MFB said "Could be an interesting project". As a Radio Amateur who spent many hours building and trying to improve Amateur radio Direction Finding (ARDF) equipment I must agree. Also hours spent in tramping through the Countryside often in utter bewilderment trying to find the Hidden Station. Here in darkest North East Lincolnshire this art is still practised using Top Band AM transmissions, thats 1.8 to 2.0 Mhz. Today however most people use the 80 Metre Band (3.5 to 3.8 Mhz) plus 2 Metres 144 Mhz. An interesting Powerpoint presentation on the subject can be downloaded from
www.fareham-darc.co.uk/Projects/VHF Direction Finding.ppt
There are many radio amateurs all around the world who participate in various forms of DF Hunting also called Fox Hunting in the US. It is a great mixture of technical, map reading, logic and other skills (the Dark Arts?). No doubt luck and good old fashioned cunning works as in many competitions the hidden station is well and truly hidden. All sorts of tricks and subterfuge are used to make it difficult if not impossible to locate the hidden station, such as having the hidden station on one side of a river and the aerial which transmits the signal being on the other side of the river and the nearest bridge is a mile away. Remember you have to find the hidden station NOT the aerial.
As Manuka says loop and Yagi aerial designs are usually used in the UK. The Doppler systems are more often used in the US. Also I am not sure if Doppler systems are legal in UK and european competitions. Also of course they are not really convenient when as usual the last part of the search for the hidden station is carried out on foot (some of the more serious compeditors even running as in orienteering). There is Radio Orienteering of course for the more energetic amongst you where you run all the time. Another system is "Whistling Dipoles" which uses time difference between two aerials to provide direction information.
Radio DF systems can also be used to track down interference, illegal transmissions and so on.
For anybody interested there are numerous Web sites with lots of designs for equipment.
You can also look at
http://ka7oei.com/ardf_pages.html which has a lot of relevant information on the subject.
I would certainly be interested in seeing any projects using PicAxes in ARDF.
Hope this information helps. Barry (Clockwork)