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PASSIVATED TRANSISTOR, PLANAR TRANSIS- transistor-transistor logic Abbreviation, TTL or
T2L. In computer operations, a circuit in which
TRANSISTOR, SILICON TRANSISTOR, SUR- the multiple-diode cluster of the diode-transistor
FACE-BARRIER TRANSISTOR, SURFACE- logic circuit has been replaced by a multiple-
transistor amplifier An amplifier containing only
transistors as the active components. Also called
transistorized amplifier.
transistor analyzer An instrument for measuring
the electrical characteristics of transistors. Com-
transistor battery A 9-volt electrochemical battery
consisting of six tiny zinc“carbon or alkaline cells
in series. Each of the six cells supplies 1.5 volts.
The ampere-hour capacity is small. The battery Input
has a characteristic box shape with adjacent clip- Y
on terminals at one end. These batteries are used
in low-current electronic devices such as remote- transistor-transistor logic
control garage-door openers, television channel
changers, remote videocassette recorder (VCR)
controls, electronic calculators, and smoke transistor voltmeter Abbreviation, TVM. A volt-
detectors. meter containing an amplifier that uses only
transistor-coupled logic Abbreviation, TCL. In bipolar transistors. Also called transistorized volt-
computer and automatic-control operations, logic meter. Also see ELECTRONIC VOLTMETER.
circuitry and systems using multi-emitter-cou- Compare FET VOLTMETER and VACUUM-TUBE
pled transistors. Also see RESISTOR-TRANSIS- VOLTMETER.
692 transit angle • transverse

transit angle For an electron, the angular fre- and amplifiers. The main asset of this scheme is
quency multiplied by the time required to travel the fact that it is possible to conduct split-
from one point to another. frequency communication on bands whose wave-
transit time The time taken by an electron to lengths differ greatly. Another asset is the ability
travel from one electrode to another”especially of the system, with proper design, to operate in
from the cathode to the plate in a vacuum tube. full-duplex mode. Installations of this type are of-
transistor element A metallic element whose ten used in satellite communications. Compare
atoms have valence electrons in two shells. Ex- TRANSCEIVER, 1.
amples: chromium, iron, and nickel. transmitting antenna An antenna designed ex-
transition factor See MISMATCH FACTOR. pressly for the efficient radiation of electromag-
transition region See BARRIER, 1. netic energy into space.
translation loss See PLAYBACK LOSS. transmitting station A station that only transmits
translator 1. See COMPILER. 2. See ASSEMBLER. signals (i.e., it engages in no official form of re-
transliteration 1. To change the characters in one ception). Compare RECEIVING STATION.
alphabet or code system to the characters in a transmittivity The degree to which a selective cir-
different system. 2. The function that maps the cuit transmits a desired signal. Compare REJEC-
characters in one alphabet or code system to TIVITY.
those in another. transmultiplexer A device that changes a signal
translucence 1. The transmission of radiation, es- from one multiplexed form to another while main-
pecially visible light, through a material. 2. The taining all of the information contained in the sig-
extent to which a substance can transmit radia- nal. For example, a transmultiplexer might
tion”especially visible light. 3. Pertaining to a convert time-division-multiplex data to fre-
material that partially or totally transmits radia- quency-division multiplex or vice-versa.
tion”especially visible light. transonic Equal to, or approximating, the speed of
transmission gain Current amplification, power sound in air (approximately 1100 feet per second).
amplification, or voltage amplification. transparence The practically unimpeded trans-
transmission line 1. A single conductor or group mission of radiation, such as light, through a ma-
of conductors for carrying electrical energy from terial. Compare OPACITY and TRANSLUCENCE.
one point to another. 2. A correctly dimensioned transponder An acronym for transmitter and
conductor or pair of conductors for carrying ra- responder. 1. A combination transmitter“receiver
dio-frequency energy from a transmitter to an an- that automatically transmits an identification
tenna or coupling device. signal whenever it receives an interrogating sig-
transmission mode 1. In a transceiver, the condi- nal. 2. In a communications satellite, a broad-
tion in which the transmitter is enabled and the band repeater that receives signals sent up from
receiver is disabled. 2. In a waveguide, propaga- the earth, converts them to another frequency,
tion via transverse waves. and retransmits them back to the earth. Some
transmission speed The number of information el- satellites have units that employ multiplexing,
ements (words, code groups, data symbols, bits, data storage and retrieval systems, and other
and bytes) that can be generated or received per schemes to maximize the amount and variety of
unit time (second or minute) by a system or oper- data they can handle.
ator. transponder overload A condition that occurs
transmission wavemeter A (usually simple) in- when a satellite transponder is heavily used or
ductance-capacitance-tuned wavemeter that pro- when an excessively strong uplink signal is re-
vides peak response when tuned to the frequency ceived. During heavy usage, all downlink signals
of a signal passing through it; also, the compara- are consistently weaker than they are when the
ble microwave device. Compare ABSORPTION transponder is not dealing with many signals. If
WAVEMETER. an overly powerful uplink signal is received, all
transmit-receive switch A manually or electri- downlink signals are attenuated intermittently;
cally operated switch for transferring a single an- the greater the instantaneous power of the of-
tenna between a transmitter and receiver. fending uplink signal, the greater the instanta-
transmittancy The relative ability of a substance neous attenuation of all the downlink signals.
to transmit radiation. Transmittancy depends on See TRANSPONDER, 2.
the frequency of the radiation, as well as the sub- transport See TAPE TRANSPORT.
stance. transportable equipment Portable electronic
transmitter 1. An equipment for producing and equipment. See, for example, PORTABLE TRANS-
sending signals or data. 2. See MICROPHONE. 3. MITTER.
One who originates signals or data. transuranium An element whose atomic number
transmitter“receiver A transmitter and receiver is higher than that of uranium.
usually contained in a single enclosure, but with transverse Occurring in a direction or directions
separate and independent oscillators, mixers, perpendicular to the direction of propagation.
transverse electric mode • triangulation

transverse electric mode In a waveguide, the con-
dition in which the electric lines of flux are per-
pendicular to the direction of propagation.
transverse electromagnetic wave An electromag- x
netic wave having electric-field vectors and mag-
netic-field vectors perpendicular to the direction
of propagation.
transverse magnetic mode In a waveguide, the
condition in which the magnetic lines of flux are
perpendicular to the direction of propagation.
trap 1. See WAVETRAP. 2. In a semiconductor
crystal, an imperfection capable of trapping cur-
rent carriers.
( )
Modulation (%) = 100 x + y
trapezoid 1. A polygon having four sides, of which
only two are parallel. 2. See TRAPEZOIDAL PAT-
TERN. 3. See TRAPEZOIDAL WAVE. trapezoidal pattern
trapezoidal distortion In television or facsimile, a
form of distortion in which the frame is wider at
the top than at the bottom, or vice versa. When wave and electron velocities are equal, a
power gain is obtained in the signal coupled out
of the helix. Also see BACKWARD-WAVE OSCIL-
Top of screen
Travis discriminator A discriminator circuit in
which the diodes are operated from separately
tuned halves of the secondary winding of the in-
put transformer. Compare FOSTER-SEELEY
treasure locator See METAL LOCATOR.
treble The higher portion of the sound spectrum”
especially the upper end of the musical scale
(middle C and above). Compare BASS.
treble boost 1. Amplification of high audio fre-
Bottom of screen quencies (the treble notes) in an audio system”
especially in high-fidelity music reproduction.
trapezoidal distortion
2. The extent of amplification of high audio
frequencies in audio applications”especially in
music reproduction. 3. A control that allows
trapezoidal pattern An oscilloscope pattern used adjustment of the relative treble gain in an audio
to check the percentage of modulation of an am- system.
plitude-modulated wave. Its name is derived from treble control See TREBLE BOOST, 3.
its trapezoidal shape. tree 1. A cause-and-effect chain with two or more
trapezoidal wave A nonsinusoidal wave that is a independent branches. 2. A circuit with two or
combination of a rectangular component and a more branches but no meshes.
sawtooth component. It is the required waveform TRF Abbreviation of tuned radio frequency.
of the voltage applied to a magnetic deflecting coil TRF amplifier See TUNED RADIO-FREQUENCY
(oscilloscope or television) to ensure a sawtooth AMPLIFIER.
wave of current in the coil. TRF receiver See TUNED RADIO-FREQUENCY
traveling-wave amplifier Abbreviation, TWA. An RECEIVER.
amplifier based on the unique operation of the triac A three-terminal, gate-controlled, semicon-
traveling-wave tube. ductor switching device. Compare DIAC.
traveling-wave tube Abbreviation, TWT. A micro- triangular wave See BACK-TO-BACK SAWTOOTH.
wave tube containing an electron gun, helical triangulation A method of radiolocation in which
transmission line, collector, and input and out- directional bearings are obtained for the signals
put couplers. A microwave signal is coupled into from two transmitters whose positions are
the helix, through which it travels while the gun accurately known. The position of the receiver is
projects an electron beam through the helix. indicated by the intersection of two lines on a
694 triangulation • Trinitron

