PA8W Amateur Radio              

Radio Direction Finding Mapping Program 

Revised 201004

During the 2020 Balloonfoxhunt it seemed the default server of RDFMapper was overloaded sometimes.
So I set up my own server  to avoid that.
Please feel free to use my server for your hunts.
Simply type or paste  in the erased bearing server box in RDFMapper.
It will automatically add HTTP:// infront of that.
I generally put bearings on the server using the station names:  pa8w, pa8wMobile and pa8wSHF.
You might see some activity from me if you add these names in the stations list :)

Tijdens de ballonvossenjacht van 2020 leek de standaard RDFMapper server overbelast.
Ik heb daarop een eigen server ingericht die iedereen gerust kan gebruiken voor zijn eigen doeleinden.
Maak het vakje Bearing Server leeg en typ of plak  erin.
HTTP:// wordt automatisch toegevoegd.
Ikzelf upload mijn bearings onder mijn call naam:  pa8w, pa8wMobile en pa8wSHF.
Mogelijk kan je mij dus ook aan het werk zien als je die namen in de stationlijst toevoegt.

In the summer of 2016 I called for help in order to create a mapping program for RDF work.
A New Zealand wizard Jonathan Musther helped me out; this genius developed just the right tool for me: RDF-Mapper.

In 2018 he developed a new version of RDF-Mapper that can display plus upload its bearings and at the same time download and display the bearings of multiple remote mobile and fixed RDF stations.

The microprocessor based Doppler RDF (PA8W RDF41/42) automatically exports the very best bearings it calculates.
This data is sent over a USB cable to a laptop or computer running RDF-Mapper.
RDF-Mapper needs no installation, just throw it somewhere on your computer and execute it.
Jonathan offers the program for approx. 23,- euro, with excellent support.
He also offers to customize it for a very modest price.
A few RDF41/42 radio direction finders, linked together via Jonathan's RDF-Mapper make an affordable but yet extremely capable radio direction finding system. 

Link to RDF-Mapper

Short demonstration video

Here's is how the setup works:

1,  Connect the working RDF41/42/43 with its USB output to a USB port of your computer.

2, Run RDF-Mapper on your laptop.

3, In the right menu column, click RDF.

4, click in the RDF port window and select the correct serial port and 9600 Baud for the RDF41/42/43.
If no port number appears your computer doesn't yet have a USB driver for the CH340 USB controller of the RDF41/42/3.
You can download it here:
CH340 driver
and then repeat the above steps.

Remark: The older RDF41/42 models reset as soon as a serial connection with an computer (running RDF-Mapper) is made.
This can be disabled by adding a 220nF capacitor according to the wiring diagrams of both RDF's.

5, Mobile use: Get a GPS mouse that outputs a NEMEA GGA ($GPGGA) sentence.
A low cost USB device like the Beitian BS-708 USB GPS does fine.
(Some GPS devices use different output modes or sometimes the output mode can be user-set.)
Plug it into your computer, click on GPS in the right menu column and select the right GPS serial port and baud rate.
(Generally a GPS mouse runs at 4800 or 9600 Baud.)
Leave the USE MANUAL INPUT box unchecked.
Now the program calculates your driving direction and as soon as you drive faster than the set minimum speed,
bearings will be displayed in case the RDF41/42 thinks they are good enough for display.
So if you stop the car or drive too slow, no bearings will be plotted!

6, Fixed applications:  No GPS is needed, just check in the USE MANUAL INPUT box in the GPS menu and set the heading
so that the bearing lines point into the correct direction of a known test signal.
You will have to manually set your location by clicking on the map.
You can also set heading to zero and callibrate the system using the RDF41/42/43 azimuth calibration.

As mentioned, RDF-Mapper can upload your bearings and download bearings from other RDF stations to present them on your screen,
using Jonathan's or my server. (

These options are highly self-explanatory but Jonathan and I will help out if you encounter any problem.
And if you would like to use your own server that's no problem either.

Some test results on UHF (424MHz) are shown in the below pictures:

The red arrow is me being a mobile RDF station.
Additionally, you see two blue remote stations being downloaded and displayed.
Obviously, the transmitter is likely to be very close to or even in the crossing area of all bearing lines.


Here, the mobile is closing in on the transmitter, with the assisting remote stations one being about 3 degrees off and the other being spot on.
The black star is the actual location of the tracked transmitter.

Just as the previous RDF-Visualisation, the new RDF-mapper can also run in multiple lines mode,
so that a mobile station can collect a number of bearings which reveil the transmitters location:

You can see lines emerging from the highway I drove on, and after some time most of them cross the area in 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.

Obviously we could do with fewer lines than displayed in this example:
A lower audio input level into the RDF41/42 would reduce the number of bearings that would be exported to the RDF mapper.

Important note:  RDF-Mapper adds the incoming bearings to the current driving direction (heading) to plot them on the map.
Due to the typical time-lag of GPS, bearings that are drawn right after a sharp curve may have rather bad accuracy.
Only after a few seconds driving into the new direction, the GPS heading calculation becomes accurate again and so does any bearing that is sent to RDF-Mapper.
In RDF-Mapper you can set the minimum GPS speed for acceptance of a bearing. I generally set it to 20kmh so the effects caused by the GPS-lag are highly reduced.

I think I can safely claim that the RDF41/42 plus RDF-Mapper are much closer to professional RDF performance than any other kit or amateur design found on the internet.
Given the soft-commutation of the RDF41/42 and therefore its excellent sensitivity, its proven accuracy and smart suppression of corrupt (multipath) measurements,
given the mapping and networking options offered by RDF-Mapper, I can't think of any affordable kit or amateur design that comes anywhere close to this.

A big thank you to my friend and genius Jonathan Musther from New Zealand!

73, Wil.