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Mysteries Over Shortwave Radio: Numbers Stations
What is commonly known as shortwave radio is a range of frequencies from 1.6 to 30 megahertz, and has long been used for international broadcasting, ham radio and utility transmissions. But the BBC World Service, religious programs and the Voice of America are far from the only things you can hear on shortwave. Even to this day, you may come across cryptic, unadverstised transmissions on certain frequencies, often in the middle of the night. These transmissions are usually of a voice (almost always female) reading sets of numbers in a monotonic voice. Sometimes, the broadcasts are in Morse Code. In recent years, the sets of numbers can be interrupted by modem-like sounds. These weird, unidentified broadcasts are referred to as spy stations or numbers stations.
The classic Lincolnshire Poacher numbers station
What ARE numbers stations?
Numbers stations have been in use for many decades, from at least as far back as the beginning of the Cold War in the late 1940s, but according to the Conet Project, numbers stations have been reported since World War I. It has long been assumed that espionage agencies of different countries have been behind the operation of numbers stations. The numbers -- or whatever is broadcast over a numbers station -- are believed to be coded messages which are sent to espionage agents by their home country. The agent would be told when and on what frequency to look for a broadcast. Thanks to the portability and ease of use of a shortwave receiver, the agent could catch the transmission pretty much anywhere, with minimal equipment.
The recipient of the transmission would tune in, write down the sequences of numbers that are read over the air, and then decode the message with a one-time pad, which would help the spy break the code. The one-time pad, as the name suggests, would only be useful in decoding one particular transmission or set of transmissions. This provides a safe and easy way for undercover operatives to receive instructions. In recent years, stations that transmit data bursts can be decoded by the recipient using software. Some stations will play a distinctive piece of music before the numbers are read to make it easier to pick up or identify the broadcast by the transmission's recipient. In the case of the Cuban stations, the broadcast will begin with a female voice saying "Atencion" ("attention" in Spanish).
Who is behind numbers stations?
The main producers of numbers transmissions these days (at least of the ones that can be heard in the USA) seem to be the Cuban intelligence services. Their broadcasts (always in Spanish) can be found relatively easily, mostly late at night, but sometimes during the day. It is suspected that North Korea still produces similar broadcasts. Vietnam and Israel also seem to be behind recently heard numbers broadcasts. It is also believed that some numbers stations are operated by those involved in illegal drug trafficking or terrorism. It is hard to tell for sure where a numbers station originates, as there is no reliable way to trace shortwave transmissions to their source, and not one government or entity has come forward to admit that they use numbers stations.
Israeli Numbers Station
How do you find numbers stations?
The easiest way to find numbers stations is to get a shortwave radio (portable or base station) with a decent antenna. The easiest spy stations to find are the Cuban ones, so if you live in the southern or eastern U.S., you should be able to pick one up with a portable shortwave radio's factory-attached whip antenna. Do a scan of the shortwave bands, preferably at night. Midnight to 3:00 AM (Central Time) seems to be a particularly productive time span. If you hear a station broadcasting modem-like sounds or a voice reading sets of numbers, you have likely found a numbers station. Transmissions often begin on the hour or half-hour, and sometimes start with a piece of music or code word.
I've added a couple of links below to some sources which can help you more easily find numbers stations.
The Case of The Cuban Five
In 1998, five Cuban intelligence operatives were arrested in Miami, Florida for espionage. The five were in Florida mostly to spy on anti-Castro exile groups. During the trial of the Cuban Five, it came to light that they had been receiving messages through the Atención numbers stations, which they listened to on handheld shortwave radios. FBI agents had secretly entered one spy's apartment and copied the decryption software that the Cubans had been using to type in the numbers they heard in order to translate them into coherent messages. All five Cuban agents went to prison, and four of them are still incarcerated.
Numbers Stations in Media and Entertainment
Numbers stations have appeared or used as plot devices in TV shows such as Lost, Scandal and The Americans. There is also a 2013 John Cusack action movie titled The Numbers Station, in which Cusack plays a CIA operative who oversees an American numbers station in the UK. The alternative band Wilco's album Yankee Hotel Foxtrox also makes references to numbers stations.
Some recordings of Cuban numbers stations in MP3 format
Below are links to a couple of suspected Cuban numbers broadcasts, which I recorded off of my portable shortwave radio. Creepy! Feel free to download and share these as you wish: