Learn more about Numbers station
The voices that can be heard on these stations are often mysterious: mechanically generated; spoken in a wide variety of languages; usually female, but sometimes male or those of children.
Evidence supports popular assumptions that the broadcasts are channels of communication used to send messages to spies. This has not been publicly acknowledged by any government that may operate a numbers station, but in one case, numbers station espionage has been publicly prosecuted in a United States court.
Numbers stations appear and disappear over time (although some follow regular schedules), and their overall activity has increased slightly since the early 1990s. This increase suggests that as spy-related phenomena, they were not unique to the Cold War.
 Suspected origins and use
According to the notes of The Conet Project,<ref>"The Shortwave And the Calling: For Akin Fernandez, Cryptic Messages Became Music To His Ears", The Washington Post, August 3, 2004.</ref> numbers stations have been reported since World War I. If accurate, this would make number stations among the earliest radio broadcasts.
It has long been speculated, and was charged in one case, that these stations operate as a simple and foolproof method for government agencies to communicate with spies working under cover (sometimes literally<ref>http://www.myspystory.com/chap6.html "So here she was with a pillow over her head and over the radio..."</ref>). According to this theory, the messages are encrypted with a one-time pad, to avoid any risk of decryption by the enemy. As evidence, numbers stations have changed details of their broadcasts or produced special, nonscheduled broadcasts coincident with extraordinary political events, such as the Russian constitutional crisis of 1993 .
Others speculate that some of these stations may be related to illegal drug smuggling operations. Unlike government stations, smugglers' stations would need to be lower powered and irregularly operated, to avoid location by triangulated direction finding, followed by government raids. Numbers stations have transmitted with impunity for decades, so they are presumed to be operated or sponsored only by governments. Also, numbers station transmissions in the international shortwave bands typically require high wattage electricity that is unavailable to ranches, farms, or plantations in isolated drug-growing regions.
Radio transmitter signals under 40 watts can travel around the world under ideal conditions of frequency band, local RF noise level, weather, season, sunspots, big receiving antenna, and a superb receiver. However, spies have to work with available hand held receivers, sometimes under pressured local conditions in all seasons and sunspot years.<ref>http://www.miaminewtimes.com/issues/2001-02-08/kulchur.html</ref><ref>http://www.myspystory.com</ref> Only very large transmitters, perhaps up to 500,000 watts, are guaranteed to get through to nearly any basement-dwelling spy, nearly any place on earth, nearly all of the time. Some governments may not need a numbers station with global coverage if they only send spies to nearby countries.
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, at that time, regulated 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."<ref>http://www.salon.com/people/feature/1999/09/16/numbers/print.html</ref> 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. Indeed, one could argue that a listener could not be prosecuted for listening to stations that officially do not exist and in any case, operate illegally on frequencies not allocated to them by the ITU.
Numbers stations are often given nicknames by enthusiasts, often reflecting some distinctive element of the station. For example, "The Lincolnshire Poacher", one of the best known numbers stations (generally thought to be run by MI6 as its transmissions have been traced to RAF Akrotiri in Cyprus), plays the first two bars of the folk song "The Lincolnshire Poacher" before each string of numbers. "Magnetic Fields" plays music from French electronic musician Jean Michel Jarre before and after each set of numbers. The "Atención" station begins its transmission with the Spanish phrase "¡Atención! ¡Atención!"
Although it is time-consuming and may require costly global travel to pinpoint the source of a radio transmission in the shortwave band, errors at the transmission site, radio direction-finding, and a knowledge of shortwave radio propagation have provided armchair detective clues to some number station locations.
For example, the "Atención" station was originally presumed to be from Cuba, as a supposed error allowed Radio Habana Cuba to be carried on the frequency. Whether the frequency of Radio Habana Cuba and the frequency of the "Atención" station merely interfered with each other or whether the operator of the station was listening to the radio and it accidentally ended up on the air is unclear. (Circa 2000-2001, Atención was officially identified as Cuban by the USA.)
Also, several articles in the radio magazine Popular Communications published in the 1980s and early 1990s described hobbyists using portable radio direction-finding equipment to locate numbers stations in Florida and in the Warrenton, Virginia area (Smolinski reported by Mays,2005) From the outside, they spotted the station's antenna inside a military facility. The station hunter speculated that the antenna's transmitter at the facility was connected by a telephone wire pair to a source of spoken numbers in the Washington, DC area. The author said the Federal Communications Commission would not comment on public inquiries about USA territory numbers stations.
