Sooner or later every Shortwave Listener will hear them, the Number Stations: 5-figure/rarely letter-groups are read by a synthezised male or female voice, are keyed in Morse code or are sent in digital mode. All transmissions start with an identifier/call, usually a 3-figure group, repeated several times. The following figure-groups specify the decryption key/group-count of the message which ends, for example, with a series of "Zero"s (or "out" if spoken).
Every network has its own "fingerprint": transmission schedule, modulation and format are typical for a specific network and will help the listener assigning it to a certain country. An increasing number of utility listener are into the hunt for Number Stations, many of them being members in the ENIGMA2000 (E2k) YAHOO group. Results are published in newsletters, or Ary Boenders "Number & Oddities" Website. For more see here: Links .
2. The story behind Number Stations
Much has been written so far about the purpose of Number Stations. After all we may quite safely assume, that they are a robust and reliable tool of Secret Services to keep in touch with their "staff" abroad, namely their agents.
The powerfull broadcasts can be received anywhere by anyone -even with a cheap portable radio, thus hiding perfectly the true addressees. Successfull reception can be confirmed by any means at any time.
After listening for a while to Number Stations we may ask ourselves: Can we interprete the messages? No, we can't. We can write down (decode) them, but we can't decrypt them. The addressees use One Time Pads (picture) for decryption, a key of the same length as the message, which is used only once. Any attempt to decrypt a message requires at least two specimens with comparable properties (e.g. decryption key has been used twice or same message is encrypted with two keys). This is not the case with OTPs and any results produced are not conclusive - they are ambiguous; this means, they can be true or not.
3. Active Number Stations
Number Stations are on the air since many years, in fact soon after the first use of Shortwaves for military, and have had their heyday during the cold war. A variety of voice stations with all sort of musical intros only could be classified with names like:
Cynthia, Magnetic Fields, Edna Sednitzer, Swedish Rhapsody or Tyrolian Music.
That's long ago and our world became less colourful. Only one station, probably from Egypt, still uses a musical intro.
Now we regularly can hear maybe 12 voice networks in Russian, English, German, Czech, Arabic and Spanish and less than 10 Morse stations. Not amazingly Russia, Israel and Cuba are the most active players in the Numbers game.
The people from E2k a long time ago started to classify all networks. Morse stations are "M", voice stations are "E" (English), "S" (Slavic), etc followed by a number. As a country may operate several networks in different modes, they are listed as "families" I to XVIII. The current situation is reflected in E2k's "Control List", available at there website. A quick Guide to Morse Networks I can offer here: Downloads.
The current skeds of all networks are reflected with great accuracy on several websites.
4. The fascination of Number Stations
We can't understand the messages, we don't know the purpose of a specific message, so why bother? Because it's great fun to find a new frequency, a new sked or even a new network.
We can perform traffic analysis, e.g. try to look for correlations: density of traffic vs. political tensions. We can note the number of addressees (agents)/ decryption keys and the time slots. Maybe we find out, if several transmission sites are involved. And there are the highlights: an operator makes a fault, the wrong tape is played or a faulty equipment reveals how they do it. Even the impossible once became possible: Israels MOSSAD greetings to all, the words "GOOD NIGHT" properly separated by dummy figures sent in a short message.
Number Stations have a long tradition and despite the end of the Cold War, the Warsaw Pact and the Wall of Berlin: they still are here. Googling with "Number Station" will lead you to an overwhelming amount of information, sound samples and background information.
Number Stations is not just Morse - and voice transmissions. The trend towards sophisticated digital modes cannot be ignored. The XPA or XPA2 networks for example are Russian Multitone AM Systems with 20, resp. 15 tones narrowly spaced at 40, resp. 15 Hz. They belong to the same family as M12.
SK01 in turn describes Cuban transmissions, found 2007, in Phase Modulated PSK31 mode. Other modes BPSK125 and BPSK220 are still under investigation.
5. Samples of Number stations
Russian Morse Number Station M12
This is a busy network with constantly changing schedules at any time. Transmissions normally start at the hour and are repeated at h+20 and h+40 min. Some frequency sets are re-used in the following year. M12 keeps local time during Summer Time period.
The 3-figure identifier is sent 3 times followed by the number of messages (1,2 or 000 for "no message"), e.g. 463 463 463 1 (repeated for 2 minutes),
decryption key and group-count follow: 4578 112 4578 112,
the message follows: 77895 44208 56196 34777 ...,
after a pause of a few seconds the end of message bit follows: 000 000 (zero sent as T).
The MOSSAD Voice Number Station E10
A big network, based in Israel, with rarely changing identifiers. The messages are 5-letter-groups, English spoken in NATO phonetics by a female voice.
Transmissions take place at h+00 and h+30 and can be, at a certain degree, predicted.
There are many parallel frequencies.
The table with calls and frequencies I have copied from Newsletter 50 produced by ENIGMA2000, where all networks are described in every detail (and where the copyright remains).
The identifier, repeated for 5 min means: 1 message follows,
the identifier plus 1, repeated for 5 min means: test message,
the identifier plus 2, repeated for 10 min means: no message.
Then: "Message, message, group 34, group 34, text, text"
the message follows: "hghfg ruopt lmgnb....",
"End of message, repeat, repeat"....
after the repeated text follows: "End of message, end of transmission"
E10 is, most probably, the most investigated Number Station and that since many years. There are quite interesting findings about the interaction and content of some messages found by Number Station specialists.
It is worth noting that many of E10 transmissions are jammed by a Bubble Jammer. Preliminary RDF results point towards the region of Iran as transmitter site and we certainly agree, that this would make sense...
E10 operation on all frequencies ceased in Spring 2010.
It is not known, how its task is carried on.
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