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{{short description|Shortwave radio stations broadcasting only numbers}}
'''Numbers stations''' are [[shortwave]] radio stations of uncertain origin. They generally broadcast people reading streams of numbers, words, or letters (sometimes using a [[phonetic alphabet]]).
{{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 (numbers station)|Lincolnshire Poacher]]" interval signal, followed by a coded transmission of five numbers, 0-2-5-8-8.|format=[[Ogg]]}}
[[File:Estacion de números HM01.ogg|thumb|Cuban numbers station HM01]]
[[File:Gong numbers station.ogg|thumb|A recording of ''The Gong'' numbers station, run by the [[National People's Army]] of the German Democratic Republic, from 1988.]]


A '''numbers station''' is a [[shortwave]] [[radio station]] characterized by broadcasts of formatted numbers, which are believed to be addressed to [[intelligence officer]]s operating in foreign countries.<ref>{{cite news |url= https://www.bbc.co.uk/news/magazine-24910397 |title=The spooky world of the 'numbers stations' |author=Olivia Sorrel-Dejerine |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 not uncommon. Most stations have set time schedules, or schedule patterns; however, some appear to have no discernible pattern and broadcast at random times. Stations may have set frequencies in the [[high frequency|high-frequency]] band.<ref name= "Number stations basic">{{cite web |url= http://priyom.org/number-stations |title=Number stations |website= Priyom}}</ref>
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.


Numbers stations have been reported since at least the start of [[World War I]] and continue in use today. Amongst amateur radio enthusiasts there is an interest in monitoring and classifying numbers stations, with many being given nicknames to represent their quirks or origins.
Evidence supports popular assumptions that the broadcasts are channels of communication used to send messages to [[spy|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{{fact}}.


==History==
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]].
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&nbsp;MHz) and DFD21 (4.010&nbsp;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 |journal=Cryptologia |volume=31 |issue=4 |pages=343–357 |doi=10.1080/01611190701578104 |issn=0161-1194 |s2cid=205487634}}</ref>
==Suspected origins and use==
According to the notes of ''[[The Conet Project]]'',<ref>[http://www.washingtonpost.com/wp-dyn/articles/A35647-2004Aug2.html "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.


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 [[Ministry of the Interior (Czech Republic)|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. Few [[QSL card|QSL]] responses have been received from numbers stations<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 |url-status=dead}}</ref> by [[shortwave listening|shortwave listeners]]<ref>{{Cite book|last=AMARAL|first=Cristiano Torres|title=Guia Moderno do Radioescuta|publisher=Amazon|year=2021|isbn=978-65-00-20800-9|location=Brasília|pages=333}}</ref> who sent reception reports to stations that identified themselves or to entities the listeners believed responsible for the broadcasts, which is the expected behaviour of a non-clandestine station.<ref>{{Cite web|date=2015-01-24|title=OLX|url=http://www.simonmason.karoo.net/page61.html|url-status=dead|archive-url=https://web.archive.org/web/20150124031223/http://www.simonmason.karoo.net/page61.html|archive-date=2015-01-24|access-date=2020-09-23}}</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>
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 [[spy|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]] {{fact}}.


One well-known numbers station was the E03 "[[Lincolnshire Poacher (numbers station)|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>
Others speculate that some of these stations may be related to [[illegal drugs|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.


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>
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.


=== Atención spy case ===
Although no broadcaster or government has acknowledged transmitting the numbers, a 1998 article in ''[[Daily Telegraph|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]].
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" />
Numbers stations are often given nicknames by enthusiasts, often reflecting some distinctive element of the station. For example, "[[Lincolnshire Poacher (numbers station)|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]] "[[Lincolnshire Poacher (folk song)|The Lincolnshire Poacher]]" before each string of numbers. "Magnetic Fields" plays music from French [[electronic music]]ian [[Jean Michel Jarre]] before and after each set of numbers. The "Atención" station begins its transmission with the [[Spanish language|Spanish]] phrase "¡Atención! ¡Atención!"


* "prioritize and continue to strengthen friendship with Joe and Dennis"
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.
* "Under no circumstances should [agents] German nor Castor fly with BTTR or another organization on days 24, 25, 26 and 27." (BTTR is the 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 [[One-time pad#Perfect secrecy|cannot be broken]].
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.{{citation needed}} 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.)


=== Recent cases ===
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|Warrenton]], [[Virginia]] area <small>(Smolinski [http://filebox.vt.edu/users/tmays/classdocs/Final%20Project.doc reported by Mays,]2005)</small> 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.
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 (professor)|Carlos Alvarez]] and his wife, [[Elsa Alvarez|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}}
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 [[modulation|modulating]] the tones, perhaps using a technology such as [[burst transmission]].


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" />
==The Atención spy case evidence==
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&nbsp;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&nbsp;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>
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.


== Suspected use for espionage ==
USA government evidence included the following three examples of decoded Atención messages. (Not reported whether the original clear texts were in Spanish.):


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&nbsp;6 – So here she was, with a pillow over her head and over the radio&nbsp;... |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 & [[H. Keith Melton|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>
* ''"prioritize and continue to strengthen friendship with Joe and Dennis"'' <small>[68 characters]</small>


: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" />
* ''"Under no circumstances should [agents] German nor Castor fly with BTTR or another organization on days 24, 25, 26, and 27."'' <small>[112 characters]</small> (BTTR is the anti-Castro airborne group [[Brothers to the Rescue]])
: 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 [[1991 Soviet coup d'état attempt|attempted coup of August&nbsp;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 |url-status=dead |archive-date=25 April 2006 }}</ref>
* ''"Congratulate all the female comrades for International Day of the Woman."'' <small>[71 characters]</small> (Probably a simple greeting for [[March 8]], [[International Women's Day]])


A 1998 article in ''[[The Daily Telegraph]]'' quoted a spokesperson for the [[Department of Trade and Industry (United Kingdom)|Department of Trade and Industry]] (the government department that, at that time, regulated radio broadcasting in the United Kingdom) as saying
At the rate of one spoken number per character per second, each of these sentences takes a minute or more to transmit.
: "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 ==
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>
[[File:Russian Man signoff 2013-04-23.ogg|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 [[spelling alphabet|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}}
==Formats==


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}}
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.


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}}
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 [[Israel]]i 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{{citation needed}}). Often the prelude repeats for a period before the body of the message begins.


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" />
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.


Because of the secretive nature of the messages, the [[cryptography|cryptographic function]] employed by particular stations is not publicly known, except in one (or possibly two<ref>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.</ref>) 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>
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.


