So I just sat and watched the waterfall for a bit in Spectrum Lab on 20m (14.070MHz). To my surprise I observed the noise suddenly start and stop (see below).
That’s making me think it’s more likely some kind of electronic device, and just maybe something like a reverse cycle heater (or heat pump as they seem to call them in VK7). Anyway, I’ve now setup spectran to go nice and slow and do 15 minutes captures – so I’ll see what that yields.
But still, if anyone has any ideas, please drop me a comment. 🙂