Digital Radio Mondiale Receiver
Uses a single tube!
I have been asked to explain DRM. DRM is a digital radio transmission format that can be heard on shortwave in the US and on medium wave in certain other places in the world. When decoded (and this is what I am working on now), the audio is better than regular shortwave audio. Some say it is near FM quality. It moves towards FM quality anyway. It is pretty much in the experimental phase right now. Once you take a listen on a regular receiver, you will know what it sounds like. This is not the same as the current US AM radio digital transmissions they are experimenting with now. If you are the type of person that likes to experiment, then DRM might keep you happy. This section of my site is very new and will likely get it's own area. It depends on if I have anything worthwhile to say about the subject. So I am learning now. Below are some of my progress notes. They aren't dated, but you get the idea.
Well folks, this is my third try at receiving DRM signals.
So far, no success. I am beginning to wonder if the problem is my soundblaster
sound card? I have tried 6140 and 9800 khz.
My first attempt was to use my Regen-O-Flex receiver that I recently built. I saw on Jogis' German Tube Site site that someone was receiving DRM with a regenerative radio. All I could get was the station ID. Then I tried my NC-125 by tapping off at the detector and moving the BFO 12 khz off center. Still only a station ID.
My third attempt is with a tube direct conversion receiver. I haywired a little
6BE6 tube as a mixer with a 12 khz output. Still no reception.
One person suggests that my oscillator is not stable enough and that this might be the problem. A crystal controlled oscillator might be what is needed. This is next on my list.
Guess what? It works! It is off more than it is on but it is decoding! With crystal control and maybe a little audio filtering, it should work better. As I learn more, I will post more here. Not bad for one tube (and a Pentium III computer).
Below are screen shots during reception of Radio China broadcast on 6140 khz as relayed by the CBC. This system is not ready for primetime yet and perhaps it never will. If I can get this together well enough, I will put up a separate DRM section on my website.
My future thoughts are:
To add an rf amplifier with a little agc
To build a bandpass filter for the DRM output.
Have optional crystal control and vfo tuning.
Build this all on a chassis and make a stable vfo.
Add an audio stage for monitoring and a stand alone direct conversion radio (cw and ssb reception).
Should I use solid state instead of tubes?
Your comments are welcome. Bitte schreib' mich an.
DRM Receiver Schematic