On some stations, tones can be heard in the background. It has been suggested that in such cases the voice may be an aid to tuning to the correct frequency, with the coded message being sent by modulating the tones, perhaps using a technology such as burst transmission.
 The Atención spy case evidence
Atención of Cuba became the world's first numbers station to be officially and publicly accused of transmitting to spies. It was the centerpiece of a USA federal court espionage trial following the arrest of the Wasp Network of Cuban spies in 1998. The U.S. prosecutors claimed the accused were writing down number codes received from Atención, using Sony hand-held shortwave receivers, and typing the numbers into laptop computers to decode spying instructions. The FBI testified that they had entered a spy's apartment in 1995, and copied the computer decryption program for the Atención numbers code. They used it to decode Atención spy messages, which the prosecutors unveiled in court.
USA government evidence included the following three examples of decoded Atención messages. (Not reported whether the original clear texts were in Spanish.):
- "prioritize and continue to strengthen friendship with Joe and Dennis" [68 characters]
- "Under no circumstances should [agents] German nor Castor fly with BTTR or another organization on days 24, 25, 26, and 27." [112 characters] (BTTR is the anti-Castro airborne group Brothers to the Rescue)
- "Congratulate all the female comrades for International Day of the Woman." [71 characters] (Probably a simple greeting for March 8, International Women's Day)
At the rate of one spoken number per character per second, each of these sentences takes a minute or more to transmit.
The moderator of an e-mail list for global numbers station hobbyists claimed "Someone on the Spooks list had already cracked the code for a repeated transmission [from Havana to Miami] if it was received garbled." Such code-breaking is possible if a one-time pad decoding key is used more than once. <ref>Chris Smolinski of Spooks to Miami New Times reporter Brett Sokol, 2001. http://www.miaminewtimes.com/issues/2001-02-08/kulchur.html</ref>
Generally, numbers stations follow a basic format, although there are many differences in details between stations. Transmissions usually begin on the hour or half-hour.
The prelude or introduction of a transmission (from which stations' informal nicknames are often derived) includes some kind of identifier, either for the station itself and/or for the intended recipient. This can take the form of numeric or phonetic "code names" (e.g. "Charlie India Oscar", "250 250 250"), characteristic phrases (e.g. "¡Atención! ¡Atención!", "1234567890"), and sometimes musical or electronic sounds (e.g. "The Lincolnshire Poacher", "Magnetic Fields"). Sometimes, as in the case of the Israeli phonetic alphabet stations, the prelude can also signify the nature or priority of the message to follow (e.g. "Charlie India Oscar-2", indicating that no message follows). Often the prelude repeats for a period before the body of the message begins.
There is usually an announcement of the number of number-groups in the message, then the groups are recited. Groups are usually either four or five digits or phonetic letters. The groups are typically repeated, either by reading each group twice, or by repeating the entire message as a whole.
Some stations send more than one message during a transmission. In this case, some or all of the above process is repeated, with different contents.
Finally, after all the messages have been sent, the station will sign off in some characteristic fashion. Usually it will simply be some form of the word "end" in whatever language the station uses (e.g. "end of message, end of transmission"; "ende"; "fini"; "final"; "konec"). Some stations, especially those thought to originate from the former Soviet Union, end with a series of zeros, e.g. "000 000"; others end with music or other sundry sounds.
These messages are normally encrypted with a one-time pad; hence, the contents of these groups are indistinguishable from randomly generated numbers or digits. See If It Had Not Been For 15 Minutes for a simplified explanation of decoding numbers messages without a computer.
 Transmission technology
Although few numbers stations have been tracked down by location, the technology used to transmit the numbers has historically been clear -- stock shortwave transmitters using powers from 10 kW to 100 kW.
Amplitude modulated (AM) transmitters with optionally variable frequency, using class-C power output stages and plate modulation, are the workhorses of international shortwave broadcasting, including numbers stations.