A2 trigger 1. A pulse used to start or stop the opera-
tion of a circuit or device, such as a flip-flop. 2. To
place a circuit or device into or out of operation
with a start or stop pulse, as defined in 1.
trigger diode See DIAC and FOUR-LAYER DIODE.
triggered multivibrator See DRIVEN MULTIVI-
triggered sweep In an oscilloscope or similar de-
vice, a driven sweep.
A1 triggering point The voltage level at which the ac-
tion of an electronic switching device is initiated.
trigistor A three-junction semiconductor device
that exhibits two-state operation, and is useful as
map, drawn emanating from the transmitter a flip-flop or switch. Also see NPNP DEVICE.
locations 180 degrees opposite their respective trigonometric functions See CIRCULAR FUNC-
Triax A double-shielded coaxial cable. A center trigonometry The branch of mathematics devoted
conductor is surrounded by two concentric, inde- to the application of CIRCULAR FUNCTIONS in a
pendent shield conductors. plane. It is useful in electronics for determining
triaxial connector A male or female connector impedance and phase.
having three concentric contacting surfaces. By trim To make a fine adjustment, as of a tuning
contrast, the coaxial jack and coaxial plug have control, balance control, output adjustment, etc.
only two such surfaces. trimmer A low-valued variable capacitor, inductor,
triaxial speaker A dynamic loudspeaker contain- or resistor operated in conjunction with a main
ing three coils and three cones, for high-, unit (usually of the same sort) for vernier
low-, and middle-frequency ranges. It is, in effect, adjustment or range setting. See, for example,
three speakers in one. It is commonly used in HIGH-FREQUENCY TRIMMER and OSCILLATOR
high-fidelity music reproduction systems. Also TRIMMER.
called triaxial driver. Compare THREE-WAY trimmer capacitor A variable capacitor used as a
SPEAKER. trimmer.
triboelectric Pertaining to frictional electricity.
triboelectric series See ELECTROSTATIC SE-
Adjustable screw
triboluminescence Luminescence produced by
means of friction. Dielectric
trickle charge A continuous slow charge of a stor-
age battery, in which the charging rate is just suf-
ficient to compensate for internal losses or Mounting
normal discharge. contact
trickle charger A light-duty unit for charging a
battery gradually at low current.
tricorner reflector A device that reflects a ray of
incident energy at a 180-degree angle, regard- Porcelain
less of the direction from which the ray ap- base
proaches. Thus, the ray will return to its source,
unless some obstruction intervenes. It consists trimmer capacitor
of three mutually perpendicular reflecting plane
surfaces that intersect in a common point. The
geometry is identical to that in a typical room, trimmer coil See TRIMMER INDUCTOR.
where the ceiling meets two walls. It is useful at trimmer inductor A variable inductor used as a
microwave, infrared, visible, and ultraviolet trimmer.
wavelengths. trimmer resistor A variable resistor used as a
triethanolamine An amino alcohol that precipi- trimmer.
tates metallic silver from a silver-nitrate solution trinary number system The base-3 system of no-
in the deposition of a silver surface on a sub- tation. This system uses the digits 0, 1, and 2, the
strate, such as glass or a ceramic. positional values being successive powers of 3
trig Abbreviation of TRIGONOMETRY. (e.g., decimal 14 equals trinary 112). Also called
trigatron A form of electrically operated switch. ternary number system.
The circuit is closed by the breakdown of an elec- Trinitron 1. A single-gun color-television picture
trical gap. tube developed by Sony. 2. A television set using
Trinitron • tropospheric propagation

this tube. The gun has three cathodes that mod- tropospheric bending A common type of radio-
ulate the three color beams (red, green, and blue). wave propagation that takes place when radio
The beams are accelerated by common grids and waves are refracted in the lower atmosphere.
are focused at different angles by convergence This effect is most dramatic near weather fronts,
plates. where warm, relatively light air lies above cool,
Trinoscope See TRINITRON. heavy air. The cooler air has a higher index of re-
triode A three-electrode tube or transistor, em- fraction than the warm air, causing radio-
bodying an anode, cathode, and a control elec- frequency electromagnetic fields to be bent
trode as the principal elements. downward at a considerable distance from the
triple-diffused transistor A diffused transistor in transmitter. It is often responsible for anomalies
which the base and emitter are diffused into the in reception of FM and TV broadcast signals.
top face of the chip, and the collector into the bot- Compare TROPOSPHERIC DUCTING, TROPO-
triple diode An assembly of three (often closely tropospheric ducting Also called duct effect. A
matched) semiconductor diodes in a single form of tropospheric propagation that occurs
housing. close to the earth™s surface at very-high
tripler 1. A rectifier that delivers a direct-current frequencies (VHF) and ultra-high frequencies
output voltage at approximately triple the peak (UHF). A duct forms when a layer of cool air
value of the alternating-current input voltage. becomes sandwiched between two layers of
2. An amplifier or other circuit that delivers an warmer air. Total internal reflection of the
output signal at triple the frequency of the input electromagnetic (EM) field takes place inside
signal. the duct. For this phenomenon to provide
triplexer In radar, a device that facilitates the use communications, both the transmitting and
of two receivers at the same time. receiving antennas must be located within the
same duct, and this duct must be unbroken and
unobstructed between the two locations. A duct
C2 CR3
R1 might measure only a few feet from top to bot-
+ tom, but cover thousands of square miles
parallel to the surface. Compare TROPO-
Erms tropospheric propagation Also called tropo. Over-
+ the-horizon propagation of radio-frequency elec-
C1 tromagnetic waves that occurs as a result of
reflection, scattering, and/or refraction in the
’ troposphere, the lowest 10 or 12 miles of the
earth™s atmosphere. At wavelengths shorter than
about 15 m (frequencies above 20 MHz), refrac-
tion and reflection can take place within and be-
tripler, 1
tween air masses of different density. The air also
produces some scattering of EM energy at
Tri-state logic Digital logic in which there are wavelengths shorter than about 3 m (frequencies
three possible states, rather than the usual two. above 100 MHz). “Tropo” can often allow
The conditions are defined as 0, 1, and unde-
cided. Trade name of National Semiconductor.
tritium Symbol, T or H3. An isotope of hydrogen
whose nucleus contains two neutrons and one
proton. Compare DEUTERIUM.
TRL Abbreviation of transistor-resistor logic (see
Trojan horse A program written with the malicious
intent of sabotaging the operating system and/or
files in a computer. It is somewhat similar to a
VIRUS; it is occasionally spread via software
whose origin is questionable or unknown.
troposphere The portion of the atmosphere in
which virtually all weather phenomena occur. It
extends from the surface to an altitude of 8 to 12
miles above sea level.
696 tropospheric propagation • tuned circuit

communications over distances of several hun- truth table
dred miles. Also see TROPOSPHERIC BENDING,
(x + y)' + xz
SCATTER PROPAGATION. x y z x+y (x + y)' xz (x + y)' + xz
tropospheric-scatter propagation Also called tro- 0 0 0 0 1 0 1
poscatter. A form of tropospheric propagation 0 0 1 0 1 0 1
that occurs at frequencies above about 100 MHz, 0 1 0 1 0 0 0
where the atmosphere has a scattering effect on 0 1 1 1 0 0 0
radio waves. Dust in the air increases the scatter- 1 0 0 1 0 0 0
ing effect, but some troposcatter occurs regard- 1 0 1 1 0 1 1
less of the weather. Troposcatter takes place 1 1 0 1 0 0 0
mostly at low altitudes where the air is the most 1 1 1 1 0 1 1
dense. This mode can provide reliable communi-
cation over distances of several hundred miles
when the appropriate equipment is used. Com- TTL Abbreviation of TRANSISTOR-TRANSISTOR
LOGIC. (Also, T2L.)
munication via troposcatter requires the use of
high-gain antennas. Scatter is often observed TTT In radiotelegraphy, a signal indicating that a
along with other modes of tropospheric propaga- message concerning safety is to follow (equivalent

tion. Compare TROPOSPHERIC BENDING, to securite in radiotelephony).

troubleshoot 1. To look for the cause of equipment T-type antenna See TEE ANTENNA.
failure. 2. To look for flaws in computer software T-type attenuator See TEE PAD.
or to debug a program. tube 1. Generic term for any electron tube (e.g.,
troubleshooting test A test that is part of the pro- vacuum tube, gas tube, cathode-ray tube, X-ray
cedure for finding the cause of faulty electronic tube, etc.). 2. Glow lamp: argon bulb, neon bulb,
equipment operation. Also see DIAGNOSTIC mercury-vapor lamp, etc.
TEST. Compare PERFORMANCE TEST. tube capacitances The internal capacitances be-
trough value The minimum amplitude of a com- tween the elements of an electron tube.
posite current or voltage. tube diode A two-element (cathode and anode)

true complement See RADIX COMPLEMENT. electron tube for current rectification. Also see
true ground The earth, as opposed to an artificial DIODE.
ground, such as that provided by the radials of tube of flux A group of flux lines within a circular
a ground-plane antenna or an equipment cross section. It can vary in diameter as the den-
chassis. sity of the flux lines changes.
true power In an alternating-current (ac) circuit, tube parameters Operating coefficients of electron
the power actually dissipated in the resistive tubes (e.g., plate current, grid voltage, screen
component; the reactive component consumes no current, transconductance, amplification factor,
power. In ac circuits containing reactance, the etc.).
true power is less than the product of the voltage tube tester An instrument for checking one or
and current. Also see AC POWER and POWER more of the parameters of an electron tube.
FACTOR. tubular capacitor A fixed capacitor consisting of a
truncation A method of approximating a quantity wound section enclosed in a cylindrical can.
by cutting off its digits beyond a certain point. For tune 1. To adjust a selective circuit to accept or re-
example, 3.44 and 3.46, when truncated to two ject a signal. 2. To correct the natural frequency
significant digits, both become 3.4. Compare of vibration of a body. 3. To adjust a radio trans-
ROUNDING. mitter for optimum output. 4. To adjust the fre-
trunk 1. A communications link between two quency of an oscillator”especially in a radio
points, one usually being external. 2. The inter- transmitter or receiver. 5. To adjust the resonant
face between a central processing unit and a pe- frequency of an antenna, antenna coupler, or an-
ripheral device. tenna system.
trunk link In computer systems, an interface per- tuned AF amplifier 1. An audio amplifier that is
mitting access to main storage via a peripheral. continuously tunable over a band of frequencies.
truth table In logic analysis and logic circuit de- 2. An audio oscillator that is set to a fixed, precise
sign, a table in which are listed all combinations frequency. See, for example, PARALLEL-TEE AM-
of input values and the corresponding output val- PLIFIER.
ues for a given logic function. tuned-base oscillator A self-excited, common-
ts Abbreviation of tensile strength. emitter connected, bipolar-transistor oscillator in
Tschebyscheff filter See CHEBYSHEV FILTER. which the tuned tank is in the base circuit.
TSS Abbreviation of TIME-SHARING SYSTEM. tuned circuit A (usually series-resonant or paral-
T switch See TEE SWITCH. lel-resonant) circuit adjusted to accept or reject a
TST switch See TIME-SPACE-TIME SWITCH. signal. Also see RESONANCE.

