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Digital TV Transmitter Using a VGA card

Posted by ryuzaki0 on from the useful-reuse dept.

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."

33 of 187 comments (clear)

  1. Now lets get some NTSC by ankhcraft · · Score: 5, Interesting

    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...

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    1. Re:Now lets get some NTSC by terrymr · · Score: 2, Informative

      Both of those are interlaced too ... pal is really NTSC with some minor tweaks and I expect the same goes for SECAM

    2. Re:Now lets get some NTSC by b1t+r0t · · Score: 3, Informative

      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.

      --

      --
      "Open source is good." - Steve Jobs
      "Open source is evil." - Microsoft
    3. Re:Now lets get some NTSC by nightznoe · · Score: 2, Informative

      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.

    4. Re:Now lets get some NTSC by Anonymous Coward · · Score: 2, Informative

      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.

    5. Re:Now lets get some NTSC by Cramer · · Score: 2, Informative

      You're confusing fields and frames... NTSC has 60 interlaced fields per second generating 30 frames per second. The reason you generally cannot see that flickering is due to the retentative properties of your eyes and the phosphor pixels in the TV. PAL is the same at 50 fields / 25 frames.

    6. Re:Now lets get some NTSC by JLF65 · · Score: 2, Informative

      No, 60*1000/1001 Hz is just a close approximation made by video player programs. The actual frequencies are derived in this manner:

      The color sub-carrier is 3,579,545 Hz. This was chosen because it makes all the harmonics work to interleave the color and luminance spectrums.

      There are exactly 227.5 phase changes per horizontal line. This is the source of the saying Never The Same Color. It is also why PAL inverts the phase on every other line. Their sub-carrier isn't the same frequency, but it's derived in a similar manner.

      3579545/227.5 = 15,734.26374 Hz which is the number of lines per second. There are 525 lines in a frame yielding 29.97002616 frames per second. Since NTSC is interlaced, this yields 59.94005233 fields per second.

      Now you know where all the numbers come from. :)

  2. Has been done with music for a while by m50d · · Score: 5, Interesting
    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.

    --
    I am trolling
    1. Re:Has been done with music for a while by Evil+W1zard · · Score: 2, Interesting

      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).

      --
      News Reporters Make Tasty Polar Bear Treats!
    2. Re:Has been done with music for a while by Rei · · Score: 4, Informative

      You're talking about Tempest For Eliza". 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 ;)

      --
      "This wallpaper is killing me. One of us has got to go." -- Oscar Wilde on his deathbed
    3. Re:Has been done with music for a while by UserChrisCanter4 · · Score: 2, Interesting

      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.

    4. Re:Has been done with music for a while by csnydermvpsoft · · Score: 2, Interesting

      I used to have one of these as well. I always thought that it worked by displaying a pattern of lines on the screen, which the device then picked up.

  3. Re:ANOTHER one!! by gg3po · · Score: 5, Insightful

    I know he's the guy behind ffmpeg (used by most *nix media players) and the excellent qemu emulator that I use every day.

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  4. It Won't Be Long by geomon · · Score: 2, Insightful

    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!)

    --
    "Rocky Rococo, at your cervix!"
    1. Re:It Won't Be Long by HTH+NE1 · · Score: 2, Informative

      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).

      --
      Oh, say does that Star-Spangled Banner entwine / The myrtle of Venus with Bacchus's vine?
    2. Re:It Won't Be Long by tylernt · · Score: 2, Interesting

      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 hundred feet at best.

      My understanding of Part 15 is limited to FM voice communications. I have no idea if images (TV) are also allowed under Part 15.

      --
      DRM 'manages access' in the same way that a prison 'manages freedom'
  5. very clever by Anonymous Coward · · Score: 2, Interesting


    +1 point
    shame he wont tell/show anyone how its done (ie. the source code)
    -2 point

  6. oh man.. by p373 · · Score: 2, Funny

    The slashdot effect + a nudie photo. Say goodbye to that server.

    --
    http://www.thelung.org
  7. The Lenna Story. by British · · Score: 4, Interesting

    ....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.

    1. Re:The Lenna Story. by Qzukk · · Score: 2, Informative

      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.

      --
      If I have been able to see further than others, it is because I bought a pair of binoculars.
    2. Re:The Lenna Story. by kureido · · Score: 3, Informative

      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.

  8. crap .. by macaulay805 · · Score: 3, Informative

    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!

    1. Re:crap .. by harrkev · · Score: 2, Interesting

      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?

      --
      "-1 Troll" is the apparently the same as "-1 I disagree with you."
    2. Re:crap .. by Bishop · · Score: 2, Insightful

      a naked shoulder will get you fired? Where the hell do you work?

