Digital TV?

[WB4JFI]

It depends on what you mean by digital TV.

I've been out of it for three years now, but I think the problem is still
the encoder.  They are not cheap.  Our first encoders cost over $540,000.
We bought one for each of 23 stations.  They are much cheaper now, but I'm
guessing still in the tens of thousands.

That is for a high definition MPEG-2 encoder. For standard definition, they
are cheaper.

A few years ago, there was a European effort to use a low-end
standard-definition encoder, which was available on a single board for under
$1000, I think.

About four years ago, I suggested that we try to use a TiVo device for
encoding and decoding.  The original TiVo had a decent MPEG-2 encoder (for
recording onto the drive), and cheap MPEG-2 decoder, all in a single box.
Figuring out how to program the chips may not have been too difficult, as
the TiVo is/was Linux-based, and easily hacked to get a shell prompt.

These days, FPGA boards are fairly inexpensive, so the hardware to do an
MPEG-2 (or MPEG-4) encoder is not that costly.  Doing the software is
another issue.

Another way to go is to use a comodity PC/MAC to do the encoding/decoding.
There are MPEG-2, MPEG-4, WMV, etc encoders and decoders that are used daily
with desktop computers.  The issue there is how to get the digital bitstream
in and out of the PC hardware in a manner that you can hook to a
transmitter, and reverse for a receiver.  I'm sure there are smart
programmers that could do that, given a hard-defined target.

I would suggest that just because over-the-air broadcasters use MPEG-2, that
doesn't mean amateurs should follow.  However, the proliferation of
below-$60 over-the-air DTV tuners makes receiving an MPEG-2 encoded, 8-VSB
signal much easier.  Satellite TV receivers are another option, but DirecTV
does not transmit a true MPEG-2 stream, so you would need to recreate their
bitstream for your off-the-shelf satellite receiver.  Newer satellite TV is
also moving to MPEG-4.

Next is how do you plan to transmit it?  What frequency/band do you want to
use?  European broadcasters use DVB-T (terrestrial), DVB-S (satellite), and
COFDM.  American broadcasters use 8-VSB.  Of course, there are other options
as well.  The issue is how many bits you shove into a given bandwidth, and
how you address patents, etc.  I'm not sure what is available for the
amateur market.  8-VSB may not be the best for aamateurs for the same reason
it will not be as good for broadcasters.  Except that amateurs are more
familiar with the vagarities of UHF paths.

Even test and monitoring equipment is more difficult in a digital plant than
analog.

I could be terribly mistaken, but I am not aware of any real, active pocket
of digital amateur television in the US.

You may read the above and think that I'm trying to dissuade you from
digital, but I'm not.  I would like to see some experimental amateur digital
television.  But, the price of admission is pretty high in my mind.

The over-the-air digital television standard(s) are/were set down by the
ATSC (Advanced Television Systems Committee).  There is a web site at
www.atsc.org.  I think the actual standards/recommendations are available on
that site.  Good luck studying them, a sure cure for insomnia.  Do a google
search for ATSC, HDTV, digital television, etc for more info on the
broadcast side.  Harris is one company that makes/sells a full suite of DTV
equipment.

Hope that helps.
Terry
WB4JFI


> -----Original Message-----
> From: tacos-bounces+wb4jfi=amrad.org at amrad.org
> [mailto:tacos-bounces+wb4jfi=amrad.org at amrad.org]On Behalf Of Dan
> Romanchik KB6NU
> Sent: Tuesday, May 19, 2009 7:12 PM
> To: Tacos
> Subject: Digital TV?
>
>
> For our Ham Radio at the Hands-On Museum project
> (http://www.w8pgw.org/ham-radio-at-the-hands-on-museum
> ), we want to set up a television station. My first thought was to buy
> a transmitter from PC Electronics that sends standard-scan analog TV.
> Then, I got to thinking, why bother with that? If our goal is to show
> that we're at least up with current technology, then shouldn't we be
> doing digital TV?
>
> So, where can I find information on digital TV?  Is anyone making gear
> or am I going to have to make it myself?
>
> 73!
>
> Dan KB6NU
> ----------------------------------------------------------
> CW Geek, ARRL MI Section Training Manager
> Read my ham radio blog at http://www.kb6nu.com
> LET'S REALLY MAKE THE ARRL THE NATIONAL ASSOCIATION FOR HAM RADIO
>
>
>
>
>
>
>
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