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Date Posted: 07:18:18 01/31/02 Thu
Author: Jain
Subject: Re: AGC sampling added to Rev7t1d2. For Potter and Phil
In reply to: Potter 's message, "Re: AGC sampling added to Rev7t1d2" on 06:50:11 01/31/02 Thu

You have much more experience that I have, related to this 3chip. Alow me to say that sampling for AGC would be good if it is done durring 90% of the VBI (AGC level must be the same for that period of time). It's important to mention that the 47 uF cap on AGC pin must be removed (the original one should be in place). If Potter is thinking to use the AGC hack pulse for seting the blancking level, then it is justified to have it short, and in the place mentioned. Otherwise that pulse could be as long as 1 mSec or so.
Jain

>I chose a line that is always black on all channels
>(16 for me) and sampled from the end of the burst to
>near the end of the line (~50uSecs). This is the line
>after the one carrying the data packet. I'm also
>considering the DigitalMan DC restoration as this
>could be driven by the same sampling pulse and
>eliminate the clamping level adjustment for even
>better all-round results.
>
>>Folks,
>>
>>I did a very quick hack to my Rev7t1d2 code for SA and
>>added AGC sampling support for Potter's circuit. It
>>uses RA3 (audio privacy on Canton 4.2, available on
>>the 3 pin header), and samples for about 800 nSec.
>>during line 23. I haven't properly timed it to the
>>front porch or anything like that, I just threw it in.
>> 800 nSec. may not be long enough, and since I haven't
>>built Potter's circuit to test it may not work at all,
>>but let me know how it goes and I'll fix it when I
>>have some time.
>>
>>I sent the code to Jain and Sakman, I don't have
>>Potter's email address. Once it's working the way we
>>want it to, I'll zip it up like the Rev7t1d2 code and
>>Tom can post it if he likes.
>>
>>- Phil

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