18WuD2x

lowest usable frequency • low power 421
lowest usable frequency Abbreviation, LUF. The
lowest frequency that can be used successfully at
a given time for communication via the ionosphere.
Compare MAXIMUM USABLE FRE-
QUENCY.
low filter A highpass filter that removes lowfrequency
audio noise from the modulating waveform
of a broadcast station. The result is a lower
level of transmitted hum and rumble.
low-frequency Abbreviation, LF. 1. Pertaining to
radio frequencies in the band from 30 kHz to 300
kHz (wavelengths from 10 kilometers to 1 kilometer).
Also see RADIO SPECTRUM. 2. Pertaining to
audio frequencies below 500 Hz.
low-frequency compensation 1. In videoamplifier
design, special measures, such as use
of high coupling and bypass capacitances, to
boost low-frequency gain. 2. Use of special circuits
to increase the low-frequency response of an audio
amplifier. Also see BASS BOOST, 1, 2.
low-frequency direction finder Abbreviation,
LDF. A direction finder operated in or below the
standard amplitude-modulation (AM) broadcast
band, that is, below 1.605 MHz.
low-frequency padder See OSCILLATOR PAD-
DER.
low-frequency parasitics Parasitic oscillations of
a frequency lower than that being processed by
the amplifier or generated by the oscillator in
which they occur.
low-level 1. A logic term for the more negative of
the two (binary) logic levels. 2. Having an amplitude
that is below that normally available in comparable
circuits or systems. 3. In computer
operations, pertaining to programming languages
(such as assembly language or machine language)
that control the machine, but do not directly
interface with the operator.
low-level audio signal In audio operations, a signal
that has not been amplified by any means
(e.g., the output of a dynamic microphone). Compare
HIGH-LEVEL AUDIO SIGNAL.
low-level contact A switch or relay contact intended
for use with low values of current and voltage.
low-level input current 1. A test used to check an
input pull-up resistor in an integrated circuit to
ensure that the fan-in is as specified. 2. The current
flowing from an input when the highest lowlevel
output voltage specified is applied to the
input of the device.
low-level language A computer programming language
in which each instruction has only one
equivalent machine code. Examples are machine
language and assembly language. Compare
HIGH-LEVEL LANGUAGE.
low-level logic Abbreviation, LLL. In digitalcomputer
operations, any logic system that
operates at low voltage or current levels.
low-level modulation Modulation of a radio or
television transmitter at a stage preceding the final
radio-frequency (RF) power amplifier.
low-level output current 1. A test to ascertain
that the fan-out and current-sinking capability of
an integrated circuit are as specified. 2. The current
flowing into an output with input conditions
that cause the output to be at logic low.
low-level signal 1. A signal with small amplitude.
2. A signal with peak-to-peak voltage so low that
it does not drive an amplifier circuit out of the linear
range of operation.
low-loss material A material, particularly a dielectric,
having low electrical loss at a given frequency.
Also see LOSS.
low-noise Pertaining to circuits, especially weaksignal
communications receiving amplifiers and
converters, designed to generate the smallest
possible amount of internal noise.
low-noise down converter In a satellite television
receiving system, a circuit that converts the signals
from the dish antenna to frequencies that
correspond to the channels on a conventional
television set.
low order The lesser-value place(s) of characters or
digits in the hierarchy of a group (number or
word). For example, 5 and 6 are low-order digits
in the number 123,456.
low-order position The extreme right-hand (least
significant) position in a number or word.
low-pass filter A combination of capacitance, inductance,
and/or resistance, intended to produce
large amounts of attenuation above a certain frequency
and little or no attenuation below that frequency.
The frequency at which the transition
occurs is called cutoff. At cutoff, the power attenuation
is 3 dB with respect to the minimum attenuation.
At frequencies below cutoff, the power
attenuation is less than 3 dB. At frequencies
above cutoff, the power attenuation is more than
3 dB. The simplest circuit consists of a series inductor
or a parallel capacitor. The inductancecapacitance
(LC) circuit has a combination of
series inductors and parallel capacitors. In the
resistance-capacitance (RC) circuit, resistors are
substituted for the inductors. Compare BAND-
PASS FILTER, BAND-REJECTION FILTER,
HIGH-PASS FILTER.
low power Abbreviation, LP. Power considerably
lower than that ordinarily encountered in a
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low-pass filter
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