== Transmission technology ==
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.
[[High-frequency]] radio signals transmitted at relatively low power can travel around the world under ideal [[Radio propagation|propagation]] conditions – which are affected by local [[electromagnetic interference|RF noise]] levels, weather, season, and [[sunspot]]s – 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 [[transmitter]]s using powers from 10{{nbsp}}kW to 100{{nbsp}}kW.{{citation needed|date=December 2015}}
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 [http://www.myspystory.com/chap7.html If It Had Not Been For 15 Minutes, Chapter 7] for a simplified explanation of decoding numbers messages without a computer.


[[Amplitude modulation|Amplitude modulated]] (AM) transmitters with optionally–variable frequency, using [[Class-C amplifier|class-C]] power output stages with [[radio transmitter design#Plate AM modulators|plate modulation]], are the workhorses of international shortwave broadcasting, including numbers stations.{{citation needed|date=December 2015}}
==Transmission technology==


Application of [[Spectrum analyzer|spectrum analysis]] to numbers station signals has revealed the presence of data bursts, [[radioteletype]]-modulated [[subcarrier]]s, [[Phase-shift keying|phase-shifted carriers]], and other unusual transmitter modulations like [[Multiple frequency-shift keying|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>)
Although few numbers stations have been tracked down by location, the technology used to transmit the numbers has historically been clear -- stock shortwave [[transmitter]]s using powers from 10 kW to 100 kW.
[[File:Sprach-Morse-Generator.jpg|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 [[burst transmission|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 |url-status=dead }}</ref>
[[Amplitude modulation|Amplitude modulated]] (AM) transmitters with optionally variable frequency, using [[Electronic amplifier#Class_C|class-C]] power output stages with [[Radio_transmitter_design#Plate_AM_modulators|plate modulation]], are the workhorses of international shortwave broadcasting, including numbers stations.


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}}
Application of [[Spectrum analyzer|spectrum analysis]] to number station signals has revealed the presence of data bursts, [[Radioteletype|RTTY]]-modulated [[subcarrier]]s, [[Phase-shift keying|phase-shifted carriers]], and other unusual transmitter modulations like [[Multiple frequency-shift keying|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&ndash;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&ndash;49 (July 1997).</ref>).


== Interference ==
The frequently reported use of high tech modulations like [[Burst transmission|data bursts]], in combination or sequence with spoken numbers, suggest transmissions for differing intelligence operations[http://www.cvni.net/radio/nsnl/nsnl015/nsnl15vs.html].


=== Interfering with other broadcasts ===
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<ref>Even a non-standard civilian shortwave radio can be difficult to obtain in a totalitarian state. See [http://www.myspystory.com/chap6.html If It Had Not Been For 15 Minutes, chapter 6] for the problems of obtaining a numbers station receiving radio in East Germany during the Cold War.</ref>, 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 North Korean foreign language service [[Voice of Korea]] began to broadcast on the E03 [[Lincolnshire Poacher (numbers station)|Lincolnshire Poacher]]'s former frequency, 11545&nbsp;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 (numbers station)|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 |url-status=dead }}</ref>


On 27 September 2006, amateur radio transmissions in the 30&nbsp;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" />
===The USSR and superpower number stations===


In October 1990, it was reported that a numbers station had been interfering with communications on 6577&nbsp;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" />
* During the [[Cold War]] there was substantial and substantive evidence that the USSR may have used 500 kW transmitters on the eastern side of the [[Ural Mountains|Urals]] to reach agents in Western Europe, North Africa and possibly North America.
* [[High frequency|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.


A [[BBC]] frequency, 7325&nbsp;kHz, has also been used. This prompted a letter to the BBC from a listener in [[Andorra]]. She wrote to the [[BBC World Service|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 |url-status=dead }}</ref>
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.


The Cuban numbers station "HM01" has been known to interfere with shortwave broadcaster Voice of Welt on 11530&nbsp;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>
==Interference with documented broadcasts==
The [[North Korea]]n propaganda station [[Voice of Korea]] began to broadcast on the [[Lincolnshire Poacher (numbers station)|Lincolnshire Poacher's]] frequency, 11545 kHz, in 2006, possibly to deliberately interfere with its propagation. This clash can be viewed in video format here: [http://www.simonmason.karoo.net/page500.htm]


=== Attempted jamming ===
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 (numbers station)|Cherry Ripe]].
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=dead }}</ref>


== Identification and classification ==
On [[27 September]] [[2006]], radio amateur transmissions in the 30m band were affected by the E7 "Russian Man" number station at 1740 UTC. The interference can be heard here: [http://www.simonmason.karoo.net/page505.htm]
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}}


{{Undue weight|date=January 2023}}
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".


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>
A station operated by the [[West Germany|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: [http://www.swldxer.co.uk/radiomoscow.wma]
The BND station's callsign was "Hotel Kilo". [http://www.swldxer.co.uk/hk.wma]


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/ |url-status=dead }}</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 |pages=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:
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.
* E indicates a station broadcasting in English.
[http://www.swldxer.co.uk/4880kHz.wmv]
* G indicates a station broadcasting in German.
* S indicates a station broadcasting in a [[Slavic languages|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:
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.
* SK: Digital mode
[http://www.swldxer.co.uk/6855kHz.wmv]
* 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>
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." [http://www.simonmason.karoo.net/page34.html] 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.


== Recordings ==
==Attempted jamming of number stations==
* ''[[The Conet Project]]: Recordings of Shortwave Numbers Stations'' is a four-[[compact disc|CD]] set of recordings of numbers stations. It was first released in 1997 by the Irdial-Discs record label.
Number station transmissions have been the target of jamming for many years now. In fact, it is surprising that more jamming hasn't taken place given the potential deadly nature of the messages. There may be a couple of theories to explain this. Firstly, there is only a finite number of jamming transmitters available and it may be more effective to block clandestine stations that many people can hear, rather than a single message for one person.


