Martin,  I have read about the next generation of HDTV due out in about
2020 and they are talking about throughputs 5 times or more the 19.2
figure.  More and more down the pipe.  Now if I could recall where I
found that web page.   

-----Original Message-----
From: For blind ham radio operators
[mailto:[log in to unmask]] On Behalf Of Martin McCormick
Sent: Monday, March 10, 2008 6:49 PM
To: [log in to unmask]
Subject: Re: Digital to analog TV converter boxes

Terri Pannett writes:
>What do these boxes do besides convert the signal?  What do we need to 
>be able to use them?

	They are meant for over-the-air reception. If you live in a
city, a pair of rabbit ears might work and then again, they might work
sporadically. Most of the signals you will be receiving will be UHF
channels but a few digital channels had to be stuck on VHF channels
because there wasn't enough room.

	What I have been told by someone who has a VCR with a digital
tuner is that when you first connect the antenna, you need to give it
the program command at which point, it scans all the broadcast TV
channels. There is apparently a continuous ID signal embedded in the
data which tells your digital converter which channels in the digital
world belong with which analog channels. If, for instance, you have
Channel 4 over the air, your digital tuner will scan and hopefully pick
up a digital channel serving Channel 4.1. If Channel 4 sends multiple
digital feeds, then you will have 4.1, 4.2 and so forth. If the station
is not sending high definition video, you might have Channels
4.1 through 4.6. 4.1 is usually the same feed as just 4 but 4.2 through
whatever can be several independent program sources.

	In Oklahoma and other states in what is called Tornado Alley,
many stations run a continuous weather feed with radar on one of their
digital channels.

	We have a religious broadcaster in Oklahoma City who sends 5
feeds, one of which is a Spanish Language version of the channel.

	Our Educational channel has a couple of feeds and used to have 3
or 4 feeds but dropped a couple of them due to signal quality
considerations. There are just so many bits to go around and the more
feeds, the more compression they have to use so the signal becomes bad
to see and hear.

	I think the plan is to remove the few digital channels that are
on HF after the analog UHF stations go away so the end result at least
one day, will be that TV in the United states is all UHF.

	I realize that this is a long message and is not amateur-radio
related, but it is communications technology on the cutting edge.

	Each TV channel has 19 megabits per second to play around with
and there may come a time when hams will be allowed to generate those
same signals on the amateur bands.  I don't know how much overhead for
error correction and the like there is, but that is a pretty healthy
pipe which could make for some really neat repeater backbones instead of
the traditional analog links. Something to think about, anyway.

Martin McCormick WB5AGZ  Stillwater, OK Systems Engineer OSU Information
Technology Department Network Operations Group