18WuD2x

552 preamplifier • preset counter
preamplifier
approximately 15 MHz, where most of the noise
comes from the receiver, rather than from outside
sources. 2. A low-noise amplifier used for boosting
weak signals for television reception. 3. A lownoise,
low-level amplifier used for boosting signal
levels from transducers, such as microphones or
photocells.
prebiased relay A relay through which is maintained
a steady current that is just lower than
that needed to close the relay. The actuating signal,
then, need only be a small amount of additional
current.
precedence effect See FUSION, 1.
precipitation 1. Water falling from the atmosphere
in some form (rain, snow, hail, or sleet). See PRE-
CIPITATION STATIC. 2. The amount of precipitation
occurring in a given period of time at a
specific location. 3. Separation of a solid material
from a solution, as a result of a chemical or physical
action.
precipitation static 1. Radio noise that sometimes
occurs when it rains or snows. It can be
mistaken for artificially generated noise. 2. Radio
noise caused by atmospheric electricity arising
from rain, snow, ice crystals, hail, or dust clouds,
through which an aircraft carrying the radio flies.
precipitator See DUST PRECIPITATOR.
precipitron See DUST PRECIPITATOR.
precision 1. Pertaining to electronic hardware, especially
test instruments and measuring devices,
designed and built to function with a high degree
of accuracy. 2. The relative accuracy of a meter or
other indicating device. 3. The accuracy of the results
of an experiment, test, or measurement.
precision approach radar A radar aimed along the
approach path to guide an aircraft during approach.
precision instrument An instrument possessing
high accuracy and stability (i.e., one capable of
reproducing readings or settings for various trials
under set circumstances).
precision potentiometer 1. A POTENTIOMETER
possessing highly accurate resistance calibration,
linearity, and repeatability of settings. 2. A
potentiometer-type voltage-measuring instrument.
+
Output
preconduction current 1. The cutoff current in a
transistor. 2. In a thyratron, the small (anode)
current flowing before the tube is fired.
predetermined counter A counter programmed to
count to a desired number and stop.
predistortion See PREEMPHASIS.
pre-Dolby 1. To record a tape with DOLBY compression.
2. A tape that has been recorded with
Dolby compression.
preemphasis In frequency modulation, the introduction
of a rising-response characteristic (response
rises as modulation frequency increases).
Compare DEEMPHASIS.
preequalization 1. In sound recording and reproduction,
equalization during recording. 2. See
PREEMPHASIS.
preferred values of components A number system
used by the Electronics Industries Association
(EIA) for establishing the values of
composition resistors and small fixed capacitors.
prefix multiplier See MULTIPLIER PREFIX.
prefix notation As used with complex expressions
involving many operators and operands, a type of
notation in which the expressions, rather than
containing brackets, are given a value, according
to the relative positions of operators and
operands.
preform
1. A small wafer, usually dry-pressed
from powdered plastic, from which the body of a
component, such as a capacitor or resistor, is
heat-molded. Also called a pill or biscuit. 2. The
preformed slab used in molding a phonograph
disc. 3. To shape a moldable circuit before fixing
the final configuration or package.
preliminary information For manufactured electronic
components, data that is released prior to
the actual availability of the device. Subject to
change when units are produced.
premix A molding compound of reinforced plastic.
prerecorded disc A phonograph disc on which a
recording has been made (i.e., a recorded disc).
prerecorded tape Magnetic tape on which a program
or data has been recorded. Also called
RECORDED TAPE.
p region See P LAYER.
prescaler A device operated ahead of a counter to
establish a new, usually higher-frequency, range
over which frequency measurements can be
made.
preselector A tuned or untuned radio-frequency
amplifier operated ahead of a radio or television
receiver to boost the sensitivity of the receiver.
presence 1. In sound reproduction, the quality of
being true to life. 2. The effect of boosted uppermidrange
frequencies in music.
preset counter A pulse counter that delivers one
output pulse for a number of successive input
pulses, determined by the settings of countercircuit
controls. Thus, a preset counter might
give an output pulse for each train of 125 input
pulses.