brainwagon

I believe that it was the Amateur Radio newsline podcast which mentioned the following:

A Miami based Radio Station – The Disco Palace – has started broadcasting a DRM SW channel of ‘best of Disco music’ for listeners in Europe and North America.

via New DRM channel of Disco Music  :: DRM.

So, today I tuned in and recorded some of it using the SDR-IQ, and then processed it with GNU DREAM, the GPL’ed DRM decoder. The signal was very strong, no drop outs, and well, it’s disco. Here’s a couple minutes of the decode.

The Disco Palace broadcast using Digital Radio Mondiale on 17.755Mhz

As part of my delvings into things vacuum tubes, I of course found that many others have been down this road, including this rather interesting receiver built by Alan Yates. Being a novice at this, I was intrigued by the fact that his circuit used the 12DZ6 tube, which could apparently be powered by ordinary 12 volt supplies. Its application was in automobile radio circuits, where high voltages were inconvenient (when needed, they were often generated by “vibrators”, which created an AC voltage from a DC battery voltage, which could then be stepped-up by a transformer). When I mentioned this to Tom, he thought (as I did) that it was odd, and that he didn’t understand how tubes could operate with such low plate voltages. But of course, if you search, you shall find, so I uncovered this terrific page that describes some theory and circuits that use these low voltage (and presumably safer) tubes in radio circuits. Nifty.

Low Voltage Tubes

For the last week, I’ve been embarking on a ham radio “trip down memory lane”. Well, it would be memory lane if I had any real memories of the tube-based equipment that were staples of the ham shack until probably the 1970’s or so. But if I have a personal philosophy of my little projects, it’s that one has to look back to gain perspective about our current technology. Or something like that. Perhaps that’s just a rationalization for spending time reading old books about vacuum tube design. Or perhaps this is all motivated by the idea of building a radio that glows from scratch. Or, perhaps to demonstrate that I understand the similarities between tubes and FETs.

Whatever the motivation, I’ve been looking around at projects that people have done. A popular project seems to be “twinplex” radio, which uses a single dual triode tube in a regenerative receiver. Staring at circuits and reading Basic Theory and Application of Electron Tubes, I’m beginning to understand the functioning of these circuits. And, it turns out youtube has a lot of nice inspirational videos of people’s projects, such as the following:

Now that the winter is over, our local flea markets at Livermore and De Anza should be starting up again soon. Perhaps I’ll keep an eye out for the components.

Addendum: Here’s another link for inspiration.