== In popular culture ==
Secondly, there may be a "gentlemen's agreement" whereby a "we won't jam yours if you don't jam ours" arrangement is in progress. That said, examples of jamming do exist.
{{Primary sources |section|date=December 2023}}


=== Film ===
Here is E10 YHF being jammed by the mystery "Chinese Music Station".[http://www.swldxer.co.uk/yhf-dec06.wma] Apparently, this jammer has been dubbed the ''Chinese Firedragon Jammer'' and supposedly comes from Hainan Island which is located in the Gulf of Tonkin and is a part of the PR of China.
* The British–American action thriller ''[[The Numbers Station]]'', released in 2013 and starring [[John Cusack]] and [[Malin Åkerman]], features a [[Central Intelligence Agency|CIA]]‑run numbers station in the British countryside.<ref name="Dowd2013">{{cite web |url=http://www.avclub.com/review/the-numbers-station-96938 |title=Movie Review: The Numbers Station |work=The A.V. Club |date=25 April 2013 |archive-url=https://web.archive.org/web/20160312201645/http://www.avclub.com/review/the-numbers-station-96938 |archive-date=12 March 2016 |url-status=live |first=A.&nbsp;A. |last=Dowd |location=Chicago |df=dmy-all }}</ref>
Report on Firedragon jammer[http://www.iarums-r1.org/iarums/prcdragon.pdf]. (Adobe document)
* The 2013 American horror film ''[[Banshee Chapter]]'', starring [[Ted Levine]] and [[Katia Winter]], features a numbers station transmitting from the [[Black Rock Desert]] in [[Nevada]].<ref>{{cite web |url=https://variety.com/2014/film/reviews/film-review-banshee-chapter-1201037926/ |title=Film Review: 'Banshee Chapter' |first=Dennis |last=Harvey |website=[[Variety (magazine)|Variety]] |date=8 January 2014 |access-date=28 December 2023}}</ref>


=== Television ===
The E3 Lincolnshire Poacher station was at one time in the early 1990's the target for "bubble" or "warble" jammers. In this example, the jammer appears to be in some difficulty. [http://www.swldxer.co.uk/jam.wma]
* In the British television spy drama ''[[Spooks (TV series)|Spooks]]'' episode "[[Nuclear Strike (Spooks)|Nuclear Strike]]", a Russian [[sleeper agent]] is awoken by a numbers station broadcast to detonate a nuclear suitcase bomb in central [[London]]. The radio broadcast states in Russian, "2.5.0.0.2.5, Finland Red, Egypt White, It is twice blest, It is twice blest, rain from heaven, rain from heaven."{{citation needed|date=September 2023}}
* The American science fiction series ''[[Fringe (TV series)|Fringe]]'' has an episode, "[[6955 kHz]]", featuring a numbers station that induces amnesia.<ref>{{cite web |url=https://www.avclub.com/fringe-6995-khz-1798166505 |title=''Fringe'': '6995&nbsp;kHz' |first=Noel |last=Murray |work=The A.V. Club |date=12 November 2010 |access-date=1 October 2012}}</ref>
* In the British mystery series ''[[Endeavour (TV series)|Endeavour]]'' episode "[[List of Endeavour episodes#Series 5 (2018)|Quartet]]", a spy ring in [[Oxford]] communicates using a numbers station, which has a female voice that speaks German and uses "[[London Bridge Is Falling Down]]" as an interval signal.<ref>{{cite episode |title=Quartet |series=Endeavour |series-number=5 |number=5 |url=https://www.pbs.org/wgbh/masterpiece/episodes/endeavour-s5-e5/ |network=[[PBS]] |time=1:09:00 |time-caption=At}}</ref>
* In the 2020 British show ''[[Truth Seekers]]'', the protagonists listen to a parody of the [[Lincolnshire Poacher (numbers station)|Lincolnshire Poacher]].<ref>{{cite web |title=The truth is way, way out there: how Cold War radio signals inspired new series Truth Seekers |url=https://www.theguardian.com/amazon-prime-video-truth-seekers/2020/oct/30/the-truth-is-way-way-out-there-how-cold-war-radio-signals-inspired-new-series-truth-seekers |archive-url=https://web.archive.org/web/20221025074155/https://www.theguardian.com/amazon-prime-video-truth-seekers/2020/oct/30/the-truth-is-way-way-out-there-how-cold-war-radio-signals-inspired-new-series-truth-seekers |archive-date=25 October 2022 |url-status=dead |website=[[The Guardian]] |date=29 October 2020 |access-date=1 November 2020 }}</ref> <!-- Primary source (sponsored content) -->


=== Literature ===
The E5 CIA station dubbed "Cynthia" by number station monitors has also been the target of the same type of jammer as the above example.
* The first section of ''In the Dark'', a Chinese novel by [[Mai Jia]], focuses on a [[Cryptography|cryptographer]] in Special Unit 701, part of China's effort to track down and decode enemy number stations. The novel has been adapted into a TV series and a movie.<ref name="Forbes2016">{{cite web |url=http://www.pressreader.com/uae/the-national-news-the-review/20150829/281547994649041/TextView |title=Book review: Mai Jia's In the Dark shines a light on China's secret world |access-date=12 March 2016 |work=[[The National (Abu Dhabi)|The National]] |date=27 August 2015 |archive-url=https://web.archive.org/web/20160303153738/http://www.thenational.ae/arts-lifestyle/the-review/book-review-mai-jias-in-the-dark-shines-a-light-on-chinas-secret-world |archive-date=3 March 2016 |url-status=live |first=Malcolm |last=Forbes |df=dmy-all }}</ref>
[http://www.swldxer.co.uk/e14.wma]


=== Music ===
==Numbers messaging on loop lines==
* American band [[Wilco]] named its 2001 album ''[[Yankee Hotel Foxtrot]]'' after a segment of a recorded numbers station transmission. Samples from E10, an Israeli numbers station, appear in the album's song "Poor Places".<ref name="Shachtman2004">{{cite magazine |url=http://archive.wired.com/entertainment/music/news/2004/06/63952 |magazine=Wired |date=23 June 2004 |title=Wilco Pays Up for Spycasts |access-date=12 March 2016 |archive-url=https://web.archive.org/web/20080421131324/http://www.wired.com/entertainment/music/news/2004/06/63952 |archive-date=21 April 2008 |first=Noah |last=Shachtman |url-status=dead |df=dmy-all }}</ref>
* American musician [[Neil Cicierega]]'s 2014 [[mashup (music)|mashup]] album ''[[Mouth Silence]]'' includes the track "Transmission", which rearranges samples of the [[David Bowie]] song "[[Space Oddity]]" to resemble a numbers station broadcast.<ref>{{cite web |title=Neil Cicierega – Transmission Lyrics |url=https://genius.com/Neil-cicierega-transmission-lyrics |access-date=30 November 2017 |website=[[Genius (company)|Genius]]}}</ref> <!-- Better source? -->
* Icelandic composer [[Jóhann Jóhannsson]] sampled tape recordings of German numbers station broadcasts in the track "A Song for Europa" on his 2016 album ''[[Orphée (album)|Orphée]]''.<ref>{{cite web |last=Robertson |first=Derek |title=Jóhann Jóhannsson's Track By <!--sic--> Track Guide to Orphée |url=http://drownedinsound.com/in_depth/4150386-j-hann-j-hannssons-track-by-track-guide-to-orph-e |website=[[Drowned in Sound]] |date=15 September 2016 |access-date=28 December 2023 |language=en |archive-date=15 February 2018 |archive-url=https://web.archive.org/web/20180215143940/http://drownedinsound.com/in_depth/4150386-j-hann-j-hannssons-track-by-track-guide-to-orph-e |url-status=live}}</ref>
*American [[metalcore]] band [[Norma Jean (band)|Norma Jean]]'s 2016 album ''[[Polar Similar]]'' includes a track titled "II. The People" that samples a recording of the Lincolnshire Poacher.<ref>{{Cite news |last=Zorgdrager |first=Bradley |date=7 September 2016 |title=Norma Jean: Polar Similar |website=[[Exclaim!]] |url=http://exclaim.ca/music/article/norma_jean-polar_similar |access-date=1 November 2020}}</ref>


