One-way voice link · OWVL
A numbers station, also known as a one-way voice link (OWVL),
is a special type of unusual radio broadcast, generally on the Short Wave
(SW) radio bands, transmitting seemingly random sequences of (spoken) numbers
or morse coded tokens.
In the most common form, it features a female voice,
reading long strings of numbers, generally in groups of five, often preceeded
by a preamble or a simple musical tune.
In most cases, such stations carry OTP encrypted messages.
In the 1970s and 80s, it was often speculated that numbers stations were
used by drugs cartels for smuggling and organising clandestine droppings.
This seemed highly unlikely however, as a clandestine high-power transmitter
could easily be located and would certainly have been taken down
by the authorities. It has since become known, that Numbers Stations are
operated by governments as a simple and secure method for sending secret
messages to agents anywhere in the world, using the SW radio bands,
whilst the recipient of the message remains untraceable.
In 2014, the Czech Government confirmed the existence of
at least two numbers stations in Czechoslovakia during the
In reply to a request by Priyom.org,
they released several official documents .
In 2015, this was confirmed by the Swedisch Intelligence Agency SÄPO .
OWVL equipment on this website
Radio Amateurs will certainly remember
the artificial female voice on the short wave (SW) bands,
that read endless sequences of seemingly random numbers, with a distinct pronunciation.
Many of the broadcasts were in German, as this language
was understood in most European countries, but there were also broadcasts
in Polish, Russian and even in English. In the late 1950s, the messages
were commonly read 'live' by a team of speakers – usually women –
and recorded onto tape. The messages were later transmitted by high-power
radio SW stations.
Short wave radio (SW) has the advantage that it spans the entire globe
without the need for satellites or the internet.
The reason that female voices were often used, is that due to the higher pitch,
they could be discriminated more easily on the narrow-band poor-quality fading
radio channels. In addition,
the words were pronounced in such a way that they were unambiguous.
As this method was labour-intensive and prone to mistakes, the intelligence
services started looking for ways to automate the entire process. One of the
first electronic numbers stations – developed for the East-German Stasi –
was Device 2028
– Codenamed: Schnatterinchen,
shown above. It consisted of a rotating drum with 13 discs,
each of which held a piece of magnetic tape with a spoken word or number.
The device was driven by a punched paper tape that could be prepared offline
on a teleprinter (telex). It made the female speakers redundant.
In the early 1980s, the disc-based systems were gradually replaced by
digital alternatives, such as the East-German Device 32620
shown above. It no longer had moving parts and degrading magnetic
tapes, and could easily be converted for other languages.
In the following years they were also used in other countries like Poland,
Czechoslovakia, Cuba and the Soviet Union.
The agents were instructed to listen to specific SW frequencies
at fixed days and times, often using a
commercially available SW-receiver, from brands like
Sony, Panasonic and Grundig.
The image on the right shows a Sony ICF-2001D –
a commonly available receiver – that became very popular amongst
Eastern spies in the 1980s.
In most cases, the messages hidden behind the numbers,
were encrypted by means of the truely unbreakable
One-Time Pad (OTP) cipher
and the spies were trained to decode such messages and
destroy the keys immediately after reception.
Replying to a message was much more difficult. In some cases, the agent posted
a hand-written message in a so-called
dead letter box,
after which it was picked up and handled by someone else.
They were then forwarded to their destination (i.e. the homeland)
by means of a diplomatic courier or – in encrypted form – by radio,
often with the help from an East-European embassy.
Some spies however, had their own transmitter that they could use
to reply to a message.
Such transmitters are commonly known as 'spy radio sets',
many of which are covered on this site.
Sending a message from a spy radio station is very dangerous, as
the authorities of the guest country were well aware of their presence and
are constantly monitoring the waves
for illegal transmissions.
Once a clandestine transmission is intercepted, the
authorities will try to locate the station by means of
using fixed or mobile Radio Direction Finding (RDF).
