* Astronomy

For more than 30 years the Shortwave radio spectrum has been used by the worlds intelligence agencies to transmit secret messages. These messages are transmitted by hundreds of “Numbers Stations”.

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.

These stations use very rigid schedules, and transmit in many different languages, employing male and female voices repeating strings of numbers or phonetic letters day and night, all year round.

"Although no broadcaster or government has acknowledged transmitting the numbers, a 1998 article in The Daily Telegraph quoted a spokesperson for the Department of Trade and Industry (the government agency that regulates radio broadcasting in the United Kingdom) as saying, "These (numbers stations) are what you suppose they are. People shouldn't be mystified by them. They are not for, shall we say, public consumption."
Listening to numbers stations in the UK is illegal under the Wireless Telegraphy Act 1949, since it is unlikely that it is possible to get official permission to listen to them, however it is unlikely that the legislation would be used to prosecute those who listen to the stations privately."
Source

After the Cold War, many of the transmissions that were originating from Communist countries stopped. Many number stations today can be linked with Cuba, China, and Taiwan.

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