Manual Squelch - Albrecht AE 6491 NRC Manual

Advantage: highest sensitivity and thus highest communiction
range
Disadvantage: due to interferences e.g. sunspot activity,
electronic devices, etc., it may open without actually receiving
any signal. In this case either the manual or tone squelch will
work better.

6.5.2. Manual squelch

By turning the manual squelch clockwise it eliminates the
background noise. The further the squelch is turned, the stronger
the receiving signal has to be to open the squelch.
The normal setting is usually the point at which the squelch
barely mutes the speaker.
Advantage: when set to a high level it can be used to only hear
near stations and block all stations further away.
Disadvantage: needs to be set manually. When accidentally set
too high, it results in a loss of sensitivity and thus range
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