{{Short description|Shortwave radio stations broadcasting only numbers}} {{For|the 2013 film|The Numbers Station}} {{Use dmy dates|date=March 2016}} {{Listen | filename = Poacher.ogg | title = "Lincolnshire Poacher" | description = Recording of the E03 "Lincolnshire Poacher" interval signal, followed by a coded transmission of five numbers: 0–2–5–8–8 | format = Ogg | alt = Recording of the Lincolnshire Poacher interval signal and five-number voice transmission }} thumb|alt=Audio recording of a voice transmission from a Cuban numbers station|Cuban numbers station HM01. The numbers read: 56284 66144 55861 42346 62801 20863 – 56284 [[File:Gong numbers station.ogg|thumb|alt=Audio recording of the Gong numbers station used by East German military|A recording of ''The Gong'' numbers station, operated by the National People's Army of the German Democratic Republic in 1988]]
A '''numbers station''' is a shortwave radio station characterized by broadcasts of formatted numbers, which are believed to be addressed to intelligence officers operating in foreign countries.<ref>{{cite news |url=https://www.bbc.co.uk/news/magazine-24910397 |title=The spooky world of the 'numbers stations' |last=Sorrel-Dejerine |first=Olivia |date=16 April 2014 |work=BBC News}}</ref> Most identified stations use speech synthesis to vocalize numbers, although digital modes such as phase-shift keying and frequency-shift keying, as well as Morse code transmissions, are also used. Stations may operate on set schedules and frequencies in the high-frequency band, while others broadcast at irregular times.<ref name="Number stations basic">{{cite web |url=http://priyom.org/number-stations |title=Number stations |website=Priyom}}</ref>
Numbers stations have been documented since at least World War I and reached peak activity during the Cold War.<ref>{{cite web |url=https://explorethearchive.com/numbers-stations |title=Numbers Stations: The Secret Signals That Haunt Radio Airwaves |website=Explore the Archive |date=2 October 2024}}</ref> Several espionage prosecutions have confirmed the practice: the conviction of the Cuban Five in the United States in 2001,<ref>{{cite web |url=https://www.hfunderground.com/wiki/index.php/Number_Stations|title=Number Stations |website=HF Underground |access-date=9 March 2026|quote=In 2001, the United States tried the Cuban Five on the charge of spying for Cuba. That group had received and decoded messages that had been broadcast from Cuban numbers stations.}}</ref><ref>{{cite news |url=https://www.miaminewtimes.com/opinion/espionage-is-in-the-air-6353856/|title=Espionage Is in the Air |work=Miami New Times |date=6 February 2001}}</ref> and the arrest of members of the Russian Illegals Program in 2010,<ref>{{cite news |url=https://www.slate.com/articles/technology/technology/2010/07/7887_khz_your_home_for_classic_cuban_espionage_radio.html |title=7,887 kHz: Your Home for Classic Cuban Espionage Radio |last=Beam |first=Alex |work=Slate |date=5 July 2010}}</ref> both involved the use of shortwave number broadcasts to transmit instructions to agents.<ref>{{cite news |url=https://www.bbc.co.uk/news/magazine-24910397 |title=The spooky world of the 'numbers stations' |last=Sorrel-Dejerine |first=Olivia |date=16 April 2014 |work=BBC News}}</ref> Messages are typically encrypted using a one-time pad, a method considered theoretically unbreakable when applied correctly.<ref>{{cite web |url=https://archive.org/details/ird059 |title=The Conet Project – Recordings of Shortwave Numbers Stations |publisher=Internet Archive |date=25 December 2003}}</ref>
Shortwave signals can propagate over intercontinental distances by reflecting off the ionosphere, allowing a single transmitter to reach agents worldwide. The receiving agent requires only an ordinary consumer shortwave radio, possession of which carries a degree of plausible deniability. These properties, combined with independence from satellite and internet infrastructure, have led analysts to argue that numbers stations retain operational relevance even in the 21st century.<ref name="Ingesson-Andersson-2024">{{cite journal |last1=Ingesson |first1=Tony |last2=Andersson |first2=Magnus |title=Clandestine communications in cyber-denied environments: Numbers stations and radio in the 21st century |journal=Journal of Policing, Intelligence and Counter Terrorism |volume=19 |issue=2 |pages=144–165 |date=2024 |doi=10.1080/18335330.2023.2209578 |doi-access=free}}</ref>
