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Sol-20 vertical sync pulse non-standard

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    #16
    I had a look in my library of American vintage television books. One book,Television Today & Tomorrow, by Lee De Forest (the inventor of the triode or Audion, but some argue against that) Dial press, New York 1942. It describes the sync signals defined by the RMA (Radio Manufacturers Association) for the "RMA Standard Television Signal". The same is also shown in Principles of Television Engineering by Fink (McGraw Hill) 1940.

    Both texts shows the vertical sync pulse to be to 3 horizontal periods long or 190uS. So it is interesting how long this standard has been in place.

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      #17
      Perhaps the designers of both boards were following a "bible" of the day, the "TV Typewriter Cookbook" written by Don Lancaster. In his book, Don Lancaster recommends 400us for the vertical sync pulse width. This is more than twice the RS-170 spec. He doesn’t say why other than stating:

      "For most TV typewriter uses, we need not provide the exact EIA sync used by commercial stations. Instead, we can approximate the pulses and the video we need, as in Fig. 4-3"

      Mike

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        #18
        Originally posted by deramp5113 View Post
        Perhaps the designers of both boards were following a "bible" of the day, the "TV Typewriter Cookbook" written by Don Lancaster. In his book, Don Lancaster recommends 400us for the vertical sync pulse width. This is more than twice the RS-170 spec. He doesn’t say why other than stating:

        "For most TV typewriter uses, we need not provide the exact EIA sync used by commercial stations. Instead, we can approximate the pulses and the video we need, as in Fig. 4-3"

        Mike
        I'm getting ready to fire up my Poly88. It seems like I recall the tearing of the horizontal at the top of the screen. It was always something I lived with. I'd adjust the two pots for the best image but the tear was still there. I suspect this explains what was happening.
        Dwight

        Comment


          #19
          Originally posted by Dwight Elvey View Post
          I'm getting ready to fire up my Poly88. It seems like I recall the tearing of the horizontal at the top of the screen. It was always something I lived with. I'd adjust the two pots for the best image but the tear was still there. I suspect this explains what was happening.
          Dwight
          Here's a mod to shorten the Poly VTI vertical sync from 8h down to 4h

          http://deramp.com/downloads/polymorp...Sync%20Mod.pdf

          Mike

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