Application of spectrum analysis to number station signals has revealed the presence of data bursts, RTTY-modulated subcarriers, phase-shifted carriers, and other unusual transmitter modulations like polytones<ref>Schimmel, Donald W., The Underground Frequency Guide: A Directory of Unusual, Illegal, and Covert Radio Communications (3rd ed.) [Solana Beach, CA: High Text Publications, Inc., 1994], pp. 27–28.</ref>. (RTTY-modulated subcarriers were also present on some U.S. commercial radio transmissions during the Cold War<ref>Collins, Barry W., W4TLV, "The day the U.S. Army invaded W4TLV," QST, pp. 48–49 (July 1997).</ref>).
For spies in the field, low tech spoken number transmissions continue to have advantages in the 21st century. High tech data receiving equipment is difficult to obtain, and being caught with more than a civilian shortwave news radio is evidence of spying. Yet governments' embassies, aircraft, and ships at sea are known to possess complex receiving equipment that could make regular use of encrypted data transmissions from the home country. These probably include charts and photos that require more transmitted data than can be sent timely by spoken numbers.
 The USSR and superpower number stations
- During the Cold War there was substantial and substantive evidence that the USSR may have used 500 kW transmitters on the other side of the Urals to reach agents in Western Europe, North Africa and possibly North America.
- HF direction finding evidence that was collected by many different sets of amateurs in Europe, Africa and the Americas during the Cold War substantiates number stations broadcasting from the East of the Urals.
- Existing USSR technical literature shows that the USSR pioneered HRS 8/8/1 directional HF antennas for shortwave news and information broadcasting in the late 1960s - mid 1970s. Thus it is possible that lower transmitter powers (like 100 kw) were used in the 1980s -- the later part of the Cold War.
- Superpower number station broadcasting from the USSR cannot be concretely proven to this day: The USSR jammed HF broadcasts from the west making many HF direction finding attempts nearly impossible. The HF bands in the European region were very crowded during most of the Cold War making good HF direction problematic.
Class-C transmitters may achieve 70-90% efficiency for converting electric power into radio energy, with the rest wasted as heat. This fact might help retrospective superpower numbers station locators. A class-C transmitter rated at half a million watts RF output, would need to dissipate between 55,000 and 215,000 watts of heat continuously into a nearby river, or into a large cooling tower probably visible in commercial satellite photos.
 Interference with documented broadcasts
The North Korean propaganda station Voice of Korea began to broadcast on the Lincolnshire Poacher's frequency, 11545 kHz, in 2006, possibly to deliberately interfere with its propagation. This clash can be viewed in video format here: 
The allegation of jamming by the Voice of Korea is not likely to be true. Firstly, the Lincolnshire Poacher transmits on two additional frequencies in simulcast to 11545 kHz which are not "jammed". Also, the intended target zone is the Middle East, not the Far East which is covered by its sister station Cherry Ripe.
The late "Havana Moon" reported that "one particularly dangerous station has been interfering with air to ground traffic on 6577 kHz, a frequency allocated to international aeronautical communications in the busy Caribbean sector". "On at least one monitored transmission, the air traffic controller at ARINC moved the pilot to an alternate frequency as the numbers transmission was totally blocking the frequency from effective use".
A station operated by the West German BND used to transmit on 9450 kHz which interfered with Radio Moscow (now The Voice of Russia) which used the same frequency. A tape recording of the interference was submitted to Radio Moscow which prompted this response:  The BND station's callsign was "Hotel Kilo". 
SW Radio Africa transmits from Meyerton, South Africa on 4880 kHz and is the "Independent Voice of Zimbabwe". Here you can view a video of the MOSSAD E10 station "Uniform Lima X-Ray" interfering with the African station. 
The religious station WYFR transmits from Okeechobee, Florida USA on 6855 kHz. It is regularly affected by the Cuban Spanish number station "V2". You can view a video of V2 interfering with the American station. 
A BBC frequency, 7325 kHz, has also been used. This prompted a letter to the BBC from a lady listener in Andorra. She wrote to the "Waveguide" program complaining that her listening had been spoiled by a female voice reading out numbers in English and she asked the announcer what this interference was. Could it be spies? The BBC presenter laughed at such an idea. He had consulted the experts at Bush House (BBC headquarters) who declared that the voice was reading out nothing more sinister than snowfall figures for the ski-slopes near the listener's home. With more research into this case, short wave enthusiasts are fairly sure that there was more to it than just "A voice reading out nothing more sinister than snowfall figures for the ski-slopes."  They were almost certain that this was a numbers station being broadcast on a random frequency. The likelihood of the broadcast being snow readings is in doubt because it would have been illegal to broadcast on an already used frequency.
