Sexy Jihad

In what must be one of the coolest hacks I’ve seen so far this year, someone has written a howto on transmitting TV with your VGA card:

How does it work ?

Every VGA card contains high speed Digital to Analog Converters (DACs), one for each Red, Blue and Green component. Here we use only the red DAC. The provided images have been computed so that the signal output to the DAC is a valid RF signal.

As we did not want to generate a 176 MHz signal directly, we use the fact that the VGA DACs generate a lot of harmonics. The real generated DVB-T signal has a central frequency of 25.71 MHz. Then the second harmonic has a frequency of 25.71+2*76.5 = 178.71 MHz which is almost exactly the central frequency of the VHF TV channel 5.

The DVB-T signal is generated with a DVB-T and DVB-H modulator I wrote from scratch. This is the most complicated step because the DVB-T modulation is quite complicated (COFDM modulation). A custom polyphase filter is used to interpolate the baseband COFDM complex signal. Then it is translated to the 25.71 MHz frequency.

I used a patched version of FFmpeg to generate a custom DVB Transport Stream containing two DVB services. Each one contains a still MPEG picture. One of the still picture is the very nice Lena.

For PAL and SECAM, I also wrote a simple TV black and white PAL encoder. Adding color would be possible, but I am not motivated enough to do it

Wow, a low cost analog and digital TV modulator that almost anyone can build. Too bad I don’t have digital TV reciever to play with it

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