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Date Posted: 05:47:06 02/16/02 Sat
Author: Potter
Subject: Re: How to bypass unscrambled Channel?
In reply to: Jain 's message, "Re: How to bypass unscrambled Channel?" on 10:31:00 02/14/02 Thu

Wobbling lines usually mean the coarse locking routine is operating (lock is barely being maintained) and the cure for this is to fine tune the code to the oscillator or vice versa). If the jitter is worse at the top of the screen it may be that the accumulated error on return from MAKEVBI takes a lot of correcting. This can also be the result of edge detector output pulses being too short or too long on the edges of interest (sync).
If you removed the edge pulses after locking the code would be unable to check & maintain lock (used by MAKEVBI, MAKEHLINE) and interpret the video as bad.
MAKEHLINE checks the edge of the (real) hsync to see if it's fast or slow and drives the oscillator (vcxo) or adds/removes cycles (SX) to correct the error - a software phase-locked loop.
MAKEVBI checks that the serration pulses during the VBI (actual signal) are all where they should be in each frame - if any are missed the LOCKON code is called again.


>Hi Ronald
>In order to get rid of wobling lines (or shifting) I
>give you the idea (which I already posted on forum)
>to try to stop video to the pulse detectors as long as
>the 3 chip is locked. I'm going to try that in a few
>days (I mean I have a non tested hardware solution).
>I have the advantage of never inverted video, so I
>think I'm going to use only one emiter follower at the
>input and one at the output, everything DC coupled and
>synchro restored (not built) at the proper level
>Cheers
>Jain

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