Re: Some comments on calibrating a Tektronix CFC250 100MHz frequency counter.
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NTSC was the "National Television Standards Committee' which originally set the standards for Monochrome Television, then later chose the modifications to allow color without a severe beat in the Chroma. From memory, vertical was 59.94 Hz and horizontal was 15, 734.34 Hz. Stations typically ran 60/15,750 if they only transmitted in monochrome. I was the engineer at a station like that in 1973'74.which made it difficult but not impossible to transmit our station ID in color without? any color equipment. Our master sync generator had a Genlock input that I drove from a color bar generator. It was first generation Grass Valley, and used RTL or DTL logic. There were circuits that used frequency multiplication and dividers to convert Colorburst to 5 000 MHz, but it was only accurate if it was a network feed that wasn't modified at a local TV station, which was rare. The stations I worked at used a cheap 14.318.189 MHz crystal instead of a rubidium master oscillator. On Thu, Mar 30, 2023 at 7:41?PM Ed Breya via <edbreya=[email protected]> wrote: As I recall, the "60 Hz" vertical scan rate for NTSC is not supposed to be exactly 60 Hz, but slightly different, to provide color and still maintain integer counting values. Likewise, the horizontal is not 15,750 Hz as in monochrome, but something like 15,734. This was all part of the trick to squeeze the vector modulated color info into the spaces between the normal monochrome scan spectral lines, and magically work for both color and B&W TV sets, with "mostly" full compatibility, and without needing any extra channel bandwidth. If you study up on NTSC, you can get the exact values and rationale of the scheme. I've always found it quite fascinating how this was figured out and done way back when. I used to understand it, but it's been a lot of years. |
Michael A. Terrell