Page 68 - The Illustrated Dictionary of Electronics

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auxiliary equipment • avalanche breakdown 53

available gain The ratio P o /P i , where P i is the avail-
able power at the input of a circuit and P o is the
available power at the output.
available line The percentage of the length of a fac-
simile scanning line that is usable for picture sig-
nals.
available power The mean square of the open-
circuit terminal voltage of a linear source divided
by four, times the resistive component of the
source impedance. The available power is the
maximum power delivered to a load impedance,
equal to the conjugate of the internal impedance
of the power source.
available power gain In a power transistor, the ra-
tio of available transistor output power to the
power available from the generator. It depends on
auxiliary equipment 1. Also known as peripher- the generator resistance, but not on the transis-
als. An apparatus not directly governed by the tor load resistance.
central processing unit of a digital computer, available signal-to-noise ratio The ratio P s /P n ,
such as a printer or personal robot. 2. Peripheral where P s is the available signal power at a given
equipment in any system. 3. Backup equipment. point in a system and P n is the available random-
auxiliary memory In a digital computer, a unit noise power at that point.
that is supplementary to the main memory, available time 1. The time during which a com-
which it augments. puter is available and ready for immediate use. 2.
auxiliary receiver Also called standby receiver. In The amount of time a computer is available to an
a radio communications system, a receiver that is individual.
available for use if the main receiver fails. avalanche The phenomenon in semiconductors
auxiliary relay 1. A standby relay. 2. A relay operated at high reverse bias voltage, whereby
whose operation supports that of another relay. carriers acquire sufficient energy to produce new
3. A relay that is actuated by the operation of an- electron-hole pairs as they collide with atoms.
other relay. The action causes the reverse current to increase
auxiliary switch 1. A standby switch. 2. A switch sharply.
wired in series or parallel with another switch. 3. avalanche breakdown In a semiconductor P-N
A switch that is operated by another switch. junction, a condition that occurs when the re-
verse bias voltage exceeds a certain value. If the
electric field in the vicinity of the junction be-
comes strong enough, charge carriers are dis-
lodged from the atoms and the carriers (electrons
and holes) flow freely across the P-N junction in
the opposite direction from normal. The mini-

auxiliary transmitter Also called standby trans-
mitter. In a radio communications system, a
transmitter that is available for use if the main
transmitter fails.
a/v Abbreviation of AUDIO-VISUAL.
aV Abbreviation of attovolt.
availability The proportion of time during which
an apparatus is operating correctly. It is usually
given as a percentage.
available conversion gain The ratio of the input
power to the output power of a transducer or con-
verter. It is generally given in decibels.