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Digital TV Transmitter Using a VGA card

Posted by timothy on Mon Jun 13, 2005 02:59 PM
from the useful-reuse dept.
Hardware Hacking Media Television Hardware
An anonymous reader writes "Yet Another Project from Fabrice Bellard : with any PC and a standard VGA card, you can build a real Analog or DVB-T Digital TV transmitter by directly generating the VHF signal. The provided example shows a Lena picture transmitted as a real Digital TV channel."
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  • Now lets get some NTSC (Score:5, Interesting)

    by ankhcraft (811009) on Monday June 13 2005, @03:03PM (#12805790) Homepage
    Once someone posts how to do this with NTSC (which you'll need if you're in the U.S. like me), I'll be all over this! Anyone? Enlighten me...
    • it would be an MPEG2 encoded stream, not PAL nor NTSC ... the picture size and/or frame rate may be different but with any reasonable system you should be able to do exactly the same thing in the US

    • Guerrilla television in 2007 (Score:5, Interesting)

      by Simonetta (207550) on Monday June 13 2005, @04:10PM (#12806554)
      I suspect we may start to see illegal broadcasts in 2007 in poorer urban neighborhoods of the USA.

      With all broadcast television on VHF/UHF scheduled to cease on New Years Day 2007, there are going to be a lot of pissed off people who don't have cable getting nothing but static on every channel.

      This is assuming that UHF/VHF broadcasting actually does go off the air Jan 1, 2007. It doesn't seem likely at this time, but it is mandated by the TeleCom Act of 1996. And one never knows what the current administration is going to do.

      Let's assume that it does happen. All the middle-class people won't notice it because they are paying monthly cable fees and cable TV will not be affected by the VHF/UHF shutdown. However, let's assume that in poor neighborhoods the convertor boxes don't work well, or are prohibitively expensive, or are too technically complex for the general population. Suddenly there's no television.

      Well politics abhors a vacuum. We may find ourselves in a situation where people simply start pirate broadcasting on the unused television channels. This will probably cause problems with the new uses of the spectrum (private cell phone communications, I believe). The FCC will be really busy trying to track down pirate TV stations. Pirate TV stations are rare now because they can't compete with broadcast network quality, and there are outlets on local cable access for speciality and non-professional broadcasters.

      But with the UHF/VHF channels gone off the air, people will start filling it up with DVD broadcasts. Maybe even porn broadcasts. Unregulated, and without commercials. All illegal.

      These channels could become political if there is an economic downturn or a return of conscription into the permanent, endless war that the administration has promised the defense contractors and campaign contributors. Alternative broadcasts of police beatings at demonstrations made by tiny CamCorders alternating with current Hollywood movies downloaded from the DarkWeb could become common content on the new pirate channels.

      I wonder if anyone is considering the possibility of this happening before they decide to shut down UHF/VHF broadcasting in 2007?
      • Sorry for disspelling your very original fantasies... but nothing of that kind seems to be happening here in Berlin, where they did shut down analog TV broadcasts some two years ago.

        The frequencies are reused for the new digital broadcasting -- there are now about five times as much stations available, and posing a considerable threat to cable television: As cable is still analog, you get the same number of channels in a better quality for free on air... Only thing you need to pay is buying the receiver (
      • The Telecom Act does not shut down analog TV in 2007.

        The FCC does have a mandate to shut down analog TV -- TV stations now have two channels, one analog and one digital, and once the transition is complete, new users of former channels 52-70 (some of which have already been auctioned off) can go ahead with them.

        But the date is not firm yet. The current rule is that it will be delayed a year at a time, until 2010 at the latest, until 85% of households have digital reception capability. That includes DTV
      • Both of those are interlaced too ... pal is really NTSC with some minor tweaks and I expect the same goes for SECAM
        • Actually no. PAL is pretty different from NTSC, PAL used 50Hz and NTSC is on 60HZ (interlaced). This has to do with the electrical system used in Europe vs. NA. Also PAL and SECAM uses different scanning velocities than NTSC, mainly due to the fact that PAL has more lines. Another major difference is PAL and NTSC signal bandwidth, IRC from my digital video compression course. PAL has an 8MHz per channel bandwidth, and NTSC only has 6Mhz.

