Surely as a former broadcast engineer you're acquainted with a circuit
called a "DC restorer". This is a circuit which is always present in a
TV receiver. In its simplest form, it's just a diode clamping circuit,
although I've made very good ones with an FET switch and hold capacitor.
What it does is to set the sync pulse tip to a fixed DC value, which
then causes the rest of the TV waveform to be at a fixed DC value. This
is how the DC information is "transmitted". The actual TV waveform is AC
coupled, as it must be, and its DC values are established in the
receiver by the DC restorer.

No DC value is transmitted.

You should be able to find an explanation of this in any basic text on
the principles of television transmission and reception.

Roy Lewallen, W7EL

Richard Fry wrote:
______________

You mis-read. There is a DC component _required_ to convey the steady
voltage values preceding and following the step pulse transition. He's
not saying that the step pulse transition itself is comprised of "DC."

RF