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From: sde@Mitre-Bedford@sri-unix.UUCP
Newsgroups: net.ham-radio
Subject: Anti-eavesdropping method
Message-ID: <12733@sri-arpa.UUCP>
Date: Thu, 23-Aug-84 08:38:37 EDT
Article-I.D.: sri-arpa.12733
Posted: Thu Aug 23 08:38:37 1984
Date-Received: Thu, 30-Aug-84 00:44:53 EDT
Lines: 2

At a guess, I would think freq hopping would e used.
   David   sde@mitre-bedford