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Topband: Re: AGC

To: "Tom Rauch" <w8ji@contesting.com>, <jkaufmann@alum.mit.edu>,"Topband" <topband@contesting.com>
Subject: Topband: Re: AGC
From: "Oleg Skydan" <skidan@mail.ints.net>
Date: Wed, 11 Feb 2004 18:02:06 +0200
List-post: <mailto:topband@contesting.com>
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

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