Sunday, 6 June 2010

Success at last DVB-T works

Well I am glad to report that after weeks of frustration I have managed
to successfully transmit my first DVB-T signal using my trusty USRP2!

The transmission was using 8K mode QPSK with 1/4 guard period. The channel
bandwidth was 7 MHz. The photo above is not very good because my hands
were shaking so much with the excitement.

The final bug was the fact I was had got the bit order of the symbols reversed.
Unlike the satellite box the Samsung TV either detects the signal or not so you
are pretty much working in the blind until it works.

The USRP2 has about 70% load on one of the cores to do this, so I am going
to have to optimise the code.

Update! I have now managed to test both 2K and 8K, QPSK, 16QAM,64QAM
various guard periods and FEC rates from 1/2 through 7/8 and all of them
decode correctly on the TV set. The tests were done under suppressed
radiation conditions on 177.5 MHz as I have not made a 1.3 GHz down
converter for the TV set yet.


  1. How do you generate the MPEG2 elementstream?

    FFMPEG does not generate constant bitrate?
    But you need constant bitrate to feed the DVB-T TS.

    Thank you


  2. I am using a Hauppauge PVR500 MPEG encoder card.
    This can be programmed to operate at a fixed rate.
    It produces a program stream.
    I convert that into a transport stream and add NULL packets to keep the bitrate constant.
    The PVR cards can be found on eBay for about $15.
    I have also used a Hauppauge USB encoder as well (that is what I use on my laptop).