Numbers stations have long been monitored by shortwave listeners, and many are known by informal nicknames based on distinctive interval signals. Hobbyist groups including ENIGMA 2000 have also developed systems for classifying identified stations.<ref>{{cite web |url=http://www.signalshed.com |title=ENIGMA 2000 Number Stations Group |website=signalshed.com |access-date=9 March 2026}}</ref><ref>{{cite web |url=https://www.sigidwiki.com/wiki/Category:Numbers_Stations |title=Numbers Stations and Enigma Stations |website=Signal Identification Wiki |access-date=9 March 2026}}</ref>
==History== According to the notes of ''The Conet Project'',<ref>{{cite news |first=David |last=Segal |date=3 August 2004 |title=The shortwave and the calling: For Akin Fernandez, cryptic messages became music to his ears |newspaper=The Washington Post |page=C01 |url=https://www.washingtonpost.com/wp-dyn/articles/A35647-2004Aug2.html}}</ref><ref>{{harvnb|Mason|1991|pages=5–6}}</ref> which has compiled recordings of these transmissions, number stations have been reported since {{nobr|World War I}} with the numbers transmitted in Morse code. It is reported that Archduke Anton of Austria in his youth during World War I used to listen in to their transmissions, writing them down and passing them on to the Austrian military intelligence.<ref name="first-stations">{{cite web |url=https://www.numbers-stations.com/articles/the-first-numbers-stations/ |title=The First Numbers Stations |date=30 November 2014 |publisher=NSRIC |first=Ryan |last=Schaum |df=dmy-all }}</ref>
Numbers stations were most abundant during the Cold War era. According to an internal Cold War-era report of the Polish Ministry of the Interior, numbers stations DCF37 (3.370 MHz) and DFD21 (4.010 MHz) were transmitted from West Germany beginning in the early 1950s.<ref>{{cite journal |last=Bury |first=Jan |date=October 2007 |title=From the archives: The U.S. and West German agent radio ciphers |url=http://www.swldxer.co.uk/polish.mht |archive-url=https://web.archive.org/web/20121223120639/http://www.swldxer.co.uk/polish.mht |url-status=usurped |archive-date=23 December 2012 |journal=Cryptologia |volume=31 |issue=4 |pages=343–357 |doi=10.1080/01611190701578104 |issn=0161-1194 |s2cid=205487634|url-access=subscription }}</ref>
Many stations from this era continue to broadcast and some long-time stations may have been taken over by different operators.<ref>{{Cite news|date=2014-04-16|title=The spooky world of the 'numbers stations'|language=en-GB|work=BBC News|url=https://www.bbc.com/news/magazine-24910397|access-date=2021-07-12}}</ref><ref>{{cite web|url=https://www.numbers-stations.com|title=Numbers Stations Research|website=Numbers Stations Research}}</ref> The Czech Ministry of the Interior and the Swedish Security Service have both acknowledged the use of numbers stations by Czechoslovakia for espionage,<ref name="Säkerhetspolisen2015">{{cite web |title=Lyssna på ett hemligt telegram |url=http://www.sakerhetspolisen.se/ovrigt/pressrum/aktuellt/aktuellt/2015-01-23-lyssna-pa-ett-hemligt-telegram.html |publisher=Säkerhetspolisen |access-date=12 March 2016 |language=sv |date=23 January 2015 |archive-url=https://web.archive.org/web/20160308174151/http://sakerhetspolisen.se/ovrigt/pressrum/aktuellt/aktuellt/2015-01-23-lyssna-pa-ett-hemligt-telegram.html |archive-date=8 March 2016 |url-status=live |trans-title=Listen to a secret telegram |df=dmy-all }}</ref><ref name="Swedish Security Service">{{cite web |url=https://www.numbers-stations.com/articles/the-swedish-security-service-releases-info-on-a-numbers-station/ |title=The Swedish Security Service Releases Info on a Numbers Station |date=24 July 2015 |access-date=12 March 2016 |publisher=NSRIC |df=dmy-all }}</ref><ref>{{cite news |author1=Catinka Mannerfelt Agneskog |title=Säpos hemliga radiotelegram |url=http://www.svd.se/nyheter/inrikes/sapos-hemliga-radiotelegram_4273023.svd |access-date=23 January 2015 |publisher=SvD Nyheter |language=sv}}</ref> with declassified documents proving the same. In rare cases, shortwave listeners who sent reception reports to stations that identified themselves received QSL responses, an unusual occurrence for a clandestine operation.<ref>stations KKN44, BFBX and OLX {{cite web |url=http://www.simonmason.karoo.net/page30.html |title=Shortwave Espionage |last=Mason |first=Simon |access-date=28 October 2011 |archive-url=https://web.archive.org/web/20111203183625/http://www.simonmason.karoo.net/page30.html |archive-date=3 December 2011 }}</ref><ref>{{cite book |last=Helms |first=Harry L. |title=How to Tune the Secret Shortwave Spectrum |year=1981 |publisher=TAB Books |location=Blue Ridge Summit, Pennsylvania |isbn=0-8306-1185-1 |page=52 |chapter=Espionage Radio Activity}}</ref>
One well-known numbers station was the E03 "Lincolnshire Poacher",<ref name="E03 › Priyom.org">{{Cite web|url=http://priyom.org/number-stations/english/e03|title=E03|website=Priyom.org|language=en|access-date=2017-06-17}}</ref> which is thought to have been run by the British Secret Intelligence Service.<ref>{{cite web |url=https://www.numbers-stations.com/E03 |title=E03 The LincolnShire Poacher |access-date=6 September 2014}}</ref> It was first broadcast from Bletchley Park in the mid-1970s but later was broadcast from RAF Akrotiri in Cyprus. It ceased broadcasting in 2008.<ref name=":0">{{Cite web|last=Gorvett|first=Zaria|title=The ghostly radio station that no one claims to run|url=https://www.bbc.com/future/article/20170801-the-ghostly-radio-station-that-no-one-claims-to-run |date=15 July 2020 |access-date=2021-07-12|website=BBC Future |language=en}}</ref>
In 2001, the United States tried the Cuban Five on the charge of spying for Cuba. The group had received and decoded messages that had been broadcast from the "Atención" number station in Cuba.<ref name="MNT">{{cite news|last=Sokol|first=Brett|date=8 February 2001|title=Espionage Is in the Air|work=Miami New Times|url=http://www.miaminewtimes.com/issues/2001-02-08/kulchur.html|archive-url=https://web.archive.org/web/20010221161138/http://www.miaminewtimes.com/issues/2001-02-08/kulchur.html|archive-date=21 February 2001}}</ref>
=== Atención spy case === The "Atención" station 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 United States 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.<ref name="MNT" />
The United States government's evidence included the following three examples of decoded Atención messages.<ref name="MNT" /> * "prioritize and continue to strengthen friendship with Joe and Dennis" * "Under no circumstances should [agents] German nor Castro fly with BTTR or another organization on days 24, 25, 26 and 27." (BTTR is a CIA affiliated anti-Castro airborne group Brothers to the Rescue) * "Congratulate all the female comrades for International Day of the Woman."
The moderator of an e-mail list for global numbers station hobbyists claimed that "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 may be possible if a one-time pad decoding key is used more than once.<ref name="MNT" /> If used properly, however, the code cannot be broken.
=== 21st century cases === In 2001, Ana Belén Montes, a senior US Defense Intelligence Agency analyst, was arrested and charged with espionage. The federal prosecutors alleged that Montes was able to communicate with the Cuban Intelligence Directorate through encoded messages, with instructions being received through "encrypted shortwave transmissions from Cuba".
In 2006, Carlos Alvarez and his wife, Elsa, were arrested and charged with espionage. The U.S. District Court for the Southern District of Florida<ref>''United States v. Alvarez'', 506 F. Supp. 2d 1285 (S.D. Fla. 2007)</ref>{{which|date=January 2020}} stated that "defendants would receive assignments via shortwave radio transmissions".{{citation needed|date=January 2020}}
In June 2009, the United States similarly charged Walter Kendall Myers with conspiracy to spy for Cuba, and receiving and decoding messages broadcast from a numbers station operated by the Cuban Intelligence Directorate to further that conspiracy.<ref>{{cite web |first=Dirk |last=Rijmenants |url=https://www.ciphermachinesandcryptology.com/papers/cuban_agent_communications.pdf |title=Cuban Agent Communications |year=2013 |type=PDF |website=Cipher Machines & Cryptology |access-date=30 December 2013}}</ref><ref>{{cite web |url=http://i.cdn.turner.com/cnn/2009/images/06/05/myers.indictment.pdf |title=United States v. Walter Kendall Myers, United States District Court, District of Columbia, no. xxx. |access-date=26 August 2010}}</ref> As discovered by the FBI up to 2010, one way that Russian agents of the Illegals Program were receiving instructions was via coded messages on shortwave radio.<ref name=":0" /> It has been reported that the United States has used number stations to communicate encoded information to persons in other countries.<ref name="MNT" /> There are also claims that State Department-operated stations, such as KKN50 and KKN44, used to broadcast similar "numbers" messages or related traffic, although these radio stations have been off the air for many years.<ref>{{cite book |last=Helms |first=Harry L. |title=How to Tune the Secret Shortwave Spectrum |year=1981 |publisher=TAB Books] |location=Blue Ridge Summit, Pennsylvania |isbn=0-8306-1185-1 |page=58 |chapter=Government and Military Communications}}</ref><ref>{{cite book |last=Schimmel |first=Donald W. |title=The Underground Frequency Guide: A Directory of Unusual, Illegal, and Covert Radio Communications |edition=3 |location=Solana Beach, California |publisher=High Text Publications |year=1994 |isbn=1-878707-17-5 |pages=88–95}}</ref>