          • Re:Now lets get some NTSC (Score:2, Informative)

            by Anonymous Coward
            You might want to mention the primary difference, the very reason why PAL is called PAL (Phase Alternating Line). Contrary to NTSC, PAL inverts the phase of the signal every other line. This cancels out phase errors and provides a much more stable color reconstruction. NTSC is jokingly referred to as "Never The Same Color" because it uses a manual tint control to correct phase errors.
      • PAL is also interlaced.

        The correct analog (as in "analogy," not as in the opposite of digital) for this would be a mechanism for making an ATSC transmission. which could be tuned into from an OTA HDTV tuner. You could encode 1280x720 progressive ("720p") or 1920x1080 interlaced ("1080i") video signals into MPEG-2 then send that to an HDTV.

        Not sure how far people have gotten rolling their own ATSC transmitters, tho.
      • a) NTSC wouldn't be a good comparison, as NTSC (AFAIK) only defines analog color broadcasting. ATSC would be the equiv here in the states.

        b) The interlaced part wouldn't be the stumbling block -- 720p (aka progressive scan) is one of the ATSC standard modes. The hard part would be the 8VSB modulation, which is a totally different creature than the 16QAM modulation used in the european standard.

        That said, WHAT A NICE HACK!
        • HDTV in North America uses ATSC/8VSB, not DVB-T/COFDM. It also sounds like the guy in the article "cheated" by using a DVB-T modulator. I can't see anywhere that shows where the MPEG stream to feed into the modulator came from.

          The best part of TFA is at the end where he gushes about "This project can be the basis for foo, bar, and baz", then at the end "Where is the source code? It is currently not available, although I plan to release it someday, provided enough people ask me to." Sounds like "this pro

          • Re:Now lets get some NTSC (Score:4, Informative)

            by b1t r0t (216468) on Monday June 13 2005, @03:40PM (#12806245)
            Oh gee whiz... I think I figured it out now. What he did was make a grayscale image that resulted in a signal which was equivalent the unmodulated data stream. So the VGA card was esentially being used as an enormous shift register. In that case, it would definitely take some work (and an 8VSB modulator) to make it generate ATSC.

  • Has been done with music for a while (Score:5, Interesting)

    by m50d (797211) on Monday June 13 2005, @03:06PM (#12805823) Homepage Journal
    There's an X program that can transmit an MP3 to your radio by displaying pictures in certain ways. Quality's not too good, but it works. I guess it was just a matter of time before people did it with television.

    It also goes to show TEMPEST attacks are real. Your screen is transmitting what's on it in a way that's detectable over quite a distance. Shielding is worth looking at if you're doing something sensitive.

    • TEMPEST based attacks have been proven as viable a long time ago and I'm not sure this would qualify as a TEMPEST issue as you are purposefully broadcasting a signal for reception... Now if you are only considering sending the signal to your TV set and only your TV set then TEMPEST would be a concern (but considering the cost of some TEMPEST equipment I don't think that is much of a worry for a home user trying to mod out their home equipment).

    • Re:Has been done with music for a while (Score:5, Informative)

      by Rei (128717) on Monday June 13 2005, @03:19PM (#12805986) Homepage
      You're talking about Tempest For Eliza" [erikyyy.de]. I never got the "broadcast an mp3" function to work, however - only the broadcast using their special midi-like files. A shame, really. Still, even the midi-like broadcasts make for a neat geeky party trick, and demonstrate the power of tempest ;)
    • It's called Tempest for Eliza [erikyyy.de]. I remember it being pretty cool when I tried it a few years ago in high school.
    • About ten years back, my brother had a very simple watch/PIM (Personal info manager, for those of you unfamiliar with term) made by Casio, IIRC. The unique feature was that you installed a driver which allowed the data input program to mess with your refresh rate (I'm guessing) and transmit the information to the watch. It usually took four or five tries to get it right, but I remember being pretty impressed with the unique method that helped avoid keeping track of a dongle/connector.
  • This is a great idea. If there is a way to make the signal just a bit stronger you can hack your own wireless media center.

