Sunday, 5 October 2008

DRM - Digital Radio Mondial

I am not really a Shortwave Listener, but I have been experimenting lately with Digital Radio Mondial ( DRM ). This is a new digital mode designed for short medium and long wave bands so intended to be more resistant to fades and noise. If you tune the broadcast bands you will come across blocks, arounf 10 kHz wide, that sounds like noise - that's DRM.

There are several commercial DRM receivers now on the market - Google will point the way, but I went the home-brew route. I bought a 455 kHz -> 12 kHz mixer from Sat-Service Schneider in Germany. This is a circuit, about the size of a postage stamp, that does what it says on the can. I then opened up my Yaesu FT-817 and picked off the 455 kHz IF from the plug intended for the narrow CW or SSB filter (most receivers will have somwhere that the IF can be found easily). I connected this IF, which would contain the 10 kHz-wide DRM signal before it would be crushed by the narrow filtering in the receiver, and passed it to the 455 kHz input of the SSS mixer.

The output at 12 kHz is then passed to my lap top sound card which is running DREAM software that decodes the DRM signals. (Google Dream +drm +radio). DREAM if free and does a lot more than just decode DRM, but more of this on a later post.

I am currently listening to the German stations RTL from their tranmitter in Luxembourg cool music (ghost from the past for those who remeber 208?) - almost error free. I will post more on this subject later.


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