K6HX QRSS Grabber

For fun, I’ve got my new RFSPACE SDR-IQ running on my laptop using Spectrum Lab and monitoring the 30m QRSS beacon subband. I enabled its HTTP server, and now have set up a little cronscript to copy its display to my webserver once a minute. You can see an example display below (showing KC7VHS, AA5CK and WA5DJJ) or you can click on the link below, and get the live version on QRSS.info


K6HX QRSS Grabber.

I’m not sure why the frequency display on the right is wrong. Anybody have any ideas? I probably have missed something in the configuration of Spectrum Lab, but it’s rather like operating the Space Shuttle…

Digital Radio Mondiale, recorded on the SDR-IQ, decoded with GNU Dream

Digital Radio Mondiale is a new digital broadcasting standard that is being used on shortwave. Sadly, its one of those annoying standards that relies on all sorts of patented technology, which makes experimentation really difficult and annoying. But I heard that Sackville Canada echoed Radio Chinas DRM broadcasts here to the U.S. for an hour a day, so I set up my new SDR-IQ to record ten minutes of it while I was at work the other day. Here’s the spectrogram, showing the near solid block of DRM right in the middle:


It took me a few tries to figure out how to decode this. In the end, what I did was playback the I/Q recording with Spectravue. The signal was centered around 6.080Mhz, so I tuned the SDR-IQ ten kiloherz below, and put it into WUSB mode, after adjusting the filters to pass between 3Khz and 18khz (I left some slop on both sides). I then re-recorded the demodulator output into a wav file. While you can’t open wav files directly from the menus, if you invoke the drm decoder with the wav file as an argument, it will use the wav file as input. I then recorded the resulting decode using Audacity. Here’s a sample. There are some drop outs, but overall the quality is quite good. It would be a bit better if I didn’t recompress the output as an MP3, but hey, it’s a faster download this way.

Digital Radio Mondiale of Radio China, via Sackville, CA

I’m not sure what this is good for, but it was an interesting experiment for my new radio.

New gadget in the shack: an RFSPACE SDR-IQ

Well, I got a new gadget in the mail today: an SDR-IQ from rfspace.com. It’s a cute little gadget: a general purpose receiver that can deliver the quadrature signals for any 192Khz of the spectrum anywhere from 100Hz (yes, Hz) to 30Mhz. It is a small black box, with only three connectors: a USB, a regular serial port (used for rig control) and a BNC port for attaching an antenna. I fired it up, and right away started to find interesting things: for instance, here is the frequencies around 5.8Mhz:


If you look carefully, you can see that this is actually an AM signal. The carrier and a couple of sidebands are visible to each side of the received signal. If you click on the signal, and select the AM demodulator, you get the following audio:

AM modulated Morse code at 5.8Mhz, recorded around 06:30, Jan 5, 2010

A quick google of the web indicates that this is a Cuban numbers station. Pretty nifty, and probably never would have discovered it without using the RFSPACE SDR-IQ.

You’ll be hearing more about this gadget in the future.

Addendum: I’m not the only person (obviously) to hear these guys.