Page 36 - The Illustrated Dictionary of Electronics

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alloy diode • alternating-charge characteristic 21

n-type) to form the junction. Also called alloy- alphabetic-numeric Also called alphabetical-
junction diode. numerical and alphanumeric. In computer opera-
alloy junction In a semiconductor device, a posi- tions, pertaining to letters of the alphabet and
tive/negative (pn) junction formed by alloying a special characters, and to numerical digits.
suitable material (such as indium) with the semi- alpha cutoff frequency Also called alpha cutoff. In
conductor (silicon or germanium). a bipolar transistor circuit, the frequency at
alloy transistor A transistor whose junctions are which the alpha (current gain) becomes 0.707
created by alloying. Also see ALLOY JUNCTION. (70.7 percent) of its value at 1 kHz. A bipolar
transistor can have considerable gain at its alpha
cutoff. This specification denotes how rapidly a
transistor loses gain as the frequency increases,
an important consideration in the design of radio-
frequency (RF) amplifiers. See ALPHA. Compare
GAIN BANDWIDTH PRODUCT.
alpha decay The decay of a substance in which the
nuclei of the atoms emit alpha particles, resulting
in a change of the atomic number and atomic
weight of the substance over a period of time.
alphanumeric See ALPHABETIC-NUMERIC.
all-pass filter Also called all-pass network. A filter alphanumeric code In computer operations or in
that (ideally) introduces a desired phase shift or communications, a code composed of, or using,
time delay, but has zero attenuation at all fre- both letters and numbers.
quencies. alphanumeric readout A type of digital readout
all-relay central office In telephone service, an that displays both letters and numerals.
automatic central-office switchboard that uses alpha particle A nuclear particle bearing a positive
relay circuits to make line interconnections. charge. Consisting of two protons and two neu-
all-wave Pertaining to a wide operating-frequency trons, it is given off by certain radioactive sub-
range. Few systems are literally all-wave. For ex- stances. Compare BETA RAYS and GAMMA RAYS.
ample, a so-called “all-wave radio receiver” might alpha system An alphabetic code-signaling sys-
cover 500 kHz to 30 MHz only. tem.
all-wave antenna An antenna that can be operated alphatron An ionizing device in which the radia-
over a wide frequency range with reasonable effi- tion source is an emitter of alpha particles.
ciency and preferably without needing readjust- alteration An inclusive-OR operation.
ment. Examples are the DISCONE ANTENNA and alternate channel In communications, a channel
the LOG-PERIODIC ANTENNA. situated two channels higher or lower than a
all-wave generator A signal generator that will given channel. Compare ADJACENT CHANNEL.
supply output over a wide range of frequencies. alternate-channel interference Interference
all-wave receiver A radio receiver that can be caused by a transmitter operating in the chan-
tuned over a very wide range of frequencies, such nel beyond an adjacent channel. Compare
as 10 kHz to 70 MHz. ADJACENT-CHANNEL INTERFERENCE.
allyl plastics Plastics, sometimes used as dielectrics alternate digit inversion In multiplex equipment,
or for other purposes in electronics, based on a method of switching the binary signals to the
resins made by polymerization of monomers (such opposite state, in accordance with A-law com-
as diallyl phthalate) that contain allyl groups. panding.
alnico Coined from the words aluminum, nickel, alternate frequency A frequency allocated as an
and cobalt. An alloy used in strong permanent alternative to a main assigned frequency and
magnets, it contains the constituents noted plus used under certain specified conditions.
(sometimes) copper or titanium. alternate-mark inversion signal A signal that
alpha 1. Symbol, α. The current gain of a common- conveys bits in which the successive signals are
base-connected bipolar transistor. It is the ratio of of opposite polarity (positive, then negative, then
the differential of collector current to the differen- positive, etc.). They are equal in absolute value
tial of emitter current; α = dI C /dI E . For a junction amplitude.
transistor, alpha is always less than unity, but alternate mode The technique of displaying sev-
very close to it. 2. In voice communications, the eral signals on an oscilloscope screen by rapidly
phonetic representation of the letter A. switching the signals in sequence at the end of
alphabet The set of all characters in a natural lan- each sweep.
guage. alternate routing A secondary, or backup, com-
alphabetic coding In computer practice, an abbre- munications path, used when primary (normal)
viation system for coding information to be fed routing is impossible.
into the computer. The coding contains letters, alternating-charge characteristic In a nonlinear
words, and numbers. capacitor, the relationship between the instanta-