In article ,
"Lenny" wrote:

Could some kind soul please explain the whole AGC thing to me ? And
keep it simple please. What does it do? When should I use AGC Fast?
When should I use AGC Normal? If I turn off AGC, and manually adjust
the RF Gain, what am I doing, and why am I doing it? Anything else I
should know? FYI, I have an Icom R75 with all the Kiwa mods, and an
Antenna Supermarket Eavesdropper dipole.

Basically the radio has to adapt to the signal level you are tuned to by
changing its sensitivity. A weak signal will cause the AGC voltage,
which stands for Automatic Gain Control (this is a feedback loop in the
radio) to change to a level for maximum sensitivity. If the radio is
tuned to a strong signal the AGC voltage will change to cause the radio
to be less sensitive. This same AGC voltage also drives the "S" meter on
most radios so when the "S" meter swings up to indicate a strong signal
the radio is also being driven to be less sensitive.

Generally I set the AGC to the fastest settings that does not cause an
annoying pumping of the signal for AM. If the AM broadcast has a rapidly
changing amplitude I would then switch the AGC to a slower rate of
change.

For SSB usually you want a slow AGC so you don't get the noise between
the audio peaks for SSB broadcast. Generally you will want slow AGC for
ham SSB for the same reason.

For any kind of digital mode you want fast AGC and if it is an option on
your radio you would also want to use fast response IF filters.

Band scanning for any type of signals I use the fastest AGC.

The ICOM R75 AGC is a more complicated thing than on most radios and
some of the "Mods" may well have changed the way the radio AGC behaves
so I'll have to leave the commentary to someone else that owns one.

--
Telamon
Ventura, California