North Korea revived number broadcasts in July 2016 after a hiatus of sixteen years, a move which some analysts speculated was psychological war;<ref name="Choe-2016-07-21-NYT">{{cite news |last=Choe |first=Sang-Hun |date=2016-07-21 |title=North Korea revives coded spy broadcasts after 16 year silence |newspaper=The New York Times |url=https://www.nytimes.com/2016/07/22/world/asia/north-korea-spy-radio-broadcasts.html |access-date=2016-07-30}}</ref> sixteen such broadcasts occurred in 2017, including unusually timed transmissions in April.<ref name="Osbourne-2017-05-12-DExp">{{cite news |last=Osbourne |first=Simon |date=2017-05-12 |title=North Korea sends chilling coded radio messages to South Korea amid fears of WW3 |newspaper=Daily Express |url=http://www.express.co.uk/news/world/803845/North-Korea-broadcasts-coded-radio-messages-South-Korea-Kim-Jong-un-World-War-3}}</ref>
In late February 2026, coinciding with the outbreak of the 2026 Iran war and subsequent internet blackouts, a new Farsi-language numbers station began broadcasting on 7910 kHz (USB). The station, designated V32 by the ENIGMA 2000 monitoring group on March 3, 2026,<ref>{{cite web |url=http://www.signalshed.com/ |title=ENIGMA Control List & News |website=signalshed.com |publisher=ENIGMA 2000 |access-date=8 March 2026}}</ref><ref>{{cite web |url=https://priyom.org/number-stations/other/v32 |title=V32 |website=Priyom.org |access-date=8 March 2026}}</ref> features a male voice reading structured numeric groups in Farsi, frequently repeating the word "Tavajjoh" (Persian for "Attention").<ref>{{cite web |url=https://swling.com/blog/2026/03/new-farsi-numbers-station-reported-on-7910-khz/ |title=New Farsi Numbers Station Reported on 7910 kHz |website=The SWLing Post |date=5 March 2026}}</ref>
== Suspected use for espionage == It has long been speculated, and was argued in one court case, that these stations operate as a simple and fool-proof method for government agencies to communicate with spies working undercover.<ref>{{cite book |last=Wagner |first=Thomas |year=2004 |title=If it had Not Been for Fifteen Minutes: A true account of espionage and hair-raising adventure |chapter=Chapter 6 – So here she was, with a pillow over her head and over the radio ... |chapter-url=http://radio-weblogs.com/0101986/stories/2002/04/24/ifItHadNotBeenFor15MinutesChapter6.html |access-date=30 October 2013}}</ref> According to this hypothesis, the messages must have been encrypted with a one-time pad to avoid any risk of decryption by the enemy. Writing in 2008, Wallace and Melton described how numbers stations could be used in this way for espionage:<ref name="Wallace-Melton-2008">{{harvnb|Wallace|Melton|2008|p=438}}</ref>
:The one-way voice link (OWVL) described a covert communications system that transmitted messages to an agent's unmodified shortwave radio using the high-frequency shortwave bands between {{nobr|3 and 30 MHz}} at a predetermined time, date, and frequency contained in their communications plan.<ref name="Wallace-Melton-2008" /> :The transmissions were contained in a series of repeated random number sequences and could only be deciphered using the agent's one-time pad. If proper tradecraft was practised and instructions were precisely followed, an OWVL transmission was considered unbreakable. As long as the agent's cover could justify possessing a shortwave radio and he was not under technical surveillance, high-frequency OWVL was a secure and preferred system for the CIA during the Cold War.<ref name="Wallace-Melton-2008" />
Evidence to support this theory includes the fact that numbers stations have changed details of their broadcasts or produced special, nonscheduled broadcasts coincident with extraordinary political events, such as the attempted coup of August 1991 in the Soviet Union.<ref>{{cite report |title=Irdial-Discs, included booklet |series=The Conet Project |website=hyperreal.org |page=59 |url=http://irdial.hyperreal.org/www/conet_project_booklet.pdf |archive-url=https://web.archive.org/web/20060425154733/http://irdial.hyperreal.org/www/conet_project_booklet.pdf |archive-date=25 April 2006 }}</ref>
A 1998 article in ''The Daily Telegraph'' quoted a spokesperson for the Department of Trade and Industry (the government department 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 name=Pescovitz1999>{{cite magazine |first=David |last=Pescovitz |date=16 September 1999 |title=Counting spies |magazine=Salon |url=http://www.salon.com/1999/09/16/numbers_2/ |url-status=live |access-date=12 March 2016 |archive-url=https://web.archive.org/web/20000119102137/http://salon.com/people/feature/1999/09/16/numbers/print.html |archive-date=19 January 2000 |df=dmy-all }}</ref>
