Subj : Numbers stations
To   : Digital Man
From : Angus McLeod
Date : Sat Aug 13 2005 12:44 am

  Re: Numbers stations
  By: Digital Man to All on Fri Aug 12 2005 17:20:00

 > What experiences do any of you have with "Numbers stations"?

I've heard them.

They are obviously coded messages being passed for clandestine purposes.  
Given the technology available today (like encrypted e-mail, or even 
encrypted digital radio transmissions on various bands and even spread 
spectrum) I'd have to assume that they are intended for reception by 
operatives under deep cover, who can not have any incriminating hardware 
lying about.  You can copy the numbers stations with a simple shortwave 
receiver and a pencil, and then (providing you have the key) decrypt the 
message.

I can see the system being used to send a message to a spy operating in a 
foreign country, rather than, say, to an /embassy/ in a foreign country.

 > From http://en.wikipedia.org/wiki/Number_station:

I find some of the analysis here interesting.  For instance, they say that 
Class-B, AM transmitters operating in the HF bands are the norm, and that 
Polyphase and PDM modulators are not used because "energy costs were not 
an issue", and then wanders off into a discussion of DRM.  Frankly, I 
wouldn't consider the energy budget to be of much concern to these people, 
and I am surprised that they (Wikipedia) do not consider the complexity of 
the *receiving* station necessary to copy these transmissions.  An 
amplitude modulated signal can be received with a single diode (a la 
crystal-set), whereas Polyphase and PDM modulated signals are not so easy 
to copy.  If, as I suspect, the point is to signal to someone in posession 
of absolutely minimum suspicious hardware, an AM transmitter in the HF 
band is about as easy as it gets.

Obviously, the transmitter would have to be class-B or class-A (less 
efficient) since class-C transmitters are only good for FM (more complex 
receiver) or CW (more training needed for the operator).  I can't imagine 
why they thought the transmitter class was germane to the discussion.

I am interested in hearing any ideas other DOVE-Netters may have.



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