On Tue, 24 May 2005 23:08:51 -0400, "Tom Holden"
wrote:


However, at the fast and medium release settings, the receiver gain
literally oscillates at a rate that seems to be a function of attack and
release time constants, manual RF/IF gain setting, AGC gain setting and
signal strength. The depth of this gain modulation is affected by AGC and RF
gain. In order to get stability, it seems that I have to slow down the
attack (and/or release) time constant and carefully tweak the AGC gain
between the onset of oscillation and receiver peak distortion caused by not
enough gain reduction.


Tom,

The problem is the system (AGC) is a servo loop and the loop lacks
damping so it overshoots then rings at the loop time constant.

Try adding a simple RC of something like 1000 ohms and 100uf in the
place where your putting a time constant. The high series resistor
will allow fast change but the series capacitor will absorb some of
the rate of change. You may have to emprically tweek the values.

Also Experimental Methods in RF Design (ARRL Press) is a good
reference and has examples plus discussion on the subject..

Allison