59.94 IIRC.? The color subcarrier frequency was chosen to put the energy of the color subcarrier in between the energy created by the monochrome image.? I think they changed the audio subcarrier frequency a bit, just to avoid the beat frequency between the audio and the color information.
Everything was derived from 14.31818 Mhz, which generated the horizontal and vertical frequencies, and kept the picture artifacts minimized.
The I and Q modulation was picked so that the major amount of energy was low (since they decided that people couldn't see certain colors, so that large objects are all three colors, and the next set of color details are only two colors.? Anything higher than 1.5 Mhz in the old NTSC is black and white, IIRC.
Harvey
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On 3/30/2023 7:41 PM, Ed Breya via groups.io 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.
Anyway, you can force your unit to run at exactly 60 Hz by tweaking the oscillator to match whatever divide ratio is used. The HP/Grass Valley thing likely wasn't intended to make exactly 60 Hz, but the NTSC version of it. Changing that to real 60 Hz would be a much bigger project.
Ed
