🚀 go-pugleaf

Owen.Lewis@purplet.demon.co.uk (Owen Lewis) writes:
:  -=> Quoting Ted Dunning to All <=-
: 
:  TD> ......... simple speech inversion really shouldn't be called a
:  TD> security device.
: 
: 
: 
:  Exactly so. I couldn't have put it better.
: 

What about the modern analog devices that use split band inversion where
one of 32 programmable split points in the voice band may be selected
and changed at 60 Hz or faster at "random?"  Two separate inversions
are performed, one for the lower sideband and one for the upper
sideband around the split point.  This seems *much* harder.  This topic
has come up before but perhaps we have new readers.  Does anyone have
any actual knowledge of or experience at trying to decode such a
signal?  With such short segments it seems to me that only brute force
"try the possibilities" could work and the combinatorics are rather
formidable with 32^60 or 2E90 possibilities in each second's worth of
speech. 

Combine this with spread spectrum or Pulson modulation and, well....

What's Pulson modulation?  It is a method where the signal is impressed
on a carrier that is a sequence of pseudo randomly spaced 1.5 ns pulses
by dithering the pulse position about its expected position.  In theory
this can only be demodulated by a receiver that knows the pseudo random
spacing of the carrier pulse train.  A transceiver has been
demonstrated by Pulson Communications using a pulse train centered at
1.9 GHz with a 100% pseudo random modulation of the pulses about the
center period (before dithering.)  Now that I think about it, a PRN
that can spit out a new number every 500 ps sounds rather difficult.
Not to mention the method for controling the pulse position that
rapidly.  Well, they say they have done it anyway.

Bob
-- 
Bob Cain    rcain@netcom.com   408-358-2007

    'The meek shall inherit the earth--the rest of us will move on..'
                                                    Sameer Parekh


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