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This a part of a video signal (NTSC). The active video part is plotted on the screen. In my understanding, there are parts cut away by the "fly back and the settle" for preparing to plot the next lines. Can someone tell me how much (%) is cut?

Assuming that all the active video part is plotted on the screen. If I see 20 squares in a row, 10 whites interlaced with 10 blacks, this means that the active video is a square wave, which repeats 10 times in 52.6us. Can I conclude that its frequency is:

52.6us/10 -> 5.26us (the period of the square signal)

--__--__--__--__--__--__--__--__--__--__
<-----------      52.6us        ------->

--__
5.26us

so, the frequency is:

1/5.26us = 190Khz

enter image description here

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The part how much is cut depends on how your set is adjusted. There will never be an exact figure.

Your frequency calculation is way off.

1 MHz is 1 us period, so visible line would have 52 square wave periods, 52 black and 52 white "pixels". So 20 squares is much less.

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