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TM-11-490-5 Army Communications Facilities Operational Electromagnetic Compatability Manual
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APPENDIX. DEFINITIONS-continued - TM-11-490-50043


TM 11-490-5
APPENDIX
DEFINITIONS
desired signal level. The gain reduction is generally
Absorption--Wave propagation energy losses due to
due to overload or saturation of some portion of the
conversion of wave energy to heat.
receiver. Can also occur when an interfering signal
Adjacent channel, audio--An audio channel immediately
causes undesired operation of the AGC system in the
above or below a specified audio channel.
receiver.
Adjacent channel, RF-An RF channel immediately
Dielectric--An  insulating  material  which  essentially
above or below a specified RF channel.
prohibits the flow of electrical current between
Analog system--A system of communications in which
conducting components of a network.
information  is  transferred  in  the  form  of  a
Dual-conversion receiver-A receiver in which RF to IF
continuously variable waveform.
conversion is accomplished in two steps, employing
Arcing--A low-voltage, high current electrical discharge,
two local oscillator/mixer systems and two IF
as contrasted with sparking.
Amplitude modulation (AM)--A method of modulating a
Decibel
(dB)--A
logarithmic
unit
used
in
carrier wave to cause it vary in amplitude according
communications work to express power ratios.
to the modulating intelligence.
Diffractions--The process by which electromagnetic
Bandwidth--The difference, expressed in Hz, between
waves curve around edges and penetrate into the
specific upper and lower limiting frequencies which
shadow region behind an opaque obstacle.
are usually specified as the upper and lower half-
Digital system--A system of communications in which
power (3 dB) points of a system or network.
information is represented by a series of discrete
Binary--A system of numbers having two as its base.
signal elements or digits (binary or other).
Used in digital data transmission systems and
Electromagnetic compatibility (EMC)--The ability of C-E
computers.
devices, together with electromechanical devices, to
Broadband emission--An emission which has a spectral
operate in their intended operational environment
energy distribution sufficiently broad and continuous
without
suffering
or
causing
unacceptable
so that the response of the measuring receiver in use
degradation because of unwanted electromagnetic
does not vary measurably when tuned over a
energy. EMC includes vulnerability to ECM.
specified number of receiver bandwidths.
Electromagnetic interference (EMI)--Interference is any
Capacitive coupling--The means by which signals are
electromagnetic  emission  causing  undesirable
transferred from one conductor to another through
responses which degrade, disturb, or disrupt the
the capacitance existing between the conductors.
design function of devices or systems which employ
Characteristic curve--As applied to transistors and
electromagnetic energy. For frequency management
electron tubes, the relationships between the various
purposes, the term "harmful interference" is used to
voltages and currents as evidenced at the external
denote any emission, radiation, or induction which
connections; for example, the curves of base current
endangers the functioning of a radionavigation
versus collector current for a transistor.
service or of other safety services, or seriously
Cochannel interference--Electromagnetic interference
degrades, obstructs, or repeatedly interrupts a radio
caused  in  one  communication  channel  by  a
communications service operating in accordance
transmitter operating in the same channel. Corona-
with international regulations. Additionally, the term
The discharge brought a out as a result of the
"harmful interference" is used to denote that type of
ionization of air (or gas) surrounding a conductor.
interference which actually causes circuit outage as
Cross modulation--A type of Intermodulation due to the
opposed to interference which is purely a source of
modulation of the carrier of the desired signal by an
annoyance.
undesired signal wave. Occurs primarily as a result
Electronic Warfare (EW)--Military action involving
of nonlinearities in the RF circuitry of a receiver.
Desensitization--The effect of an undesired signal in the
receiver band pass which causes reduction of the
A-1


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