Back in the early 1980’s, I had a radio receiver which had the usual AM and FM bands, but also had shortwave frequencies. I remember extending the aerial as far as it would go, and then twiddling the dial to see what stations I could pick up. There were stations from major broadcasting bodies, such as the BBC World Service, NHK from Japan, Voice of America and Deutsche Welle from Germany, plus services from many other smaller bodies as well. The brodacasting frequencies were very crowded, so you would have no trouble finding stations.
As I started to find out more about shortwave radio, I began to read about references to “numbers stations”. These stations are one of the great mysteries of shortwave radio. While they can be easily picked up and listened to, no-one is still 100% sure what their purpose is, and who runs them. I don’t remember listening to any of them as a teenager, as I wasn’t aware of their existence.
Here is a video of an excellent BBC Radio 4 documentary from 2005 about the strange, secretive and disturbing world of the “numbers stations”.