On May 13, 2012, at 4:44 PM, Richard Schumann wrote:
> Say, don't RTTY sigs have a 'fingerprint' just like the human hand?
In addition to the baud rate and Mark duration at the beginning and ending
(like a squelch tail) that I mentioned earlier, the shift frequency can also be
different. If this can be accurately measured, it might be able to narrow down
the rig (FSK) or sound card clock (AFSK) that is used.
RTTY signals (both FSK and AFSK) also have different rise and fall times when
they switch between Mark and Space: so the precise shape of the keyclick
spectrum can also help to "fingerprint" a signal.
With AFSK, you can try to look for the suppressed carrier/sideband. That will
also tell what the exact Mark tone is used (although this won't be fixed if the
culprit is using agile tuning by changing tone pairs on the fly).
By convention, RTTY signals come up in Mark state. The rise time from no
signal all the way to a full Mark signal (and probably accompanied by a slight
ringing) is another fingerprint.
However, a true sociopath will then fake these parameters too.
Reminds me of the Spy vs. Spy stuff in Mad Magazine :-).
73
Chen, W7AY
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