tuned-collector oscillator • tunnel-diode amplifier

tuned-collector oscillator A self-excited, com- tuned signal tracer A signal tracer that can be
mon-emitter connected, bipolar-transistor oscil- tuned sharply to the frequency of the test signal
lator in which the tuned tank is in the collector being traced.
circuit. tuned transformer An audio-frequency or radio-
frequency transformer tuned via a capacitor in
parallel with its primary winding and/or a capac-
itor in parallel with it secondary winding.
tuner A circuit or device that can be set to select
one signal from a number of signals in a fre-
quency band.
tungsten Symbol, W. A metallic element. Atomic
number, 74. Atomic weight, 183.85. Also called
C3 wolfram. It is used in switch and relay contacts,
in the elements of some electron tubes, and in in-
candescent-lamp filaments.
tuning 1. Adjustment of the frequency of a receiver
to intercept a signal on a given frequency. 2. Ad-

justment of a transmitter oscillator to a desired
VCC frequency. 3. Adjustment of an inductance-
C1 R1 C2 capacitance circuit for resonance on a desired
R2 +
frequency. 4. Adjustment of an antenna or
antenna system to a desired frequency. 5. Adjust-
ment of a radio-frequency amplifier for optimum
performance. 6. Alignment of a musical instru-
ment for correct tone frequency.
tuned-collector oscillator tuning capacitor A variable capacitor used to tune
an inductance-capacitance circuit (series-
tuned coupler An antenna coupler (transmatch) resonant or parallel-resonant).
that can be adjusted independently of the trans- tuning coil A variable inductor used to tune an in-
mitter or receiver with which it is used. ductance-capacitance circuit (series-resonant or
tuned dipole A half-wave, center-fed, resonant an- parallel-resonant).
tenna. tuning core See TUNING SLUG.
tuned feeders An antenna feed line that is ad- tuning diode See VOLTAGE-VARIABLE CAPACI-
justed or trimmed so that the entire system (feed- TOR, 1.
ers and radiating element) is resonant at the tuning fork A metal device that vibrates at a pre-
transmitted-signal frequency. cise audio frequency when struck physically. It
tuned headphones Headphones used in radio-teleg- usually has two prongs and looks something like
raphy that are fix-tuned to a single audio frequency a fork.
(e.g., 1 kHz) by means of a small parallel capacitor. tuning-fork oscillator See FORK OSCILLATOR.
tuned line An antenna wire or transmission line tuning indicator 1. A meter or display that indi-
that provides a resistive load at a specific reso- cates when a receiver is properly tuned to the fre-
nant frequency. quency of an incoming signal. 2. Sometimes, a
tuned pickup A pickup circuit or device (such as a bridge null detector.
radio-frequency sampling coil) that is tuned to tuning meter A meter-type resonance indicator.
the signal frequency. tuning potentiometer A single or ganged poten-
tuned radio-frequency amplifier An amplifier cir- tiometer (depending on the circuit in which it is
cuit that is continuously tunable over a specific used) used to vary the frequency response of a
band of radio frequencies. resistance-capacitance-tuned circuit, such as
tuned radio-frequency receiver A radio receiver the bridge-tee, parallel-tee or Wien-bridge
consisting only of a tuned-radio-frequency ampli- circuit.
fier, detector, and audio amplifier. Compare SU- tuning slug A powdered-iron core that slides or
PERHETERODYNE RECEIVER. screws in and out of a coil to vary the inductance.
tuned reed A vibrating reed whose length, width, tuning voltage An adjustable direct-current volt-
and/or thickness have been adjusted so that it age used to vary the capacitance of a varactor
vibrates naturally at a desired frequency. diode (serving as the capacitor in a tuned circuit).
tuned-reed frequency meter An audio frequency tuning wand See NEUTRALIZING TOOL.
meter using tuned metal reeds as the indicators. tunnel diode A specially processed junction diode
Also see POWER FREQUENCY METER, 2. whose forward conduction characteristic displays
tuned relay An electronic or electromechanical re- negative resistance.
lay that closes at one frequency. See, for example, tunnel-diode amplifier A circuit that uses the
REED SWITCH, 1. negative-resistance properties of a tunnel diode
698 tunnel-diode amplifier • two-phase

to produce gain. It is used primarily at ultra-high to prevent its use by unauthorized viewers. See
and microwave frequencies. SUBSCRIPTION TV.
tunnel-diode oscillator A circuit that uses the TV ghost See GHOST.
negative-resistance properties of a tunnel diode TVI Abbreviation of TELEVISION INTERFERENCE.
to produce oscillation at a specific frequency. It is TVL Amateur radio abbreviation of television lis-
used primarily at ultra-high and microwave fre- tener (looker).
quencies. TVM Abbreviation of TRANSISTORIZED VOLT-
turbidimeter A device used to measure the turbid- METER.
ity (relative opaqueness) of liquids. TVO Abbreviation of TRANSISTORIZED VOLT-
turbidity meter See TURBIDIMETER. OHMMETER. (Also, TVOM.)
Turing machine A hypothetical model, conceived TVOM Abbreviation of TRANSISTORIZED VOLT-
by Alan Turing in the 1930s, devised as an exer- OHMMETER. (Also, TVO.)
cise in problem solving. In effect, it was a com- TV projector A combination electronic and optical
puter programming language with a limited device for projecting television images on a large
instruction set, operating in a computer with infi- screen.
nite memory and storage capacity. TV sound marker See SOUND MARKER.
Turing test A scheme devised by Alan Turing, de- TVT Abbreviation of television terminal (computer
signed to test computers for artificial intelligence peripheral).
(AI). If the machine can fool a person into think- TW Abbreviation of TERAWATT.
ing it is another person most of the time, then the TWA Abbreviation of TRAVELING-WAVE AMPLI-
machine in effect “passes” the test, indicating FIER.
that it has some AI. tweeter A loudspeaker that favors the extreme tre-
turn One complete loop of a coil. ble (high) audio frequencies, ranging from 4000
turnaround time 1. The length of time required for or 5000 Hz to more than 20,000 Hz. Compare
a repair to be performed. 2. The length of time re- WOOFER.
quired for a computer program to be completed. twin diode See DUAL DIODE.
3. The time required for a trans-ceiver to switch twinlead See FLAT-RIBBON LINE.
from the full-transmit to the full-receive condition. twin line See FLAT-RIBBON LINE.
turn factor For a given inductor core, the number twin meter See DUAL METER.
of turns (in a standard configuration) that results twin-T measuring circuit See PARALLEL-TEE
in an inductance of 1 H. MEASURING CIRCUIT.
turn-off time The time required for the operation twin-T network See PARALLEL-TEE NETWORK.
of a circuit or device to cease completely after a twisted pair A simple wire line used for communi-
signal or operating power has been removed. cations. It consists of two wires twisted together
Compare TURN-ON TIME. to form a helix.
turn-on time The time required for a circuit or de- twister A piezoelectric crystal, such as one of
vice to come up to full (normal) operation after Rochelle salt, that generates a voltage when
application of a trigger or operating power. Com- torqued.
pare TURN-OFF TIME. twistor A magnetic-memory element consisting of
turnover pickup See DUAL PICKUP. a winding of magnetic wire on a length of non-
turns ratio For a transformer, the ratio of the magnetic wire.
number of turns in the primary winding to the two-channel amplifier See DUAL-CHANNEL AM-
number of turns in the secondary winding. PLIFIER.
turnstile antenna A polyphase antenna that re- two-channel recorder See DOUBLE-CHANNEL
sembles a turnstile gate. RECORDER.
turntable 1. The motor-driven, rotating platter on two-electrode amplifier See DIODE AMPLIFIER.
which a phonograph disc rests during recording two-electrode tube See TUBE DIODE.
or reproduction. 2. In a high-fidelity phonograph two-element amplifier See DIODE AMPLIFIER.
system, the assembly containing the platter, as two-element beam A Yagi antenna consisting of a
defined in 1. driven element and one parasitic element. The
turret tuner A television front-end tuner having a parasitic element can be either a reflector, about
separate tuned-circuit section for each channel. 5% longer than the resonant half wavelength at
Turning a knob rotates a desired section into po- the operating frequency, or it can be a director,
sition against switch contacts. Also called DE- about 5% shorter than a half wavelength at the
TENT TUNER. operating frequency.
TV 1. Abbreviation of TELEVISION. 2. Abbreviation two-element tube An electron tube having two
of terminal velocity. principal electrodes (i.e., a tube diode).
T/V Abbreviation of temperature to voltage. two-five code See BIQUINARY CODE.
TV decoder A device for unscrambling a television two-phase Pertaining to circuits or devices in
broadcast that has been intentionally encrypted which two components (two voltages, two
two-phase • Type A telephone line