=== Radio and podcasts ===
The government messaging sources for radio numbers stations may have used the telephone system in a similar manner for a period of time. In "The Numbers Game", ''The Anomalist'' [http://www.anomalist.com/downloads.html Volume 1], Martin Cannon describes his experience as a [[phone phreak]] interacting with an identical numbers phenomenon on telephone [[Loop line|loop lines]].
* Several [[BBC Radio 4]] dramas have incorporated numbers stations:
**The standalone 2015 drama ''Fugue State'', written by [[Julian Simpson]], focuses on a British government agent investigating a numbers station in a remote village, and features recordings of numbers stations.<ref>{{cite web |title=Fugue State |url=http://www.bbc.co.uk/programmes/b06kgvc4 |website=BBC Radio 4 |access-date=26 February 2016}}</ref> <!-- Primary source -->
**Numbers stations, including the Lincolnshire Poacher, feature in Simpson's 2019 adaptation of [[H. P. Lovecraft]]'s ''[[The Whisperer in Darkness]]'', the second series of ''[[The Lovecraft Investigations]]''.<ref>{{cite web |title=The Whisperer in Darkness |url=https://www.bbc.co.uk/programmes/p06spb8w/episodes/downloads |website=BBC Radio 4 Podcasts |access-date=5 December 2019}}</ref> <!-- Primary source -->
**The 5-part 2022 drama ''Dead Hand'' by Stuart Drennan features a numbers station in [[Northern Ireland]] broadcasting the voices of individuals who have mysteriously disappeared.<ref>{{cite web|title=Dead Hand|url=https://www.bbc.co.uk/programmes/m0015vls|website=BBC Radio 4 Limelight|access-date=1 April 2022}}</ref> <!-- Primary source -->
* In a 2015 episode of ''[[Welcome to Night Vale]]'', a numbers station called WZZZ begins broadcasting words along with its numbers.<ref>{{cite web |title=Welcome to Night Vale Recap: Numbers |url=https://www.themarysue.com/welcome-to-night-vale-recap-42/ |website=[[The Mary Sue]] |date=4 December 2015 |access-date=20 November 2020}}</ref>
* ''[[The Magnus Archives]]''' 2019 episode "Decrypted" features a numbers station that appears on an iPod, attached to the entity The Extinction.<ref>{{cite web |title=Magnus 144: Decrypted |url=https://play.acast.com/s/themagnusarchives/mag144-decrypted/ |website=Acast |date=11 July 2019 |access-date=1 July 2021}}</ref> <!-- Primary source -->
* A 2008 episode of ''[[Skeptoid]]'' discusses numbers stations.<ref>{{cite web |title=Skeptoid: Spy Radio: Numbers Stations |url=https://skeptoid.com/episodes/4107 |website=Skeptoid |access-date=12 February 2022}}</ref> <!-- Primary source -->


=== Visual Art ===
Loop lines are a [[central office]] wiring arrangement for free, instant conference calling without an operator. They are probably intended for use by telephone company employees, who are simultaneously repairing multiple and distant parts of a telephone system. Loop lines are a talk-circuit-only 'meeting place' without ringers or dial out capability. All conferees must call into the loop after being notified of a conference, or call on a timed schedule similar to that for numbers stations reception.
* In 2005 at the [[Mattress Factory]], Noah Lang, in conjunction with- and invited by Akin Fernandez, presented several stand-alone sculptures based on numbers stations broadcasting antennas including [[the Buzzer]], [[the Lincolnshire Poacher]], and [[Cherry Ripe (numbers station)|Cherry Ripe]]. <ref>{{cite web |title=(secret) Messages and (cryptic) Communications |url=https://wavefarm.org/wf/calendar/yddpq8 |website=Wave Farm}}</ref>


=== Video games ===
Intelligence agencies are assumed to hire persons with skills such as safe cracking, computer hacking, and surely, phone phreaking. The latter would have enabled agencies to implement numbers messaging by loop lines. This practice probably came to an end as telephone systems became computerized, with unauthorized calls to loop lines being automatically traced and logged using [[automatic number identification]].
* In ''[[Signalis]]'', the player uses in-game radio signals transmitting numbers to solve puzzles. Some frequencies feature samples from historical German number stations.<ref>{{cite web |title=Signalis Review: Numbers Stations and Numbing Dread |url=https://www.fanbyte.com/games/reviews/signalis-review-numbers-stations-and-numbing-dread/ |website=Fanbyte |date=26 October 2022 |access-date= 17 April 2023}}</ref>
* In ''[[Call of Duty: Black Ops]]'', the main character Alex Mason is brainwashed in the Soviet Gulag of [[Vorkutlag]], and receives orders from a numbers station broadcast in Cuba.<ref>{{Cite web |last=Milzarski |first=Eric |date=2018-06-27 |title=How numbers stations like the ones in 'Black Ops' worked |url=https://www.wearethemighty.com/mighty-gaming/numbers-stations-cod-black-ops/ |access-date=2024-02-20 |website=We Are The Mighty |language=en}}</ref>


== See also ==
==Popular culture references==
{{portal|Radio}}
===Music===
* [[Secret broadcast]]

* [[Letter beacon]]
In 1997, ''[[The Conet Project]]: Recordings of Shortwave Numbers Stations'', a four [[Compact disc|CD]] set of recordings of numbers stations was released by England's Irdial-Discs record label.

Recordings of numbers stations sometimes find their way onto records by other [[musician]]s via [[sampling (music)|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 (band)|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.{{citation needed}}

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''.

