mixer and
VIDER. 4. A computing circuit or device for
local local
performing mathematical division.
oscillator oscillator
divider probe A test probe that divides an applied
signal voltage by some factor (such as 2, 5, or 10)
to place it within the range of the instrument with
IF Second Audio Second IF
stages detector amplifier detector stages which the probe is used.
dividing network See CROSSOVER NETWORK.
division 1. Separating a quantity into a number of
equal parts, as indicated by the divisor. 2. Volt-
age division (see VOLTAGE DIVIDER). 3. Fre-
quency division (see FREQUENCY DIVIDER). 4.
Pulse-count division (see PULSE-COUNT DI-
diversity reception VIDER).
division of vectors 1. The quotient of two rectan-
gular vectors determined by the principle of ratio-
nalization in algebra (i.e., by multiplying the
diversity transmission Also called dual-diversity
numerator and denominator of the indicated divi-
transmission or multiple-diversity transmission. A
sion by the conjugate of the denominator, simpli-
scheme similar to DIVERSITY RECEPTION, ex-
fying, and performing the division). 2. To find the
cept applied at the transmitting end of a commu-
quotient of two polar vectors: the quotient of their
nication circuit. The signals from two or more
moduli and the difference of their arguments.
transmitters, at identical frequencies, are fed to
dj Abbreviation of diffused junction.
antennas spaced several wavelengths apart.
DKT Abbreviation of dipotassium tartrate.
diverter-pole generator A well-regulated direct-
D layer A layer of the ionosphere that is below the
current (dc) generator, whose shunt winding is on
E layer; its altitude is approximately 60 kilome-
the main field pole, the series winding being on a
diverter pole whose flux opposes that of the main
dm Abbreviation of decimeter.
divide-by-seven circuit A three-stage binary cir-
and direct memory addressing.
cuit having feedback from stage three to stage
one. Stage three is switched on by the fourth in-
put pulse; at that time, the feedback pulse
switches on stage one, simulating one input
DMOS Abbreviation for double-diffused metal-oxide
pulse and reducing the usual counting capacity
semiconductor, a type of field-effect transistor
from eight to seven.
that exhibits extremely low capacitance and low
divide-by-two circuit A circuit that delivers one
source-drain resistance when conducting.
output pulse for each two successive input pulses
(i.e., a flip-flop).
206 DNS • donut pattern

DNS Abbreviation of Doppler navigation system. domestic electronics Also called consumer elec-
doctor To use unconventional (sometimes sub- tronics. The branch of electronics concerned with
standard) methods in fixing a circuit or device or appliances, automatic controls, protective de-
in correcting a bad design. vices, entertainment systems, communications
document 1. In digital computer operations, espe- devices, and other equipment for the home.
cially in file maintenance, a form that provides in- domestic induction heater A household cooking
formation pertinent to a transaction. Also see utensil heated by currents induced in it. A pri-
TRANSACTION. 2. To perform documentation (see mary coil (connected to the power line) is imbed-
DOCUMENTATION, 2). 3. A computer text file. ded in the utensil, which acts as a short-circuited
documentation 1. Paperwork explaining the scope secondary coil.
of programs and how they can be optimized. 2. An- dome tweeter A speaker designed for high-
notating a computer program at critical points dur- frequency (treble), high-fidelity audio, and often
ing its writing (e.g., so that the purpose of various functional at frequencies considerably above the
segments are understood). A measure of good pro- limit of the human hearing. Characterized by a
gramming, documentation becomes especially convex diaphragm. Usually part of an assembly
valuable for program modification or debugging. including a woofer and midrange speaker.
document reader An electronic device that reads dominant In statistical analysis, the nature of any
printed cards, usually for data entry into a com- quantity that imposes its effects even in the pres-

puter. ence of other quantities.
dog 1. A malfunctioning circuit or device. 2. The dominant mode In a waveguide, the propagation

cause of a circuit or device malfunction. mode exhibiting the lowest cutoff frequency.
doghouse An enclosure for antenna loading induc- dominant wave In a waveguide, the wave having
tors and other resonating components, placed at the lowest cutoff frequency.
the base of a vertical broadcasting tower. dominant wavelength For visible light of a given
dog whistle See ULTRASONIC WHISTLE. hue, the wavelength at which the emitted energy
Doherty amplifier A highly efficient linear radio- is the greatest.
frequency (RF) amplifier in which a carrier tube and donor An electron-rich impurity added to a semi-
a peak tube operate jointly, both receiving ampli- conductor to make it into an n-type material. So
tude-modulated RF excitation. During unmodu- called because it donates its excess electrons.

lated intervals, the carrier tube supplies carrier Compare ACCEPTOR.
power to the load, while the peak tube, biased to donor atom An atom having an excess electron.
cutoff, idles. On positive modulation peaks, the When a substance having such atoms is added to
peak tube supplies output power that combines an intrinsic semiconductor, the extra electron is
with that of the carrier tube, the increase in power donated, making the semiconductor into an n-
corresponding to the condition of full modulation of type material.
the carrier. On negative modulation peaks, the donor impurity A substance whose atoms have
peak tube does not supply power, and the output excess electrons, and that donates electrons to
of the carrier tube is reduced to zero. the atomic structure of the semiconductor crystal
Dolby An electronic method of improving the audio to which it is added. Donor elements make semi-
reproduction quality of magnetic-tape systems. conductors into n-type materials. Also see
The gain is increased for low-level sounds during DONOR ATOM. Compare ACCEPTOR IMPURITY.
the recording process. During playback, the gain do-nothing instruction A computer program in-
of the low-level sounds is reduced back to its orig- struction that causes no action to be taken. Can be
inal level. used to provide space for future program updating,
Dolby A A Dolby system with four frequency or to fill out a block of instructions, as needed by a
ranges, operated independently. It is used mostly compiler. Also called dummy instruction.
by recording professionals. don™t-care state In a logic function or gate, an in-
Dolby B A modified form of Dolby A, with only one put digit whose state (high or low) does not affect
band of noise-reducing circuitry. It is used pri- the output.
marily by hobbyists. donut capacitor A flat, ring-shaped capacitor.
Dolezalek electrometer See QUADRANT ELEC- donut coil See TOROIDAL COIL.
TROMETER. donut crystal A relatively large, zero-temperature-
dolly 1. A low, wheeled frame or platform for trans- coefficient piezoelectric quartz crystal cut in the
porting electronic equipment. 2. A tool with form of a torus with the y-axis passing through
which one end of a rivet is held while the head is the center of rotation.
hammered out of the other end. donut magnet See RING MAGNET.
DOM Abbreviation of DIGITAL OHMMETER. donut pattern The three-dimensional radio-
domain 1. A region of unidirectional magnetization frequency (RF) radiation/response pattern of a
in a magnetic material. 2. A region of unidirec- free-space straight antenna element measuring
tional polarization in a ferroelectric material. 3. A „2 wavelength, neglecting the effects of ground
region in which a variable is confined. and nearby objects.