== Formats == thumb|The "Russian Man" station signing off. The numbers read: 83912 83912 10080 10080 46543 46543{{spnd}}257 257 143 143{{spnd}}000 00 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.{{citation needed|date=December 2015}}
The prelude, introduction, or call-up of a transmission (from which stations' informal nicknames are often derived) includes some kind of identifier,<ref name="Numbers Stations">{{cite web |url=https://www.numbers-stations.com/ns/ |title=Intro to Numbers Stations |date=8 February 2016 |access-date=12 March 2016 |publisher=NSRIC |df=dmy-all}}</ref> for the station itself, the intended recipient, or both. This can take the form of numeric or radio-alphabet "code names" (e.g. "Charlie India Oscar", "250 250 250", "Six-Niner-Zero-Oblique-Five-Four"), characteristic phrases (e.g. "¡Atención!", "Achtung!", "Ready? Ready?", "1234567890"), and sometimes musical or electronic sounds (e.g. "The Lincolnshire Poacher", "Magnetic Fields"). Sometimes, as in the case of radio-alphabet stations, the prelude can also signify the nature or priority of the message to follow (e.g., it may indicate that no message follows). Often the prelude repeats for a period before the body of the message begins.{{citation needed|date=December 2015}}
After the prelude, there is usually an announcement of the number of number-groups in the message,<ref name="Numbers Stations" /> the page to be used from the one-time pad, or other pertinent information. The groups are then recited. Groups are usually either four or five digits or radio-alphabet letters. The groups are typically repeated, either by reading each group twice or by repeating the entire message as a whole.{{citation needed|date=December 2015}}
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.{{citation needed|date=December 2015}}
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", "конец"). Some stations, especially those thought to originate from the former Soviet Union, end with a series of zeros, e.g., "00000" "000 000"; others end with music or other sounds.<ref name="Numbers Stations" />
Because of the secretive nature of the messages, the cryptographic function employed by particular stations is not publicly known, except in one (or possibly two){{efn|In the possible case, the underlying type of encryption might have been stated in the court record of the Atención case when the secretly copied decryption software was introduced into evidence.}} cases. It is assumed that most stations use a one-time pad that would make the contents of these number groups indistinguishable from randomly generated numbers or digits. In one confirmed case, West Germany did use a one-time pad for numbers transmissions.<ref>{{cite web |last1=Wagner |first1=Thomas |title=If it had not been for 15 Minutes, Chapter 7 |url=http://radio-weblogs.com/0101986/stories/2002/12/08/ifItHadNotBeenFor15MinutesChapter7.html |website=Radio Weblogs |access-date=18 March 2022 |archive-url=https://web.archive.org/web/20131102124519/http://radio-weblogs.com/0101986/stories/2002/12/08/ifItHadNotBeenFor15MinutesChapter7.html |archive-date=2 November 2013 |date=8 December 2012 |url-status=live}}</ref>
== Transmission technology == High-frequency radio signals transmitted at relatively low power can travel around the world under ideal propagation conditions – which are affected by local RF noise levels, weather, season, and sunspots – and can then be best received with a properly tuned antenna (of adequate, possibly conspicuous size) and a good receiver.<ref name="MNT" />
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{{nbsp}}kW to 100{{nbsp}}kW.{{citation needed|date=December 2015}}
Amplitude modulated (AM) transmitters with optionally–variable frequency, using class-C power output stages with plate modulation, are the workhorses of international shortwave broadcasting, including numbers stations.{{citation needed|date=December 2015}}
Application of spectrum analysis to numbers station signals has revealed the presence of data bursts, radioteletype-modulated subcarriers, phase-shifted carriers, and other unusual transmitter modulations like polytones.<ref>{{cite book |last=Schimmel |first=Donald W. |title=The Underground Frequency Guide: A Directory of Unusual, Illegal, and Covert Radio Communications |edition=3 |location=Solana Beach, California |publisher=High Text Publications, Inc. |year=1994 |isbn=1-878707-17-5 |pages=27–28}}</ref> (RTTY-modulated subcarriers were also present on some U.S. commercial radio transmissions during the Cold War.<ref>{{cite journal |last=Collins |first=Barry W. |title=The day the U.S. Army invaded W4TLV |journal=QST |volume=81 |pages=48–49 |date=July 1997 |issn=0033-4812}}</ref>) thumb|The speech/Morse generator (pictured here) is a machine that has been used for many well-known numbers stations.