  9. ATV by leighklotz · · Score: 3, Interesting

    You can do ATV 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, which is also a ham band.

    1. Re:ATV by leighklotz · · Score: 2, Informative

      < 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.

      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 about the 2nd, 3rd, and 4th, (and higher?) Doing this with the support of other people who know what they're doing will help you avoid these problems:

      Let's see:

      • Fundamental: 25.71Mhz
        25.550-25.670Mhz is assigned for radio astronomy. So you'd be interfering with SETI research (slightly away from the band but close enough to interfere if the signal isn't clean, which it won't be).
      • 2nd harmonic mixed with 76.5: 178.71MHz
        The article said TV channel 5, but it's not so in the US. See this chart.
      • 3rd harmonic mixed with 76.5: 153.64MHz
        Police and fire VHF radio frequencies, in the US.

      The list goes on, since mixing both adds and subtracts the frequencies and their harmonics.

      And who can forget the plasma TV transmitting the 121.5 MHz international distress signal?

      Bottom line: don't hook this thing to an antenna.

  10. Guerrilla television in 2007 by Simonetta · · Score: 4, Interesting

    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?

    1. Re:Guerrilla television in 2007 by antrik · · Score: 3, Interesting

      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 (< $100) once.

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      All my comments get moderated +-0, spotless.
    2. Re:Guerrilla television in 2007 by modecx · · Score: 2, Insightful

      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.

      That's a joke, in my experience. My family rents out many (small) appartments, and several houses. Many of the tenants certianly qualify as poor, certianly they're on fixed incomes... And the overwhelming majority have cable today, and always have had it in the past. You can't blame it on poor reception, either. It's fine.

      A couple of tenants have even gone as far as losing their water service, but they still had to have their $60/month cable service. It's like goddamned crack. They'll do anything, as long as they have a roof over their heads, food in their bellies, and America's Funniest Home Videos on the TV.

      My family dosn't belive in much TV. We're too busy managing our small corner of the universe, and actually having fun when we're not doing that. I only got cable a year ago when Qwest pissed me off to the point where I had to ditch DSL through them.

      For $3 extra than the cable internet service I get basic, anaglog cable, and that's fine because I get a few chanels that I do enjoy. Discovery (love them motorcycles!), Food Network, and I think TBS. There's some others but they mostly have crap/reruns(crap).

      I think many Middle Class Americans hold off on overly superfluous things like pay-TV. Not to sound clichéd, but do people really need more than 64 channels? Unless you spend all day in front of the boobtube, you can't remotely hope to watch enough to justify it--if you don't have money to throw away, that is.

      I suspect that this phenomenon echos throught our country. I think many lower-class people (from the Blacks in the ghetto, to the whites in the trailer courts) are either too lazy to do anything else, unable (by injury, or illness, including mental--including TV addiction), or they just don't know what the hell else to do.

      Having that said, I doubt pirate broadcasts will pop up all over. There's the thing about the price of the equipment (unless they steal it that is), the knowledge of how to hook it up, and, well, it takes effort. People don't like effort.

      --
      Constitutional rights may be respected, repealed, or modified; but they must never be ignored.
    3. Re:Guerrilla television in 2007 by isdnip · · Score: 2, Informative

      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 sets, as well as cable boxes that convert.

      The FCC has just passed a rule requiring most TV sets to have digital tuners by 2006. The channel election process (by which stations choose which of their two channels to keep and which to give up -- for instance, some VHF stations will stick with UHF DTV, some won't -- is being accelerated. See the FCC web site.

      But it's highly unlikely that analog will be shut down before 2008. And since that's an election year....

  11. Guys, this is no small feat by o'reor · · Score: 4, Insightful
    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 !

    --
    In Soviet Russia, our new overlords are belong to all your base.
    1. Re:Guys, this is no small feat by Anonymous Coward · · Score: 3, Informative

      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.

  12. Re:Killing a Cop to See Lena by Ge10 · · Score: 2, Informative

    You're glossing over several issues. * high frequencies are decay very quickly (by distance)Even with an antenna connected, it would be very short range * he's using the harmonic of the 76.5 Mhz pixel clock, so the harmonics will repeat in multiples of this. If you're talking about sidebands, the bandwidth is limited to 25.1Mhz so you will only have to worry about harmonics of the sidebands * The second harmonic of an 80m rig is only 7.5Mhz - still in that shortwave region used by hams FOR LONG DISTANCE TRANSMISSIONS * Interference would be primarily AM in nature, and (since all police radios use FM) will be mitigated by the AM rejection circuitry in their receivers * the power output is incredibly small - bear in mind that a direct connection is being used and it still comes up as only 60%.