Tuesday, September 22, 2020

Ham radio in lockdown

Although I moved from Sydney to Melbourne, the COVID lockdown has ironically led to me staying in touch with my Sydney friends more than I would have under normal circumstances. Here in Melbourne we are under a strict "stage 4" lockdown which means that very few shops are open (basically food, alcohol and chemists) and we can't visit anyone.

Happily people have gotten used to using video conferencing and so each week a bunch of us meet for a shared lunch while on Zoom. We did try Skype but the consensus is that Zoom worked better.

During the call Kevin, VK2KB and I made contact on 40m using JS8Call which we've been playing with lately. Conditions are not great and it's been useful to check the Sydney/Melbourne path using WSPR before attempting voice contacts.

The terrible RF noise here has stayed away and my end fed antenna is working pretty well although I'm getting a bit of RF into computer gear so I think the counterpoise which lays on the ground is not a good enough ground.

I'm very interested in all this new SDR development using small CPUs and have been following the uSDX project with great interest. Bill & Pete discussed this on a recent Soldersmoke podcast.

In an attempt to understand a bit more about how I & Q samples are transformed into a nice spectrum display and even demodulated I've been hacking some code to read samples from devices and trying to get those samples into the right format for FFT. So far I have code that can find and read samples from an RTL-SDR and an AirSpyHF+. I'm doing this on macOS and naturally I want to use the accelerated DSP libraries in Apple's Accelerate Framework. This is all changing thanks to a new "overlay" which makes it easy to use from Swift. My thanks to Barry Medoff for drawing my attention to the WWDC presentation on this.

It's starting to work, here's what the 40m band looks like with a few CW stations on it:

I've done some work on my WSPR Watch app for iOS and macOS recently. Graphs are better and some of the tiny text is now more legible. WSPR Watch can pull data from PSKReporter and JS8Call sends reception reports there so it's handy to be able to use the app to see who I'm hearing.

1 comment:

Clifford Heath said...

I've been working on an FFT analyser like rtl_power, rx_power, etc, but using Soapy for cross-SDR and remote support, and FFTW for fast FFTs (like hackrf_sweep). Trying to use exemplary C coding style. All code framework is in place and I'm now trying to figure out downsampling (decimation), windowing, etc, before FFT, but you might find something useful and I'd appreciate input. Also want to add chunked HTTP server support for a web-based waterfall display.