  • It Won't Be Long (Score:3, Insightful)

    by geomon (78680) on Monday June 13 2005, @03:12PM (#12805889) Homepage Journal
    Until this project is rendered illegal in the US under some DMCA-style bullshit. After all, you might be able to (gasp!) record something off of your incoming television signal.

    Of course, only pirates and pedophiles will have a use for this project.

    (The last part of this post is a JOKE, gawddammit!)
    • Until this project is rendered illegal in the US under some DMCA-style bullshit.

      More likely it would be something originating from the FCC. Unlawful use of radio bandwidth without a license, use of a class B device to intentionally generate interference (a competing unlicensed coherent signal is interference, but I may have the wrong class of device).
      • Consumer electronics that are unintentional radiators (FCCspeak for 'transmitters') are Part 15 devices. Actually, you can have intentional radiators under Part 15 was well, but the rules (power levels etc) are higher. Part 15 is usually where cordless phones and garage door openers operate.

        You are allowd to build up to, I think, 5 homemade Part 15 intentional radiators without getting them certified by the FCC. The maximum power levels are pretty low though, 100mW IIRC. A 100mW signal will go a few hundre
      • Thanks for chiming in, Orrin. Here's the latest amendment [arl.org] to the DMCA for you to peruse.

        Its only ten pages, so you should be able to wade through it in about two days.
          • You go to Radioshack for legal advice?

            I'm bookmarking your post for posterity. It is a classic.

            I also said, if you cared to read the original post, that it would be illegal in the future. That would mean this device would *also* be illegal.

            And Radioshack's attorneys would just advise the production staff to quit making them.

            Radioshack - for legal advice... That's good.

  • very clever (Score:2, Interesting)

    by Anonymous Coward

    +1 point
    shame he wont tell/show anyone how its done (ie. the source code)
    -2 point
  • The slashdot effect + a nudie photo. Say goodbye to that server.

  • The Lenna Story. (Score:5, Interesting)

    by British (51765) <british1500@gmail.com> on Monday June 13 2005, @03:16PM (#12805947) Homepage Journal
    ....is more interesting than the main one. At my company when I started 6 years ago, I stumbled upon the Lenna picture, just thinking it was an ordinary pic. Few years later I saw the er, um "full" pictures. Didn't know she had a cult following.

    Yes, that Lenna picture I assure you is still in use after all these years. A pretty "hello world" image.

    • I've been tinkering with that business of hiding a greyscale image in the spectral data of audio (a la Aphex Twin, etc.). At the moment, it's still in Mathmatica code, and I've been looking for a decent test image.

      Seems like I've found it.

      Oh, and Lena looks nice on my desktop. I wonder what her image sounds like.

    • Lenna is one of the many "standardized" images used in image processing research, akin to the well-understood strains of Norway rats used by medical researchers all over the world so that their peers can reproduce their experiments. For more examples of standard research images, see the USC-SIPI image database [usc.edu].
      • The story of her pictures is apparently very well known in video processing circles, and /. ran an article some time ago about it which introduced her to everyone else ;)

        I had never heard of her before, but then again, I've never dealt with any kind of photography or video processing.

  • crap .. (Score:3, Informative)

    by macaulay805 (823467) on Monday June 13 2005, @03:17PM (#12805965) Homepage Journal
    I clicked on the link while I was at work, now I'm waiting for the network security people to remove me from my workstation.

    On a side note: WARNINGS PLEASE!

    • Re:crap .. (Score:2, Interesting)

      by harrkev (623093)
      The funny thing is that I saw the edges of that picture on the original web page. That looks just like the "lena" picture that I used to use at a target back when I took my image processing class. That "lena" was a picture of a girl's face wearing a fancy hat.

      Is this new picture different?
      • Is this new picture different?

