On Tue, 13 Nov 07, "BillP" wrote:
There is no combining of channels and your standard def TV can only
display 480 lines

Phantman:
Why do they always transmit their Hi Def programs on two channels?

On Wed, 14 Nov 07, "BillP" wrote:
Which PBS is your local?

Phantman:
Mississippi Public Broadcasting, WMAH Channel 19 in Biloxi

On Wed, 14 Nov 07, "BillP" wrote:
From what I see, WMAH transmits three channels-
19 Analog
19.1 Digital
19.2 Digital HD
You may be confusing "DT" with "HD" and seeing both channels as the same.

Phantman:
On their website, I see only the schedules for Analog 19 and Digital
19.2. But on my TV, I'm picking up D19.1, D19.2, & D19.3 (plus analog
19). Analog 19 and D19.1 are always identical programing, even during
breaks between shows. And D19.2 & D19.3 normally each broadcast their
own unique programing. But just before a High Def show comes on, the
announcement is "The following broadcast is in High Definition" (or
words to that effect). At which point 19.1 and 19.2 and Analog 19 all
broadcast the exact same programming simutaneously. I've never noticed
simultaneous programming on D19.3. It's always doing it's own thing.
I don't doubt I'm confused. I don't even know what "DT" stands for.

On Wed, 14 Nov 07, "BillP" wrote:
DT Stands for "Digital Television"

oh... lol.... -duh-

What is going on in your case is 19.1 is probably always a digital simulcast
of analog 19

Exactly

19.2 is the digital national PBS feed, and 19.3 is a separate
sub channel that is carrying something such as local events, community
access, announcements, weather, etc.

Yup. 19.3 is something called "Create".
It's mostly "How to" shows like Cooking, This Old House, .... like
that.

When you see "The following broadcast
is in High Definition" and you lose 19.3 this is most likely due to the
station shutting it (19.3)down to free up the extra bandwidth necessary to
transmit in HD. At this same time your local PBS also switches to PBS's
national feed which is why you see the same show on 3 separate channels,
analog, digital, and HD.

That all makes sense except I don't lose 19.3. It just keeps
broadcasting its own thing no matter what the other channels are
doing.
I knew Hi Def takes more bandwidth though, and that's why it made
sense to me when I was told HD broadcasts used 19.1 plus 19.2
simultaneously to get enough signal out. As an aside, analog always
broadcasts the HD programming simultaneously but otherwise has nothing
to do with Hi Def transmission.

Here's some info on DT subchannels-
http://en.wikipedia.org/wiki/Digital_subchannel
also on this page-

Thanks, I'll check it out.

Rick