Tracking a radio signal

[DonRotolo]

Mike,

What you want to do is a well-known science, no need to reinvent the wheel. Ham radio operators do this all the time, there is even an international sport of RDF (Radio direction finding)

What you want is a Doppler array for RDF. Ramsey Electronics makes a kit (DDF1) that works with a computer sound card and displays the direction to the transmitter in 22 degree increments. Google "Doppler Radio Direction Finder" for loads of other kits, articles, and reference papers. There is a LOT of info out there.

Your antenna array for 433 MHz would be 4 antennas each about 8" long arranged in a square pattern about a foot on each side.

As for picking the strongest transmitter, FM receivers have an unusual characteristic known as the "Capture Effect", where only the strongest signal is demodulated, all other signals (even just a little weaker) are ignored by the receiver. The receiver controls this.

It would also be possible to use the receiver's RSSI (Received Signal Strength Indicator) to roughly determine proximity, but radio signal strength at 433 MHz is not always linear with distance, research the terms Multipath Interference and Foliage Signal Attenuation.

Your part in all this would be some software that combines what you know about the aircraft's speed, direction and location, what you know about the transmitter's identity, location and signal strength, and the flight characteristics of the aircraft, to guide the aircraft to the beacon.

Let me know if you need more information. As I said, this wheel's been invented already. You're just painting it a different color.

(Cool stuff like this is why I became a Ham in the first place)

Don

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