doohickey • dot

doohickey A usually unnamed device”especially
one used to achieve some significant modification
of circuit performance.
doorknob capacitor A high-voltage fixed capaci-
tor, so called from its round package, which
somewhat resembles a doorknob.
doorknob tube A special UHF vacuum tube, so
called from its characteristic shape. The unique
design provides short electron-transit time and
low interelectrode capacitance. Largely replaced
in recent years by semiconductor devices.
dopant An impurity added in controlled amounts
to a semiconductor to make it an n-type or p-type
material. Also see ACCEPTOR and DONOR.
dope To add impurities to a semiconductor mate-
rial. Doping allows the manufacture of n-type or
p-type semiconductors with varying degrees of
conductivity. In general, the greater the extent of
doping, the higher the conductivity.
doped junction In a semiconductor device, a junc-
tion produced by adding a dopant to the semi-
conductor melt.
doping Adding a dopant to a semiconductor to al-
ter the way it conducts current.
doping agent See DOPANT.
doping compensation Opposite doping (i.e., add-
ing a donor impurity to p-type semiconductor Doppler enclosure See DOPPLER CABINET.
material or adding an acceptor impurity to n-type Doppler radar A radar that uses the change in car-
semiconductor material). rier frequency of the signal returned by a moving
doping gas A gas diffused into a semiconductor target (approaching or receding) to measure its
material to dope it. For example, phosphorus velocity. Used by law enforcement officers to de-
pentoxide gas can be used to create an n-type re- termine the speed of moving vehicles. Also used
gion in a p-type silicon chip. by meteorologists to evaluate air circulation pat-
doping level The relative concentration of impurity terns in thunderstorms, and to determine wind
added to a semiconductor material to obtain a speeds in hurricanes and tornadoes.
certain resistivity and polarity. The greater the Doppler ranging See DORAN.
doping level, the lower the resistivity. Doppler shift The extent to which the frequency or
Doppler broadening In a spectrum, the spreading wavelength of a signal changes because of
out or blurring of a spectral line caused by DOPPLER EFFECT. Can be measured in Hertz
DOPPLER EFFECT, in turn resulting from motion (for frequency) or in meters (for wavelength). In
of molecules, atoms, or other particles in the astronomy, the shift is also measured as dis-
medium. placement of absorption or emission lines in an
Doppler cabinet A loudspeaker enclosure with infrared, visible, or ultraviolet spectrum.
which a vibrato effect is achieved by rotating or Doppler™s principle See DOPPLER EFFECT.
reciprocating either the loudspeaker or a baffle doran A continuous-wave trajectory-measuring
board; the length of the sound path is altered system utilizing Doppler shift (see DOPPLER EF-
cyclically. FECT). The name is a contraction of doppler rang-
Doppler effect A change in the frequency of a wave ing.
that occurs when the source and observer are in dorsal column stimulator Abbreviation, DCS. A
relative motion. The frequency of the wave in- machine that generates radio-frequency energy
creases (the wavelength shortens) as the source that is applied to human tissues for the tempo-
and observer approach each other; the frequency rary relief of pain.
decreases (the wavelength becomes greater) as dosage meter See DOSIMETER.
the source and observer recede from each other. dose The total quantity of radiation received upon
This effect is often observed with sound waves, as exposure to nuclear radiation or X-rays.
when the pitch of an automobile horn seems to dosimeter An instrument for measuring the
rise as the car approaches and to fall as the car amount of exposure to nuclear radiation or
passes. The effect is also observable in electro- X-rays.
magnetic radiation at all wavelengths. It affects dot 1. The shorter of the two characters (dot and
satellite communication and space communica- dash) of the telegraph code. The dot, a short
tion. sound, mark, or perforation, is one-third the
208 dot • double buffering

