In 1999, I wrote an article for the bOING bOING Digital site about the CONET Project, a multi-CD collection of mysterious "numbers stations" heard on shortwave. For decades, intelligence organizations have reportedly broadcast one-way messages to their agents in the field via shortwave, and the transmissions happen to sound weirder than any Stockhausen score or minimalist electronica you've ever heard — a child's voice, or the obviously synthesized intonation on what's known as the "Lincolnshire Poacher" station, named for the folk song accompanying the numbers. Wilco's album Yankee Hotel Foxtrot is named for, and samples, a numbers station. The CONET Project has been available for several years for free download from various places online, including Archive.org. Now, the original compilers, Irdial-Discs MMX, have re-released The Conet Project in a special CD edition that includes the four original discs plus a fifth CD containing recordings of very strange "noise stations."
"The CONET Project: Recordings of Shortwave Numbers Stations / 1111"
"Spy vs. Spy: The Soundtrack" (bOING bOING Digital)