The BBC Radio 4 Broadcast of "Tracking The Lincolnshire Poacher," first aired in 2005.
"BBC Radio's Simon Fanshawe embarks on a detective journey into the clandestine world of radio cryptography and attempts to solve one of the most unusual broadcast mysteries of all time."
The phenomenon of so-called "number stations," mysterious shortwave radio broadcasts that seem to exist only to transmit spoken-word numbers, snippets of weird songs and enigmatic codes, is a genuine mystery.
Exactly who is broadcasting these transmissions and why is unknown. One theory holds that the transmissions are part of espionage efforts by the intelligence agencies of different countries, another, that they are the work of organized drug smugglers, while still another claims that they are actually communications between extraterrestrial space aliens! (One commentator on an Internet message board even referred to them as "the aural equivalent of crop circles").
The espionage theory seems to be the most plausible. Akin Fernandez, creator of The Conet Project CD, states that, "Shortwave numbers stations are a perfect method of anonymous, one way communication. Spies located anywhere in the world can be communicated to by their masters via small, locally available, and unmodified shortwave receivers. The encryption system used by numbers stations, known as a "one time pad" is unbreakable. Combine this with the fact that it is almost impossible to track down the message recipients once they are inserted into the enemy country, it becomes clear just how powerful the numbers station system is."While shortwave radio buffs have been aware of them for years, the number station phenomenon remains largely unheard of by the general public.
More info at: http://labyrinth13.com/OtherWorks_Num...
Some raw footage from the Conet Project here: