NORTHROP GRUMMAN T6MC, Пользовательская документация

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Glossary of Terms
The following terms are used in this documentation.
E and M Signalling
Refers to PTT and the squelch indication signalling between a radio site and the control equipment.
E represents ‘Ear’ (what is heard, or received) and M represents ‘Mouth’ (what is sent). Therefore:

A PTT signal sent from the control equipment is referred to as the M signal; the same signal at the
transmitter is referred to as the E signal

A squelch indication at the receiver is referred to as the M signal; the same signal at the control
equipment is referred to as the E signal.
Squelch
Squelch (also referred to as Mute in older receivers) is a circuit function that:

Mutes a receiver’s audio output during periods of no reception

Mutes a receiver’s audio output when signals weaker than the squelch threshold are received.
Phantom Keying
Phantom keying is when the keying potential is superimposed on the audio lines.