Technology communications

 Elektor electronics - 12/2006 www.elektor.com

Those of you who choose to do a spot of short wave surfing during their idle moments will no doubt have hit upon one or two stations where the programme content is made up entirely of someone (usually female) monotonously reading out a series of numbers. Your first assumption may be that you have gate crashed a pirate radio version of Bingo until you notice that some of the numbers are repeated and grouped either in fours or fives.

The enigmatic nature of these broadcasts is further enhanced by the station identification which can take the form of a repeated short extract of music played on what sounds like a Stylophone. Once you add in ionospheric distortion and fading the overall effect is quite spooky. Recording artists have exploited this aspect of the transmissions and used sampling and mixing to produce interesting effects. The film �Vanilla Sky� also features them in the soundtrack.

Directional antennas have been used to pin-point the sources of these transmissions but they do not appear on any official broadcast schedule and when the authorities have been asked what the transmissions actually represent their explanation seems to favour �meteorological data�.

Emerging Patterns
Transmissions from the number stations conform to a regular pattern: They begin (usually on the hour or half hour) with an interval signal (tone sequence, melody or call sign), followed by a three number ID (usually), a count value corresponding to the number of code groups in the transmission followed by transmission of the code groups. The former West German BND transmissions were always terminated by a combination of two characters from the NATO alphabet (over 80 different combinations were used) followed by a tone burst.

The �Lincolnshire Poacher� is an active station purported to emanate from the RAF base at Akrotiri in Cyprus. Each transmission begins on the hour and lasts for 45 minutes. Transmission starts with the first 15 notes of the English folk tune repeated 12 times followed by a 5 figure ID repeated six times and two notes from a glockenspiel. The message follows and is always composed of 200 groups of five numbers (the last number in each group is pronounced with a rising terminal). The message ends with six repeats of the poacher tune.

Number Stations do not exclusively use voice transmission; Morse is also used as well as tone signalling where each tone represents a different number. These �polytone� stations are thought to be operated by the Russian authorities.

Some irregularities
Not all the stations retain their original identity; take for example a German speaking station which had been broadcasting for over 30 years from a site in Poland. Its station identification was an extract of the �Swedish Rhapsody� by Mantovani played on a music-box chime or �ice cream van� as it became more affectionately known. The station closed after the catastrophic floods of 1997 but today it is again in operation, at the same site and frequency but this time thought to be run by the British SIS. The mechanised voice which popped up on this station was instantly recognised by Number Station listeners as belonging to �Cynthia� who they had heard before on a station thought to be used by the American security department.

The American security department ceased all Number Stations activity in October 2003 but up until then they were thought to be operating (like the Russian security services) in Europe, transmitting in many languages including English, German and Spanish. Up until a few years ago there was also an Arabic speaking station.

It has never been established which government was responsible for the �Swedish Rhapsody� transmissions and some stations are not always what they first appear; recent example was heard broadcasting from the Indian subcontinent in July 2005 and given the designation �E22�, the transmissions bore the hallmarks of a Number Station but it was finally identified in December 2005 as test transmissions by �All India Radio� for a new transmitter site. The station has since become fully operational and reclassified as a broadcast station. More details of the transmissions can be found at [1] under the heading �E22 private room and study page�.

Current activity
Number Stations first appeared at a time when there were no alternative paths available to relay messages worldwide. Today we have a number of options which offer global coverage including satellite communication and the Internet which you might reasonably assume would eventually supplant radio broadcasts but in recent months short-wave activity has actually grown more intense. Among the organisations thought to be making use of these stations are the British Secret Intelligence Service (formerly MI6) The Israeli intelligence agency (a.k.a. Mossad) and the Russian Federal Security Service (FSB) together with other organisations broadcasting from Chechnya, Cuba, Korea and two English speaking stations in Egypt. Their continued use by many countries highlights the advantages of this form of broadcast which includes low

Tools of the trade
One of the advantages of communicating via Number Stations is that no specialised equipment is needed to pick up the message, just a regular travel or �world band� radio which can be purchased on the high street (some stations use upper side band). The operative just needs patience and an undisturbed period of time to take down the numbers. Communication is only one-way of course but small portable two-way HF radios have also been developed for use in the field.

An example of this type of radio equipment is the SP-15 short wave set developed in the late 50s by Wandel & Goltermann together with Pfitzner. The receiver was fully transistorised while the transmitter used valves. The entire kit including aerial, headphones, Morse key, fast code generator, crystals, NiCd batteries and mains charger are all contained in a neat briefcase which enables the set to be ready for use in a very short time. A notable design feature is the simple superhet receiver covering 2.5 to 24 MHz in two ranges with a BFO. For its time it had an extremely good specification with a sensitivity of 22 μV at 10 dB S/N. Current consumption is just 8 mA. It was used by the German secret service �Gehlen� (later the BND) and also by the German armed forces for military reconnaissance.

