Tuesday, February 13, 2007
Getting in to Digital Radio Mondiale (DRM)
I'm really interested in the next step for broadcast radio, called DRM. (Yes another DRM). Digital Radio Mondiale sends audio as a low bit rate AAC stream. At this stage there aren't many radio sets out there, and they're pretty expensive.
An alternative for technical folks, like you and me, is to modify a radio to get the 455Khz intermediate frequency out and mix it down to a low (audio) frequency that can be decoded on a computer with software. (Find DREAM).
I've ordered, and quickly received, a tiny mixer board that should do the trick. While it came with a circuit, they skipped the pinouts and I figured this might be handy for other too, so it's shown above. Note that I may well have this wrong at this point, I'll update this post if I find an error while getting it going. (1 update so far).
Now, to start pulling my nice radio apart...
Update: I pulled my FRG-100 apart, tapped the 455kHz IF, and have started to receive DRM transmissions. It's pretty bad at this stage as you can hear but I'm sure I can improve things with tweaking.
The dream software is amazing and if you understand it I'm sure let's you really see what's going on. Here's a screenshot.
Having just returned from this year's Wyong field day I'm all fired up to look at GNURadio.
Notes on DRM with the Yaesu FRG-100: I took the suggestions from here and tapped VR1002 to get 455kHz. I didn't change out the filter and perhaps that's why I'm not having much luck. The waveform looks 10kHz wide though.
My antenna is a 20m long wire across the back yard and in the evening it overloads the receiver, I now have an attenuator that I hope will help in that regard.