two-state device A device having two stable states
(e.g., a flip-flop).
two-state logic Digital logic in which there are two
Boom Boom possible conditions (called high and low, true and
false, or 1 and 0).
two-tone keying See FREQUENCY-SHIFT KEY-
two-track recording Recording on two adjacent
tracks on magnetic tape. The separate recordings
Driven Director Reflector Driven
can be in the same direction (as in stereo) or in
element element
opposite directions.
two-way amplifier An amplifier whose input and
two-element beam
output terminals can be used interchangeably.
two-way communication The exchange of mes-
currents, or a current and a voltage) are 90° out sages between two or more stations that transmit
of phase with each other. as well as receive. Compare ONE-WAY COMMU-
two-phase system See QUARTER-PHASE SYSTEM. NICATION, 1.
two-phase, three-wire circuit A circuit using three two-way radio 1. Any form of TWO-WAY COMMU-
conductors, one of which (the common return) is NICATION using electromagnetic waves. 2. A ra-
90° out of phase with the other (outer) two. dio transceiver”especially one used for voice
two-pincher gripper A simple robotic end effector communication at very-high or ultra-high fre-
using two tongs, and resembling large tweezers or quencies.
needle-nosed pliers. It grasps objects by “pinch- two-way repeater In telephony, a device that am-
ing” them. plifies and retransmits a signal in either direc-
two-point tuning See DOUBLE-SPOT TUNING. tion. Also see TWO-WAY AMPLIFIER.
two-space A two-dimensional mathematical con- two-way speaker A woofer/midrange speaker and
tinuum in which each point is uniquely defined a tweeter occupying the same enclosure, and in-
by two variables in an ordered pair, such as (x,y), terconnected by a crossover network for wide-
and each ordered pair corresponds to exactly one band frequency response.
point in the continuum. A common scheme is the TWT Abbreviation of TRAVELING-WAVE TUBE.
Cartesian coordinate system; another scheme is TWX Abbreviation of TELETYPEWRITER EX-
the polar coordinate system. See CARTESIAN CHANGE.
COORDINATES and POLAR COORDINATES. Twystron A form of microwave-oscillator tube,
two-space coordinates A coordinate system for similar to the Klystron.
defining points in two-space. See CARTESIAN Type A telephone line A telephone line serving
COORDINATES and POLAR COORDINATES. one subscriber (as opposed to a party line).
U 1. Symbol for URANIUM. 2. Abbreviation of UHF capacitor A button-type capacitor. Because
UNIT. of its unique design, it is an efficient bypass ca-
u Symbol (ital.) for UNIFIED ATOMIC MASS UNIT. pacitor at ultrahigh frequencies.
Ua Abbreviation of unit of activity (electro- UHF converter 1. A circuit, usually consisting of a
encephalography). radio-frequency amplifier and mixer, for convert-
UAM Abbreviation of underwater-to-air missile. ing ultra-high-frequency (UHF) signals to a lower
ubiquitous carrier A current carrier (especially an band of frequencies. 2. A circuit for converting
electron) whose velocity is so high, or mechanism UHF television signals to very-high-frequency
of transfer so subtle, that it appears to be in two (VHF) signals so that they can be accommodated
places simultaneously. Thus, in the tunnel diode, by an older (VHF only) television receiver. See
during the interval of tunneling a single electron, UHF TELEVISION CHANNELS and VHF TELEVI-
appears to be on both sides of the barrier at the SION CHANNELS.
same time.
Ubitron A tube in which a periodic magnetic field
causes an electron beam to undulate. Through its UHF
transverse velocity component, the beam inter- in
acts with a radio-frequency wave, and its kinetic
energy is converted into radio-frequency energy.
The ubitron can be used as an amplifier or oscil-
UDC Abbreviation of universal decimal classifica- Mixer out
amp. amp.
UDOP Abbreviation of ultra-high-frequency Dop-
pler. A 440-MHz phase-coherent tracking system
used to determine the velocity and position of
missiles and space vehicles. Osc.
UEP Abbreviation of underwater electric potential.
UFET Abbreviation of unipolar field-effect transis-
tor. (Also, UNIFET.) See UNIPOLAR TRANSISTOR. UHF converter, 1
UG Abbreviation of underground.
UHF Abbreviation of ULTRAHIGH FREQUENCY. UHF diode A semiconductor diode whose rectifica-
UHF adaptor See UHF CONVERTER, 1. tion efficiency is good at ultra-high frequencies.

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UHF generator • ultra-low frequencies

UHF generator 1. An oscillating device (such as a ultimate ratio The limiting value of a ratio (i.e., the
transistor, tunnel diode, Klystron, or magnetron) value approached by a ratio).
used to produce radio-frequency energy at ultra- ultimate sensitivity 1. In an instrument or sys-
high frequencies (UHF). 2. The equipment in tem, the maximum degree of perception of, or re-
which such a device is used. 3. An ultra-high- sponse to, a quantity or condition. 2. In a graphic
frequency test-signal generator. recorder, half the deadband.
UHF loop A (usually single-turn) loop antenna with ultimate threshold See ULTIMATE SENSITIVITY,
a toroidal radiation pattern perpendicular to the 2.
loop; the antenna has a natural wavelength in the ultimate trip current For a specified set of envi-
ultra-high-frequency (UHF) range. ronmental conditions, the lowest value of current
UHF receiver A receiver tunable to frequencies in that will trip a circuit breaker.
any band in the range 300 MHz to 3000 MHz. ultimate trip limits For a circuit breaker, the
UHF television channels Television channels 14 maximum and minimum current at which the
through 69, whose frequencies lie in the ultra- breaker trips and drops out.
high range. ultor anode The second anode of a television pic-
UHF transistor A transistor specially designed and ture tube or oscilloscope tube.
fabricated for ultra-high-frequency (UHF) opera- ultor element In a television picture tube, the ele-
tion. It is characterized by extended beta cutoff ment that receives the highest direct-current
frequency, low junction capacitance, and fast re- voltage. Also called ultor electrode. Also see UL-
covery time. TOR ANODE.
UHF translator A television broadcast translator ultor voltage The high direct-current voltage ap-
station transmitting in an ultra-high-frequency plied to the second anode of an oscilloscope tube or
(UHF) channel. television picture tube. Also see ULTOR ANODE.
UHF transmitter A transmitter that is specially ultra- A prefix meaning above, larger than, greater
designed for operation at ultra-high frequencies. than, or higher than. See the following several def-
In such a transmitter, stray parameters are min- initions for examples.
imized and special tubes or transistors are re- ultra-atomic Pertaining to particles smaller than
quired. atoms (i.e., SUBATOMIC).
UHF tube A vacuum tube specially designed for ul- ultra-audible frequency A frequency higher than
tra-high-frequency operation. It is characterized the highest audible frequency. Also called ULTRA-
by low interelectrode capacitance, low input and SONIC FREQUENCY and supersonic frequency.
output capacitances, short electron transit time, ultra-audion oscillator See ULTRAUDION OSCIL-
and low lead inductance. LATOR.
UHF tuner 1. A superheterodyne receiver front end ultracentrifuge A centrifuge that spins at a very
tunable in the ultra-high-frequency (UHF) range. high speed.
It is usually arranged to deliver the mixer output ultrafast switch An electronic switch capable of
to a lower-frequency receiver. 2. A television re- microsecond operation.
ceiver front end tunable to the UHF channels. Ultrafax A system for high-speed transmission of
UHR Abbreviation of ULTRA-HIGH RESISTANCE. printed matter by facsimile, radio, or television.
U index The difference between consecutive daily ultra-high frequency A radio frequency in the
mean values of the horizontal component of the range 300 MHz to 3000 MHz, corresponding to
geomagnetic field. free-space wavelengths between 1 meter and
UJT Abbreviation of UNIJUNCTION TRANSISTOR. 10 centimeters.
UL 1. Abbreviation of UNDERWRITERS LABORA- ultra-high-frequency band See UHF BAND.
TORIES. 2. Abbreviation of ULTRALINEAR. ultra-high resistance Resistance of 100 meg-
ULD Abbreviation of ULTRA-LOW DISTORTION. ohms or higher.
ULF Abbreviation of ULTRA-LOW FREQUENCY. ultra-large-scale integration An integrated-circuit
U-line section A short section of coaxial cable or process that goes several orders of magnitude
hardline having the shape of a squared U. beyond VERY-LARGE-SCALE INTEGRATION.
More than 4 — 106 transistors could be on a single
ultimate attenuation The maximum attenuation chip.
in a circuit or device when it is operated outside ultra-linear Pertaining to the most linear operation
its passband, or within its stopband. obtainable with state-of-the-art electronic equip-
ultimately controlled variable In an automated ment.
system, the quantity or operation (e.g., liquid ultra-linear amplifier A high-fidelity audio-
level, temperature, pressure, precision drilling, frequency power amplifier having wide frequency
etc.), whose control is the end purpose of the sys- response and very low distortion.
tem. ultra-low distortion Total harmonic distortion
ultimate-range ballistic missile A ballistic missile (THD) of less than 0.1 percent.
whose range is greater than half the earth™s cir- ultra-low frequencies 1. Radio frequencies be-
cumference (approximately 12,000 miles). tween 300 Hz and 3 kHz, pertaining to
702 ultra-low frequencies • ultrasonic light diffraction