Numbers stations are not the exclusive domain of the former
and the Warsaw Pact countries.
America and its Allies had spies operating under (diplomatic) cover behind
the Iron Curtain,
and used Numbers Stations to pass coded messages to them.
Likewise, countries like Cuba and China
have operated similar stations, some of which are still active today.
In fact, even Russian and European Numbers Stations can still be heard
on the SW-bands to this day.
The following types of Numbers Stations are known:
- Voice stations (reading numbers)
- Morse code stations (CW)
- Multi-tone stations (RTTY, FSK, MFSK)
- Digital stations
- A combination of the above
Although in some cases dedicated receivers were supplied to an agent,
standard off-the-shelf commercial receivers were often used for the reception
of the Number Stations. The reason for this is that such receivers
could be bought in nearly every Western country without attracting any attention of the authorities. Furthermore, it gave Eastern Block countries
access to the latest technology that was available commercially in the West.
One of the first domestic receivers used for this purpose was the
Zenith Royal 1000;
the first all-transistor SW-receiver from the USA.
It was eventually surpassed by the
Grundig Satellit 2000 and finally the
digital Sony ICF-2001D.
Although Numbers Stations are typically something from the
Cold War, some of them are
still active today (2021).
Countries are still actively spying on each other,
and short-wave (SW) radio is one of the most reliable means
of communication, that does not reveal the identity or location of the
Below is an example of a message that was intercepted in 2014.
➤ More examples
G06 · Russia
5422 kHz (German)
06132 75514 79681 94217 21443 31441 81797 17512 62689 33103
48930 93432 25709 93628 48683 18809 85052 49870 63962 04884
532 20 00000
Sender ID is in bold (947).
Recipient is in red (532) followed by the number of groups in the message (20).
Recipient and number of groups are repeated at the end of the message (532 20).
All number groups are repeated (except for the terminator).
00000 is the message terminator.
Sample kindly supplied by Karsten Hansky .
As the Numbers Stations that broadcast coded messages are illegal,
they are not officially identified by a name or number.
In the past, such stations were often given nicknames, such as
Lincoln Poacher and Cherry Ripe, often based on certain
characteristics of the transmission, such as the opening tune.
For this reason, a group of amateur interceptors, known as ENIGMA, 1
has assigned unique ID number to each station, along with prefixes,
suffixes and family IDs.
In the example above 06 is the station ID.
The prefix G indicates that the (voice) transmission is
in German. The suffix 'a'
indicates that it is a variant of the regular station G06.
In some cases, if a stations belongs to a family of stations,
the Family ID is given in Roman numerals. In this case the family ID
is IA, which means it is related to family I
For a full list of Station IDs, prefixes, suffixes and familiy IDs,
please refer to the current Enigma Control List .
S17e Bulgarian Betty
In some cases, the (nick)name of the station is written behind the
station ID, such as in the example of the S17e above. In this case,
the station was operated by the Czechoslovakian
StB, just like
S05 OLX (with the OLX callsign officially being assigned to a Czech news
In this context, ENIGMA does not refer to the
German Enigma Cipher machine,
but is the abbreviation of European
Numbers Information Gathering and
Monitoring Association. Although the original ENIGMA
group still exists, the list of station IDs, known as the Enigma
Control List, is now maintained by ENIGMA 2000 .
If you want to know more about Number Stations, their locations, frequencies
and the time at which they are expected to broadcast, here are a couple of
useful links to websites with the latest information.
Enigma 2000 are the
current maintainers of the Enigma Control List, whilst website
offers a real-time schedule of expected transmissions. In addition,
The Conet Project
has compiled an impressive collection
of sound samples, past and present, onto a stack of CDs.
Any links shown in red are currently unavailable.
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© Crypto Museum. Created: Sunday 15 March 2015. Last changed: Friday, 03 June 2022 - 05:20 CET.