18WuD2x

54 avalanche breakdown • AX.25
mum reverse-bias voltage required to cause this
phenomenon varies among different kinds of
diodes. Some diodes are manufactured to have
precise avalanche voltages. See ZENER DIODE.
avalanche conduction In a semiconductor junction,
the enhanced reverse-bias conduction
caused by a condition of AVALANCHE.
avalanche current The high current that flows
through a semiconductor junction when
AVALANCHE occurs.
avalanche diode See ZENER DIODE.
avalanche impedance The reduced impedance of
a diode during avalanche.
avalanche noise Electrical noise generated in a
junction diode operated at the point at which
avalanche just begins.
avalanche transistor A transistor that operates at
a high value of reverse-bias voltage, causing the
pn junction between the emitter and base to conduct
because of avalanche breakdown.
avalanche voltage In a semiconductor P-N junction,
the minimum applied reverse-bias voltage
that produces AVALANCHE BREAKDOWN.
AVC Abbreviation of automatic volume control.
avdp Abbreviation for Avoirdupois, a weightmeasurement
scheme that is used in Englishspeaking
countries and is based on the pound.
average absolute pulse amplitude The average
(disregarding algebraic sign) of the absolute amplitudes
of a pulse, taken over the duration of the
pulse.
average brightness The average brilliance of a
television (TV) picture, cathode-ray-tube (CRT)
computer display, or oscilloscope image.
average calculating operation The operating time
considered typical for a computer calculation
(i.e., one that is longer than an addition and
shorter than a multiplication); it is frequently
taken as the average of nine additions and one
multiplication.
average current Abbreviation, I avg . The average
value of alternating current flowing in a circuit.
Taking polarity into account, this value is zero for
a pure sine wave. For other waveforms, it can
vary. When polarity is not considered, the sinewave
value of I avg is equal to 0.637 times I pk , the
peak value of current; I avg = 0.637 I pk .
average life See MEAN LIFE.
average noise figure The ratio of the total noise
output from a circuit to the thermal noise output
at 290 degrees Kelvin. It is usually expressed in
decibels, with the noise taken at all frequencies.
average power The average value of power in an ac
circuit. In a resistive circuit, it is the square of the
effective (rms) current times the resistance; P avg =
(I rms ) 2 R (for sine waves).
average pulse amplitude Also called effective
pulse amplitude. The value obtained by integrating
the pulse amplitude, with respect to time,
from the start of the pulse to its end, then dividing
this integral by the pulse duration.
average rectified current Abbreviation, I avg . The
average value of rectifier output current before filtering.
For a full-wave rectifier with a sine wave
input and a resistive load, I avg is equal to the maximum
current I m multiplied by 0.637.
average rectified voltage Abbreviation, E avg . The
average value of rectifier output voltage before filtering.
For a full-wave rectifier with a sine-wave
input and a resistive load, E avg is maximum voltage
E m multiplied by 0.637.
average value 1. The arithmetic mean of two or more
quantities. 2. The geometric mean of two or
more quantities. 3. The harmonic mean of two
or more quantities. 4. In ac operation, the average
current, voltage, or power.
average voltage Abbreviation, E avg . The average
value of ac voltage in a circuit. Taking polarity into
account, this value is zero for a pure sine wave.
For other waveforms, it can vary. When polarity is
not considered, the sine-wave value of E avg is equal
to 0.637 times E pk , the peak value of voltage.
avg Abbreviation of average.
aviation channels Frequency channels assigned
to the AVIATION SERVICES.
Aviation services The radio-communication services
used by aeronautical-mobile and radio navigation
personnel.
avigation Acronym for aviation navigation. Aircraft
navigation by means of electronic equipment.
avionics Acronym for aviation electronics. The design,
production, and application of electronic devices
and systems for use in aviation, navigation,
and astronautics.
Avogadro’s constant (Amedeo Avogadro, 1776–
1856.) Symbol, NA. The number of molecules in a
kilogram-molecular weight of any substance; NA
equals 6.025 × 10 26 (kg-mole) –1 .
A voltage The filament voltage in a vacuum-tube
circuit.
aW Abbreviation of attowatt.
AWG Abbreviation of AMERICAN WIRE GAUGE.
AX.25 A signal format used in some digital communications
systems, notably amateur packet radio.