APPENDIX. DEFINITIONS

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.

amplifiers.

Amplitude modulation (AM)--A method of modulating a

Decibel

(dB)--A

logarithmic

unit

used

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

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

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