Page 34 - The Illustrated Dictionary of Electronics

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airwaves • aliasing noise 19

mistaken notion that radio signals are propa-
gated by the air. 2. Skywaves.
Al Symbol for ALUMINUM.
alabamine See ASTATINE.
alacratized switch A mercury switch in which the
tendency of the mercury to stick to the parts has
been reduced.
alarm 1. An electronic security system. 2. A silent
and/or audible alert signal transmitted by an
electronic security system when an intrusion oc-
curs. 3. A silent and/or audible signal that in-
forms personnel of the occurrence of an
equipment malfunction.
alarm circuit A circuit that alerts personnel to a
system malfunction, a detected condition, or an
intruder.
alarm condition 1. An intrusion or equipment
malfunction that triggers an alarm circuit. 2. The
operation of an alarm circuit that occurs in re-
sponse to an intrusion or equipment malfunc-
tion.
alarm hold A device that keeps an alarm sounding
once it has been actuated.
alarm output The signal sent from an alarm cir-
cuit to a siren, buzzer, computer, or other exter-
nal device to alert personnel to an ALARM
CONDITION.
alarm relay A relay that is actuated by an alarm
device.
A-law A form of companding law frequently used in
European electronics (the mu-law is more often
used in North America). A nonlinear transfer algebraic adder In computer operations, an adder
characteristic in companding circuits. It can be that provides the algebraic sum, rather than the
continuous, or can be a piecewise linear approxi- arithmetic sum, of the entered quantities.
mation of a continuous function. algebraic operation A form of electronic calculator
A-law companded Companding by means of an 8- operation, in which the keystrokes proceed in an
bit binary code following the A-LAW, a specific intuitive sequence, following the way in which the
companding function. calculation is written down. Compare REVERSE
albedo For an unpolished surface, the ratio of re- POLISH NOTATION.
flected light to incident light. It can vary from 0.0 algebraic sum The sum of two or more quantities
to 1.0, or from 0 to 100 percent. with consideration of their signs. Compare
albedograph An instrument for measuring the ARITHMETIC SUM.
albedo of planets. algorithm A step-by-step procedure for solving a
ALC Abbreviation of AUTOMATIC LEVEL CON- problem, (e.g., the procedure for finding the
TROL. square root of a number). It can be expressed in a
alerting device An audible alarm that includes a line-by-line instruction set or as a flowchart.
self-contained solid-state audio oscillator. Pow- algorithmic language A computer language used
ered from the ac line or a battery, the device pro- to describe a numeral or algebraic process.
duces a raucous noise when actuated. alias A label that is an alternate term for items of
Alexanderson antenna A very-low-frequency the same type; a label and several aliases can
(VLF) and low-frequency (LF) vertically polarized identify the same data element in a computer
antenna, designed to minimize ground losses in program.
structures of manageable height. It usually con- aliasing 1. In analog-to-digital (A/D) conversion, a
sists of several wires, each quarter-wave reso- false output signal that results from a sampling
nant with a loading coil, and all connected rate that is too slow. Ideally, the sampling rate is at
together at the apex of a tower. The antenna is least twice the highest input signal frequency. 2.
fed between the ground and the base of one of Sawtooth-like irregularities, also called jaggies,
the wires. which are sometimes introduced into a bit-mapped
Alford antenna A loop antenna, in a square config- computer image when it is changed in size.
uration, with the corners bent toward the center aliasing noise A form of signal distortion caused
to lower the impedance at the current nodes. by a signal with an excessive bandwidth.