It might be possible to replace the electronics used by this sound card based direction finding system with a PICAXE. Could be an interesting project. http://www.pi4wag.nl/index.php/pseudo-doppler-radio-direction-finder
RF Direction Finding
- Thread starter MFB
- Start date
techElder
Well-known member
You might also be interested in this DF unit: https://www.ramseyelectronics.com/cgi-bin/commerce.exe?preadd=action&key=DDF1
Pseudo-Doppler DF units can indeed be a marvel, & they certainly excel for transmitter fixes if target or observor are moving - aircraft/cars etc- or transmissions are fleeting. However they're prone to multipath reception & their resolution is only modest beside traditional techniques (loop/sense or even Yagi).
These later approaches can almost split hairs - a classic example occured in WW1 when "Y station" DF bearings on the German fleet were detected (from several 100 km cross channel) to have altered VERY slightly. This was (correctly) interpreted as an in harbour mooring shift prior to battle (Dogger BanK).
Before you get too excited about the Ramsey kit perhaps read this. Stan (ZL2APS & 50 years a DFer)
These later approaches can almost split hairs - a classic example occured in WW1 when "Y station" DF bearings on the German fleet were detected (from several 100 km cross channel) to have altered VERY slightly. This was (correctly) interpreted as an in harbour mooring shift prior to battle (Dogger BanK).
Before you get too excited about the Ramsey kit perhaps read this. Stan (ZL2APS & 50 years a DFer)
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Maybe, yes.
What'[s happening if it's not obvious, is that the 4 antennas are being switched to the Receiver sequentially, usually clockwise from a reference point perhaps the antenna that is nominally assigned as North, then the signal is read, then the next antenna is switched in, others out, signal is read and so on. Then when the signals are either plotted or combined you get direction. Enhancements include time difference of arrival to give even more accuracy of direction and relative range, which is what the designer of this circuit has done, used the same reference signal for the Left audio channel.
So you would need to find a reference signal source, so check if the PICAXE can produce a tone say 2KHz continuously whilst still switching the output pins that select the antennas, they would be synchronous enough to detect phase difference. I think the tone generator is a so-called blocking command, so maybe not. If it can’t then the solution becomes a little more complicated in that there has to be a phase relationship between the switching and reference, for example a switching source (PICAXE) and a reference oscillator would not be phased locked together and lead to measurement problems.
If you can solve that, then you can measure the output of the receiver using the PICAXE ADC input to get magnitude and measure the time between the reference oscillator (say) leading edge and the received signal peak, do this 4 times (i.e. four different delay times as the antennas are in a different positions and you get the vectors that the PICAXE can combine to give direction and relative amplitude.
techElder
Well-known member
Most any time you say "multiplex" and "picaxe" in the same sentence, then you should seriously consider designing with two picaxes; one for the multiplex and one for the general program. Synchronization or "heartbeat" would be easier than programming it all into one picaxe.
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)
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)
Before the introduction of GPS I used a couple of DIY radio direction finding stations to track small low cost drift buoys in the Irish Sea. Then progressed to larger and more expensive buoys that repeated signals received from hyperbolic radio navigations networks. It would be difficult to justify using either of these technique now that small GPS trackers are available at such low cost. The UKHAB community have developed extremely lightweight units that transmit a few mW on 433MHz and run for hours from a single AA cell. Zoologists still use basic RDF on small animals but GPS technology is even now even available for tracking bats. I certainly find the subject of tracking technology, and its history, continually interesting.