[rescue] Radio DF equipment (was Ham radio license question)

[James Sharp]

> Hrmmm...since the topic came up, anyone have a good line on either some DF
> equipment(something functional, not horribly fancy/expensive) *or* some
> decent DIY projects for someone who is OK with a soldering iron and not
> afraid of bare copper?
>

I picked up the Doppler DF-1 kit from Ramsey Electronics
(http://www.ramseyelectronics.com).  It was about $140, IIRC.  Took me
about 2 days to build and it seems to work fairly well.  All you need is
an outboard receiver with an audio out jack.

It electrically rotates a set of 4 antennas to induce a dopper shift in
the signal which shows up as a tone in the receiver audio, which it then
decodes for relative bearing.

I'm going to hang a PIC chip off of it for digital out, then mix that in
with input from a GPS and a compass.  I'll then wash it through some
computerized trig functions for triangulation...take a few spaced out
samples, and suddenly you have an absolute lat/long position that can be
presented to you on a display.