First you have to determine ow many 'base' frequencies are utilized.
it's likely a small number, likely 8, 16 at the most. If it's a variable
scale, it could be a larger number, but again, not an impossible task.

You will have to determine how the key is sent, or if it's a rolling
sequence. (a rolling sequence would not require continuous sync pulses,
so it's likely the receiver looks for the next key (base freq) and
changes the mix frequency accordingly.

To analyze it manually (to at least get some details about the
transmission format) just grab a small (perhaps a few seconds) sample
and tear it apart manually. Break it up with a computer sound editing
program and play each slice repeatedly into a frequency inversion
circuit (Ramsay sold one, there are also a few schematics floating about
the net) until you recover natural sounding snippits of audio. Splice it
all back together and see how it sounds. Document each mixer freq
needed, and compare them to each 'tick' data byte. (you'll need a data
slicer for this, again, see the net.) This will give you a good
selection of raw data.

Just to clairfy things, when I said "...it should be pretty
straightfroward to decode." I was not suggesting it would not be labour
intense. It could turn out to be a royal pain in the a$$, however, if
it's simply inversion with a variable mixer freq, there's no real
security there. It would be inconvienent to analyze, but again, the
process is straightforward. To automate it will also take a lot of time,
but again, unlike with digital ciphering, you're not up against large
numbers and even larger permutations.

Is there a sample of the audio somewhere on the net that could be
downloaded?

B.




Ralph A. Schmid, DK5RAS wrote:
bob wrote:


If it's voice inversion, even if the base freq shifts about, should be
pretty straight forward to decode. Any .wav (or whatever format) samples
on the net available to download and examine?


How do you want to find out what inversion frequency is used at what
moment?



regards - Ralph