On Wed, 20 Jan 2010 19:53:33 +1100, Sylvia Else
wrote:

mm wrote:
On Wed, 20 Jan 2010 18:25:14 +1100, Sylvia Else
wrote:

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

But I did get ghosting.

- digital TV simply
doesn't work that way.

Who am I going to believe, your theory-based answer, or my own eyes?

They are not necessarily inconsistent. You may have seen something, but
it wasn't ghosting, in the sense that it wasn't caused by your antenna
receiving a main signal and some delayed reflections.


Do you watch OTA tv these days?

Maybe it matters that the station is 30 or 40 miles away. Do you watch
stations like that?

Sylvia.

I also saw what was probably ghosting during a commercial right after
that show. The commercial had big thick red letters against a white
background, and the red continued about an eighth or three sixteenths
of an inch to the right, lighter than the main red image.



If you're using a set-top-box and feeding a composite video signal into
a conventional TV, you may just be seeing an effect where abrupt changes
in luminance feed into the colour signal.

No. I'm using a DVDR with a hard drive and a digital tuner and
sending an RF signal on channel 3 to an analog tv.

Isn't that what people with digital cable and satellite do if they
don't have composite or component inputs on their tvs?

Assuming for the sake of this paragraph that this makes a difference,
those many people who promoted the high quality of digital tv never
said anthing about this making a difference.

Sylvia.