        No. This "new" picture is the same one you used, just possibly a different crop of the original.
        You probably should have followed the other link [cmu.edu] in the article summary before posting.

    • Re:crap .. (Score:3, Insightful)

      by Bishop (4500)
      a naked shoulder will get you fired? Where the hell do you work?

  • ATV (Score:4, Interesting)

    by leighklotz (192300) on Monday June 13 2005, @03:26PM (#12806068) Homepage
    You can do ATV [nasa.gov] legally in the US with NTSC, with a ham license.

    You can see this the video for yourself, with stuff you have at home right now. There are cable channels that are on ham bands, but it's OK because their signals stay on the cable.

    If you live in the SF ba area, hook a UHF antenna (vertically polarized) to your cable-ready TV or VCR with TV out, and tune to cable channel 57 (421.25 MHz), and aim it at Mt. Hamilton (east of San Jose).

    Here are some tests on 1.2GHz [nasa.gov], which is also a ham band.
    • I forgot to mention that the NASA Ames folks plan to re-transmit live space shuttle video from STS-114 over the K6BEN repeater, so you can pick it up on cable channel 57.

      • Re:ATV (Score:3, Informative)

        by leighklotz (192300)

        < Cool! So instead of pounding out morse code, you can instead send pictures of dots and dashes!

        The original post has some questionable legality issues; I'm showing you a way to do it legally, and get peer support. It's still bog-standard TV modulation, not morse code. And you don't need to learn morse code to get a license to do ATV [arrl.org].

        Probably the biggest problem is the use of harmonics -- the proposed system uses the 5th harmonic of a VGA output, which happens to fall in the VHF TV band. What abo

  • Hey editors, how about a NSFW warning on stories such as this!
    • What are you talking about? Yes, some of the Lenna pictures that can be accessed indirectly from the site are not safe for work but all the pages you open when clicking on the links in the story description are safe for work unless a portrait picture of a woman is not safe and in that case, please let us know where you work so we can avoid that place...

  • Now can someone turn up the original photo that Tim Skelly used for the starfield in Star Castle... The stars are nice, but I'd like to see the actual photo he happened to have in the drawer to pick coordinates.
  • I'm interested in this, but I don't understand the practical implications (mainly because I have no idea what most of the acronyms mean). Does this mean I could plug my computer into my digital TV tuner somehow and be able to watch it on my TV? If so, does it work with US digital TV equipment (such as the Motorola set-top boxes that Comcast provides)?
  • Just hook everything up to the pc and let it do the conversion and display your video at the native resolution on your DTV.

  • Guys, this is no small feat (Score:5, Insightful)

    by o'reor (581921) on Monday June 13 2005, @04:53PM (#12806957) Journal
    and yes, I am a (former) DVB-T engineer (and a consultant in digital video broadcasting at large -- yes, I know a bit about the US and Japanese standards too).

    What Fabrice is telling us here is that he has managed to produce a real-time (or close-to-real-time) DVB-T/DVB-H software COFDM modulator, the output of which may be broadcast via the DAC converters of the video board. Given the complexity of the generated signal (more than 6000 subcarriers, not including pilot subcarriers which are used as beacons for the demodulator, and paying respect to the guard interval -- sorry for the technical gobbledygook), this usually requires a dedicated ASIC. Don't forget to include the preliminary phases of the encoding : creating an MPEG-2 video channel, an MEPG-2 transport stream (OK, he did it using a modified MPEG library), then encapsulate this into MPEG-2/DVB frames, add the Reed-Solomon code, perform the interleaving procedure, pour in some Viterbi encoding for redundancy, and feed it to the input of the DVB-T modulator, phew ! you're done.

    I want to say hats off, ladies and gentlemen, to this outstanding performance. The Free Software movement definitely needs more guys like Fabrice, and we all need to encourage him into publishing more of his code.

    Chapeau bas, mon cher Fabrice !

    • Re:Guys, this is no small feat (Score:3, Informative)

      by Anonymous Coward
      It's not realtime. He's rendering to a PGM file, and then by displaying it. Not easy, but it's not a replacement for custom hardware.

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