The UK based group [[65daysofstatic]] sample "[[The Lincolnshire Poacher]]" along with several other stations on the song "No Station."

The UK group [[Cinerama (band)|Cinerama]] released a cover of [[The Smiths]] song "London" as a b-side to their single "Manhattan", in 2000. The track contains a couple of numbers station samples.

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 [http://www.simonmason.karoo.net/page494.htm]

In the [[1950]] [[Jean Cocteau]] film ''[[Orphée]]'', the poet Orpheus listens to such a station in Death's chauffeured Rolls Royce.

[[Cameron Crowe]] also featured parts of ''[[The Conet Project]]'' in scenes of the movie ''[[Vanilla Sky]]''. He said he used the station recordings to create a sense of confusion.

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|Mark Thomas Comedy Project]]

[[Mythology of Lost#The numbers|The numbers]] 4, 8, 15, 16, 23, & 42 were transmitted from a numbers station on the island in ABC's drama series ''[[Lost (TV series)|Lost]]''.

In the 1991 film [[Toy Soldiers (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==
* [[shortwave]]
* [[radioteletype]]
* [[secret broadcast]]
* [[letter beacon]]
* [[Lincolnshire Poacher (numbers station)|Lincolnshire Poacher]]
* [[Cherry Ripe (numbers station)|Cherry Ripe]]
* [[Yosemite Sam (shortwave)]]
* [[Yosemite Sam (shortwave)]]
* [[UVB-76]]
* [[Warrenton Training Center]]
* [[Radio Londres]]
* [[Markovian Parallax Denigrate]]


==References==
== References ==
{{reflist|25em}}
<references/>

==External links==

===Overviews===

* [http://www.freewebs.com/meterbands/numberstations.html Welcome to number stations] Overview of number stations with recordings and schedules
* [http://www.spynumbers.com/ SpyNumbers.com] - a good introduction
* [http://www.dxing.com/numbers.htm DXing.com Numbers Stations] Easy read overview paragraphs with red-letter emphasized facts and speculations.
* [http://www.crypticuniverse.com/?page_id=150 Cryptic Universe] An explanation of Number Stations, and some samples
* [http://filebox.vt.edu/users/tmays/classdocs/Final%20Project.doc Introduction to Voice Numbers Stations] (NSNL Newsletter) by Chris Smolinski, well-known moderator of ''Spooks'' numbers station elist (stale URL www.cvni.net/radio/nsnl/nsnl2vs.html archived [[2005-05-02]] by Tim Mays)

===Feature articles===

* [http://www.salon.com/people/feature/1999/09/16/numbers Counting Spies] - Salon.com's Article on Numbers Stations
* [http://www.wired.com/news/technology/0,1282,65698,00.html Dark Side of the Band] - Wired.com's article about Numbers Stations

===In use===

*[http://www.myspystory.com/intro.html If It Had Not Been For 15 Minutes] Thomas Wagner's dramatic first hand account including numbers station use, during a notable Cold War defection from the former East Germany.
* [http://www.miaminewtimes.com/issues/2001-02-08/kulchur.html 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.

===In depth===

* [http://groups.yahoo.com/group/enigma2000 ENIGMA 2000 Number Stations Monitoring Group] - expert discussion group with documents and newsletters - best available info about a subject with no official existance
* [http://www.simonmason.karoo.net/page30.html Shortwave Espionage] - a large amount of information, including sound recordings. Read the book [http://www.simonmason.karoo.net/page32.html "Secret Signals - The Euronumbers Mystery"]
* [http://www.clandestineradio.com Clandestine Radio] Open-source Intelligence on Subversive Radio & TV

===As experienced===


== Bibliography ==
* [http://www.alienhub.com/website/forum9/223.html Alien Hub] - discussion forum features populist notions and personal responses to the surreal experience of numbers station listening
{{refbegin|25em|small=yes}}
* {{cite book
|last=Mason |first=Simon
|year=1991
|title=Secret Signals: The Euronumbers Mystery
|publisher=Tiare Publications
|place=Lake Geneva, WI
|isbn=0-936653-28-0
|url=http://www.simonmason.karoo.net/page32.html
|access-date=24 December 2013 |url-status=dead
|archive-url=https://web.archive.org/web/20060613195836/http://www.simonmason.karoo.net/page32.html
|archive-date=13 June 2006
}}
* {{cite journal
|first1=Robert |last1=Wallace
|last2=Melton |first2=H. Keith |author2-link=H. Keith Melton
|date=June 2008
|title=Spycraft: The secret history of the CIA's spytechs, from communism to al-Qaeda
|journal=Intelligence Studies
|series=Studies in Computational Intelligence
|volume=52 |issue=2
|doi=10.1007/978-3-540-76361-1
|isbn=978-3-540-76359-8
|url=https://www.cia.gov/enwiki/static/66a33964c68ff18076cee58bf68b2c68/Review-Spycraft-Secret-History.pdf
|via=The U.S. [[Central Intelligence Agency]]
}} {{cite web |title=alternate source |date=2016-10-07 |website=[[The Internet Archive]] (archive.org) |url=https://archive.org/details/SPYCRAFTTHESECRETHISTORYOFTHECIASSPYTECHSFROMCOMMUNISMTOALQAEDA2008}}
* {{cite book
|first1=Robert |last1=Wallace
|last2=Melton |first2=H. Keith |author2-link=H. Keith Melton
|date=26 May 2009
|title=Spycraft: The secret history of the CIA's spytechs, from communism to al-Qaeda
|place=New York, NY
|publisher=Plume
|isbn=978-0452295476
|edition=illustrated, print
}}
{{refend}}


