I have written software for a VHF DSP Doppler Direction Finder
The project is called a SuperSimpleSoundDoppler.
You can build it for about 20$
A PC with a stereo input Soundcard
A VHF FM porto, scanner or mobile set
A GPS Mouse with NMEA0183 output
The homebuild SuperSimpleDopplerPeiler
The SuperSimpleSoundDoppler consists off:
4x vertical whips(abt 50 cm ) mounted on a round board
of about 60 cm diameter with a switcher unit.
A electronics board with 3 transistors
and 2 cheap ic's 4013 and 4001 and
a 5 volt voltage regulator.
The software shows a pelorus and has it's
own MyMapping software witch works with UI-View32 Maps
But it also can plot on Google-Earth through a kml file.
You can also use Mymapping with a doppler
that gives a mixed GPS and Agrelo format.
Existing Dopplerfinders can be very easy interfaced by just a lowpass filter
of some R, c's and a transistor connected to one of the antenna switch signals.
You can find the free software on our Radio Club site.http://www.pi4wag.nl/index.php/pseudo-doppler-radio-direction-finder
The software is updated regualairy.
In the software are all the circuit diagrams.