length (duration) of a dash. Compare DASH. 2. dots move horizontally or vertically; the red and
One of the small spots of red, green, or blue phos- green dots, diagonally.
phor on the screen of a color-television picture dot OR Externally connected circuits or functions
tube or cathode-ray-tube (CRT) computer dis- whose combined outputs result in an OR func-
play. 3. A small spot of material alloyed with a tion. Compare DOT AND.
semiconductor to form an alloy junction. 4. The dot pattern In color television testing with a dot
junction of two lines on a schematic diagram, generator, dots of color (a red group, green group,
representing a wired connection; also called and blue group) produced on the screen. With
solder dot. overall beam convergence, the three groups blend
dot AND Externally connected circuits or functions to produce white.
whose combined outputs result in an AND func- dot-sequential system The color television system
tion. Compare DOT OR. in which the image is reproduced by means of pri-
dot-and-dash telegraphy Telegraphy (wire or ra- mary-color dots (red, green, blue) sequentially ac-
dio) by means of dot and dash characters. tivated on the screen of the picture tube.
dot cycle One period of an alternation between two Compare FIELD-SEQUENTIAL SYSTEM and
signaling conditions, each of which is of unit du- LINE-SEQUENTIAL SYSTEM.
ration (e.g., a unit mark followed by a unit space). double-amplitude-modulation multiplier A mod-
dot encapsulation A method of packaging cylin- ulating system in which a carrier is amplitude-
drical components by pressing them into the modulated first by one signal and then by a sec-
holes of perforated disks; interconnections are ond signal. The resulting signal is fed to a
made, to complete a circuit, on each face of the detector, the output of which contains the prod-
disks. uct of the two modulating signals.
dot generator A special radio-frequency (RF) sig- double-anode diode A semiconductor diode hav-
nal generator used to produce a pattern of red, ing two anodes and a common cathode.
green, and blue dots on the screen of a color tele- double armature An armature (such as that of a
vision receiver. dynamotor or a two-voltage generator) that has
dot matrix A rectangular array of spaces, some of two separate windings on a single core, and has
which are filled in to form alphanumeric and two separate commutators.
punctuation characters. double-balanced mixer See BALANCED MIXER.
double-balanced modulator See BALANCED
double-base diode See UNIJUNCTION TRANSIS-
double-base junction transistor A junction tran-
sistor having the usual emitter, base, and collec-
tor electrodes, plus two base connections, one on
either side of the base region. The additional base
connection acts as a fourth electrode to which a
control voltage is applied. Also called tetrode tran-
double-beam CRT See DUAL-BEAM OSCILLO-
double-beam oscilloscope See DUAL-BEAM OS-
double-bounce calibration In radar operations, a
calibration technique for determining zero-beat
dot matrix
error. Round-trip echoes are observed, the cor-
rect range being the difference between the two
dot-matrix display A display that shows charac-
double-bounce signal A signal that is received af-
ters in dot-matrix form.
ter having been reflected twice.
dot-matrix printer A computer output peripheral
double-break contacts The member of a set of
that prints characters and images on paper as a
contacts that is normally closed on two others.
fine grid of dots. A print head, containing several
pins, presses the ribbon against the paper as it
double-break switch A switch that opens a previ-
moves laterally across each line. Can be used to
ously closed circuit at two points simultaneously
print text and/or graphics.
on closing. Compare DOUBLE-MAKE SWITCH.
dot movement pattern The movement of the red,
double bridge See KELVIN DOUBLE BRIDGE.
green, and blue dots on the screen of a color tele-
double buffering In the input/output operation of
vision picture tube as the red, green, and blue
a computer peripheral, the use of two memory ar-
magnets and the lateral magnet are adjusted for
eas for temporary storage.
convergence of the dots at the center. The blue
double-button microphone • double-extended Zepp antenna

double-button microphone A carbon microphone rates the signal from the image; the low second IF
having two buttons mounted on each side of the allows superior selectivity to be achieved at a rea-
center of a stretched diaphragm, and connected sonable cost. Also called dual conversion. 2. Per-
in push-pull. Also see BUTTON MICROPHONE. taining to a superheterodyne receiver with two
double-channel duplex Two-way communication intermediate frequencies.
over two independent channels. One station double-conversion receiver Also called double-
transmits on one channel, and the other station conversion superheterodyne. A superheterodyne
transmits on the other channel. The result is con- receiver using DOUBLE CONVERSION to achieve
versation-mode communications, in which one optimum selectivity and image rejection.
operator can interrupt the other at any time; both double-current generator 1. A dynamo-type gener-
receivers are always operational. ator supplying both alternating current (ac) and di-
double-channel simplex A system of communica- rect current (dc) from one armature winding. 2. A
tion in which two channels are used. One station rotary converter operating on dc and delivering ac.
transmits on one channel, and the other station double-diamond antenna A broadband antenna
transmits on the other channel. Interruption is consisting of two rhomboid plates, one attached
not possible because whenever either operator to each side of the feeder.
transmits, the station receiver is muted. double-diffused epitaxial mesa transistor A tran-
double-checkerboard pattern In a magnetic core sistor in which a thin mesa crystal is overlaid on
memory, the maximum noise that appears when another mesa crystal. Also called epitaxial-growth
half of the half-selected cores are in the one state mesa transistor.
and the others are in the zero state. Also called double-diffused transistor See DIFFUSED-
worst-case noise pattern. EMITTER-AND-BASE TRANSISTOR.
double circuit tuning A circuit whose output and double diode See DUODIODE.
input are tuned separately. Such tuning provides double-diode limiter A limiter in which two diodes
increased selectivity when the input and output are connected back to back in parallel, to limit
are resonant at the same frequency, and decreased both peaks of an alternating-current (ac) signal.
selectivity when they are tuned to different fre- double-doped transistor See GROWN-JUNCTION
double clocking A phenomenon that occurs in double edit In audio tape recording, to make two
some digital circuits when the input pulse is changes in a given span of the tape. For example,
nonuniform, and appears as two pulses to the de- a producer might dislike the wording of a certain
vice. The device is thus actuated at twice the de- sentence, and re-record the sentence. Then,
sired frequency. changing his or her mind, the producer might
double-coil direction finder A radio direction record the original sentence back over the re-
finder (RDF) using an antenna that consists of recorded sentence. These changes increase the
two identical, perpendicular coils. The directivity risk of audible irregularities appearing in the final
of the antenna is the resultant of the directivity of recording.
the individual coils. double emitter follower See COMPOUND CON-
double conversion 1. Two complete frequency NECTION.
conversions in a superheterodyne system. For ex- double-ended amplifier See PUSH-PULL AMPLI-
ample, the incoming signal might be converted to FIER and DOUBLE-ENDED CIRCUIT.
a 9-MHz first intermediate frequency (first IF); at double-ended circuit A symmetrical circuit (i.e.,
a later stage, this signal might be converted to a one having identical halves, each operating on a
455-kHz second IF. The high first IF widely sepa- half-cycle of the input signal). Example: a push-
pull amplifier.
double-extended Zepp antenna A horizontal,
1st 2nd collinear, center-fed antenna, in which each sec-
IF IF tion measures 0.65 wavelength. This antenna
gives increased gain over that of the Zepp and
double Zepp (see DOUBLE ZEPP ANTENNA).
1st 2nd
In Amp. Out
mix. mix. Radiator
0.65»/2 0.65»/2

