"Roy Lewallen" wrote

But the DC information is transmitted as a level difference
between the sync tip and the "porches". At the receiver (as I mentioned in
another post), this voltage *difference* is turned into a DC value. No DC
is transmitted.
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As I wrote in my slightly earlier post to you on this, the actual video
waveform is DC coupled through an analog TV transmitter. Please refer to
that post for more on this topic.

RF