Path: utzoo!censor!geac!torsqnt!lethe!yunexus!ists!helios.physics.utoronto.ca!news-server.csri.toronto.edu!cs.utexas.edu!usc!wuarchive!mit-eddie!media-lab!minsky
From: minsky@media-lab.MEDIA.MIT.EDU (Marvin Minsky)
Newsgroups: sci.electronics
Subject: Re: request for FM transmitter
Message-ID: <4929@media-lab.MEDIA.MIT.EDU>
Date: 18 Jan 91 22:34:11 GMT
References: <1991Jan18.104512.6350@newcastle.ac.uk>
Reply-To: minsky@media-lab.media.mit.edu (Marvin Minsky)
Organization: MIT Media Lab, Cambridge MA
Lines: 14

Depends on what precision-stability you want.  I once built an FM
transmitter to fly on a bat, for Prof. Griffin's research.  It weighed
300 milligrams:

 /----------------------------------\
 \--Cu-paper-Zn-R-tunnel diode-|--L-/
                               |-C-/ 

The paper is acidified.  Resistor R is not very critical.  The
inductor L was a 1/4" coil of three turns of wire.  The capacitor iof
the parallel LC circuit was a capacitance microphone made by
stretching a bit of aluminized mylar over a disk of metal screening
that was slightly dented in the middle.

The bat didn't like it much but managed to fly around anyway.