== Further reading ==
===Media and music===
{{refbegin}}
* {{cite journal |last=Beaumont |first= Paul |journal=Radio User |date= November 2012 |title=Numbers Stations: A Modern Perspective (Part&nbsp;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&nbsp;2) |pages=50–55 |publisher=PW Publishing |location=Poole, UK |issn=1748-8117}}
* {{cite journal |journal=Cryptologia |volume=31 |issue=4 |date=October 2007 |title=From the Archives: The U.S. and West German Agent Radio Ciphers |first= Jan |last=Bury |pages=343–57 |doi=10.1080/01611190701578104 |s2cid= 205487634 |url= http://www.swldxer.co.uk/polish.mht |issn=0161-1194}}
* {{cite journal |journal=[[Radio World]] |date=15 January 2014 |pages= 12, 14 |last=Friesen |first= Christopher |title=Spy 'Numbers Stations' still enthrall |issn= 0274-8541 |volume=38 |issue=2}}
* {{cite book |author=Havana Moon |title=Uno, Dos, Cuatro: A Guide to the Numbers Stations |publisher=Tiare Publications |location=Lake Geneva, WI |isbn=0-936653-06-X |year=1987 |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 |isbn=0-9519783-4-9 |year=1994}}
* {{cite book |last=Schimmel |first= Donald W. |title=The Underground Frequency Guide: A Directory of Unusual, Illegal, and Covert Radio Communications |edition=3rd |location= Solana Beach, [[California|CA]] |publisher= High Text Publications |year=1994 |isbn=1-878707-17-5 |chapter= 1. Numbers Stations |pages= 1–28}}
* {{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 ==
* [http://www.irdial.com/conet.htm ''The Conet Project''] from Irdial, and MP3s of the 4 CD set at [http://irdial.hyperreal.org/ hyperreal.org] and [http://www.archive.org/audio/audio-details-db.php?collection=irdial&collectionid=ird059 archive.org]
{{Commons category|Numbers stations}}
* [[NPR]]'s [http://www.npr.org/templates/topics/topic.php?topicId=1074 Lost and Found Sound], [[2000-05-26]]: [http://www.npr.org/programs/lnfsound/stories/000526.stories.html The Shortwave Numbers Mystery]
* [https://www.numbers-stations.com/ Numbers Stations Research and Information Center]
* [[NPR]]'s [[All Things Considered]], [[2004-11-12]]: [http://www.npr.org/templates/story/story.php?storyId=4167689 Music By The 'Number Stations']
* [http://spook007.atwebpages.com/ Numbers Stations Audio recordings from 80's and 90's]
* [http://www.simonmason.karoo.net/page485.htm Tracking The Lincolnshire Poacher] BBC Radio 4 programme on Number Stations - Streaming audio - use the ''DOWNLOAD THE SHOW HERE:'' link.
* [http://www.izumix.org.uk/c/spynumbers/ Numbers Monitoring], A website containing .wav recordings of transmissions from Number Stations
* [http://home.freeuk.com/spook007/ The Numbers Game], another site offering .wav recordings including that of voices and songs played.


{{Espionage}}


{{intelligence cycle management}}
[[Category:Cryptography]]
[[Category:Espionage]]
[[Category:International broadcasting]]


[[Category:Cold War broadcasting]]
[[de:Zahlensender]]
[[Category:Numbers stations| ]]
[[es:Emisoras de números]]
[[Category:Secret broadcasting]]
[[it:Numbers station]]
[[Category:Radio stations]]
[[he:תחנות מספרים]]
[[Category:Cold War terminology]]
[[ja:ナンバーステーション]]
[[ru:Числовые радиостанции]]

Latest revision as of 03:01, 18 December 2024

Cuban numbers station HM01
A recording of The Gong numbers station, run by the National People's Army of the German Democratic Republic, from 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.[1] 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 not uncommon. Most stations have set time schedules, or schedule patterns; however, some appear to have no discernible pattern and broadcast at random times. Stations may have set frequencies in the high-frequency band.[2]

Numbers stations have been reported since at least the start of World War I and continue in use today. Amongst amateur radio enthusiasts there is an interest in monitoring and classifying numbers stations, with many being given nicknames to represent their quirks or origins.

History

[edit]

According to the notes of The Conet Project,[3][4] which has compiled recordings of these transmissions, number stations have been reported since 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.[5]

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.[6]

Many stations from this era continue to broadcast and some long-time stations may have been taken over by different operators.[7][8] The Czech Ministry of the Interior and the Swedish Security Service have both acknowledged the use of numbers stations by Czechoslovakia for espionage,[9][10][11] with declassified documents proving the same. Few QSL responses have been received from numbers stations[12] by shortwave listeners[13] who sent reception reports to stations that identified themselves or to entities the listeners believed responsible for the broadcasts, which is the expected behaviour of a non-clandestine station.[14][15]

One well-known numbers station was the E03 "Lincolnshire Poacher",[16] which is thought to have been run by the British Secret Intelligence Service.[17] 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.[18]

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.[19]

Atención spy case

[edit]

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.[19]

The United States government's evidence included the following three examples of decoded Atención messages.[19]

  • "prioritize and continue to strengthen friendship with Joe and Dennis"
  • "Under no circumstances should [agents] German nor Castor fly with BTTR or another organization on days 24, 25, 26 and 27." (BTTR is the 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.[19] If used properly, however, the code cannot be broken.

Recent cases

[edit]

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[20][which?] stated that "defendants would receive assignments via shortwave radio transmissions".[citation needed]

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.[21][22] 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.[18] It has been reported that the United States has used number stations to communicate encoded information to persons in other countries.[19] 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.[23][24]

North Korea revived number broadcasts in July 2016 after a hiatus of sixteen years, a move which some analysts speculated was psychological war;[25] sixteen such broadcasts occurred in 2017, including unusually timed transmissions in April.[26]

Suspected use for espionage

[edit]

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.[27] 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 & Melton described how numbers stations could be used in this way for espionage:[28]

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 3 and 30 MHz at a predetermined time, date, and frequency contained in their communications plan.[28]
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.[28]

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.[29]

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."[30]

Formats

[edit]
The "Russian Man" station signing off. The numbers read: 83912 83912 10080 10080 46543 46543 – 257 257 143 143 – 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]

The prelude, introduction, or call-up of a transmission (from which stations' informal nicknames are often derived) includes some kind of identifier,[31] 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]

After the prelude, there is usually an announcement of the number of number-groups in the message,[31] 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]

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]

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.[31]

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[32]) 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.[33]

Transmission technology

[edit]

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.[19]

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.[citation needed]

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]

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.[34] (RTTY-modulated subcarriers were also present on some U.S. commercial radio transmissions during the Cold War.[35])

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.[36]

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).[19] 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.[37] Being caught with just a shortwave radio has a degree of plausible deniability, for example, that no spying is being conducted.[citation needed]

Interference

[edit]

Interfering with other broadcasts

[edit]

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] 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.[38][39]

On 27 September 2006, amateur radio transmissions in the 30 m band were affected by an S06 "Russian Man"[40] numbers station at 17:40 UTC.[39]

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.[39]

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.[41]

The Cuban numbers station "HM01" has been known to interfere with shortwave broadcaster Voice of Welt on 11530 kHz.[42]

Attempted jamming

[edit]

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).[43]

Identification and classification

[edit]