Osc. Osc.

double-extended Zepp antenna
double conversion
210 double-hump resonance curve • double-sideband system

double-hump resonance curve A resonant re- precision operands, sometimes also accommo-
sponse that is flattened by double tuning; it dating floating-point arithmetic.
exhibits two resonance peaks. Also see DOUBLE- double-precision number In digital computer op-
TUNED AMPLIFIER. erations, a number represented by two words for
double-hump wave See DOUBLE-PULSE WAVE. greater precision.
double image Two overlapping television pictures, double pulse reading Pertaining to a magnetic
one usually fainter than the other. Caused by the core in a computer memory, recording bits as two
signal arriving over two different paths (one pos- states held simultaneously by one core having
sibly attributable to reflection of the wave) and, two areas that can be magnetized with alternate
hence, at different instants in time. The fainter polarities. For example, positive-negative could
image is called a GHOST. represent zero, and negative-positive could repre-
double insulation The use of two layers of insula- sent one.
tion on a conductor, made of different materials. double-pulse wave An alternating-current (ac)
double ionization Ionization resulting from an wave having two successive positive peaks fol-
electron colliding with an ion. In a gas, for exam- lowed by two successive negative peaks within
ple, a neutral atom might collide with an electron, each cycle. The output voltage of a varistor bridge
which can knock an electron out of the atom. The has such a waveshape for an ac input.
atom then becomes a positive ion; it might in turn double-pulsing station A loran station that trans-
be bombarded by an electron, releasing still an- mits at two pulse rates upon receiving two pairs
other electron. of pulses.
double-junction photosensitive semiconductor double pumping A method of obtaining increased
See PHOTOTRANSISTOR. peak output power from a laser by pumping it for
double layer See HELMHOLTZ DOUBLE LAYER. a comparatively long interval and then immedi-
double local oscillator A mixer system in which a ately pumping it for a short interval.
local oscillator generates two accurate radio- doubler 1. A circuit or device for multiplying a fre-
frequency (RF) signals separated by a few hun- quency by two (see FREQUENCY DOUBLER). 2.
dred hertz. The difference frequency is used as a A circuit or device for multiplying a voltage by two
reference in some applications. (see VOLTAGE DOUBLER).
double-make contacts A set of normally open con- double probe A test probe that multiplies an ap-
tacts of which one closes against two others plied signal voltage by two, so it can be handled
simultaneously. Compare DOUBLE-BREAK more effectively by the instrument with which the
CONTACTS. probe is used.
double-make switch A switch that closes a previ- double punching In perforating a punched card,
ously open circuit at two points simultaneously. putting two holes in one column; it is an error if it
Compare DOUBLE-BREAK SWITCH. occurs in a field of a card that is part of a record.
double moding In microwave operations, the double rail A form of logic system in which two
abrupt changing of frequency at irregular inter- lines are used, with three possible states. The
vals. output can be high, low, or undecided.
double modulation Using a modulated carrier to double response 1. Two-point response, as that
modulate another carrier of a different frequency. associated with tuning a receiver to a signal and
double-play tape A thin magnetic recording tape then to its image. 2. See DOUBLE-HUMP RESO-
that has approximately twice the playing time of NANCE CURVE.
the usual tape. Although the playing time is double screen A cathode-ray tube having a two-
longer, double-play tape is more subject to jam- layer screen on which there is an additional,
ming and stretching than standard-thickness long-persistence coating of a different color.
recording tape. double shield Two independent electromagnetic
double-pole Having two poles or switchable cir- shields for a circuit enclosure or cable. The
cuits (e.g., a double-pole switch). shielding structures are concentric, and can be
double-pole, double-throw switch or relay Ab- connected together at a single point (the common
breviation, DPDT. A switch or relay having two point).
contacts that can be closed simultaneously in double sideband Abbreviation, DSB. In a modu-
one of two directions, to close or open two cir- lated signal, the presence of both sidebands.
cuits. double-sideband suppressed carrier Abbreviation,
double precision The use of two computer words DSSC. A transmission technique in which both
to represent a single number to gain precision. sideband products of modulation are transmitted
double-pole, single-throw switch or relay Abbre- and the carrier is suppressed. Compare LOWER
viation, DPST. A switch or relay having two con- SIDEBAND, SUPPRESSED CARRIER, UPPER
tacts that can be closed in only one direction, to SIDEBAND, and SUPPRESSED CARRIER.
simultaneously close or open two circuits. double-sideband system A modulation or demod-
double precision hardware Within a computer, ulation system utilizing both sidebands, with or
arithmetic units permitting the use of double- without the carrier.
double-sideband transmitter • double Zepp antenna

