Page 28 - The Illustrated Dictionary of Electronics

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active satellite • adapter 13

ily in the same physical location as the true
ground surface (i.e., the earth itself). An actual
ground can be an artificial ground plane, such as
that provided in some antenna structures. Actual
ground can also be modified by nearby rooftops,
buildings, guy wiring, and utility wiring.
actual height The highest altitude where radio
wave refraction actually occurs.
actual power Also called active or AVERAGE
POWER. Symbol, P avg. In a resistive circuit under
sine-wave conditions, average power is the prod-
uct of the rms voltage and the rms current. It is
also equal to half the product of the maximum
current and maximum voltage.
actuating device A device or component that oper-
ates electrical contacts to affect signal transmis-
sion.
active satellite See ACTIVE COMMUNICATIONS actuating system 1. An automatic or manually
SATELLITE. operated system that starts, modifies, or stops an
active sensor In an electronic security system, a operation. 2. A system that supplies energy for
transducer that generates an electromagnetic ACTUATION.
field or acoustic-wave field, and detects changes actuating time Also called actuation time. The
in the field resulting from the presence or move- time interval between generation of a control sig-
ment of objects in the vicinity. nal, or the mechanical operation of a control de-
active substrate In an integrated circuit, a sub- vice, and the resulting ACTUATION.
strate consisting of single-crystal semiconductor actuation 1. The starting, modification, or termi-
material into which the components are formed; nation of an operation or process. 2. Activation of
it acts as some or all of the components. This is in a mechanical or electromechanical switching de-
contrast to a substrate consisting of a dielectric, vice.
where the components are deposited on the sur- actuator An electromechanical device that uses
face. electromagnetism to produce a longitudinal or ro-
active system A radio and/or radar system that tary thrust for mechanical work. It is often the
requires transmitting equipment to be carried in end (load) device of a servosystem.
a vehicle. ACU Abbreviation of automatic calling unit.
active tracking system A system in which a ac voltage A voltage, the average value of which is
transponder or responder on board a vehicle re- zero, that periodically changes its polarity. In one
transmits information to tracking equipment cycle, an ac voltage starts at zero, rises to a max-
(e.g., azusa, secor). imum positive value, returns to zero, rises to a
active transducer 1. A transducer that contains maximum negative value, and finally returns to
an active device, such as a transistor or inte- zero. The number of such cycles per second is
grated circuit, for immediate amplification of the termed the ac frequency.
sensed quantity. 2. A transducer that is itself an ac voltmeter See AC METER.
active device. acyclic machine Also called ACYCLIC GENERA-
active wire In the armature of a generator, a wire TOR. A dc generator in which voltage induced in
experiencing induction and, therefore, is deliver- the active wires of the armature is always of the
ing voltage. same polarity.
activity 1. Intensity of, as well as readiness for, os- A/D Abbreviation for ANALOG-TO-DIGITAL. See
cillation in a piezoelectric crystal. 2. Radioactive ANALOG-TO-DIGITAL CONVERSION.
intensity. 3. Intensity of thermal agitation. 4. Ada A microcomputer language designed primarily
Thermionic emission of electrons. for use in multi-computer systems, where each
activity ratio The ratio of active to inactive records small computer communicates with the others,
in a computer file. providing some of the advantages of a larger com-
ac transducer A transducer that either requires an puter.
ac supply voltage or delivers an ac output sig- Adam A communications code word sometimes
nal—even when operated from a dc supply. used for phonetic verbalizing of the letter A. More
ac transmission The use of an alternating voltage commonly, ALPHA is used.
to transfer power from one point to another, usu- adapter 1. A fitting used to change either the ter-
ally from generators to a distribution center, and minal scheme or the size of a jack, plug, or socket
generally over a considerable distance. to that of another. 2. A fitting used to provide a
actual ground The ground as “seen” by an an- transition from one type or style of conductor to
tenna. The actual ground surface is not necessar- another (e.g., waveguide to coaxial line). 3. An