wavelengths between 1000 kilometers and 100 ful in situations where other techniques, such as
kilometers. 2. Audio frequencies lower than those radiology or the use of catheter probes, are risky.
in the human hearing range. Also see ULTRASOUND.
ultramicrometer An electronic instrument for ex- ultrasonic disintegrator In biology and related
tremely small linear measurements. fields, a device that uses ultrasonic energy to rup-
ultramicroscope An optical microscope using re- ture or shatter cells, tissues, or foreign bodies,
fracted light to illuminate minute particles. such as kidney stones.
ultramicrowave Pertaining to wavelengths in the ultrasonic drill A drill running at speeds corre-
range 10-3 to 10-6 meter (300 GHz to 300 THz). sponding to ultrasonic frequencies. The tool is
ultraminiature See SUBMINIATURE. valuable in drilling hard or brittle materials and
ultraphotic rays Collectively, infrared and ultravi- in dentistry.
olet rays. ultrasonic filter 1. A bandpass filter whose opera-
ultrared rays See INFRARED RAYS. tion is based on the natural (ultrasonic) vibration
ultra-short waves Waves whose length correspond frequency of small disks or rods of magnetostric-
to ultra-high frequencies (i.e., wavelengths be- tive metal. See MAGNETOSTRICTION. Also called
tween 0.1 and 1 meter). mechanical filter. 2. Generally, a filter operating
ultrasonic Of higher frequency than those that are at ultrasonic frequencies.
audible (supersonic). See, for example, ULTRA- ultrasonic flaw detector A system analogous to
SONIC FREQUENCY. radar, in which an ultrasonic wave is transmitted
ultrasonic bonding A method of bonding metal by through a solid material and is reflected back to a
means of physical vibration at frequencies above detector and display device to reveal flaws,
the human hearing range. cracks, and strain in the material.
ultrasonic brazing Forming a nonporous bond be- ultrasonic frequency For an acoustic distur-
tween metal parts through the use of ultrasonic bance, any frequency above the limit of human
energy and a second, different metal (or alloy) hearing (higher than 20 kHz).
having a lower melting point. ultrasonic generator 1. An oscillator that operates
ultrasonic cleaning A method of cleaning delicate at frequencies above the range of human hearing,
or intricately structured items (such as dentures, and the output of which is intended for coupling
contact lenses, or jewelry) in which the soiled to an electroacoustic transducer. 2. Any device
items are immersed in a fluid that is agitated by that produces ultrasonic waves.
ultrasonic transducers; the foreign particles are ultrasonic grating constant For a sound wave
shaken away. producing a diffraction spectrum, a figure indi-
ultrasonic cleaning tank A thick-walled stainless- cating the distance between diffracting centers of
steel tank with ultrasonic transducers mounted the wave.
within its walls and used for ultrasonic cleaning. ultrasonic heating The production of heat in a
ultrasonic coagulation The coagulation of a sub- specimen by means of ultrasonic energy directed
stance through ultrasonic agitation. into or through it.
ultrasonic communication Underwater tele- ultrasonic image converter A device that makes
graphic communication between ships and/or visible acoustic field patterns.
submarines by keying the echo-ranging sonar ultrasonic inspection The use of ultrasonic waves
equipment. to detect internal flaws in solid materials, such as
ultrasonic delay line A delay line, such as the metals. It is valued particularly because it is non-
mercury type, through which an ultrasonic signal destructive. Also see ULTRASONIC FLAW DE-
is propagated. The delay results from the rela- TECTOR.
tively slow propagation of the ultrasonic wave ultrasonic intrusion alarm A security system ac-
through the substance in the line. tivated when an intruder disturbs a pattern of ul-
ultrasonic densitometer A density-measuring ap- trasonic waves in the protected area; a sensitive
paratus whose operation is based on the time re- relay closes, setting off an alarm.
quired for an ultrasonic signal to penetrate the ultrasonic level detector A level-monitoring sys-
material under test, or for the signal to penetrate tem in which an ultrasonic transmitter and de-
the material and be reflected back to the trans- tector are mounted together on one wall of a tank
mitter. or chamber. When the tank is empty, the trans-
ultrasonic depth finder See ACOUSTIC DEPTH mitted signal is reflected by the opposite wall
FINDER. back to the detector. When the liquid rises, the
ultrasonic detector A device that responds to ul- reflection time is reduced; this change is used to
trasonic waves by indicating their presence, in- operate a device that indicates that the tank has
tensity, and/or frequency. been filled to a desired level.
ultrasonic diagnosis The medical determination of ultrasonic light diffraction Diffraction resulting
the condition of tissues or structures within the from the periodic variation of light refraction
body, in terms of reflection of ultrasonic waves by when a beam of light passes through a longitudi-
those tissues or structures. The technique is use- nal sound-wave field.
ultrasonic light modulator • ultraviolet altimeter

of the propagation time (or echo time) of ultra-
alarm sonic waves through the specimen.
ultrasonic transducer A transducer that converts
electrical energy into ultrasonic energy, or vice-
versa. Common types are the quartz crystal, ce-
ramic crystal, and magnetostrictive disk.
ultrasonic waves Acoustic waves whose length
corresponds to ultrasonic frequencies (i.e., fre-
Osc. Amp.
quencies above 20 kHz).
ultrasonic welding A below-melting-point tech-
nique of joining two metallic bodies by clamping
them tightly together and applying ultrasonic en-
ergy, rather than heat, in the plane of the desired
ultrasonic whistle A whistle whose pitch is be-
Moving yond the range of human hearing. Although some
objects are of the simile (blown) type, others are (usually
miniature) electronic sound generators. These de-
vices can be used for the remote control of televi-
ultrasonic intrusion alarm
sion receivers, garage-door openers, and other
ultrasonic light modulator A device that modu- ultrasonography A method of examining human
lates a light beam passing transversely through a tissues or organs by transmitting ultrasonic
fluid agitated by sound waves. waves into the body and receiving the echoes.
ultrasonic material dispersion The use of the ag- ultrasound 1. Acoustic disturbances at frequen-
itative action of high-intensity ultrasonic waves cies above 20 kHz. 2. See ULTRASONIC FRE-
to disperse or emulsify one substance in another. QUENCY. 3. See ULTRASONOGRAPHY.
ultrasonic plating The use of ultrasonic energy to ultraviolet 1. Electromagnetic radiation at wave-
deposit or bond one material onto the surface of lengths somewhat shorter than those of visible
another. light. Longwave or near ultraviolet extends from
ultrasonic probe A rodlike director of ultrasonic approximately 390 nanometers (nm) down to
energy. 50 nm. Shortwave or far ultraviolet extends from
ultrasonic relay An electronic relay actuated by 50 nm down to 4 nm. 2. Pertaining to the behav-
ultrasound. ior and effects of electromagnetic radiation in the
ultrasonics 1. The use of high-frequency acoustic range of approximately 390 nm to 4 nm.
energy in industry, medicine, research, and the
use of high-frequency acoustic energy for medical 100
X rays
diagnosis and treatment. 3. The branch of
physics dealing with the effects and behavior of
Wavelength (angstroms)

acoustic disturbances at frequencies above the Far ultraviolet
range of human hearing.
Near ultraviolet
ultrasonic soldering See ULTRASONIC BRAZING.
ultrasonic sounding Determining the depth of a Visible light
body of water in terms of the time taken for a
transmitted ultrasonic signal to be reflected back 105
to a transmitting point on the surface of the water.
ultrasonic space grating A periodic variation in
the index of refraction when acoustic waves are 107

present in a light-transmitting medium. Also see EHF
Radio waves
ultrasonic storage cell See ULTRASONIC DELAY
ultrasonic stroboscope A stroboscope that uses 1010
an ultrasonically modulated beam of light.
ultrasonic switch An electronic switch actuated ultraviolet
by ultrasound.
ultrasonic therapy The use of ultrasonic energy in
medicine for treatment of certain disorders. ultraviolet altimeter An altimeter that uses ultra-
ultrasonic thickness gauge An instrument that violet rays instead of radio waves to determine the
determines the thickness of a specimen in terms altitude of an aircraft or spacecraft.
704 ultraviolet lamp • unblanking interval

