Re: AGC fix Schematic -- New 3C

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Date Posted: 17:34:08 12/02/01 Sun
Author: Tom
Subject: Re: AGC fix Schematic
In reply to: Potter 's message, "Re: AGC fix Schematic" on 10:40:48 12/02/01 Sun

The video signal should be 1 v pp including the sync. For NTSC, the signal is measured in IRE with -40 IRE being the lowest point in the signal(the bottom of the sync) and 100 IRE being the highest point in the signal(brightest white in the video. 140 IRE units is equal to 1v pp. If the video is clamped correctly, -40 IRE should be -.286 vdc, 0 IRE(or the blanking level) should be 0v pp, +7.5 IRE(black level) should be .054v pp and 140 IRE(white level) should be .714vdc. The signal from the IF is not usually clamped to the specification and it doesn't make a difference since the signal passes through a cap anyway. Regardless, the 3chip is looking for a 1v pp signal, including the sync. Since the sync is raised in a scrambled signal, the total peak to peak value of the scrambled signal would consist of the video. The size of the negative falling edge of the sync determines the width of the NED. The falling edge of the NED locks to the start of the "A" section. This is for Rev7t1a code and NTSC. The width of the NED should be 1-1.8 us, if I remember right.

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Replies:

This should be read by everyone atempting to build 3 chip -- Jain, 09:16:27 12/09/01 Sun
- Instability on scrambled channels -- Phil Q., 08:35:09 12/12/01 Wed
  - Re: Instability on scrambled channels -- Jain, 18:36:54 12/12/01 Wed
  - Re: Instability on scrambled channels -- vg, 14:52:00 12/13/01 Thu
    - Re: Instability - test it first -- lcs, 20:03:22 12/13/01 Thu
      - re: Instability -- Phil Q., 12:27:42 12/14/01 Fri
        Re: re: Instability -- lcs, 20:17:34 12/14/01 Fri
        Re: re: Instability -- Potter, 04:31:38 12/17/01 Mon
        Re: re: Instability - edge detectors mod. -- lcs, 22:00:33 12/27/01 Thu

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