mm wrote:
Before the advent of mandatory digital over-the-air TV, it was said
that the picture would be near perfect, and that there woudl be no
ghosts. Tonight I saw one, for a full half hour if the scene had the
right kind of lines, including vertical lines.

From the beginning I had doubts about the claim there would be no
ghosts. I gleaned or understood that, aiui, if a ghost signal was
less than, say, 50% as strong as the direct signal, and the direct
signal were 0, the electronics would "round down" and output a zero.
If the direct signal were 1 and the ghost was less than 0.5 and more
than zero, or more than -0.5 and less than zero, the sum might be 1.5,
but the electronics would interpret that as a 1.

But that didn't account for every situation. What if the ghost signal
was 0.6 the strength of the direct signal and the direct signal was a
zero? Now, although I've never seen it discussed (and I do read a
bit) I presume there are 3 signals making up the OTA video signal, and
I'm ignoring that for now.

It doesn't matter what the relationship is between the main signal and
any reflected signals, they still won't cause ghosting in digital TV.
They may mess the signal up to the point where the television doesn't
produce a picture, but you won't get ghosting - digital TV simply
doesn't work that way.

Sylvia.