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Date Posted: 01:06:47 01/20/02 Sun
Author: Potter
Subject: A simple test...
In reply to: Ronald 's message, "Re: AGC Hack Question to Potter or those who knows" on 11:13:49 01/18/02 Fri

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)

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