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UHF generator • ultra-low frequencies 701
UHF generator 1. An oscillating device (such as a
transistor, tunnel diode, Klystron, or magnetron)
used to produce radio-frequency energy at ultrahigh
frequencies (UHF). 2. The equipment in
which such a device is used. 3. An ultra-highfrequency
test-signal generator.
UHF loop A (usually single-turn) loop antenna with
a toroidal radiation pattern perpendicular to the
loop; the antenna has a natural wavelength in the
ultra-high-frequency (UHF) range.
UHF receiver A receiver tunable to frequencies in
any band in the range 300 MHz to 3000 MHz.
UHF television channels Television channels 14
through 69, whose frequencies lie in the ultrahigh
range.
UHF transistor A transistor specially designed and
fabricated for ultra-high-frequency (UHF) operation.
It is characterized by extended beta cutoff
frequency, low junction capacitance, and fast recovery
time.
UHF translator A television broadcast translator
station transmitting in an ultra-high-frequency
(UHF) channel.
UHF transmitter A transmitter that is specially
designed for operation at ultra-high frequencies.
In such a transmitter, stray parameters are minimized
and special tubes or transistors are required.
UHF tube A vacuum tube specially designed for ultra-high-frequency
operation. It is characterized
by low interelectrode capacitance, low input and
output capacitances, short electron transit time,
and low lead inductance.
UHF tuner 1. A superheterodyne receiver front end
tunable in the ultra-high-frequency (UHF) range.
It is usually arranged to deliver the mixer output
to a lower-frequency receiver. 2. A television receiver
front end tunable to the UHF channels.
UHR Abbreviation of ULTRA-HIGH RESISTANCE.
U index The difference between consecutive daily
mean values of the horizontal component of the
geomagnetic field.
UJT Abbreviation of UNIJUNCTION TRANSISTOR.
UL 1. Abbreviation of UNDERWRITERS LABORA-
TORIES. 2. Abbreviation of ULTRALINEAR.
ULD Abbreviation of ULTRA-LOW DISTORTION.
ULF Abbreviation of ULTRA-LOW FREQUENCY.
U-line section A short section of coaxial cable or
hardline having the shape of a squared U.
ULSI See ULTRA-LARGE-SCALE INTEGRATION.
ultimate attenuation The maximum attenuation
in a circuit or device when it is operated outside
its passband, or within its stopband.
ultimately controlled variable In an automated
system, the quantity or operation (e.g., liquid
level, temperature, pressure, precision drilling,
etc.), whose control is the end purpose of the system.
ultimate-range ballistic missile A ballistic missile
whose range is greater than half the earth’s circumference
(approximately 12,000 miles).
ultimate ratio The limiting value of a ratio (i.e., the
value approached by a ratio).
ultimate sensitivity 1. In an instrument or system,
the maximum degree of perception of, or response
to, a quantity or condition. 2. In a graphic
recorder, half the deadband.
ultimate threshold See ULTIMATE SENSITIVITY,
2.
ultimate trip current For a specified set of environmental
conditions, the lowest value of current
that will trip a circuit breaker.
ultimate trip limits For a circuit breaker, the
maximum and minimum current at which the
breaker trips and drops out.
ultor anode The second anode of a television picture
tube or oscilloscope tube.
ultor element In a television picture tube, the element
that receives the highest direct-current
voltage. Also called ultor electrode. Also see UL-
TOR ANODE.
ultor voltage The high direct-current voltage applied
to the second anode of an oscilloscope tube or
television picture tube. Also see ULTOR ANODE.
ultra- A prefix meaning above, larger than, greater
than, or higher than. See the following several definitions
for examples.
ultra-atomic Pertaining to particles smaller than
atoms (i.e., SUBATOMIC).
ultra-audible frequency A frequency higher than
the highest audible frequency. Also called ULTRA-
SONIC FREQUENCY and supersonic frequency.
ultra-audion oscillator See ULTRAUDION OSCIL-
LATOR.
ultracentrifuge A centrifuge that spins at a very
high speed.
ultrafast switch An electronic switch capable of
microsecond operation.
Ultrafax A system for high-speed transmission of
printed matter by facsimile, radio, or television.
ultra-high frequency A radio frequency in the
range 300 MHz to 3000 MHz, corresponding to
free-space wavelengths between 1 meter and
10 centimeters.
ultra-high-frequency band See UHF BAND.
ultra-high resistance Resistance of 100 megohms
or higher.
ultra-large-scale integration An integrated-circuit
process that goes several orders of magnitude
beyond VERY-LARGE-SCALE INTEGRATION.
More than 4 × 10 6 transistors could be on a single
chip.
ultra-linear Pertaining to the most linear operation
obtainable with state-of-the-art electronic equipment.
ultra-linear amplifier A high-fidelity audiofrequency
power amplifier having wide frequency
response and very low distortion.
ultra-low distortion Total harmonic distortion
(THD) of less than 0.1 percent.
ultra-low frequencies 1. Radio frequencies between
300 Hz and 3 kHz, pertaining to