Table 4-1. Audio Output Responses Characteristic of Various Types of Interference

TM 11-490-5

the effect on an audio signal of some of the terferers

listed in table 4-1.

Table 4-1. Audio Output Responses Characteristic of Various Types of Interference

Receiver audible output

Character of interference

Possible source or mechanism

Reduced noise level (or steady tone

Carrier (only)

Cochannel, spurious, intermodulation

with beat frequency oscillator

(BFO) operating)

Pulsed variation in noise level (or

Pulsed continuous wave (CW) or

Adjacent channel, co-channel,

pulsed tone with BFO operating)

digital transmission

spurious, intermodulation, cross

modulation

Pulsed variation in noise level (two

Unwanted radio teletypewriter

Adjacent channel, co-channel,

pulsed tones with BFO operating)

(RATT) frequency shift keying

spurious, intermodulation, cross

(FSK) transmission

modulation

Added normal or distorted voice

Unwanted voice transmission

Adjacent channel, co-channel,

spurious, intermodulation, cross

modulation

Whistling or squealing

Unwanted transmission or in-

Adjacent channel, co-channel,

termediate frequency oscillation

spurious, intermodulation, cross

modulation, parasitic and IF

oscillation

Rapid variation in noise level (or

Unwanted facsimile transmission

Adjacent channel, co-channel,

several pulsed tones with BFO

spurious, intermodulation, cross

operating)

modulation

Steady tone or whining

High rate periodic pulses

Radar, rotating machines

Buzzing

Medium rate periodic pulses

Buzzers, vibrators

Popping

Low rate periodic pulses

Ignition systems, magnetos

Hum

Low (60 Hz) rate

Power lines

Frying

High rate random pulses

Electric arcs, continuously arcing

contacts

Sputtering

High rate random pulses

Arc welders, arc lamps, diathermy

Clicking

Low rate random pulses

Code machines, electric calculating

machines, mercury arc rectifiers,

relays, switches, teletypewriters,

thermostatic controls, electric

typewriters

Crackling

Static or corona discharges

Sharp crackle

Ambient noise

4-5