OTA reception question -- weird problem

Archived from groups: alt.tv.tech.hdtv (More info?)

I have an RCA HDTV antennae that I bought a couple of years ago but
have not used for HDTV until recently. I have a Hughes receiver and a
Samsung 46" DLP set. When I look at the OTA locals I'm experiencing a
weird problem. Of the 5 main locals in Dallas I receive 2 of them
perfectly. The remaining 3 seem to come in perfectly but there is a
thin strip of snow that runs across the top of the picture.
Otherwise, there is no problem with the picture at all. Has anyone
run across this problem? I've checked out antennae.org and I think I
have the antennae pointed in the right direction. I don't have it
raised up in my attic -- which I'm thinking of trying. I just find it
strange that the picture comes in just fine with the 3-5 pixel wide
snow line at the top. Any help would be appreciated.

Thanks

Archived from groups: alt.tv.tech.hdtv (More info?)

On Tue, 22 Jun 2004, it was written:
> The remaining 3 seem to come in perfectly but there is a
> thin strip of snow that runs across the top of the picture.

Is this truly "snow", or does it seem to be following some sort of digital
pattern?

I suspect the latter, and that what you are seeing is closed-captioning
data, which is sent in the vertical blanking interval. Most TVs are set
to overscan so there's a margin of error before the VBI appears on the
screen; there's a similar overscan on horizontal. I'll bet that the rest
of that area with "snow" is black as opposed to picture.

Adjusting the vertical height control will make the problem go away. On
many TVs, the vertical height is accessed through a hole in the case that
you insert a plastic tool (not a metal screwdriver). On some newer TVs,
it requires getting into the service menu mode.

This is normally not a consumer adjustment (you can really screw things
up!), and to do it properly you need access to test signals. On top of
this, many CRT based TVs drift as they get warmer.

-- Mark --

http://staff.washington.edu/mrc
Science does not emerge from voting, party politics, or public debate.
Si vis pacem, para bellum.