Topband: Re: AGC

[Oleg Skydan]

Hi,

> A hardware AGC system must have something unusual inside if it has a
> threshold and then clamps perfectly. Perhaps very high gain and a
threshold.
>

I suspect, that Icom781 uses a combination of closed loop and forward AGC
system.
I used such system in my previous (analog) design, and it works fine. It
controled the
gain of 3 IF stage before AGC detector and one after. With such system you
can
make even "negative" slope of the AGC. Usually signal changes by 20-30dB at
the
AGC detector, but can be nearly constant at the IF strip output. Such system
has a lower loop gain than usual one and has a very good dynamic
characteristics.
If somebody is interested I can post the schematics of my design.

I also remember an article in QEX about such design (it used a lot of OP
amps
and costly chips from AD).

As for the other AGC thoughts  I am completely agreed with you (Tom).

All the best !
Oleg
73 de UR3IQO