The frequently reported use of high-tech modulations like data bursts, in combination or in sequence with spoken numbers, suggests varying transmissions for differing intelligence operations.<ref>{{cite web |url=http://www.cvni.net/radio/nsnl/nsnl015/nsnl15vs.html |title=NSNL 15: Voice stations |publisher=Cvni.net |date=3 July 1999 |access-date=26 August 2010 |archive-date=26 January 2021 |archive-url=https://web.archive.org/web/20210126030846/http://www.cvni.net/radio/nsnl/nsnl015/nsnl15vs.html }}</ref>
Those receiving the signals often have to work only with available hand-held receivers, sometimes under difficult local conditions, and in all reception conditions (such as sunspot cycles and seasonal static).<ref name="MNT" /> However, in the field low-tech spoken number transmissions continue to have advantages even in the 21st century. High-tech data-receiving equipment can be difficult to obtain and even a non-standard civilian shortwave radio can be difficult to obtain in a totalitarian state.<ref>{{cite web |last1=Wagner |first1=Thomas |title=If it had not been for 15 Minutes, Chapter 6 |url=http://radio-weblogs.com/0101986/stories/2002/04/24/ifItHadNotBeenFor15MinutesChapter6.html |website=Radio Weblogs |access-date=18 March 2022 |archive-url=https://web.archive.org/web/20141101065629/http://radio-weblogs.com/0101986/stories/2002/04/24/ifItHadNotBeenFor15MinutesChapter6.html |archive-date=1 November 2014 |date=24 April 2002 |url-status=live}}</ref> Being caught with just a shortwave radio has a degree of plausible deniability, for example, that no spying is being conducted.{{citation needed|date=December 2015}}
== Interference ==
=== Interfering with other broadcasts === The North Korean foreign language service Voice of Korea began to broadcast on the E03 Lincolnshire Poacher's former frequency, 11545 kHz, in 2006, possibly to deliberately interfere with its propagation.{{citation needed|date=October 2017}} However, Lincolnshire Poacher broadcasts on three different frequencies, and the remaining two have not been interfered with. The apparent target zone for the Lincolnshire Poacher signals originating in Cyprus was the Middle East, not the Far East, which is covered by its sister station, E03a Cherry Ripe.<ref>{{Cite web|url=http://priyom.org/number-stations/english/e03a|title=E03a|website=Priyom.org|language=en|access-date=2017-06-17}}</ref><ref name="karoo514">{{cite web |url=http://www.simonmason.karoo.net/page514.htm |title=Secret Signals |publisher=Simonmason.karoo.net |access-date=7 November 2015 |archive-date=10 February 2016 |archive-url=https://web.archive.org/web/20160210010724/http://www.simonmason.karoo.net/page514.htm }}</ref>
On 27 September 2006, amateur radio transmissions in the 30 m band were affected by an S06 "Russian Man"<ref>{{cite web |url=http://priyom.org/number-stations/slavic/s06 |title=S06|website=Priyom.org |language=en |access-date=2017-06-17}}</ref> numbers station at 17:40 UTC.<ref name="karoo514" />
In October 1990, it was reported that a numbers station had been interfering with communications on 6577 kHz, a frequency used by air traffic in the Caribbean. The interference was such that on at least one monitored transmission, it blocked the channel entirely and forced the air traffic controller to switch the pilot to an alternative frequency.<ref name="karoo514" />
A BBC frequency, 7325 kHz, has also been used. This prompted a letter to the BBC from a listener in Andorra. She wrote to the World Service ''Waveguide'' programme in 1983 complaining that her listening had been spoiled by a female voice reading out numbers in English and asked the announcer what this interference was. The BBC presenter laughed at the suggestion of spy activity. He had consulted the experts at Bush House (BBC World Service headquarters), who declared that the voice was reading out nothing more sinister than snowfall figures for the ski slopes near the listener's home. After more research into this case, shortwave enthusiasts are fairly certain that this was a numbers station being broadcast on a random frequency.<ref>{{cite web |url=http://www.simonmason.karoo.net/page34.html |title=Secret Signals |publisher=Simonmason.karoo.net |access-date=26 August 2010 |archive-url=https://web.archive.org/web/20070220145145/http://www.simonmason.karoo.net/page34.html |archive-date=20 February 2007 }}</ref>