The excellent receiver design also saw service in other NATO roles. An example of a similar piece of kit �from the other side� is the Soviet built R-353 set, the transmitter and receiver are housed in a light metal case together with the power supply. In contrast to the SP-15 the R-353 receiver is a valve double superhet. An interesting feature of this unit is the programmable magnetic band cassette shown attached to the front of the radio. Number sequences can be recorded onto the tape using a 10-way dial and then sent very quickly in a short transmission burst. This dramatically reduces the risk of the transmitter being discovered by direction finding.

Low cost, low tech equipment (the signals can be picked up on a relatively inexpensive �world band� type of radio), broad coverage (assuming the signals are not subject to Electronic Counter Measures) and excellent message security. The stations usually operate at frequencies between the recognised short-wave bands, using either AM (Amplitude Modulation) or USB (Upper Side Band). They can be located by sweeping these frequencies on the hour and half hour. The table gives details of two stations which are currently active. The �E03� refers to the station identity assigned by ENIGMA. Those of you interested in exploring this subject in more depth are recommended to pay a visit to the website of Simon Mason it contains many fascinating curiosities. A popular American site is also included [3] � it has a link to the �FRS Commander Bunny� transmissions complete with an attempt at decoding.

The Usergroup
The Number Station broadcasts have fascinated listeners for decades. Since the end of the 1990s there has been a European mailing list covering this subject from a Yahoo group with the name ENIGMA 2000 (European Number Information Gathering and Monitoring Association) which evolved form the earlier ENIGMA group. This organisation has catalogued and classified all the known Number Stations and given them the designations E = English speaking, G = German speaking, M = Morse transmissions, S = Slavic speaking (Russian, Polish etc.), V = various for transmissions in other languages and X = transmissions using special types of modulation (e.g. polytones as already mentioned). The mailing list for ENIGMA 2000 has currently grown to around 700 subscribers.

Securing the information
It�s a sobering thought that while most radio programmes are designed to capture the greatest number of listeners this must be one of the few examples where the intended audience for an international broadcast may be just a single listener who alone possesses the key to unlock the message. When transmitting cipher text to what is potentially an entire global audience it is vital that the encryption method employed is absolutely bullet proof otherwise government counter intelligence departments with their vast computational resources will surely resolve (eventually) any encryption scheme based upon a mathematical algorithm. One such cipher which has proved to be perfectly secure is the Vernam cipher or �one time pad�. The encryption key is a series of random numbers each of which are added to each character in the plain text message. The resulting cipher text is transmitted and the receiver subtracts the key on their �one time pad� to recover the plain text message. Even with knowledge of some part of the message it does not help to decipher the rest of the message provided truly random keys are used. The weakness of this method is that a �one time pad� containing the keys must be carried securely by the operator and then destroyed (by both sender and receiver) after use, if it is stolen or copied security will be jeopardised.

Over the years many agents working in foreign lands (both east and west) have been found in possession of tiny �one time� pads sometimes concealed in a hollowed out soap bar, sometimes inside the shell of a walnut (the most literal form of code cracking?). Governments are obliged to remain silent on matters of national security and have never acknowledged the existence of Number Stations or their possible role in espionage, the identical nature of sequences transmitted by Number Stations and those found on agent�s one time pads may of course prove to be purely coincidental.

Without any hard evidence we are forced to accept the official account that the transmissions are in fact reporting snow fall levels in the Mediterranean but if you find that explanation too difficult to swallow then maybe that thought about pirate radio Bingo (at the tax payer�s expense) really is the only plausible alternative.

The Author
Jochen Sch�fer is 34 years old and has been blind from birth. He works as a documentation assistant at the German Blind Studies Institute (Blista) in Marburg. He has been tuning into Number Stations in his free time since 1977 when he first started listening to short wave. His archive contains more than 1000 cassettes documenting Number Station broadcasts; he is a subscriber to the ENIGMA 2000 mailing list and one of four site moderators. In his capacity as Germany�s leading Number Stations specialist he has made contributions to many publications on the subject.

His Email address is ([email protected]). He is keen to get in touch with anyone who has any recordings of earlier broadcasts (from the 60�s to the 80�s) to add to his collection, he has particular interest in broadcasts made by West German BND stations with a two-letter call sign.