Monitoring and chronicling transmissions from numbers stations has been a hobby for shortwave and ham radio enthusiasts from as early as the 1970s.[44] 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.[45] 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.[46][full citation needed]

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.[47]

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.[48] 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.[49] This classification scheme takes the form of a letter followed by a number (or, in the case of some "X" stations, more numbers).[50] 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[31] 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.[51]

Recordings

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  • 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.
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Film

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Television

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  • In the British television spy drama Spooks episode "Nuclear Strike", a Russian sleeper agent is awoken by a numbers station broadcast to detonate a nuclear suitcase bomb in central London. The radio broadcast states in Russian, "2.5.0.0.2.5, Finland Red, Egypt White, It is twice blest, It is twice blest, rain from heaven, rain from heaven."[citation needed]
  • The American science fiction series Fringe has an episode, "6955 kHz", featuring a numbers station that induces amnesia.[54]
  • In the British mystery series Endeavour episode "Quartet", a spy ring in Oxford communicates using a numbers station, which has a female voice that speaks German and uses "London Bridge Is Falling Down" as an interval signal.[55]
  • In the 2020 British show Truth Seekers, the protagonists listen to a parody of the Lincolnshire Poacher.[56]

Literature

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  • The first section of In the Dark, a Chinese novel by Mai Jia, focuses on a cryptographer in Special Unit 701, part of China's effort to track down and decode enemy number stations. The novel has been adapted into a TV series and a movie.[57]

Music

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Radio and podcasts

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  • Several BBC Radio 4 dramas have incorporated numbers stations:
    • The standalone 2015 drama Fugue State, written by Julian Simpson, focuses on a British government agent investigating a numbers station in a remote village, and features recordings of numbers stations.[62]
    • Numbers stations, including the Lincolnshire Poacher, feature in Simpson's 2019 adaptation of H. P. Lovecraft's The Whisperer in Darkness, the second series of The Lovecraft Investigations.[63]
    • The 5-part 2022 drama Dead Hand by Stuart Drennan features a numbers station in Northern Ireland broadcasting the voices of individuals who have mysteriously disappeared.[64]
  • In a 2015 episode of Welcome to Night Vale, a numbers station called WZZZ begins broadcasting words along with its numbers.[65]
  • The Magnus Archives' 2019 episode "Decrypted" features a numbers station that appears on an iPod, attached to the entity The Extinction.[66]
  • A 2008 episode of Skeptoid discusses numbers stations.[67]

Visual Art

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Video games

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  • In Signalis, the player uses in-game radio signals transmitting numbers to solve puzzles. Some frequencies feature samples from historical German number stations.[69]
  • In Call of Duty: Black Ops, the main character Alex Mason is brainwashed in the Soviet Gulag of Vorkutlag, and receives orders from a numbers station broadcast in Cuba.[70]