The Cuban numbers station "HM01" has been known to interfere with shortwave broadcaster Voice of Welt on 11530 kHz.<ref>{{Citation|last=Anthony Spinelli|title=HM01 and Voice of Welt 11530 AM 10 18 2018 1743z|date=2018-10-18|url=https://www.youtube.com/watch?v=JgzyVNGdbzM |archive-url=https://ghostarchive.org/varchive/youtube/20211211/JgzyVNGdbzM| archive-date=2021-12-11 |url-status=live|access-date=2018-11-26}}{{cbignore}}</ref>
=== Attempted jamming === Numbers station transmissions have often been the target of intentional jamming attempts. Despite this targeting, many numbers stations continue to broadcast unhindered. Historical examples of jamming include the E10 (a station thought to originate from Israel's Mossad intelligence agency) being jammed by the "Chinese Music Station" (thought to originate from the People's Republic of China and usually used to jam "Sound of Hope" radio broadcasts which are anti-CCP in nature).<ref>{{cite web |url=http://www.swldxer.co.uk/yhf-dec06.wma |title=Chinese Music Station |format=Windows Media Audio |access-date=16 July 2012 |archive-url=https://web.archive.org/web/20120308232621/http://www.swldxer.co.uk/yhf-dec06.wma |archive-date=8 March 2012 |url-status=usurped }}</ref>
== Identification and classification == Monitoring and chronicling transmissions from numbers stations has been a hobby for shortwave and ham radio enthusiasts from as early as the 1970s.<ref>Māris Goldmanis, [https://www.numbers-stations.com/articles/before-enigma-the-early-numbers-stations-monitors/ Before enigma; the early numbers stations, monitors] NSRIC; retrieved 13 December 2019</ref> Numbers stations are often given nicknames by enthusiasts, often reflecting some distinctive element of the station such as the interval signal. For example, the "Lincolnshire Poacher" station played the first two bars of the folk song "The Lincolnshire Poacher" before each string of numbers.<ref>{{harvnb|Mason|1991|pages=20–21}}</ref> Sometimes these traits have helped to uncover the broadcast location of a station. The "Atención" station was thought to be from Cuba, because a supposed error allowed Radio Havana Cuba to be carried on the frequency.<ref>{{cite book |last=Poundstone |first=William |title=Big Secrets |page=197}}</ref>{{full citation needed|date=December 2022}}
Although many numbers stations have nicknames which usually describe some aspect of the station itself, these nicknames have sometimes led to confusion among listeners, particularly when discussing stations with similar traits. M. Gauffman of the ENIGMA numbers stations monitoring group originally assigned a code to each known station.<ref name="NSRIC">{{cite news |title=ENIGMA: The European Numbers Information Gathering and Monitoring Association |url=https://www.numbers-stations.com/enigma |publisher=NSRIC |access-date=24 February 2015}}</ref>
Portions of the original ENIGMA group moved on to other interests in 2000 and the classification of numbers stations was continued by the follow-on group ENIGMA 2000.<ref>{{cite web |title=ENIGMA 2000 |url=http://apul64.dsl.pipex.com/enigma2000/ |access-date=1 March 2015 |archive-date=15 September 2009 |archive-url=https://web.archive.org/web/20090915175228/http://www.apul64.dsl.pipex.com/enigma2000/ }}</ref> The document containing the description of each station and its code designation was called the "ENIGMA Control List" until 2016, after which it was incorporated into the "ENIGMA 2000 Active Station List"; the latest edition of the list was published in September 2017.<ref>{{cite web|date=September 2017|title=ENIGMA 2000 Active Station List|url=http://www.signalshed.com/docs/ENIGMA%202000%20Active%20Stations%20List%20V1.3.pdf|access-date=2020-08-25|website=signalshed.com|publisher=ENIGMA 2000|type=Booklet|version=1.3}}</ref> This classification scheme takes the form of a letter followed by a number (or, in the case of some "X" stations, more numbers).<ref>{{cite journal |journal=Radio World |year=2014 |page=14 |last=Friesen |first=Christopher |title=Spy 'Numbers Stations' still enthrall |issn=0274-8541 |volume=38 |issue=2}}</ref> The letter indicates the language used by the station in question: * E indicates a station broadcasting in English. * G indicates a station broadcasting in German. * S indicates a station broadcasting in a Slavic language. * V indicates all other languages. * M is a station broadcasting in Morse code. * X indicates all other transmissions, such as polytones, in addition to some unexplained broadcasts which may not actually be numbers stations.
