Sending numbers in CW in five-digit groups has been used by military,
governments and (I think) marine/commercial/weather HF stations. It's even
done on code lessons.
Someone might look up to see which international allocations (aero, marine,
embassy, etc) are shared with 10.130. If it is a "none of the above"
operation those folks don't 'need no stinkin' badge' and will operate on
whatever clear frequency they choose for their intended coverage.
There are also voice numbers stations which have been heard by SWLs, around
6, 9.4 and 11.5 MHz. These have been reported as a male or female
synthesized voice reading out groups of five numbers in Spanish. German and
Korean have also been heard by SWLs. The mode is AM or AME. This has been
going on for years, back to the "cold war era" and has been the subject many
SWL articles, no great secret to talk about these stations. The times and
frequencies of the numbers broadcasts are unpredictable, but non-ham and ham
frequencies alike can be chosen for time/coverage into a certain area (rather
than the longest DX path).
Hearing at least some of the numbers stations near popular SWL broadcast
bands is cause for further conjecture. Shortwave broadcasting is "normal" in
many countries. Where travellers with suitcase HF transceivers (heh
heh...moi? I'm just a happy ham operator on vacation!) might arouse
suspicious customs officials, a cheap SWL/AM/FM portable receiver would not.
But a one-way coded broadcast? Why not... kind of like a pager perhaps.
I don't care to speculate on the nature of the encryption used on these
broadcasts or whether they are encrypted at all, but there are books in many
libraries on the subject of codes or ciphers...Enigma machines, Purple,
rolling key ciphers, book ciphers and "crossword" or Vigenere ciphers where
the user draws a grid or crossword from memory and plugs in the key and
encrypted message to get the decrypted product. All very interesting stuff.
73, Jay
W6CJ
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