brainwagon "There is much pleasure in useless knowledge." — Bertrand Russell

7Jan/106

Digital Radio Mondiale, recorded on the SDR-IQ, decoded with GNU Dream

Digital Radio Mondiale is a new digital broadcasting standard that is being used on shortwave. Sadly, its one of those annoying standards that relies on all sorts of patented technology, which makes experimentation really difficult and annoying. But I heard that Sackville Canada echoed Radio Chinas DRM broadcasts here to the U.S. for an hour a day, so I set up my new SDR-IQ to record ten minutes of it while I was at work the other day. Here's the spectrogram, showing the near solid block of DRM right in the middle:

2010-01-07_1919_001

It took me a few tries to figure out how to decode this. In the end, what I did was playback the I/Q recording with Spectravue. The signal was centered around 6.080Mhz, so I tuned the SDR-IQ ten kiloherz below, and put it into WUSB mode, after adjusting the filters to pass between 3Khz and 18khz (I left some slop on both sides). I then re-recorded the demodulator output into a wav file. While you can't open wav files directly from the menus, if you invoke the drm decoder with the wav file as an argument, it will use the wav file as input. I then recorded the resulting decode using Audacity. Here's a sample. There are some drop outs, but overall the quality is quite good. It would be a bit better if I didn't recompress the output as an MP3, but hey, it's a faster download this way.

Digital Radio Mondiale of Radio China, via Sackville, CA

I'm not sure what this is good for, but it was an interesting experiment for my new radio.