I got pointed at this rather large collection of shortwave recordings which are archived on the archive.org website:
They have many crazy recordings of radio pirates, some of which are pretty dull, but some of which were pretty interesting. I was interested to find that there was a recording of a “digital” pirate radio station: station “XYZ”. It was easily recognizable to me as being transmitted in Hellscrieber, an old fax-like mode that was developed in the 1920s. The amateur software “fldigi” is capable of decoding these signals, which looks like this:
There is lots of fading in the recording, but it’s still quite legible. I’ve often thought making a small QRP Hellscrieber rig would be an awesome project. Oh well, I just thought it was mildly interesting.