PA8W Amateur Radio

Wil, PA8W,  E-mail: PA8W@upcmail.nl           
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Mapping program for Radio Direction Finding

In the summer of 2016 I called for help in order to create a mapping program for RDF work.
A New Zealand wizard helped me out; this genius developed just the right tool for me.
Of course, I rewarded that by sharing information he needed in the field of RDF hardware.

Now that's what hamspirit is all about!

This is how the setup works:

The microprocessor based Doppler RDF (PA8W RDF-41) automatically exports the very best bearings it calculates.
This data is sent over a simple USB cable to a laptop or computer, running the RDF visualizer program.
The RDF visualizer program needs no installation, just unpack it somewhere on your computer and execute "RDF_Mapper.exe"


The program can be downloaded here


1,  Connect the working RDF41 with its USB output to a USB port of your computer.

2, Run the RDF visualizer program, and click to the settings page, where you select the right serial port and 9600 Baud for the RDF41.

3, Connect a GPS mouse to your computer, and select the right serial port and baud rate.

(Normally a GPS mouse runs at 4800 Baud.)

4, For fixed applications set MIN.SPEED FOR HEADING to zero.
Now the program knows that you are fixed and it will display incoming bearings from the RDF41.

5, For mobile application set
MIN.SPEED FOR HEADING to 15km/h.
Now the program calculates your driving direction and as soon as you drive faster that 15km/h bearings will be displayed.



Calibration procedure:


Fixed:
Tune to the signal of a known station and turn the calibration knob until the bearing lines on the map cross the location of the transmitter.

Mobile: Let someone transmit a signal (walky talky) and walk away in front of your car.
Now turn the calibration knob until the bearing line on the RDF41 points forward (North).
Let you helper return whilst transmitting and fine-tune the bearing.


The very first results on UHF (424MHz) are shown in the below picture:




You can see lines emerging from the highway I drove on, and eventually most of them cross the area under the circle, which I added by hand for explaining.
It is obvious that this fully automatic RDF system is a very powerful tool for mobile RDF work.
The driver only has to take a short peek at the screen to know what part of the city he has to address.

The experiment also illustrates that we could do with fewer lines, so I narrowed down the export filter to ensure that only the very best measurements are being exported.

The result in very difficult circumstances (on 433MHz) can be seen here:



Again lines emerging from the trajectory my car followed.
Still some crooked bearing lines due to massive reflections, but the bulk of the lines cross at pretty much a single block of houses.
And I can say for sure that the signal originates from there, because I double-checked that with a portable receiver and a moxon.

This  clearly illustrates that using a mobile RDF system in a city environment is not an easy task; there are always reflections that distort your measurements, and sometimes even overrule the direct signal, suggesting the signal is coming from an entirely other direction.

This setup however automatically collects enough data to show a clear correlation between several measurements,
reveiling a pretty good estimate where the source is located.

And all that for free, thanks to my friend Jonathan Musther from New Zealand!
  
The program can be downloaded here



73, Wil.


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