ultraviolet lamp A lamp that delivers ultraviolet unattenuated Not reduced in intensity of ampli-
rays. Common types are arc lamps and mercury- tude. Thus, an unattenuated signal is one that
vapor lamps. has retained its original strength during its trans-
ultraviolet light See ULTRAVIOLET RAYS. mission through a system.
ultraviolet power The power (in watts) of ultravio- unavailable energy The difference between the
let radiation. quantity of heat energy supplied to a system and
ultraviolet rays Radiation at frequencies in the ul- the available energy of the system.
traviolet region (i.e., between the highest visible- unbalance 1. Lack of balance or symmetry in a cir-
light frequencies and the lowest X-ray frequencies). cuit, line, or system. 2. The condition in which a
ultraviolet therapy The use of ultraviolet rays by bridge (or the equivalent) is not nulled.
physicians and other health personnel in the unbalanced circuit See SINGLE-ENDED CIRCUIT.
treatment of certain disorders. unbalanced delta system A three-phase circuit in
ultraviolet wavelength The wavelength range of which the elements are connected in a triangular
ultraviolet radiation [e.g., 390 nanometers (nm) (delta) configuration, but are of unequal
to 4 nm]. impedance. In an unbalanced delta system, no
ultraviolet waves See ULTRAVIOLET RAYS. definite relationship exists between line and
umbilical cord 1. A cord through which missiles phase currents. Compare BALANCED DELTA
and rockets are controlled and powered until they SYSTEM.
are launched. 2. A cord connecting an astronaut unbalanced input See SINGLE-ENDED INPUT.
to his space vehicle during extravehicular activity unbalanced line 1. A transmission line in which
(e.g., during a space “walk”). one side (conductor) is grounded (e.g., a coaxial
umbilical tower The vertical tower supporting the line). 2. A normally balanced transmission line in
umbilical cords extending to a rocket in the which the currents in the two halves are out of
launch position. balance (i.e., they are not equal in amplitude and
umbra 1. The region of total (conical) shadow be- opposite in phase).
hind an object situated in the path of a radiation. unbalanced multivibrator A multivibrator in
2. The comparatively dark central region in a which the time constant of one base or gate cir-
sunspot. cuit differs from that of the other base or gate cir-
umbrella antenna An antenna consisting of a cuit. The asymmetry results in short-duration
number of wires, extending from the top of a ver- output pulses separated by long time periods.
tical mast to points on a circle below, at the cen- unbalanced output See SINGLE-ENDED OUTPUT.
ter of which the mast is mounted. The wires are unbalanced two-phase system A two-phase cir-
usually fed in parallel from the top. cuit in which the load elements are of unequal
Umklapp process A process responsible for ther- impedance.
mal resistance in nonconducting materials. It re- unbalanced wire circuit A wire line whose (two)
sults from collision between phonons, or sides are dissimilar.
phonons and electrons. unbalanced-wye system A three-phase circuit in
UMW Abbreviation of ULTRAMICROWAVE. which the elements are connected in the familiar
unabsorbed field strength The field strength with wye, or star, configuration, but are of unequal
no absorption between transmitter and detector. impedance.
The unabsorbed field strength is an ideal quan- unbalanced-Y system See UNBALANCED-WYE
tity; the actual field strength over a given distance SYSTEM.
is always less. It is expressed in volts per meter. unbalance-to-balance transformer A transformer
unamplified back bias A negative-feedback volt- for matching an unbalanced transmission line to
age developed across a fast-time-constant circuit a balanced line (e.g., a coaxial line to a parallel-
within a single amplifier stage. wire line).
unamplified feedback A positive or negative cur- unbiased limiting Peak limiting that results from
rent or voltage taken from the output of a system overdriving an unbiased active device.
and presented to the input without being boosted unbiased unit A device or circuit operated without
through auxiliary amplification. bias [e.g., a transistor without base bias (common
unamplified ALC Automatic level control (ALC) in emitter and emitter follower) or emitter bias (com-
which the control-signal voltage is taken from a mon base)].
point in the circuit and fed to the controlled point unblanking Removal of the blanking pulse in a
without being boosted by an auxiliary amplifier. cathode-ray-tube circuit (i.e., turning on the
Compare AMPLIFIED ALC. beam).
unattended operation Operation, as of an elec- unblanking generator A (usually pulse-type) sig-
tronically programmed machine, with minimal (or nal source for turning on the beam of a blanked
no) human supervision. cathode-ray tube.
unattended time The period, excluding down time unblanking interval The period during which the
for repair or checkout, during which a computer beam of a cathode-ray tube is turned on. Com-
is unpowered. pare BLANKING INTERVAL.
unblanking pulse • unconditional jump

unblanking pulse A pulse that turns on the beam uncased transformer See UNSHIELDED TRANS-
of a blanked cathode-ray tube. Compare BLANK- FORMER.
ING PULSE. uncertainty in computation The degree of doubt
unblanking time 1. See UNBLANKING INTERVAL. concerning the exactness of computations. This
2. The instant at which unblanking begins. uncertainty is always greater than that of the
unbonded strain gauge A strain gauge that is not roughest measurement used in obtaining data for
directly attached (by cement, for example) to the the computation. Uncertainty is closely related to
strained surface. the tolerance of the instruments and formulas
unbound electron A free electron (i.e., an electron used.
not confined to a shell within an atom). uncertainty in measurement The estimated max-
unbuffered output An output (signal, power, etc.) imum amount whereby the numerical value of a
that is delivered directly from the generating de- measured quantity can differ from the true value.
vice without the benefit of an isolating stage, uncertainty principle The observation that high
such as a buffer amplifier. Compare BUFFERED precision in the location of an electron is obtain-
OUTPUT. able only at a sacrifice in the accuracy with which
unbypassed emitter resistor In a common-emit- the momentum of the electron can be deter-
ter transistor circuit, an emitter resistor without mined, and vice versa.
a bypass capacitor. The flow of output-signal cur- uncharged Without an electric charge, as opposed
rent through the resistor produces negative feed- to discharged (depleted of a charge).
back within a single stage. unclamp To switch off clamping action in a circuit.
uncoated filament 1. A plain filament (i.e., one
’VCC without a coating of electron-increasing material).
2. A stripped filament (i.e., one from which the
electron-increasing coating has been burned off).
uncompensated Not modified to produce a desired
type of performance, such as increased band-
width or reduced temperature sensitivity. Exam-
ple: an uncompensated amplifier put into service
in the (wide) video band. Compare COMPEN-
Output uncompensated amplifier An amplifier without a
provision for the automatic or manual modifica-
tion or correction of its response. Compare COM-
uncompensated capacitor A fixed or variable ca-
pacitor without a provision for the automatic or
manual correction or modification of its capaci-
unbypassed emitter resistor (RE ) tance or range or the improvement of its tem-
perature coefficient. Compare COMPENSATED
unbypassed source resistor In a common-source uncompensated inductor A fixed or variable in-
field-effect transistor circuit, a source resistor ductor without a provision for the automatic or
without a bypass capacitor. The flow of output- manual correction or modification of its induc-
signal current through the resistor produces neg- tance or range or the improvement of its temper-
ative feedback within a single stage. ature coefficient.
uncage In a displacement gyroscope system, to uncompensated resistor A fixed or variable resis-
disconnect the erection circuit. tor without a provision for the automatic or man-
uncalibrated unit A component, circuit, or instru- ual correction or modification of its resistance or
ment that has never been calibrated or has not range or the improvement of its temperature coef-
recently been calibrated and, hence, is of ques- ficient.
tionable accuracy. unconditional branch See UNCONDITIONAL
uncanny valley According to a theory put forth by JUMP.
certain Japanese roboticists, a phenomenon that unconditional jump In computer operations, a pro-
can occur among people as technology advances. gram instruction that interrupts, without a rela-
As machines rapidly get more sophisticated, a tional test being made, the normal, ordered
point is reached at which their human users be- sequence of instructions and gives the address of
come unnerved, partially offsetting the advan- (usually) the first instruction in a subroutine [e.g.,
tages the technology has to offer. BASIC™s GOTO (line number)]. Also called uncondi-
uncased choke See UNSHIELDED CHOKE. tional branch. Compare CONDITIONAL JUMP.
706 unconditional stability • underloaded amplifier

unconditional stability Stability of a system at all undercurrent relay A relay that is actuated when
frequencies and ages. Also called absolute coil current falls below a predetermined level.
stability. undercut The removal of the metal under the edge
unconditional transfer See UNCONDITIONAL of the resist in a printed circuit by the etchant;
JUMP. thus the cross section of the conductor is re-
uncontrolled multivibrator A multivibrator that duced.
is not synchronized with a signal source. Also undercutting A phonograph-disc groove that is
called ASTABLE MULTIVIBRATOR and FREE- cut too shallow or with reduced internal move-
RUNNING MULTIVIBRATOR. ment of the recording stylus.
uncontrolled oscillator See SELF-EXCITED OS- underdamping Insufficient damping of a system
CILLATOR. (i.e., not enough to prevent output oscillation fol-
uncorrected power In an alternating-current cir- lowing application of a transient force).
cuit, a power value calculated without regard for underdriven unit An amplifier, oscillator, or
power factor (i.e., the volt-ampere product). transducer whose driving signal (current, voltage,
uncorrected time Local standard time that has power, or other quantity) is lower than the pre-
not been corrected in terms of the distance of the scribed value. Compare OVERDRIVEN UNIT.
locality from the nearest standard-time meridian. underexcited Receiving lower-than-normal excita-
uncorrected tube A television picture tube oper- tion, as in an underdriven final amplifier of a ra-

ated without antipincushioning magnets. dio transmitter. Compare OVEREXCITED.
uncoupled mode A mode of vibration existing in a underflow In computer operations, the condition

system concurrent with (but independent of) in which a quantity entered into storage is
other modes. shorter than the space provided for it (e.g., a 12-
undamped galvanometer A galvanometer for digit quantity in a 16-position register).
which no provision has been made to limit over- underground antenna A transmitting or receiving
swing or prevent oscillation. antenna installed and operated below ground. In-
undamped meter 1. A meter for which no provi- cluded are buried antennas and antennas on
sion has been made to limit overswing or prevent equipment operated in tunnels, cellars, and sim-
oscillation. 2. A meter that is unprotected by a ilar areas.
short circuit for limiting vibratory movement of underground cable A cable that is buried in the

