Page 37 - The Illustrated Dictionary of Electronics

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22 alternating-charge characteristic • amateur extra-class license

neous charge and the instantaneous value of an above the earth’s surface. 3. The angle, measured
alternating voltage. in degrees, with respect to the horizon, at which a
alternating current Abbreviation, ac. A current that highly directional antenna is pointed.
periodically reverses its direction of flow. In one cy- altitude delay In a plan-position-indicating type of
cle, an alternation starts at zero, rises to a maxi- radar, the sync delay introduced between trans-
mum positive level, returns to zero, rises to a mission of the pulse and start of the trace on the
maximum negative level, and again returns to zero. indicator screen to eliminate the altitude circle in
The number of such cycles completed per second is the display.
termed the ac frequency. Also see CURRENT. ALU Abbreviation of ARITHMETIC AND LOGIC
alternating-current continuous wave An ampli- UNIT.
tude-modulated signal resulting from the opera- alumel An alloy used in the construction of one
tion of an oscillator or RF amplifier with raw ac type of THERMOCOUPLE. It is composed of
voltage. nickel (three parts) and aluminum (one part).
alternating current/direct current See AC/DC. alumina An aluminum-oxide ceramic used in elec-
alternating-current erasing head See AC ERAS- tron tube insulators and as a substrate in the
ING HEAD. fabrication of thin-film circuits.
alternating-current pulse A short-duration ac aluminum Symbol, Al. An elemental metal. Atomic
wave. number, 13. Atomic weight, 26.98. Aluminum is
alternating-current transmission 1. The propa- widely used in electronics, familiar instances be-
gation of alternating currents along a length of ing chassis, wire, shields, semiconductor doping,
conductor—especially for power-transfer pur- and electrolytic-capacitor plates.
poses. 2. A means of picture transmission in aluminum antimonide Formula, AlSb. A crystalline
which a given signal strength produces a con- compound useful as a semiconductor dopant.
stant value of brightness for a very short time. aluminized screen A television picture-tube
alternating voltage Also called alternating-current screen with a thin layer of aluminum deposited
voltage. See AC VOLTAGE. on its back to brighten the image and reduce ion-
alternation In ac practice, a half cycle. In a complete spot formation.
cycle, there are two alternations, one in the positive Am Symbol for AMERICIUM.
direction and one in the negative direction. A/m Abbreviation of ampere per meter: the SI unit
of magnetic field strength.
AM 1. Abbreviation of amplitude modulator. 2. Ab-
breviation of AMPLITUDE MODULATION.
amalgam An alloy of a metal and mercury. Loosely,
any combination of metals.
amateur 1. A nonprofessional, usually noncom-
mercial devotee of any technology (i.e., a hobby-
ist). 2. A licensed radio operator legally
authorized to operate a station in the AMATEUR
SERVICE.
amateur band Any band of radio frequencies as-
signed for noncommercial use by licensed radio
amateurs (see AMATEUR, 2). In the United
States, numerous such bands are above 1.8 MHz
(160 meters). Also see AMATEUR SERVICE and
AMATEUR STATION.
amateur call letters Call letters assigned by a gov-
ernment licensing authority—especially to ama-
teur stations. Call-letter combinations consist of
a letter prefix denoting the country in which the
station is situated, plus a number designating
alternative denial A NOT-AND operation. the location within the country, and two or more
alternator Any mechanically driven machine for letters identifying the particular station. For ex-
generating ac power. Sometimes specifically one ample: W6ABC: W (or K) = United States, 6 = Cal-
having a permanent-magnet rotor, such as a ifornia, and ABC = identification of individual
magneto. licensee (issued alphabetically, except under spe-
altimeter station An airborne transmitter whose cial circumstances).
signals are used to determine the altitude of air- amateur callsign See AMATEUR CALL LETTERS.
craft. amateur extra-class license The highest class of
altitude 1. The vertical distance of an object above amateur-radio operator license in the United
sea level. 2. The vertical distance of an object States. It conveys all operating privileges.