Hi Tom,

You might find some good info from reading the description and
data sheets for the Analog Devices SSM2165 and/or SSM2166
at www.analog.com. They address the issues of having a threshold
which can be adjusted and then varying the amount of compression
or limiting asymetrically. Perhaps you could modify your circuit to
emulate some of these features - or perhaps just use the devices
described?

Bill

wrote in message
oups.com...
This sounds like a classic negative feedback oscillation. You sense the
signal is too large, so you send a signal to kill the gain, and then
you sense the signal is too small, so you send a signal to increase the
gain.

Having different attack and release time means you have two different
time constants My guess is the quick attack leads to the instability,
since it is the lesser damped system. If this is true, then you should
concentrate on the attack time, i.e find how slow it has to be for the
sytem to be stable.

Of course this is really had to do without seeing the circuitry in
action.

Thanks for the reference, Bill. I did learn something of value from it but
the devices are clearly intended for audio frequency although one might
actually support 0dB gain at 455kHz! However, they are a closed loop system
and it's not obvious that one could bring out the required control voltage
to drive the receiver AGC.

Regards,

Tom

"Netgeek" wrote in message
...
Hi Tom,

You might find some good info from reading the description and
data sheets for the Analog Devices SSM2165 and/or SSM2166
at www.analog.com. They address the issues of having a threshold
which can be adjusted and then varying the amount of compression
or limiting asymetrically. Perhaps you could modify your circuit to
emulate some of these features - or perhaps just use the devices
described?

Bill

wrote in message
oups.com...
This sounds like a classic negative feedback oscillation. You sense the
signal is too large, so you send a signal to kill the gain, and then
you sense the signal is too small, so you send a signal to increase the
gain.

Having different attack and release time means you have two different
time constants My guess is the quick attack leads to the instability,
since it is the lesser damped system. If this is true, then you should
concentrate on the attack time, i.e find how slow it has to be for the
sytem to be stable.

Of course this is really had to do without seeing the circuitry in
action.