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Date Posted: 09:07:10 02/14/02 Thu
Author: Ronald
Subject: Re: How to bypass unscrambled Channel?
In reply to: Jain 's message, "Re: How to bypass unscrambled Channel?" on 07:59:00 02/14/02 Thu

>I can not help you with soft ideas (I'm not a
>programming expert too) and I think nobody will do
>that, not knowing how the local system works.
>But... I'm also not happy with the 3 chip results, so
>I'm trying to improve it (let's mention that I
>installed 3 chip in a cable adapter that has IF
>processing and I have the advantage to send the output
>of the addapter -- output in Ch 3-- to a two way
>spleater; from there, to the TV, one way, and I can
>see the unscrambled channels, and the second way to
>the IF imput of the cable addapter , and there 3 chip
>decodes the scrambled channels and sends the result to
>video output; the scrambled channels could be seen
>with the tv set in video mode).
>So, the first idea was to fix the AGC problem; the
>second is to insert in the right place the blanking
>part of the tv signal insted of letting 3 chip to
>build an artificial synchonization -- and this with
>the help of DC restoration circuit (I'm trying to
>clarify some things that are not too clear to me with
>this circuit in Digitalman). If you read very
>carefully the messages I changed, in the last days,
>specially with Potter, that is also an experimenter
>guy, you'll see that all apply to your wishes too.
>Tell me what it bother you (what you don't like when
>you look at the screen) and we may find hardware
>solutions, in absence of a soft one.

My TV system is PAL-BG.

I fixed my AGC problem using a 100uf in series with a VR from AGC PIN 19 of the IF IC TDA9801T to ground. The value of my VR is about 268ohm. So 100uf and 500R VR should be good enough. I can forget about build the S&H circuit which bugs me for months. Fine tune the VR and I think you can get very good picture quality and very even color. No white flashing on the top screen and no uneven color and brightness. I am using canton's Rev3 with addition of 733 to get superb quality. My oscillator ciruit is a 20Mhz Cystal and 3 capacitor and a VCXO to get super stable quality. I also need to do more sampling on the burst by adding iorwf PORTB,w to make it more stable. Now my problem is watching unscrambled channel with the decoder and I get little wavy on the VBI. I have remove some nops on the Mainloop and begin to reduce the shifting. So now shifting stop but some lines can be seen wobbling. But I think it is better than shifting.

If you are not satisfy with the picture quality by adding a 733 to the output will definitely enhance the output. I have tested it already but that will involve too many component. So I just add 1pc of 733 before Canton's Rev 3 input.

So now I testing the SX50 version to compare my present result. Thanks to Potter that has been helpful to his source code but I am still not able to get it locked.

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