Although I haven't been able to verify this actually works, I thought readers would be interested in a Web site describing how to use a PC running Linux and a current generation video card to create a modulator capable of generating a VHF DVB-T signal. At present, the system does have some limitations. It can only transmit still images and the DVB-T signal containing the images has to be computed separately before it is sent to the VGA adapter.
If you are interested in trying out this modulator, you will need a PC with a recent VGA card able to display resolutions up to 4096x2048 using 8 bits per pixel with a pixel clock of exactly 76.5 MHz. The ATI Radeon 9200SE cards are reported to work, according to the Web site. The video card's red digital to analog converter output (signal pin 1 and ground pin 6 on a standard 15 pin VGA connector) is used as the RF output. The output power is very low so you will likely need to make a cable to feed the RF to the TV set.
The DVB-T modulator also requires use of Linux and the X Window system on the PC. The X Window server allows custom configuration of the video card's output signal. Using precompiled files from the Web site, you can generate a valid 16-QAM DVB-T COFDM-2K output signal receivable on channel 5 (178.75 MHz) with two channels, each with a still picture.
For details on this interesting experiment, files, and additional links, see Use your VGA Card to Transmit DVB-T signals! A Low Cost Analog and Digital TV (DVB-T) Modulator.
Who will be the first to use similar techniques to generate an 8-VSB signal on a U.S. TV channel using a video card? As the 8-VSB signal is less complex than the COFDM signal, it seems this wouldn't be too difficult! If you succeed, please let me know! As we make the transition to digital TV, there will be a need for low-cost test equipment and ideas like this that challenge engineers to learn more about DTV transmission.
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