Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!mips!pacbell.com!pacbell!barn!everexn!mycal
From: mycal@everexn.com (Mike Johnson)
Newsgroups: sci.electronics
Subject: Re: Phone scrambler
Keywords: Phone scrambler
Message-ID: <1991Mar26.000850.11377@everexn.com>
Date: 26 Mar 91 00:08:50 GMT
References: <1991Mar23.215050.24738@sugar.hackercorp.com> <1991Mar24.012754.9816@athena.cs.uga.edu>
Organization: Everex Systems, Sebastopol
Lines: 24

In article <1991Mar24.012754.9816@athena.cs.uga.edu> mcovingt@athena.cs.uga.edu (Michael A. Covington) writes:
>Although I haven't tried it, you could make an audio scrambler out
>of an NE602 mixer-oscillator chip. Run the oscillator at about 5 kHz
>and mix it with the audio using the double balanced mixer. Out come the
>sum and difference frequencies. Low-pass-filter it so that you get only
>the difference frequencies; this gives you audio which is "scrambled"
>because its spectrum is backward. (It will sound like an SSB radio
>signal does when you're tuned for the wrong sideband.) Run the sound
>through the same setup again to descramble it.
>  
>  In sum:
>    
>    300-to-3000-Hz bandpass filter on input
>    Oscillator 5000 Hz or so
>    (no, make that 3500 Hz)
>    Doubly balanced mixer
>    300-to-3000-Hz bandpass filter again on output
>
>
>-- 
>-------------------------------------------------------
>Michael A. Covington | Artificial Intelligence Programs
>The University of Georgia  |  Athens, GA 30602   U.S.A.
>-------------------------------------------------------