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Digital TV Transmitter Using a VGA card
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."
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!
Both of those are interlaced too ... pal is really NTSC with some minor tweaks and I expect the same goes for SECAM
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
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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
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.
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.
< 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:
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).
The article said TV channel 5, but it's not so in the US. See this chart.
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.
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?
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.
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.
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.
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.
Not quite, it is still relatively easy to trace down a broadcast signal. So it wouldn't take long before the fcc comes knocking with their rabbit ears.
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%.
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.
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....