Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!ames!sunybcs!kitty!larry
From: larry@kitty.UUCP (Larry Lippman)
Newsgroups: sci.electronics,rec.humor
Subject: Re: Jamming walkmans
Message-ID: <2266@kitty.UUCP>
Date: Wed, 25-Nov-87 14:10:18 EST
Article-I.D.: kitty.2266
Posted: Wed Nov 25 14:10:18 1987
Date-Received: Sun, 29-Nov-87 02:11:26 EST
References: <4149@utai.UUCP> <1160@uhccux.UUCP> <3810@bellcore.bellcore.com>
Organization: Recognition Research Corp., Clarence, NY
Lines: 54
Summary: Other kinds of jamming...
Xref: mnetor sci.electronics:1814 rec.humor:9050

In article <3810@bellcore.bellcore.com>, copp@wind.bellcore.com (*David H. Copp) writes:
> A friend once contemplated building a machine to jam supermarket
> music systems.  Many of the markets in our area buy their music
> from an FM station--a subcarrier system--and it appeared to be
> fairly simple to put a low-power FM transmitter in a briefcase and
> capture the receiver.

	Damn!  I wish I had thought of that while I was a carefree EE
undergrad.  It would have been easier to implement that the following
escapade of my college daze...
	During my junior year, my roommate (also EE) and I came up with
a great (!) idea: to jam the audio at a drive-in movie and insert our
own "commentary".  This project required weeks of, ahem, preparation.
First, we scrounged an old Bogen 100 watt PA amplifier of 1950's vintage,
and modified it to run using an external DC power supply - which consisted
of a WW II surplus dynamotor.  Since the dynamotor required 24 volts DC,
we made a temporary installation of two 12 volt batteries in the trunk of
my car.  The dynamotor also went in the trunk, with a remote control
switch.  The amplifier sat on the rear seat, and was covered with a blanket.
	Some "preliminary investigation" at the target drive-in indicated
that a 70 volt line transformer was mounted in the base of each speaker
pedestal, and the one transformer fed two speakers.  We decided to back-feed
into the system at 70 volts.
	On the fateful night, my roommate and I along with two carloads of
"supporters" invaded the drive-in.  We parked in the last row.  Under cover
of darkness, I removed the cover plate at the base of our speaker pedestal,
and attached two 22 AWG magnet wires to the 70 volt feed.  There was enough
clearance on the cover plate to allow the magnet wires to pass when the
plate was put back.  Also, the magnet wires allowed for a rapid - and
hopefully inconspicuous - breakaway.
	I don't remember the name of the movie, but it was a low-budget
horror film about witches in England.  The movie was ripe for a "commentary".
With all connections made, I turned on the dynamotor.  After the tubes
warmed up, I cautiously advanced the master gain control.  Voila!  Feedback,
even though our own speaker was turned off.  It worked so well, that we had
to close all windows in the car.
	My roommate and I engaged in a running "commentary" [y'all can use
your imagination here :-)].  The people at drive in went wild - blowing their
car horns in delight.  The management went nuts.  After about five minutes,
two people ran out of the projection booth with flashlights and started
checking cars.  Needless to say, it was time to pull the plug.  The fellow
who came over to my car looked at us with great suspicion, since we and
the two adjacent "support" cars were all laughing hysterically.  However,
no one said anything to us - I think the drive-in management was still in
a state of shock that someone could do such a thing...
	Since many drive-ins today use an inductive loop AM radio approach,
perhaps this would be easier to do using an AM transmitter (easy to make
using the power op amps available these days).  Of course, such a transmitter
would be unlawful to use, and I could never condone such a thing for a
prank... :-)

<>  Larry Lippman @ Recognition Research Corp., Clarence, New York
<>  UUCP:  {allegra|ames|boulder|decvax|rutgers|watmath}!sunybcs!kitty!larry
<>  VOICE: 716/688-1231        {hplabs|ihnp4|mtune|utzoo|uunet}!/
<>  FAX:   716/741-9635 {G1,G2,G3 modes}   "Have you hugged your cat today?"