double-throw Operating in opposite directions as
selected (e.g., a double-throw relay or switch).
double-throw circuit breaker A circuit breaker that
Outer shield
closes in both its pull-in and dropout positions.
double-throw switch or relay A switch or relay
having two ganged poles.
double-trace recorder See DOUBLE-TRACK RE-
Inner shield CORDER, 2.
double tracing Displaying two signals simultane-
ously on the screen of an oscilloscope through
the use of an electronic switch.
Center double-track recorder 1. A tape recorder whose
head is positioned so that separate recordings
can be made as two tracks on the tape. 2. A
graphic recorder that produces two separate par-
allel tracings.
double shield
doublet trigger A two-pulse, constant-spaced trig-
ger signal used for coding.
double-sideband transmitter A modulated trans- double-tuned amplifier An amplifier whose input
mitter using a double-sideband system. and output circuits are both tuned.
double signal In reception, the property of having double-tuned circuit A circuit, such as an ampli-
a signal on either side of the carrier frequency, as fier or filter, using separate input and output tun-
in a direct-conversion receiver. The two signals ing. Also see DOUBLE CIRCUIT TUNING and
represent the sum and difference of the local os- DOUBLE-TUNED AMPLIFIER.
cillator signal and the actual received signal.
Because the two signals convey identical
information, the phenomenon is wasteful of re-
ceived spectrum, and degrading to receiver selec-
tivity and sensitivity.
double-signal receiver A receiver, such as a di-
rect-conversion type, in which the signals occur
in replicated form on either side of the local oscil-
C1 C2
L2 L3
lator signal. Compare SINGLE SIGNAL. Input L1 L4 Output
double-spot tuning In a superheterodyne receiver,
tuning in the same signal at two different places
on the dial, a condition caused by image re-
Input tuning: L2 and C1 Output tuning: L3 and C2
double squirrel-cage induction motor A poly-
double-tuned circuit
phase induction motor having a double squirrel-
cage rotor. The rotor slots contain two bars, an
upper bar having low reactance (being near the double-tuned detector A form of frequency-
air gap) and high resistance, and a lower bar hav- modulation (FM) discriminator with two resonant
ing high reactance and low resistance. This motor circuits. One is tuned slightly higher than the
has low starting current, high starting torque, channel center frequency, and the other is tuned
and a full-load slip of less than 5%. an equal amount below the center.
double-stream amplifier A traveling-wave tube in double-vee antenna A broadband, modified dipole
which microwave amplification results from the antenna resembling two vees in line. Also see
interaction of two electron beams of different av- VEE ANTENNA.
erage velocity. double-winding generator A dynamo-type genera-
double-stub tuner Two stubs (see STUB) con- tor having separate armature windings for sup-
nected in parallel with a transmission line and plying two voltages, either of which can be direct
usually spaced 0.375 wavelength (135 electrical (dc voltage) or alternating (ac voltage).
degrees) apart; it is used as an impedance double-wye rectifier A heavy-load circuit using six
matcher. rectifier diodes, each conducting for 120 degrees
double superheterodyne See DOUBLE-CONVER- of the cycle. An interphase winding is used. The
SION SUPERHETERODYNE. circuit is equivalent to two three-phase, half-wave
double superheterodyne reception See DOUBLE- rectifiers connected in parallel.
double-surface transistor See COAXIAL TRAN- double Zepp antenna A usually horizontal,
SISTOR. straight, center-fed, full-wavelength antenna.
212 double Zepp antenna • dress

Also called two half waves in phase. Its name was force introduced by an applied magnetic or elec-
derived because it is, in fact, two Zepp antennas tric field.
forming a collinear array. drag angle In disk recording, an angle of less than
doubling 1. Producing the second harmonic of a 90° between the stylus and the disk. The acute
signal. 2. In communication, unintentional si- angle causes the stylus to drag instead of digging
multaneous transmission by both operators, re- in.
sulting in missed information. 3. In a speaker, drag cup A cup of nonmagnetic metal (usually cop-
distortion resulting in large amounts of second- per or aluminum) that, when rotated in a mag-
harmonic output. netic field, acquires a voltage proportional to the
doubly balanced modulator See BALANCED speed of rotation. The device is often used as a
doughnut capacitor See DONUT CAPACITOR. drag-cup motor A servomotor whose shaft has a
doughnut coil See TOROIDAL COIL. copper or aluminum drag cup that rotates in the
doughnut crystal See DONUT CRYSTAL. field of a two-phase stator. Eddy currents set up
doughnut magnet See RING MAGNET. in the cup by the field winding produce torque;
down convert In superheterodyne conversion, to braking action, direction control, and speed con-
heterodyne a signal to an intermediate frequency trol are obtainable by means of associated elec-
lower than the signal frequency. Compare UP tronics.
CONVERT. drag magnet In a motor-type meter, a braking
down lead See LEAD-IN. magnet (i.e., one used to reduce speed through
downlink The signal sent down from an active eddy-current effects). Also called retarding mag-
communications satellite to the earth, usually on net.
a different frequency than the signal sent up. See drain 1. The current or power drawn from a signal
UPLINK. or power source. 2. A load that absorbs current
downlink beamwidth The angle subtended be- or power. 3. The electrode in a field-effect transis-
tween the half-power points of the downlink sig- tor (FET) from which the output is usually taken;
nal from an active communications satellite. equivalent to the collector of a bipolar transistor.
downlink frequency The frequency of the down- drainage equipment Devices and systems for pro-
link signal from an active communications satel- tecting circuits against transients generated by
lite. Usually, the downlink signals occupy a circuit breakers and similar safety devices.
certain band of frequencies, anywhere from sev- drain-coupled multivibrator An oscillator that
eral kilohertz to several megahertz wide. uses two field-effect transistors (FETs) in the cir-
downlink power 1. The output power of the down- cuit equivalent of a collector-coupled bipolar-
link transmitter in an active communications transistor multivibrator. The drain of one stage is
satellite. 2. The effective radiated power (ERP) of capacitance-coupled to the gate of the other
the downlink signal from an active communica- stage.
tions satellite.
down time A period of time during which elec-
tronic equipment is completely inoperative (for
any reason). R4
+ dc
downturn A usually sudden dip in a performance
C1 C2
curve. Compare UPTURN.
downward modulation Modulation in which the
average carrier component decreases during
modulation. Example: amplitude modulation of a
transmitter in which the antenna current de-
creases during modulation. Compare UPWARD
DP Abbreviation of DATA PROCESSING.
DPDT Abbreviation of double-pole, double-throw
(switch or relay).
DPM 1. Abbreviation of digital power meter. 2. Ab-
breviation of DIGITAL PANEL METER. 3. Abbrevi- drain-coupled multivibrator
ation of disintegrations per minute.
DPS Abbreviaton of disintegrations per second.
DPST Abbreviation of double-pole, single-throw D-region A low region of the ionosphere beneath
(switch or relay). the E-region, whose ionization varies with the in-
dr Abbreviation of dram. clination of the sun. The greatest ionization is at
drag 1. A retarding force, caused by friction, acting midday; the layer disappears at night.
on a moving body in contact with another moving dress The (usually experimental) arrangement of
or stationary body or medium. 2. A retarding leads for optimum circuit operation (minimum
dress • driver element

