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.


Anonymous said...

"Why don't you use DRM on Shortwave?"

"Some large companies are pushing DRM by convincing program producers and broadcasters to start airing in DRM ahead of time, but unless there is mass availability and penetration of receivers on the listeners side, this will remain - unfortunately - a technological experiment, and broadcasters using it to reach their listeners now, are clearly throwing their money out of the window."


Decetive Radio Mondiale is a bust!

sean zhang said...

I just want to ask about in the radio, how to get the 455kHz frequency as IF?

sean zhang said...

I just want to know how to get the 455kHz IF from a radio?

Peter Marks said...

Hi Sean,

I know of one radio that actually has a socket on the back providing IF output, but generally you must open up the set, find a suitable point to connect to that has amplified IF.