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Old 02-20-2018, 03:20 PM
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Quote:
Originally Posted by NewVista View Post
I think I've solved the problem for RCA's original NTSC spec with a better implementation:
Just have colorburst for almost a whole line period in the last serrated segment of the field sync pulse
at ~50% luminance level(like GE-VIR) (picture level of light complexions.)

This gives nice clean, long duration subcarrier reference every sixtieth of a second (like VIR) (no burst every line needed)(who gives a flip about airplane-flutter.)

Then 1950s era receivers simply run separated vert sync thru a HPF to obtain subcarrier phase reference (no countdown circuit chips required 1970s VIR)
Do you mean a different version of NTSC with subcarrier reference only in the vertical segment but not in each line?

1) Does not solve the problem of having it re-inserted in order to meet FCC signal specs. The original problem was in good part due to the locally reconstituted sync and burst having the wrong phase and amplitude compared to what had happened to the chroma coming over the network. Simply passing the degraded burst to the transmitter was a non-starter, as it could cause problems with color killers in receivers.
2) Not possible to use it with affordable crystal oscillator / phase-locked loop technology, since the oscillator in the receiver would need to have a free-running frequency within 30 Hz of correct, or side-lock could occur. With burst on every line, the free running crystal needs only to be within half that, or 7867 Hz. To insure quick lockup, the oscillator actually should be off no more that 10% or so of the nearest sideband and the loop bandwidth should be just wide enough to pass a beat frequency. Remember, horizontal rate sidelock is what was used in gated-rainbow color bar generators. This proposal would allow accidental vertical sidelock, and would require a crystal oven for stability and/or a customer color lock control to prevent it.

A very thorough theoretical study was done of the color burst to verify that once per horizontal was the right way.
http://ieeexplore.ieee.org/document/4051510/
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