In response to recent questions about the "Numbers"
Stations, their origin and purpose, the following summary
captures the high points. 

"Spy Numbers Transmissions" are a shortwave oddity which have
been around for the last 25 years.  They are commonly heard
in English, German, Spanish and the Slavic languages and take
the form of four and five digit groups of numbers which are
preceded by a three digit "identifier" and a "group count"   
which corresponds to the number of number groups transmitted
in the crypt.  They are generally broadcast by a mechanical-
sounding YL, although Morse code (CW) "cut number" transmissions
are also frequently reported, as are phonetic alphabet trans-  
missions.  Several distinctly different formats have been 
noted.

The "who" and "why" aspects of these transmissions are,
for the most part, unknown.  Their mysterious nature has
resulted in their common characterization as 'spy' trans-
missions.  Information on the "where" aspects below.

The spy theory has been enhanced over the years by the FCC's
inconsistent position in response to numerous inquiries by
the Shortwave Listening community.

If you've never heard a numbers transmission, tune your 
radio to 11468 kHz any Saturday at 4pm EST (2100 UTC).
You'll almost certainly hear a 'classic' numbers transmission
which will run from 15-30 minutes.  The signal from this
Saturday transmission is very powerful and can be heard
across the United States.

In regards the "where" - a number of sites have been identified
in recent years, notably in Warrenton and Remington, VA and
Miami, FL.  In addition, with the aid of sophisticated RDF
(radio direction finding) equipment and the invaluable assist-
ance of highly authoritative and professional resources, several
new transmission sites have been positively identified over the  
past several months, including sites in Nicaragua, Honduras, El
Salvador, Cuba and Cozumel.

One particularly dangerous station has been interfering with
air to ground traffic on 6577 kHz, a frequency allocated to inter-
national 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.
This regular transmission can be heard on Mondays at 0200 UTC 
(Sunday night local US time) across most of the US.

A recently identified Cuban site (Guineo) is believed to ba a major
transmitter site used by DGI (Cuban Intelligence).

There has been some suggestion that the numbers are a form of
'one-time-pad' - a crude but unbreakable form of encryption
(unless you've got the key, that is) - if that's the case,
it's very curious to note that the same five-digit groups are
often seen to repeat over and over again in the very same
crypt - and that the same transmissions are seen to
repeat from week to week, and from month to month -
so often, in fact, that tape breaks are sometimes noted.  When
spliced back together, the sloppy handling sometimes results in
truncated 5-digit groups - the end result being amixture of 4
and 5 digit groups in the very same transmission!

These facts would tend to point one away from the one-time-pad
concept and support a couple of other theories - suggesting that
the numbers are NOT a cipher, but rather a code unto themselves,
and that much of this traffic is 'dummy' in nature - broadcast
simply to keep a frequency open over a long period of time.

In addition, most five-digit Spanish numbers transmissions are
very badly over-modulated, resulting in numerous spurs up and
down frequency.  When broadcast under such conditions, the
numbers (6) seis and (7) siete are almost indistinguishable,
making it impossible to copy a crypt without numerous errors.

It is worth noting that the four-digit Spanish and English
transmissions do not reflect this same technical ineptitude.

There are a number of reference materials available which provide
detailed information about cryptography and cryptanalysis, in
general, and numbers crypts, specifically.  I'd be happy to provide
anyone interested with a list of books.   

Only two publications I know of are currently available which
provide regular coverage of numbers, clandestine, pirate and
other interesting transmissions.  The ACE Bulletin (monthly news-  
letter of the Association of Clandestine Enthusiasts - PO Box 
11201, Department KK, Shawnee Mission, KS  66207 $16/yr) and the Umbra
et Lux Newsletter (a newsletter devoted to SIGINT, covert radio 
and related topics - 10606-8 Camino Ruiz, Department KK, Suite
174, San Diego, CA  92126 $18/yr). 

                                Havana Moon