capacitance, best suppression of oscillation, min- AGE). 2. Input-signal excitation (see DRIVING
imum pickup, etc.). CURRENT, DRIVING POWER, and DRIVING
dressed contact A contact having a permanently VOLTAGE). 3. A device that moves a recording
attached locking spring member. medium (e.g., tape drive and diskette drive). 4.
drift 1. Within a conductor or semiconductor, the The transmission of mechanical energy from one
controlled, directed movement of charge carriers place to another (e.g., motor drive).
resulting from an applied electric field. 2. A usu- drive array A set of two or more hard-disk drives in
ally gradual and undesirable change in a quan- a computer system. They function together to
tity, such as current, as a result of a disturbing minimize the possibility of data loss. Such a sys-
factor, such as temperature or age. tem can also increase the amount of fast-access
drift current In a semiconductor, the current re- data storage.
sulting from a flow of charge carriers in the pres- drive belt A continuous belt used to transmit me-
ence of an electric field. The charge carriers are chanical energy from a driving pulley to a driven
electrons in n-type material and holes in p-type pulley.
material. drive circuit 1. A circuit used to provide the exci-
drift field The inherent internal electric field of a tation to a motor. 2. An amplifier that supplies
DRIFT-FIELD TRANSISTOR. drive to a more powerful amplifier.
drift-field transistor An alloy-junction, bipolar, drive control In a television receiver, the poten-
radio-frequency (RF) transistor for which the im- tiometer used to adjust the ratio of horizontal
purity concentration is graded from high on the pulse amplitude to the level of the linear portion
emitter side of the base wafer to low on the col- of the sawtooth scanning-current wave.
lector side. This creates an internal drift field that driven element In a multielement antenna, an el-
accelerates current carriers and raises the upper ement to which electromagnetic energy is fed di-
frequency limit of the transistor. rectly, as opposed to a PARASITIC ELEMENT,
drift-matched components Active or passive which is excited by a nearby radiator element.
components that have been closely matched in driven-element directive antenna A multiele-
terms of the drift of one or more parameters, with ment directional antenna whose elements are
respect to time, temperature, etc. driven from the feed line (i.e., no element is para-
drift mobility For current carriers in a semicon- sitic). Compare PARASITIC-ELEMENT DIREC-
ductor, the average drift velocity per unit electric TIVE ANTENNA.
field. driven multivibrator A multivibrator whose oper-
drift space 1. In a vacuum tube, a space that is ation or frequency is controlled by an external
nearly free of alternating-current (ac) fields from synchronizing or triggering voltage. Compare
the outside, and in which the repositioning of FREE-RUNNING MULTIVIBRATOR.
electrons is governed by the space-charge forces driven single sweep A single oscilloscope sweep
and the velocity distribution of the electrons. 2. that is initiated by the signal under observation.
In a Klystron, the space between buncher and drive pattern A pattern of interference in a facsim-
catcher cavities in which there is no field. ile system that is caused by improper synchro-
drift speed The average velocity of charge carriers nization of the recording spot.
moving through a medium. driven sweep An oscilloscope sweep that is initi-
drift transistor See DRIFT-FIELD TRANSISTOR. ated by the signal under observation.
drift velocity The net velocity of a charged particle drive pin A pin used to prevent a record from slip-
(electron, hole, or ion) in the direction of the field ping on the rotating turntable of a recorder or re-
applied to the conducting medium. producer. It is similar to, and located near, the
drift voltage The usually gradual change in volt- center pin of the turntable.
age resulting from such causes as internal heat- drive pulse In digital computer operations, a pulse
ing. Also called voltage drift. that magnetizes a cell in a memory bank.
drip loop In a transmission line for an antenna or driver 1. A device that supplies a useful amount of
power service, a loop near the point of entry to the signal energy to another device to ensure its
building for the purpose of allowing condensation proper operation (e.g., a current driver for a mag-
or rain water to drip off. netic-core memory, an oscillator driving a loud-
drip-proof motor A motor with ventilating aper- speaker). 2. A power amplifier stage that supplies
tures arranged so that moisture and particles signal power to a higher-powered amplifier stage.
cannot enter the machine. 3. In a digital computer, a stage that increases
drip-tight enclosure A housing designed to pre- the output current or power of another stage
vent entry of rain, snow, and dust; it also pre- (e.g., a clock driver). 4. The cone and magnet of a
vents accidental contact with the enclosed dynamic speaker.
apparatus or machinery. driver element In a multielement directive an-
drive 1. To excite (i.e., to supply with input-signal tenna, the element excited directly by the feeder,
current, power, or voltage) (see DRIVING CUR- the other elements (directors and reflectors) being
214 driver impedance • dropsonde

