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Originally Posted by Rinehart
The NTSC monochrome standard ran at 30 fps; when colour was introduced, it was reduced to 29.97 fps, a reduction of 0.1%. Why did it have to be reduced at all, and why by that amount?
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IIRC, the frame rate was shifted slightly to avoid an "aliasing" or "beat" effect with other components in the signal, particularly the 4.5 MHz sound carrier. The horizontal scan rate was similarly shifted from 15.750 KHz to 15.734 KHz.
The small amounts of shift were required to make sure that existing monochrome sets could still lock onto the new color sync signals.
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What exactly is the "colour burst"? Is it a kind of synchronizing signal?
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The burst is a short pulse of 3.579 MHz located on the "back porch" of each horizintal sync pulse. It provides a phase reference to lock the set's 3.58 oscillator to the transmitted signal, keeping the reproduced colors the same as they were at the transmitter.
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What were shadow masks made from? Presumably the material had a low coefficient of thermal expansion, but were there other considerations as well?
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Typical material was an alloy called invar.
http://en.wikipedia.org/wiki/Invar