Digital TV?

For our Ham Radio at the Hands-On Museum project, 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?

I have found a bunch of European hams doing digital TV using the European standard and one page of links on DXZone:

So far, though, I haven’t seen anything on ATV using the new US standard. Is anyone out there experimenting with this or even making gear that I can purchase?

Comments

  1. Chris Goosman K8MZO says:

    This is interesting. I’ve never done any amateur TV so I have no idea what’s been done in the past other than reading a few things in QST and in some of the study guides. The Europeans are obviously doing this, so why not us? What do the regs say about DTV?

    I wish I had some more time right now, because this seems like it could be a cool thing.

    I’ll keep reading your Twitter feed to see where this goes. Thanks Dan!

    Chris, K8MZO

  2. Chris KC2SYK says:

    ATSC is a poor standard for several reasons. Here are some major ones:

    1. always transmits 6mhz bandwidth on the air, even if 90% of the
    packets have no data
    2. 8VSB does not deal with multipath well
    3. audio is multiplexed in with video, if one drops, they both drop
    4. subchannels are multiplexed so that if one subchannel drops, they all drop
    5. may be hard to find an ATSC tuner in the amateur bands, can’t use
    standard TVs like NTSC cable channels
    6. was developed on MPEG-2 data streams, which is outdated and uses
    more bandwidth than would be required if a more modern MPEG-4AVC codec
    was used
    7. no support for 1080p over the air

    It is interesting for experimentation, but remember that it _always_
    takes up 6mhz, even if you are sending only a 480i (standard def)
    signal with no audio. #3 and #4 above mean that the entire 6mhz
    channel has to be relatively noise-free. Read more here:

    http://nsayer.blogspot.com/2008/10/atsc-vs-dvb-for-north-american-amateurs.html

    I hope this is helpful.

    Cheers and 73.
    -Chris KC2SYK

  3. Dan KB6NU says:

    Hmmmmm. Maybe I don’t want to try this after all. I also contacted Tom, W6ORG, of PC Electronics about this, and here’s what he had to say:

    Only one DTV ATV system running in the US that I know and it uses DVB-S – Columbus OH. There are a lot of problems with DTV for ham use besides the high cost. I have discussed a lot of the technical pros and cons in the next ARRL Handbook. I may write an app note to put on my web site soon. If you are looking to play with ATSC 8VSB, you can get a board from a company in Germany for about $1000 that puts out a few milliwatts. Tough part is having enough linearity in the amps that follow it.

    Unless a semiconductor company comes out with a cheap chip set we probably wont come out with anything. ATSC 8VSB wont work with motion so even if there is a chip set, it cant be used for mobile, R/C and some portable applications. DVB-S or DVB-T works with motion but the boards currently are just as expensive and you need a DVB Satellite receiver.

    I just don’t see much of a market or use of digital ATV except for maybe a few experimenters.

    Tom O’Hara W6ORG
    P. C. Electronics

  4. David Brodbeck N8SRE says:

    If you don’t need the extra resolution, there’s really nothing wrong with sticking with NTSC. It works, it’s well-understood, and it’s easy to implement. The CCTV surveillance camera industry is still overwhelmingly using NTSC baseband video pretty much for this reason. In many cases the recording equipment has gone digital but the cameras are mostly still analog, passing video over 75 ohm coax or (in newer installations) twisted pair.

    On that note, many of the “box cameras” meant for surveillance use are quite high quality and accept standard C-mount interchangeable lenses. I don’t know what you’re planning on using for your video source but you may want to check out some CCTV catalogs and see what’s out there. I did CCTV camera installation for a few years so if you have any questions about that end of things I may be able to help you.

  5. I agree with the others about the shortfalls of ATSC. It’s a crappy standard that never should have seen the light of day. Plus, you should be able to find some surplus NTSC gear. I have several broadcast exciters that I’m going to be playing with as soon as I find some free time, and I hope to grab a couple of UHF amplifiers after the final analog shutdown in another 22 days or so. I’ve always had an interest in ATV, but it was too much like work (I work on TV transmitters for a living), with all the surplus analog gear coming available I decided it’s time to jump in.

    If you have any interest in ATV I would suggest a subscription to ATV Quarterly. It recently changed publishers after Gene Harlan went SK, but it’s always been a decent magazine and some pretty sharp people write articles for it.

  6. Chris’s comments above are accurate about ATSC, but I believe there is a place for amateur ATSC: I believe it should be used for ATV repeater outputs.

    We hams have been fortunate that consumer cable-ready televisions have been able to be pressed into service as ATV receivers on the 70 cm band. Alas, with the arrival of digital TV, this isn’t the case anymore. As NTSC tuners head towards obsolescence, if we don’t provide signals that are compatible with consumer equipment (albiet now requiring a downconverter – still a relatively modest investment), we risk becoming like packet radio – a sub-hobby that is relatively difficult to attract newcomers because of the up-front investment requirement in the required equipment. We should endeavor to make it possible to at least *receive* D-ATV transmissions without a huge investment.

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