I remember these. The pronunciation of 'five' ("fuennef") alway stood out to me. Listening to the wav file of the voice it's there exactly as I remember it.

There were a lot of weird radio stations back in the day, plenty of them for espionage and command-and-control purposes. Sleeper agents were - and probably still are - a thing. Makes you wonder if there are still people lying in wait living normal lives waiting for the right signal to kill some head of state.