🚀 go-pugleaf

>O.K Guys, all the talk about video standards has caused me to
>remember something that's puzzled me for a long time:
>*exactly* what are the "equalizing pulses" for?

>No guesses, please; I've made and been offered lots of those.
>If you *know*, please enlighten me.

The equalizing pulses are what make the interlaced scanning work.
Basically, these are pulses at 2X the horizontal sweep frequency, which
appear for a short time immediately before and after the vertical sync
pulse.  Note that, in interlaced scanning, the normal horizontal sync pulses
of one field occur exactly betweenm those of the other, were you to line
up oscilloscope traces of the two field's timing.  The equalizing pulses,
at 2X the "normal" horizontal frequency, make for pulse edges which line up
with the horizontal pulses expected of either field.  This permits a "neat"
transition from odd to even field (or vice-versa), while keeping the vertical
sync pulse at the proper place.

A good discussion of television systems in general is found in chapter
20 of the Electronic Engineer's Handbook, ed. by Donald Fink.  The description
of timing in the text is a bit hazy in regard to these pulses, but I think 
that you'll find the example in fig. 20-42 makes it clear.


Bob Myers  KC0EW   HP Graphics Tech. Div.|  Opinions expressed here are not
                   Ft. Collins, Colorado |  those of my employer or any other
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