I have recently become obsessed by shortwave radio, specifically Number Stations.
Wikipedia described number stations as:
Numbers stations (or number stations) are shortwave radio stations of uncertain origin. They generally broadcast artificially generated voices reading streams of numbers, words, letters (sometimes using a spelling alphabet), tunes or Morse code. They are in a wide variety of languages and the voices are usually female, though sometimes male or children's voices are used.
Number Stations are reportedly run by government Intelligence groups and codes are supposedly decrypted using a one time pad system.
You can hear what Number Stations sound like here: http://www.archive.org/details/ird059
My favourite ones are "Cherry Ripe" and "Lincolnshire Poacher" both reportedly run by MI6, the international branch of the British Secret Service. They both use a lo-fi rendition of the folk song that the station is named after as a signal before the broadcast starts.
I am yet to be lucky enough to find a Number Station but I hope that I do shortly.
Have any of you found anything interesting or strange on shortwave radio?