 Popular culture references
Recordings of numbers stations sometimes find their way onto records by other musicians via sampling, such as Stereolab's song "Pause", Porcupine Tree's "Even Less", Chroma Key's "Even the Waves", or various songs by Wilco, whose album Yankee Hotel Foxtrot is named after a message sampled on it. Pere Ubu's drummer Scott Krauss is an avid fan of numbers stations, and has featured recordings in several of the group's songs. The track "On the Lamb" by 310, from the album Aug 56 lasts almost half an hour, and features samples from a numbers station throughout.
The Kraftwerk song "Numbers" is influenced by number station transmissions.
The reclusive Scottish duo Boards of Canada were influenced by numbers stations at an early age. The track "Gyroscope" on the Geogaddi album is thought to contain a sample of a child counting provided by the Conet Project.
Italian progressive metal band Madwork sampled a numbers station in the introduction to their track entitled "Null" in 2005.
The electronica song "Lifelight" by Andy Hunter on the album "Life" features a sample of a spanish number station in the background midway through the track at 5:07.
 Film and television
The West German film "Der Westen Leuchtet" shows an agent called Harald Liebe receiving a number station transmission via a Sony ICF-7800 radio. He is then shown decoding the message using his one-time pad. See 
A transcript of numbers from transmissions of the Lincolnshire Poacher station were printed on the set of a series of the UK TV Series: Mark Thomas Comedy Project
In the 1991 film Toy Soldiers, the Colombian forces utilize number stations to communicate between the school and their home base. There are multiple scenes which depict the encoding and decoding of information transmitted over portable numbers stations.
In the 1984 film Red Dawn, a band of high school guerrilla fighters hears two code phrases (each repeated twice) broadcast over the radio as they hide out in the wilderness. The phrases are: The chair is against the wall and John has a long mustache (the latter of which was actually used as a code-signal by the French Resistance during World War II).
 See also
- secret broadcast
- letter beacon
- Lincolnshire Poacher
- Cherry Ripe
- Yosemite Sam (shortwave)
 External links
- Read the book "Secret Signals - The Euronumbers Mystery" here:
- Website to discuss number stations and other technology
- ENIGMA 2000 Number Stations Monitoring Group - Guidance docs, Newsletters and other info. 
- SpyNumbers.com - a good introduction
- Dark Side of the Band - Wired.com's article about Numbers Stations
- Shortwave Espionage - a large amount of information, including sound recordings
- Counting Spies - Salon.com's Article on Numbers Stations
- The Conet Project from Irdial, and MP3s of the 4 CD set at hyperreal.org and archive.org
- NPR's Lost and Found Sound, 26 May 2000: The Shortwave Numbers Mystery
- NPR's All Things Considered, 12 November 2004: Music By The 'Number Stations'
- Tracking The Lincolnshire Poacher BBC Radio 4 programme on Number Stations - Streaming audio - use the DOWNLOAD THE SHOW HERE: link.
- Clandestine Radio Open-source Intelligence on Subversive Radio & TV
- Numbers Monitoring, A website containing .wav recordings of transmissions from Number Stations
- The Numbers Game, another site offering .wav recordings including that of voices and songs played.
- Smolinski, Chris. "Introduction to Voice Numbers Stations" NSNL Newsletter. (www.cvni.net/radio/nsnl/nsnl2vs.html stale URL accessed on May 2, 2005 by Tim Mays )
- Espionage Is in the Air Sokol, 2001. Backgrounder to trial of Wasp Network of Cuban spies accused of receiving instructions from the ¡Atención! numbers station.
- If It Had Not Been For 15 Minutes First hand account of number station usage in an actual case of espionage in the former East-Germany. See chapter 7 for details of decoding numbers.
- Numbers Stations on dxing.com
- Cryptic Universe An explanation of Number Stations, and some samples.
-  Overview of number stations with recordings and schedulesde:Zahlensender