See also

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References

[edit]
  1. ^ Olivia Sorrel-Dejerine (16 April 2014). "The spooky world of the 'numbers stations'". BBC News.
  2. ^ "Number stations". Priyom.
  3. ^ Segal, David (3 August 2004). "The shortwave and the calling: For Akin Fernandez, cryptic messages became music to his ears". The Washington Post. p. C01.
  4. ^ Mason 1991, pp. 5–6
  5. ^ Schaum, Ryan (30 November 2014). "The First Numbers Stations". NSRIC.
  6. ^ Bury, Jan (October 2007). "From the archives: The U.S. and West German agent radio ciphers". Cryptologia. 31 (4): 343–357. doi:10.1080/01611190701578104. ISSN 0161-1194. S2CID 205487634.
  7. ^ "The spooky world of the 'numbers stations'". BBC News. 16 April 2014. Retrieved 12 July 2021.
  8. ^ "Numbers Stations Research". Numbers Stations Research.
  9. ^ "Lyssna på ett hemligt telegram" [Listen to a secret telegram] (in Swedish). Säkerhetspolisen. 23 January 2015. Archived from the original on 8 March 2016. Retrieved 12 March 2016.
  10. ^ "The Swedish Security Service Releases Info on a Numbers Station". NSRIC. 24 July 2015. Retrieved 12 March 2016.
  11. ^ Catinka Mannerfelt Agneskog. "Säpos hemliga radiotelegram" (in Swedish). SvD Nyheter. Retrieved 23 January 2015.
  12. ^ stations KKN44, BFBX and OLX Mason, Simon. "Shortwave Espionage". Archived from the original on 3 December 2011. Retrieved 28 October 2011.
  13. ^ AMARAL, Cristiano Torres (2021). Guia Moderno do Radioescuta. Brasília: Amazon. p. 333. ISBN 978-65-00-20800-9.
  14. ^ "OLX". 24 January 2015. Archived from the original on 24 January 2015. Retrieved 23 September 2020.
  15. ^ Helms, Harry L. (1981). "Espionage Radio Activity". How to Tune the Secret Shortwave Spectrum. Blue Ridge Summit, Pennsylvania: TAB Books. p. 52. ISBN 0-8306-1185-1.
  16. ^ "E03". Priyom.org. Retrieved 17 June 2017.
  17. ^ "E03 The LincolnShire Poacher". Retrieved 6 September 2014.
  18. ^ a b Gorvett, Zaria (15 July 2020). "The ghostly radio station that no one claims to run". BBC Future. Retrieved 12 July 2021.
  19. ^ a b c d e f g Sokol, Brett (8 February 2001). "Espionage Is in the Air". Miami New Times. Archived from the original on 21 February 2001.
  20. ^ United States v. Alvarez, 506 F. Supp. 2d 1285 (S.D. Fla. 2007)
  21. ^ Rijmenants, Dirk (2013). "Cuban Agent Communications" (PDF). Cipher Machines & Cryptology (PDF). Retrieved 30 December 2013.
  22. ^ "United States v. Walter Kendall Myers, United States District Court, District of Columbia, no. xxx" (PDF). Retrieved 26 August 2010.
  23. ^ Helms, Harry L. (1981). "Government and Military Communications". How to Tune the Secret Shortwave Spectrum. Blue Ridge Summit, Pennsylvania: TAB Books]. p. 58. ISBN 0-8306-1185-1.
  24. ^ Schimmel, Donald W. (1994). The Underground Frequency Guide: A Directory of Unusual, Illegal, and Covert Radio Communications (3 ed.). Solana Beach, California: High Text Publications. pp. 88–95. ISBN 1-878707-17-5.
  25. ^ Choe, Sang-Hun (21 July 2016). "North Korea revives coded spy broadcasts after 16 year silence". The New York Times. Retrieved 30 July 2016.
  26. ^ Osbourne, Simon (12 May 2017). "North Korea sends chilling coded radio messages to South Korea amid fears of WW3". Daily Express.
  27. ^ Wagner, Thomas (2004). "Chapter 6 – So here she was, with a pillow over her head and over the radio ...". If it had Not Been for Fifteen Minutes: A true account of espionage and hair-raising adventure. Retrieved 30 October 2013.
  28. ^ a b c Wallace & Melton 2008, p. 438
  29. ^ Irdial-Discs, included booklet (PDF). hyperreal.org (Report). The Conet Project. p. 59. Archived from the original (PDF) on 25 April 2006.
  30. ^ Pescovitz, David (16 September 1999). "Counting spies". Salon. Archived from the original on 19 January 2000. Retrieved 12 March 2016.
  31. ^ a b c d "Intro to Numbers Stations". NSRIC. 8 February 2016. Retrieved 12 March 2016.
  32. ^ 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.
  33. ^ Wagner, Thomas (8 December 2012). "If it had not been for 15 Minutes, Chapter 7". Radio Weblogs. Archived from the original on 2 November 2013. Retrieved 18 March 2022.
  34. ^ Schimmel, Donald W. (1994). The Underground Frequency Guide: A Directory of Unusual, Illegal, and Covert Radio Communications (3 ed.). Solana Beach, California: High Text Publications, Inc. pp. 27–28. ISBN 1-878707-17-5.
  35. ^ Collins, Barry W. (July 1997). "The day the U.S. Army invaded W4TLV". QST. 81: 48–49. ISSN 0033-4812.
  36. ^ "NSNL 15: Voice stations". Cvni.net. 3 July 1999. Archived from the original on 26 January 2021. Retrieved 26 August 2010.
  37. ^ Wagner, Thomas (24 April 2002). "If it had not been for 15 Minutes, Chapter 6". Radio Weblogs. Archived from the original on 1 November 2014. Retrieved 18 March 2022.
  38. ^ "E03a". Priyom.org. Retrieved 17 June 2017.
  39. ^ a b c "Secret Signals". Simonmason.karoo.net. Archived from the original on 10 February 2016. Retrieved 7 November 2015.
  40. ^ "S06". Priyom.org. Retrieved 17 June 2017.
  41. ^ "Secret Signals". Simonmason.karoo.net. Archived from the original on 20 February 2007. Retrieved 26 August 2010.
  42. ^ Anthony Spinelli (18 October 2018), HM01 and Voice of Welt 11530 AM 10 18 2018 1743z, archived from the original on 11 December 2021, retrieved 26 November 2018
  43. ^ "Chinese Music Station". Archived from the original (Windows Media Audio) on 8 March 2012. Retrieved 16 July 2012.
  44. ^ Māris Goldmanis, Before enigma; the early numbers stations, monitors NSRIC; retrieved 13 December 2019
  45. ^ Mason 1991, pp. 20–21
  46. ^ Poundstone, William. Big Secrets. p. 197.
  47. ^ "ENIGMA: The European Numbers Information Gathering and Monitoring Association". NSRIC. Retrieved 24 February 2015.
  48. ^ "ENIGMA 2000". Archived from the original on 15 September 2009. Retrieved 1 March 2015.
  49. ^ "ENIGMA 2000 Active Station List" (PDF). signalshed.com (Booklet). 1.3. ENIGMA 2000. September 2017. Retrieved 25 August 2020.
  50. ^ Friesen, Christopher (2014). "Spy 'Numbers Stations' still enthrall". Radio World. 38 (2): 14. ISSN 0274-8541.
  51. ^ "E2K 32 – E22 is not what it seems". www.cvni.net. Archived from the original on 17 November 2007. Retrieved 5 April 2016.
  52. ^ Dowd, A. A. (25 April 2013). "Movie Review: The Numbers Station". The A.V. Club. Chicago. Archived from the original on 12 March 2016.
  53. ^ Harvey, Dennis (8 January 2014). "Film Review: 'Banshee Chapter'". Variety. Retrieved 28 December 2023.
  54. ^ Murray, Noel (12 November 2010). "Fringe: '6995 kHz'". The A.V. Club. Retrieved 1 October 2012.
  55. ^ "Quartet". Endeavour. Series 5. Episode 5. At 1:09:00. PBS.
  56. ^ "The truth is way, way out there: how Cold War radio signals inspired new series Truth Seekers". The Guardian. 29 October 2020. Archived from the original on 25 October 2022. Retrieved 1 November 2020.
  57. ^ Forbes, Malcolm (27 August 2015). "Book review: Mai Jia's In the Dark shines a light on China's secret world". The National. Archived from the original on 3 March 2016. Retrieved 12 March 2016.
  58. ^ Shachtman, Noah (23 June 2004). "Wilco Pays Up for Spycasts". Wired. Archived from the original on 21 April 2008. Retrieved 12 March 2016.
  59. ^ "Neil Cicierega – Transmission Lyrics". Genius. Retrieved 30 November 2017.
  60. ^ Robertson, Derek (15 September 2016). "Jóhann Jóhannsson's Track By Track Guide to Orphée". Drowned in Sound. Archived from the original on 15 February 2018. Retrieved 28 December 2023.
  61. ^ Zorgdrager, Bradley (7 September 2016). "Norma Jean: Polar Similar". Exclaim!. Retrieved 1 November 2020.
  62. ^ "Fugue State". BBC Radio 4. Retrieved 26 February 2016.
  63. ^ "The Whisperer in Darkness". BBC Radio 4 Podcasts. Retrieved 5 December 2019.
  64. ^ "Dead Hand". BBC Radio 4 Limelight. Retrieved 1 April 2022.
  65. ^ "Welcome to Night Vale Recap: Numbers". The Mary Sue. 4 December 2015. Retrieved 20 November 2020.
  66. ^ "Magnus 144: Decrypted". Acast. 11 July 2019. Retrieved 1 July 2021.
  67. ^ "Skeptoid: Spy Radio: Numbers Stations". Skeptoid. Retrieved 12 February 2022.
  68. ^ "(secret) Messages and (cryptic) Communications". Wave Farm.
  69. ^ "Signalis Review: Numbers Stations and Numbing Dread". Fanbyte. 26 October 2022. Retrieved 17 April 2023.
  70. ^ Milzarski, Eric (27 June 2018). "How numbers stations like the ones in 'Black Ops' worked". We Are The Mighty. Retrieved 20 February 2024.

Bibliography

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Further reading

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