the pointer during transport. earth.
undamped natural frequency In the absence of underground communication Communication
damping, the oscillation frequency of a system between a transmitter and receiver, both below
having one degree of freedom when a transient the surface of the earth.
force displaces the system momentarily from its underground image The below-ground mirror im-
position of rest. age of an antenna; it combines with the actual
undamped oscillation Continuous-wave oscilla- antenna to form the complete radiation pattern.
tion. Also see CONTINUOUS WAVE. underground line A power line laid below the sur-
undamped output circuit An audio power-ampli- face of the earth.
fier output circuit that has not been designed so underground receiver 1. A receiver situated com-
that overswing of the loudspeaker cone is pre- pletely below the surface of the earth. 2. A clan-
vented. destine receiver.
undamped speaker enclosure A loudspeaker cabi- underground reception Reception of an above-
net for which provision has not been made to ground station™s transmissions by an under-
deaden resonances and other undesired vibration. ground receiver. Compare UNDERGROUND
undeflected beam A cathode-ray beam or a light underground transmitter 1. A transmitter situ-
beam in its normal position of rest (quiescence). ated completely below the surface of the earth. 2.
underbiased unit A component, such as a transis- A clandestine transmitter.
tor or vacuum tube, whose bias voltage or current under insulation The insulation (usually a strip of
is lower than the prescribed value. Compare tape) laid under a wire brought up from the cen-
OVERBIASED UNIT. ter of a coil.
underbunching Less-than-optimum bunching of underinsulation Inadequate or insufficient insula-
electrons in a velocity-modulated tube because of tion.
lowered buncher voltage. underlap In a facsimile or television picture, a
undercompounded generator A generator in crowding of the scanned lines.
which the output voltage varies inversely with underload circuit breaker See CIRCUIT BREAKER.
load resistance. underloaded amplifier 1. An amplifier whose load
undercoupling Loose coupling, usually of an resistance (impedance) is less than the pre-
amount insufficient for optimum signal transfer. scribed value. 2. A power amplifier delivering less
undercurrent A current of lower than specified than its rated output power. Compare OVER-

underload relay • unequal alternation

underload relay A relay actuated when circuit cur- underwater antenna A transmitting or receiving
rent drops below a predetermined value. Com- antenna normally operated in a body of water. It
pare OVERLOAD RELAY. is usually associated with a submarine.
undermodulation Incomplete modulation of a car- underwater sound projector A hydroacoustic
rier wave. Compare COMPLETE MODULATION transducer that converts audio-frequency power
and OVERMODULATION. into sound waves, which it radiates through a
underpass The crossing of two conductors on a body of water to a receiver.
semiconductor wafer, without an electrical con- Underwriters Code The advisory National Electri-
nection. cal Code adopted by the National Fire Protection
underpower relay A relay actuated when power Association; it is often enforced by courts of law
drops below a predetermined level. Compare and inspection agencies.
OVERPOWER RELAY. Underwriters Laboratories Abbreviation, UL. A
underrate To assign a rating (e.g., current or private corporation that issues standards of
power) lower than the quantity of the rating an safety for electrical components and equipment,
equipment can handle, or tolerate. For safety or and for their operation.
reliability, apparatus sometimes is deliberately undistorted power output For active amplifier de-
underrated”especially in power output and max- vices, a specified maximum audio power output
imum current or voltage. level at which the total distortion does not exceed
undershoot On an oscilloscope screen or graph, a a specified low value (i.e., at which operation is
momentary swing of a current or voltage below practically distortionless).
the reference axis. Compare OVERSHOOT. undistorted wave 1. A sine wave that contains es-
sentially no harmonic energy. 2. A nonsinusoidal
wave whose shape corresponds exactly to the
equation for the wave.
undisturbed-one output In digital-memory opera-
tions, the one-output of a magnetic cell or other
Relative amplitude

memory unit that has received a full, rather than
partial, read pulse. Compare UNDISTURBED
undisturbed output signal In digital-memory op-
erations, the output of a magnetic cell or other
memory unit previously set to one or zero, and
that has received a full, rather than partial, read
Undershoot pulse. Also called undisturbed response voltage.
undisturbed response voltage See UNDIS-
undisturbed-zero output In digital-memory oper-
undershoot ations, the zero-output of a magnetic cell or other
memory unit that has received a full, rather than
partial, read pulse. Compare UNDISTURBED
undershoot distortion Distortion caused by re- OUTPUT SIGNAL.
duction of the maximum amplitude of a signal Universal Truth Machine (UTM) A hypothetical
wavefront below the steady-state amplitude that computer capable of proving any logically true
would be reached by a prolonged signal wave. statement. According to the Incompleteness The-
understudy See BACKUP. orem proved in 1930, such a machine cannot ex-
underthrow A form of signal distortion that occurs ist for a first-order logical system.
when the modulating-waveform frequency is too undoped Pertaining to a pure semiconductor ma-
high in proportion to the frequency of the wave it- terial (i.e., one containing no lattice-altering addi-
self. tives).
undervoltage A voltage of lower than specified undulating current A current, such as an alter-
value. Compare OVERVOLTAGE. nating or composite current, whose value oscil-
undervoltage protection The automatic discon- lates in the manner of a wave.
nection of a load device from its driving source undulation A wavelike alternation.
when the driving voltage falls below a predeter- undulatory theory The theory that light is transmit-
mined (threshold) level. This action is sometimes ted by means of an undulating (wavelike) move-
accomplished with a Zener diode (whose break- ment between the luminous object and the eye.
down voltage is equal to the threshold voltage) in unequal alternation In an alternating-current
series with a disconnect relay. waveform, a form of asymmetry in which the pos-
undervoltage relay A relay actuated when voltage itive and negative half-cycles are not exact mirror
drops below a predetermined level. Compare images; they might vary in peak amplitude, dura-
OVERVOLTAGE RELAY. tion, shape, etc.
708 unexpected halt • unidirectional response

Unicode Trade name for a 16- or 32-bit binary dig-
ital code that allows for the representation of
characters and glyphs in all the written lan-
guages of the world. The 16-bit code contains
65,536 code points; the 32-bit version contains
more than 1 million code points.
uniconductor cable A cable having a single con-
ductor, usually of braided or twisted wires.
uniconductor waveguide A waveguide consist-
ing of a metal sheath deposited on a solid di-
electric of cylindrical or rectangular cross

unidentified flying object Abbreviation, UFO. An
object claimed to have been seen in flight, but not
identified by reliable authorities as any known
type of vehicle.
unidirect To commutate (see COMMUTATOR).
unidirectional 1. Flowing or acting in one direc-
tion only. 2. Having a radiation or response sen-
sitivity that is maximum in primarily one
direction in space.
unidirectional antenna See UNIDIRECTIONAL
unequal alternation
unidirectional array A beam antenna that radi-
ates in one direction only, or principally in one di-
unexpected halt During a computer program run, rection, unless rotated.
an undirected (unplanned) halt (e.g., one caused unidirectional conductivity Electrical conductiv-
by a machine fault or program bug). ity in only one direction; it characterizes an ideal
unfiltered Not having been subjected to filtering diode.
action. An example is the pulsating-direct- unidirectional coupler A directional coupler sam-
current output of an alternating-current-operated pling only one direction of transmission.
rectifier circuit. unidirectional current A current that flows al-
unfocused light source In a photoelectric system, ways in the same direction, although it might
a light source that delivers diffused light. fluctuate in intensity.
unformed rectifier A newly fabricated semicon- unidirectional elements Circuit elements, such
ductor rectifier (especially selenium) or an elec- as diodes or transistors, that transmit energy in
trolytic rectifier before it has been electroformed only (or best in) one direction.
for improved characteristics. unidirectional field-effect transistor See UNI-
unfurlable antenna An antenna that can be un- LATERAL FIELD-EFFECT TRANSISTOR.
rolled to increase its length, thereby lowering its unidirectional hydrophone An underwater unidi-
fundamental resonant frequency; it can also be rectional microphone.
rolled up to decrease its length and increase its unidirectional loudspeaker A loudspeaker that
fundamental resonant frequency. radiates sound substantially in one direction.
ungrounded item A component, circuit, or circuit unidirectional microphone A microphone that re-
point having no connection to ground, except an ceives sound waves from one direction, usually
inadvertent one through common impedances or from the front, minimum response usually being
leakage paths. from the sides and back.
ungrounded system A system operated entirely unidirectional network A network that transmits
above ground, any path to ground being acciden- signals in only one direction (i.e., the input and
tal. output terminals are not interchangeable).
unguided Without electronic guidance (pertaining unidirectional pattern For a transducer (such as
to missiles, rockets, satellites, etc.). an antenna, speaker, or microphone), a radiation
uni- A prefix (combining form) meaning one or sin- or response pattern that shows a pronounced
gle and appearing in a number of electronic maximum in one direction only.
terms. See the following several definitions for ex- unidirectional pulse A single-polarity pulse.
amples. unidirectional pulse train A series of unidirec-
uniaxial 1. Having one axis. 2. Referred to one axis. tional pulses.
uniaxial crystal A crystal having one optical axis. unidirectional response For a receiving trans-
unibivalent electrolyte An electrolyte, such as ducer, such as an antenna or microphone, a
sodium carbonate (Na2CO3), that dissociates into response pattern that shows a pronounced
two univalent ions and one bivalent ion. maximum in one direction only.
unidirectional speaker • unilateral field-effect transistor

