Path: utzoo!mnetor!uunet!kitty!larry
From: larry@kitty.UUCP (Larry Lippman)
Newsgroups: sci.electronics
Subject: Re: Extremely small transmitter - help!
Message-ID: <2388@kitty.UUCP>
Date: 4 Feb 88 01:31:49 GMT
References: <1434@obelix.liu.se>
Organization: Recognition Research Corp., Clarence, NY
Lines: 36
Summary: Tunnel diodes to the rescue...

In article <1434@obelix.liu.se>, per-el@obelix.liu.se (Per Elmdahl) writes:
> My friend is attending a course where he is going to make an
> electronic construction. His project consists of constructing 
> and building a tiny transmitter for measuring the temperature
> in the stomach of a snake! (Can you believe it?). Now he is 
> wondering about how to make such a small tranmitter, how to
> power it, and how to make an antenna.

	And y'all thought that tunnel diodes were dead...  Consider using
an FM transmitter operating in the 88-108 MHz region which is built around
a tunnel diode (like a GE 1N3712 or equivalent).  The power supply need be
only a single 1.3 volt mercury hearing aid battery.  With some clever
design, the tunnel diode need be the only active component; a thermistor
can be used to frequency modulate the transmitter signal.  The resultant
temperature-frequency function will be highly non-linear, but this is
certainly no problem in this age of computer data reduction.  Under the
circumstances (snake in a captive environment), RF power in the hundreds
of microwatts range is quite satisfactory - the tunnel diode will do this
job nicely.

	There are a number of other circuit design possiblities, including
those of totally passive devices - but the tunnel diode approach is the
simplest to implement for this application.

	Incidently, during the latter 1950's when the tunnel diode was
thought to revolutionize the semiconductor world, tunnel diodes were
used in transmitter "medicine capsules" that medical researchers had people
swallow to study human digestion in vivo.  There were quite a few press
releases about this application at the time.  The transmitters primarily
measured pressure or picked up digestive sounds; the latter application
is subject to some amusing speculation... :-)

<>  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?"