18WuD2x

16 admittance • affirmative
admittance Symbol, Y. Unit, siemens (formerly
mho). The property denoting the comparative
ease with which an alternating current flows
through a circuit or device. Admittance is the reciprocal
of impedance (Z ): Y = 1/Z.
adp 1. Abbreviation of AMMONIUM DIHYDROGEN
PHOSPHATE, a piezoelectric compound used for
sonar crystals. 2. Abbreviation of AUTOMATIC
DATA PROCESSING.
adsorption Adhesion of a thin layer of molecules of
one substance to the surface of another without
absorption. An example is adsorption of water to
the surface of a dielectric. This term is often confused
with ABSORPTION because the spellings of
the two words are almost identical. Compare AB-
SORPTION.
adu Abbreviation of automatic dialing unit.
advanced-class license An amateur-radio license
conveying all operating privileges, except for a few
small bands that are allocated to extra-class licensees.
The second-highest class of amateur license.
advance information Data published prior to the
actual production or availability of a manufactured
component, circuit, or system. Advance information
is often only an approximate reflection
of the expected characteristics of a device.
advance wire A resistance wire used in thermocouples
and precision applications. It is an alloy of
copper and nickel, which has high resistivity and
a negligible temperature coefficient of resistance.
aeolight A glow lamp using a cold cathode and a
mixture of inert gases. Because its illumination
can be regulated with an applied signal voltage, it
is sometimes used as a modulation indicator for
motion-picture sound recording.
aerial See ANTENNA.
aerial cable A wire or cable run through the air, using
support structures, such as towers or poles.
aerodiscone antenna A miniature discone antenna
designed for use on aircraft.
aerodynamics The science dealing with forces exerted
by air and other gases in motion—especially
upon bodies (such as aircraft) moving through
these gases.
aerogram See RADIOGRAM.
aeromagnetic Pertaining to terrestrial magnetism,
as surveyed from a flying aircraft.
aeronautical advisory station A civil defense and
advisory communications station in service for
the use of private aircraft stations.
aeronautical broadcasting service The special
service that broadcasts information regarding air
navigation and meteorological data pertinent to
aircraft operation.
aeronautical broadcast station A station of the
aeronautical broadcasting service.
aeronautical fixed service A fixed radio service
that transmits information regarding air navigation
and flight safety.
aeronautical fixed service station A station that
operates in the aeronautical fixed service.
aeronautical ground station A land station that
provides communication between aircraft and
ground stations.
aeronautical marker-beacon signal A distinctive
signal that designates a small area above a beacon
transmitting station for aircraft navigation.
aeronautical marker-beacon station A land station
that transmits an aeronautical markerbeacon
signal.
aeronautical mobile service A radio service consisting
of communications between aircraft, and
between aircraft and ground stations.
aeronautical radio-beacon station An aeronautical
radio-navigation land station that transmits
signals used by aircraft and other vehicles to determine
their position.
aeronautical radionavigation services Services
provided by stations transmitting signals used in
the navigation of aircraft.
aeronautical radio service A service that encompasses
aircraft-to-aircraft, aircraft-to-ground,
and ground-to-aircraft communications important
to the operation of aircraft.
aeronautical station A station on land, and occasionally
aboard ship, operating in the aeronautical
mobile service.
Aeronautical Telecommunication Agency The
agency that administers the operation of stations
in the aeronautical radio service.
aeronautical telecommunications Collectively,
all of the electronic and nonelectronic communications
used in the aeronautical service.
aeronautical utility land station A ground station
in an airport control tower that provides
communications having to do with the control of
aircraft and other vehicles on the ground.
aeronautical utility mobile station At an airport,
a mobile station that communicates with aeronautical
utility land stations and with aircraft
and other vehicles on the ground.
aerophare See RADIO BEACON.
aerospace 1. The region encompassing the earth’s
atmosphere and extraterrestrial space. 2. Pertaining
to transport and travel in the earth’s atmosphere
and in outer space. This includes
aircraft, orbiting space vessels, and interplanetary
spacecraft.
AES Abbreviation for Audio Engineering Society.
AEW Abbreviation of airborne (or aircraft) early
warning.
aF Abbreviation of ATTOFARAD.
AF Abbreviation of AUDIO FREQUENCY.
AFC 1. Abbreviation of AUTOMATIC FREQUENCY
CONTROL. 2. Abbreviation of AUDIO-FRE-
QUENCY CHOKE.
affirmative In voice communications, a word often
used for “yes”—especially when interference is
present or signals are weak.