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Date Posted: 02:29:39 01/20/02 Sun
Author: Ronald
Subject: Re: A simple test...
In reply to: Potter 's message, "A simple test..." on 01:06:47 01/20/02 Sun

>I guess you've got the correct AGC filter pin on the
>IF chip? A simple way to prove it is to connect an
>electrolytic ~47 to 220uF from the pin to ground
>(check polarity & disconnect the S&H cct first). In
>most cases this will fix the problem but the time
>constant is made so large that the AGC can't
>compensate for variations in signal strength like I
>get on the local microwave system when the weather is
>bad - would be less of a problem on cable systems.
>The S&H circuit was modified for 5V only operation so
>if the AGC voltage on your filter pin is >5V then the
>opamp naturally won't be able to provide it (the
>original circuit was 12V powered and required a
>TTL-CMOS level converter stage for the PIC to drive it)

Yes I got the IF AGC PIN correct. It is originally connected to a 1uf capacitor at around 3.11V. So your circuit works. I have to put a 47uf in the S & H circuit.

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