A few days ago I built a radio receiver out of junk, because my usual radio had died a death and I wanted to listen to a specific part of the shortwave bands around 3.5 – 4 MHz.
Last night I scanned up and down the band and located what sounded like a fax transmission, a short while later and I’d recorded several minutes of the signal. A litter later still and I’d decoded it using some software I wrote nearly 10 years ago.
It looks a little messy, but it is quite obviously a weather map showing iso-bars and weather fronts over the Atlantic, the UK and Europe. Not bad for random DIY experiments.