driver impedance 1. The output impedance of a Radiator
driver stage. 2. The impedance “seen” from the
driven stage of an amplifier, through the driver Radials
transformer, to the driver stage. It is the vector Approx. 135° (grounded)
sum of driver reactance and resistance.
driver inductance In an amplifier™s driver trans-
former, the inductance, as “seen” looking through
the transformer from the driven stage into the
driver stage.
driver resistance In an amplifier™s driver trans- drooping radials
former, the resistance “seen” looking through the
transformer from the driven stage into the driver
stage. depends on the characteristic impedance of the
driver stage An amplifier stage whose chief pur- line; typically, the angle is between 45 degrees
pose is to supply excitation (input-signal current, and 70 degrees, relative to horizontal.
power, or voltage) to the next stage. Also see drop 1. In wire communications, the line connect-
DRIVER. ing a telephone cable to a subscriber™s building.
driver transformer The transformer that couples a 2. See VOLTAGE DROP.
driver stage to a driven stage. Example: the inter- drop bar A device that automatically grounds or
stage transformer inserted between the collector short-circuits a capacitor when the door of a pro-
of a single-ended driver transistor and the two tective enclosure is opened.
bases of a push-pull power-output stage in an drop cable See DISTRIBUTING CABLE, 1.
audio amplifier. drop channel In a communications system utiliz-
driving current In a power amplifier, the input ing several channels, a channel that is not used.
signal current required to produce a given drop-in The unintentional creation of bits when a
amount of output power. magnetic storage device is being read from or
driving-point admittance The reciprocal of written into. Compare DROP-OUT, 4.
DRIVING-POINT IMPEDANCE. drop indicator In a signaling system, such as an
driving-point impedance The input impedance of annunciator, a hinged flap that drops into view
a network. when the signaling device is actuated.
driving power In a power amplifier, the input sig- drop-out 1. The opening of a relay or circuit
nal power required to produce a given amount of breaker. 2. In digital computer operations, varia-
output power. tion in signal level of the reproduced tape-
drive wire The wire forming the coil around the recorded data. Such variation can result in errors
toroidal cell in a magnetic core memory; supplies in data reproduction. 3. In the production of
pulses that magnetize the cell. monolithic circuits, a special image placed at a
driving-range potential In cathodic protection, desired point on the photomask. 4. Digit loss
the difference of potential between the anode and during a read or write operation involving a mag-
(protected) cathode. netic storage device.
driving signal 1. Drive (see DRIVE, 2). 2. In televi- dropout current See DROPOUT VALUE.
sion, time-scanning signals (line-frequency pulses dropout power See DROPOUT VALUE.
and field-frequency pulses) at the pickup location. dropout value The level of current, power, or volt-
driving spring In a stepping relay, the spring that age at which a device, such as a circuit breaker or
moves the wiper blades. relay, is released.
driving voltage In a power amplifier, the input sig- dropout voltage See DROPOUT VALUE.
nal voltage required to produce a given amount of dropping resistor A series resistor providing a
output power. voltage reduction equal to the voltage drop across
DRO Abbreviation of DIGITAL READOUT. itself. For example, a 1000-ohm resistor in series
drone A pilotless radio-controlled aircraft without with a 45-V battery, and carrying a current of 10
a human pilot. mA, will provide a voltage reduction equal to 10 V
(IR = 0.01 — 1000 = 10 V), thus dropping the 45 V
drone cone An undriven loudspeaker cone that is
mounted in a bass-reflex enclosure with other to 35 V.
speakers. Also called PASSIVE RADIATOR. drop relay In a telephone system, a relay that is
droop 1. A dip in the graph of a function. 2. In a activated by the ringing signal. The relay is used
pulse train, the decrease in mean amplitude (in to switch on a buzzer, light, or other device.
percent of maximum amplitude) at a given in- drop repeater A repeater intended for a termina-
stant after attainment of maximum amplitude. tion of a communications circuit in a telephone
drooping radials In a ground-plane antenna, radi- system.
als that slope downward to provide a transmis- dropsonde A parachute-supported radiosonde
sion-line impedance match. The slope angle dropped from a high-flying aircraft.
drop-tracks • dry flashover voltage

drop-tracks The tracks of radioactive particles made drum resistor A resistor consisting of a hollow
visible by moisture in an ionization chamber. cylinder of resistive material. Such a resistor can
drop wire A wire that runs from a building to a be cooled by circulating air or liquid through the
pole (for line extension) or to a cable terminal (for cylinder.
cable extension). drum speed The speed, usually measured in revo-
drum 1. A rotating cylinder coated with a magnetic lutions per minute (rpm), of the rotating drum in
material on which digital information can be a graphic recorder, facsimile transmitter, or fac-
recorded in the form of tiny magnetized spots. simile receiver.
These spots are read as the drum rotates under drum storage The storage of data as magnetic
pickup heads, or erased when the stored infor- impulses on a cylindrical, or drum-shaped,
mation is no longer needed. 2. In some graphic medium. Largely supplanted in recent years by
recorders, facsimile receivers, etc., a rotating magnetic disks, optical disks, and magnetic
cylinder carrying the recording sheet. tapes.
drum capacitor See CONCENTRIC CAPACITOR. drum switch A sequential switch whose contacts
drum controller The device that regulates the re- are pins or teeth placed at points around the out-
cording process on a drum memory. side of a revolving drum.
drum mark On a track of a magnetic drum, a char- drum transmitter A facsimile transmitter in which
acter that signifies the end of a character group. the sheet bearing the material to be transmitted
drum memory In digital computers, a memory is wound around a revolving drum.
based on a magnetic drum (see DRUM, 1). They drum-type controller A motor-driven drum switch
have been largely replaced in recent years by elec- arranged to time various operations through se-
tronic random-access memory, in the form of in- quential switching.
tegrated circuits (ICs) and/or PCMCIA standard drum varistor A varistor that is a hollow cylinder
adapter cards. of nonlinear resistance material. This varistor
drum parity The degree of accuracy in a drum can be cooled by circulating air or liquid through
recording/reproducing system. it.
drum programmer A device for sequencing opera- drum winding In a motor or generator, an arma-
tions. Its heart is a rotating drum, around whose ture whose conductors are on the outer face of
surface contacts or points can be placed to actu- the core, the two branches of a turn lying under
ate or terminate operations at selected times. adjacent poles of opposite polarity.
drum receiver A facsimile receiver using recording drunkometer An instrument for testing the extent
paper or photographic film wound around a re- of alcoholic intoxication. It electronically mea-
volving drum. sures blood alcohol content through analysis of
drum recorder A graphic recorder in which the the subject™s breath.
record sheet is wound around a rotating drum. dry In an electric cell, a term used to describe an
electrolyte that is semiliquid or solid.
dry battery A battery of dry cells.
dry cell 1. A Leclanche primary cell in which the
positive electrode is carbon, the negative elec-
trode is zinc, and the electrolyte is a gel of ammo-
nium chloride and additives. Also see CELL and
PRIMARY CELL. 2. A cell whose electrolyte is a
gel or paste.
Armature with
marker dry circuit A circuit in which the maximum volt-
age is 50 mV and the maximum current 200 mA.
dry-contact rectifier See DRY-DISK RECTIFIER.
dry contacts Contacts that neither make nor
Meter break a circuit.
device dry-disk rectifier A solid-state rectifier, such as a
copper-oxide, magnesium-copper-sulfide, or sele-
nium type, that consists of a metal disk coated
with a semiconductor material. The name was
originally used to distinguish this rectifier from
the wet electrolytic rectifier.
dry electrolytic capacitor An electrolytic capaci-
tor whose electrolyte is a paste or solid. Compare
dry flashover voltage The breakdown voltage be-
tween electrodes in dry air when all insulation is
drum recorder clean and dry.
216 dry pile • dual-cone speaker