uniform line A transmission line having identical

electrical properties over its entire length.
uniform magnetic field A magnetic field in which
all the lines of flux are straight and parallel, and
in which the magnetic force has the same value at
all points.
uniform plane wave A free-space plane wave at an
infinite distance from the generator, having con-
stant-amplitude electric and magnetic field vec-
tors over the equiphase surfaces.
uniform precession In regions of the uniform
magnetic field of a sample of material, the state in
which the magnetic moments of all atoms are
parallel and precess in phase around the mag-
netic field.
uniform waveguide A waveguide having constant
electrical and physical characteristics along its
uniground 1. The grounding of a circuit at one
point to reduce susceptibility to hum and noise.
unidirectional pattern
2. The point at which such a connection is made.
unijunction transistor A semiconductor device
unidirectional speaker See UNIDIRECTIONAL
consisting of a thin silicon bar on which a single
pn junction acting as an emitter is formed near
unidirectional transducer A transducer that op-
one end. Two bases are provided”each an ohmic
erates in one direction only (i.e., its input and
connection made to one end of the bar. Also
output cannot be interchanged).
called double-base diode.
unidirectional voltage A voltage that never changes
polarity, although it might fluctuate in value.
unified-field theory A theory, as yet unproved, n
Base 1 Base 2
that all forces in nature are interrelated and are
controlled by the same causes and factors. Albert
Einstein worked on this theory after he success-
fully developed the theories of relativity.
unifilar Having (or wound as) one fiber, wire, fila-
ment, or thread.
unifilar magnetometer A magnetometer in which
Base 1
a bar is suspended at its center of gravity by a Emitter
single thread. Base 2
unifilar suspension A method of meter construc-
tion in which the moving part is suspended by a Symbol
single filament. The torque might be provided by
this filament or by a spring or other resisting de- unijunction transistor
vice; the greater the displacement, the greater the
unilateral area track A film sound track having
uniform circular motion Motion at a uniform rate
modulation on only one edge of the opaque area.
and describing a circle (e.g., a motor armature ro-
unilateral bearing In radio direction finding, a
tating at a constant speed).
bearing obtained with a finder that produces uni-
uniform electric field An electric field in which all
lateral response and thereby eliminates 180-
the lines of flux are straight and parallel, and in
degree error.
which the electrostatic force has the same value
unilateral conductivity See UNIDIRECTIONAL
at all points (e.g., the field between two oppositely
charged, flat, parallel plates).
unilateral element See UNIDIRECTIONAL
unilateral field-effect transistor A field-effect
uniform frequency response Frequency response
transistor whose source and drain terminals can-
that is flat throughout a specified range. Such re-
not be interchanged. Also called ASYMMETRICAL
sponse is characterized by the transmission of a
signal with no introduced amplitude or phase
710 unilateralization • unit record

unilateralization A system of neutralization used unit 1. A named, single magnitude adopted as a
in transistor amplifiers at very-high and ultra- standard by physical measurement. Thus, the
high frequencies, in which the internal capacitive unit of current is the ampere, the unit of fre-
and resistive components are compensated by quency is the hertz, the unit of capacitance is the
the neutralization feedback. farad, etc. Also see ABSOLUTE SYSTEM OF
unilateralized amplifier A transistor amplifier in UNITS, INTERNATIONAL SYSTEM OF UNITS,
which both the internal resistive and capacitive and CENTIMETER-GRAM-SECOND. 2. A single
components are compensated by the neutralizing piece or assemblage of equipment, such as ampli-
circuit. Also see UNILATERALIZATION. fier, converter, power supply, etc. 3. A quantity of
unilateral network See UNIDIRECTIONAL NET- 1 implied when unit is the adjective describing a
WORK. quantity (e.g., unit length means a distance of
unilateral transducer See UNIDIRECTIONAL 1 meter, 1 foot, etc.).
TRANSDUCER. unitary code In computer operations, a code
uninterruptible power supply Abbreviation, UPS. based on one digit. The number of times the digit
A device that provides a continuous utility cur- is repeated indicates a given number.
rent to electronic devices in the event of a utility unit cell In crystals, the simplest polyhedron ex-
power dip or blackout. It contains a battery and a hibiting all the structural features and which is
power inverter. These devices are used exten- repeated to form the crystal lattice.
sively in personal computing to prevent loss of unit charge See UNIT ELECTROSTATIC CHARGE.
data that could otherwise result from a utility unit electric charge See UNIT ELECTROSTATIC
power failure. CHARGE.
union 1. The logical inclusive-OR operation. 2. See unit electrostatic charge An electrostatic point
BOND, 1. charge that will attract or repel a point charge of
union catalog In computer operations, the com- equal strength 1 centimeter away in a vacuum,
with a force of 1 dyne (10“5 newton).
piled list of the contents of two or more tape or
disk libraries. unit function Symbol, H or 1. A time-dependent
unionic material A material having no ions (i.e., quantity that is zero before the start of a period
one in which all atoms are neutral). (when time t is zero) and 1 for all values of t
uniphase antenna See COLLINEAR ANTENNA. greater than zero. It is approximated by a square
UNIPOL Acronym for universal problem-oriented wave, and is useful in solving problems involving
language, a high-level computer-programming transients.
language. unit length 1. A fundamental unit of distance or
unipolar 1. Having or using a single pole or polar- time, used for reference in a measuring system.
ity. 2. Operating with one class of current carrier. For example, in the mks (meter-kilogram-second)
unipolar armature An electric-motor armature system, the distance unit length is the meter, and
that maintains its polarity throughout a complete the time unit length is the second. 2. The dura-
revolution. tion of a fundamental element, or bit, in a binary-
unipolar field-effect transistor See UNIPOLAR code transmission system.
TRANSISTOR. unitized construction The fabrication of an elec-
unipolar induction Induction by only one pole of a tronic equipment in subassemblies (such as
magnet. modules) that can be tested separately, and that
unipolar input The input circuit of an instrument can be easily replaced (plugged in) in the event of
or device designed for input signals of one polar- individual failure.
ity only. unit line A line of electric or magnetic flux.
unipolar pulse A pulse in which the current flows unit magnetic pole See UNIT POLE.
in only one direction, or in which the voltage oc- unit matrix A matrix whose main diagonal terms
curs with only one polarity. (all) are all at unity, the other terms being zero.
unipolar transistor A field-effect transistor (FET). unitooth Pertaining to the use in electrical ma-
It utilizes only one kind of carrier (electrons in the chinery of one slot per pole per phase.
n-channel FET, holes in the p-channel FET). unitor See OR GATE.
Compare BIPOLAR TRANSISTOR. unit pole The strength (magnetic flux) of a (hypo-
unipolar winding The winding of a UNIPOLAR AR- thetical) magnetic pole that will attract or repel
MATURE. a pole of equal strength 1 centimeter away in a
unipole 1. An all-pass filter having one pole and vacuum, with a force of 1 dyne; 1 unit pole =
1.257 — 10“7 weber.
for which there is one zero. Also see ALL-PASS
FILTER, POLES OF IMPEDANCE, and ZEROS OF unit-ramp function A function whose value is zero
IMPEDANCE. 2. A hypothetical, omnidirectional before time t, and becomes equal to the time mea-
antenna. sured from t at all other instants. The integral of
unipotential cathode An indirectly heated tube the UNIT FUNCTION.
cathode. Also called equipotential cathode. See IN- unit record In computer operations, a complete
DIRECTLY HEATED CATHODE. record consisting of many data elements and
unit record • universal-wound coil

contained within one storage medium, such as a (R). Such a bridge often is a skeletal foundation
magnetic disk. circuit with a provision for plugging L, C, or R
unitrivalent electrolyte An electrolyte, such as standards in the various arms, as required. Also
sodium phosphate (Na3PO4), that dissociates into called general-purpose bridge.
three univalent ions and one trivalent ion. universal coordinated time Abbreviation, UTC.
units position In a numbering system, the right- Greenwich mean time coordinated by the Inter-
most position in a multidigit whole number; or, if national Time Bureau for broadcast as signals
the number contains a radix point, the digit im- (on WWV, for example).
mediately to the left of the radix point. universal coupler 1. An arrangement of one or
unit-step function See UNIT FUNCTION. more inductors and variable capacitors for
unitunnel diode A special form of semiconductor matching a transmitter to virtually any antenna.
diode, used as an oscillator at ultra-high and mi- One such device is the Collins coupler. 2. A de-
crowave frequencies. vice for matching numerous generator output
unit vector A vector that is 1 unit long in terms of impedances to numerous load impedances.
the scale representing a factor of interest, and universal filter An active filter that is continu-
has the same direction as the vector of interest. ously tunable over a wide frequency range and
For example, if u is a unit vector, then 5u repre- that offers low-pass, high-pass, bandpass, and
sents a vector having the same direction and five band-suppression functions.
times the magnitude of u. universal frequency counter A digital frequency
unity 1. The figure 1 implied. 2. A ratio of 1:1. 3. A meter usable at radio and audio frequencies.
gain of 0 dB. universal motor A small series-wound motor that
unity coupling Tight coupling between two coils, runs on direct current or single-phase alternating
the turns ratio often being 1 to 1 and the coils al- current. This type of motor is used in many
ways being closely interwound. household appliances and in motor-driven tools,
such as portable electric drills, polishers, etc.
universal output transformer An output trans-
former having a number of taps on its primary
and secondary windings for use with a wide vari-
ety of impedances.
universal product code Abbreviation, UPC. The
variable-width-bar code appearing on price tags
Input Output or product labels, and yielding such informa-
tion as cost, size, and color when read by super-
market (or other retailer) optical character-
recognition equipment. Also called universal
vendor marking (UVM).


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