There are also a few other stations<ref name="Numbers Stations" /> with a specific classification: * SK: Digital mode * HM: Hybrid mode * DP: Digital-pseudo polytone
Some stations have also been stripped of their designation when they were discovered not to be a numbers station. This was the case for E22, which was discovered in 2005 to be test transmissions for All India Radio.<ref>{{Cite web|url=http://www.cvni.net/radio/e2k/e2k032/e2k32e22.html|title=E2K 32 – E22 is not what it seems|website=www.cvni.net|archive-url=https://web.archive.org/web/20071117095441/http://www.cvni.net/radio/e2k/e2k032/e2k32e22.html|access-date=2016-04-05|archive-date=17 November 2007}}</ref>
== Recordings == * ''The Conet Project: Recordings of Shortwave Numbers Stations'' is a four-CD set of recordings of numbers stations. It was first released in 1997 by the Irdial-Discs record label. <!-- Please do not add cultural references to this article, and instead add them to the article Numbers stations in popular culture (draft status); see talk page discussions -->
== See also == {{portal|Radio}} * Secret broadcast * Letter beacon * UVB-76 * Warrenton Training Center * Radio Londres
== Notes == {{Notelist}}
== References == {{reflist}}
== Bibliography == {{refbegin|small=yes}} * {{cite book |last=Mason |first=Simon |year=1991 |title=Secret Signals: The Euronumbers Mystery |publisher=Tiare Publications |location=Lake Geneva, WI |isbn=0-936653-28-0 |url=http://www.simonmason.karoo.net/page32.html |access-date=24 December 2013 |archive-url=https://web.archive.org/web/20060613195836/http://www.simonmason.karoo.net/page32.html |archive-date=13 June 2006}} * {{cite book |first1=Robert |last1=Wallace |first2=H. Keith |last2=Melton |author2-link=H. Keith Melton |date=June 2008 |title=Spycraft: The Secret History of the CIA's Spytechs, from Communism to al-Qaeda |publisher=Dutton |isbn=978-0-525-94980-0 |url=https://www.cia.gov/static/66a33964c68ff18076cee58bf68b2c68/Review-Spycraft-Secret-History.pdf |archive-date=7 October 2016 |archive-url=https://web.archive.org/web/20161007000000/https://www.cia.gov/static/66a33964c68ff18076cee58bf68b2c68/Review-Spycraft-Secret-History.pdf}} [https://archive.org/details/SPYCRAFTTHESECRETHISTORYOFTHECIASSPYTECHSFROMCOMMUNISMTOALQAEDA2008 Alt URL] * {{cite book |first1=Robert |last1=Wallace |first2=H. Keith |last2=Melton |author2-link=H. Keith Melton |date=26 May 2009 |title=Spycraft: The Secret History of the CIA's Spytechs, from Communism to al-Qaeda |location=New York, NY |publisher=Plume |isbn=978-0-452-29547-6 |edition=Illustrated, print}} {{refend}}
== Further reading == {{refbegin}} * {{cite journal |last=Beaumont |first=Paul |journal=Radio User |date=November 2012 |title=Numbers Stations: A Modern Perspective (Part 1) |pages=50–53 |publisher=PW Publishing |location=Poole, UK |issn=1748-8117}} * {{cite journal |last=Beaumont |first=Paul |journal=Radio User |date=January 2013 |title=Numbers Stations: A Modern Perspective (Part 2) |pages=50–55 |publisher=PW Publishing |location=Poole, UK |issn=1748-8117}} * {{cite journal |last=Bury |first=Jan |journal=Cryptologia |volume=31 |issue=4 |date=October 2007 |title=From the Archives: The U.S. and West German Agent Radio Ciphers |pages=343–57 |doi=10.1080/01611190701578104 |s2cid=205487634 |url=http://www.swldxer.co.uk/polish.mht |archive-url=https://web.archive.org/web/20121223120639/http://www.swldxer.co.uk/polish.mht |url-status=usurped |archive-date=23 December 2012 |issn=0161-1194 |url-access=subscription}} * {{cite journal |last=Friesen |first=Christopher |journal=Radio World |volume=38 |issue=2 |date=15 January 2014 |pages=12, 14 |title=Spy 'Numbers Stations' Still Enthrall |url=https://www.researchgate.net/publication/340451591 |issn=0274-8541}} * {{cite book |last=Moon |first=Havana |title=Uno, Dos, Cuatro: A Guide to the Numbers Stations |publisher=Tiare Publications |location=Lake Geneva, WI |year=1987 |isbn=0-936653-06-X |url=http://www.numbersoddities.nl/unodoscuatro.pdf |access-date=24 December 2013}} * {{cite book |last=Pierce |first=Langley |title=Intercepting Numbers Stations |publisher=Interproducts |location=Perth, UK |year=1994 |isbn=0-9519783-4-9}} * {{cite book |last=Schimmel |first=Donald W. |title=The Underground Frequency Guide: A Directory of Unusual, Illegal, and Covert Radio Communications |edition=3rd |chapter=1. Numbers Stations |pages=1–28 |publisher=High Text Publications |location=Solana Beach, California |year=1994 |isbn=1-878707-17-5}} * {{cite journal |last=Smolinski |first=Chris |journal=Popular Communications |date=February 1998 |pages=8–10 |title=Spy Numbers Stations: Have You Heard Them? |publisher=CQ Communications |location=Hicksville, NY |issn=0733-3315}} {{refend}}
== External links == {{Commons category|Numbers stations}} * [https://www.numbers-stations.com/ Numbers Stations Research and Information Center] * [https://priyom.org/number-stations Numbers Stations]
{{Espionage}}
{{intelligence cycle management}}
Category:Cold War broadcasting Category:Numbers stations Category:Secret broadcasting Category:Radio stations Category:Cold War terminology