On 2 Apr 2005 19:21:10 -0800, wrote:


Kenny wrote:
I am looking to build a ELT locator that works.

Last week I checked E-Bay for RDFs and found over half a dozen. Don't
think any of them hit $100. 2 of them will locate any transmitter to
within a couple hundred yards from a distance of several miles. 3 or
more makes the fix easier.

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Dear Kenny,

Try making contact with you local amateur radio club. (Go to a
meeting. Stand up, introduce yourself, explain the problem and ask for
their help.)

Tracking down transmitters, hidden and otherwise, is both a chore and
and obligation. To keep their skills sharp hams hold practice 'fox
hunts' in which the fox is the transmitter. The equipment is
inexpensive and fairly primitive but works well enough once you've
learned how to use it. The basic principle is to put an electrical
switch between a pair of antennas. The circuit switches from one
antenna to another at a rapid rate. When the antennas are broad-side
to the transmitter the signal is equal and you may scribe a line of
position. (Sexier models use multiple pairs of fixed antennas and an
array of LEDs to indicate the line-of-position.)

Once you have a line of position you move the receiver some distance
away, perpendicular to the line of position, and take another reading.
The apex of the resulting triangle will indicate the approximate
location of the transmitter's antenna. (A club or group will have
fixed locater systems at their home stations and will simply call-in
their observed line-of-position to a central controller.)

Low-end systems cost as little as $20 and connect to a hand-held
receiver.

-R.S.Hoover
-(KA6HZF)