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From: tomb@hplsla.UUCP
Newsgroups: sci.electronics
Subject: Re: Jamming walkmans
Message-ID: <5170006@hplsla.HP.COM>
Date: Tue, 17-Nov-87 12:32:03 EST
Article-I.D.: hplsla.5170006
Posted: Tue Nov 17 12:32:03 1987
Date-Received: Sat, 21-Nov-87 07:01:04 EST
References: <4149@utai.UUCP>
Organization: HP Lake Stevens, WA
Lines: 26

Re:  Jamming mobile tape players --

Since the tape head is a magnetic-field transducer, it seems to
me that you MIGHT be able to mess one up if you generate an AC
magnetic field.  This could take the form of a large coil hidden
away in a briefcase or some such, driven by some appropriate noise
generator.  Since noise is in the ear of the beholder, you might
even try some music you like -- but I suspect that you will have
more success if you use a waveform with a fairly high RMS-to-peak
ratio -- or maybe one which transmits occasional intense random
bursts.  I just tried this sort of thing with 60Hz coil about 3 cm
in diameter, and wasn't too impressed with how close I had to put
it to the tape player to make it really objectional (the tape heads
are shielded, after all).  I'm sure, though, that I could do better
with some experimentation and calculation:  expect larger coils and
higher frequencies to help a lot.

The above method has the advantage that it doesn't erase the tape,
which could get you into more serious trouble after your initial
joy wore off and the dude whose tape you erased figured out what
had happened.  

Happy experimenting!

Tom Bruhns
uucp:  !hplabs!hplsla!tomb