Wednesday, March 07, 2007

More Ham Funny Noises (This time 20M and legal)

I was trying to track down this weird noise on 20 meters. It sounded a bit like STANAG 4285, a bit like MT63, and at times a whole lot like the backscatter radar. It seemed to be centered around 14233.3 kHz. SkySweeper wouldn't do anything with it, and MultiPSK wouldn't do anything with it.

So I'm watching it on the waterfall, trying to figure out the mode - pilot tones followed by multitone 8PSK - and just then a stronger transmission started up. Here's what appeared on the waterfall:

That's right. There was writing in the waterfall, transmitted by just the right modulation of the signal. (This, in fact, is what sounds like the backscatter radar.)

See something new every day.

Other bursts had different amateur callsigns, signal reports, roger/no copy messages, and finally a smeary little identifier of a program named DIGTRX 3.11.

Google is a wonderful thing. I grabbed DIGTRX and ran it, and found out it's a digital file transfer mode popular with amateurs in South America to send SSTV pictures without the analog noise and grunge. That certainly explains why they were on 14233. The letters are called a "waterfall message," and there are also "waterfall pictures." Yes, real monochrome photos, in the waterfall. Little faxes, sort of. This is all just too cool.

Can't wait to get some amateur signals loud enough to decode the content. Terrestrial radio survives because people keep re-inventing it.