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.
I am pleased to report that the software is now working
with the new Universal Hardware Driver (UHD) from
Ettus Research. This will allow me to have much greater
control over the USRP2 + WBX from within the GUI.
This is the block diagram of the system. The bold text in the centre box
shows the parts of the system that have been implemented in the software.
The block diagram was drawn using free schematic software from PCBExpress.
Although using a USRP2 for Digital Television may appear expensive,
the USRP2 SDR can be re-programmed to implement virtually any type
of radio you desire. I consider it the best value radio I have ever bought.
The USRP2/WBX cost about the price of a new TS2000.
As promised I have uploaded a picture. This is of the G4DDK ultra
low noise preamp I built for use on DATV.
Work on sorting out the drop outs of the DATV signal progresses.
After some testing it seems the Ethernet link between my P.C
and the USRP2 is fast enough to sustain the DATV signal so
there is hope that I will be able to get the whole to work reliably.