dry pile A voltaic pile containing numerous disks
silvered or tinned on one face and covered with
manganese dioxide on the other.
dry reed A metal contact, generally used as a relay
or switch, that moves toward or away from an-
other fixed contact under the influence of a mag-
netic field.
dry-reed relay See DRY-REED SWITCH.
dry-reed switch A switch consisting of two thin,
metallic strips (reeds) hermetically sealed in a
glass tube. The tube is surrounded by a coil of
wire. When a current flows in the coil, a magnetic
field affects the reeds. In the normally open dry-
reed switch, the magnetic field causes the reeds
to come together and close the circuit. In the nor- DSS Abbreviation of direct station selection (tele-
mally closed dry-reed switch, the magnetic field phone).
causes the reeds to separate, opening the circuit. DSSC Abbreviation of DOUBLE-SIDEBAND SUP-

dry run 1. The preliminary operation of equipment DT Abbreviation of DATA TRANSMISSION.
for testing and appraisal. Such a procedure pre- DTA Abbreviation of differential thermoanalysis.

cedes putting the equipment into regular service. DT-cut crystal A piezoelectric plate cut from a quartz
2. A step-by-step, paper-and-pencil “run” of a crystal at an angle of rotation about the z-axis of
computer program before it is machine-imple- “53 degrees. It has a zero temperature coefficient of
mented. frequency at approximately 30 degrees Celsius.
dry shelf life The life of a battery cell stored with- Also see CRYSTAL AXES and CRYSTAL CUTS.
out its electrolyte. DTL Abbreviation of DIODE-TRANSISTOR LOGIC.
dry-transfer process A method of transferring DTn Abbreviation of DOUBLE TINNED.
printed-circuit patterns and panel labels from DTS 1. Abbreviation of DATA-TRANSMISSION SYS-
sheets by rubbing them onto the substrate or TEM. 2. Abbreviation of digital telemetry system.

panel. DU Abbreviation of DUTY CYCLE.
dry-type forced-air-cooled transformer A DRY- dual 1. Pertaining to a combination of two compo-
TYPE TRANSFORMER that is cooled by convec- nents such as diodes, transistors, etc., in a single
tion of air circulated by a blower or fan. This housing. The components are often carefully
increases the amount of power that the trans- matched. Compare QUAD. 2. Pertaining to a de-
former can safely handle. vice or circuit that behaves in a manner analo-
dry-type self-cooled transformer A DRY-TYPE gous to that of another operating with component
TRANSFORMER that is cooled by natural air cir- and parameter counterparts. Thus, a current am-
culation (convection), without the use of a blower plifier can be the dual of a voltage amplifier;
or fan. a series-resonant circuit, the dual of a parallel-
dry-type transformer A transformer that, rather resonant circuit; or a field-effect transistor, the
than being immersed in oil, is cooled entirely by dual of a bipolar transistor.
the circulation of air. dual-beam CRT A cathode-ray tube having two
DSB Abbreviation of DOUBLE SIDEBAND. separate electron guns, for use in a dual-beam
DSBSC Abbreviation of DOUBLE-SIDEBAND SUP- oscilloscope.
PRESSED CARRIER. Also abbreviated DSSC. dual-beam oscilloscope Also called dual-trace os-
dsc Abbreviation of double silk covered (wire). cilloscope. An oscilloscope having two electron
D scope A radar whose display resembles that of a guns and deflection systems; it can display two
C scope, the difference being that blip height phenomena on the screen simultaneously for
gives an approximation of the distance. comparison.
D service A Federal Aviation Agency service pro- dual capacitor 1. Two fixed capacitors combined
viding radio broadcasts of weather data, notices in a single housing, sometimes sharing a com-
to aircraft personnel, and other advisory mes- mon capacitor plate. 2. A two-section, ganged
sages. variable capacitor.
D-shell connector A multi-pin connector (either dual-channel amplifier An amplifier having two
male or female) with a characteristic shape that separate, independent channels (e.g., a stereo
ensures proper pin placement. Commonly used high-fidelity audio amplifier).
for computer ports, and for connections of pe- dual-cone speaker A speaker designed for a wide
ripherals to electronic equipment. range of audio frequencies. One cone responds to
dsp Abbreviation of double silver plated. the bass (low) and midrange audio frequencies,
DSR Abbreviation of DYNAMIC SPATIAL RECON- and a smaller cone responds to the treble (high)
STRUCTOR. audio frequencies.

dual diode • Duant electrometer

dual diode A discrete component consisting of two static energy, behaving as point charges in some
diodes in one package. scenarios and as force fields in other situations.
dual-diversity receiver A receiver or receiver sys- 2. The tendency of a set of principles to be dupli-
tem for DIVERSITY RECEPTION. cated in sense by predictable analogies, as be-
dual-diversity reception See DIVERSITY RECEP- tween inductance and capacitance, electrostatics
TION. and magnetics, etc.
dual-emitter transistor A low-level silicon pnp dual local oscillator See DOUBLE LOCAL OSCIL-
chopper transistor of the planar passivated epi- LATOR.
taxial type; it has two emitter electrodes. dual meter A meter having two meter movements
dual-frequency calibrator A secondary frequency and scales in a single case; the arrangement per-
standard providing two fundamental test fre- mits simultaneous monitoring of two quantities.
quencies (e.g., 100 kHz and 1 MHz). dual modulation The modulation of a single car-
dual-frequency induction heater An induction rier or subcarrier by two different types of modu-
heater whose work coils carry energy of two dif- lation”each carrying different information.
ferent frequencies. The coils heat the work either dual network A network that is the dual of another
simultaneously or successively. network having complementary parameters. For


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