RHF wrote:
Why Turn the AGC "Off" ?
http://groups.yahoo.com/group/Shortw...a/message/5946

Howdy RHF,

The AGC is typically (though not always) driven by the signal level in
the IF. Strong signals that are slightly off the listening frequency
can leak into the AGC enough to cut the gain even though you don't
hear them. Thus a nearby strong signal or even noise can reduce
receiver sensitivity when you're listening to another, weaker signal.

The same effect can cause 'pumping' of the AGC, when a signal is
either internmittant (like CW) or undergoing rapid fading - the
receiver sensitivity bounces up and down with the interfering signal.

AGC time-constants can sometimes be exactly wrong for the fading
cycle of a signal - it reduces gain just as the signal itself is
fading.
This is why it's nice to have a choice of time-constants - slow and
fast for example. When listening to sideband or CW, having a slow ACG
helps smooth out the inrush of noise in between sylables, words, etc.

Try turning off your AGC more often, if only to get an appreciation of
how much work it's generally doing. You'll be amazed at how much more
variable signal levels are than you ever thought.

- Robert [VA2ERY]


Good post. The Icom R-75 has selectable no AGC/slow AGC/fast AGC,
and each is very useful at different times for different conditions.

Tony

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