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
upload its bearings and at the same time download and display the
bearings of multiple remote mobile and fixed 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
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
He also offers to customize it for a very modest price.
few RDF41/42 radio direction finders, linked together
via Jonathan's RDF-Mapper make an affordable but yet extremely
capable radio direction finding system.
Short demonstration video
is how the setup works:
Connect the working RDF41/42 with its USB
output to a USB port of your computer.
Run RDF-Mapper on your laptop, and select the correct serial port
and 9600 Baud for the RDF41/42.
computer doesn't yet have a USB driver for the CH340 USB controller of
the RDF41/42 you can download it here:
3, Get a GPS mouse that outputs a NEMEA GGA ($GPGGA) sentence.
A low cost USB device like the Beitian BS-708 USB GPS would probably do fine
(Some GPS devices use different output modes or sometimes the output mode can be user-set.)
Plug it into your computer, and select the right
GPS serial port and baud rate.
a GPS mouse runs at 4800 or 9600 Baud.)
the USE MANUAL INPUT box unchecked.
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.
For fixed applications no GPS is needed, just check the USE MANUAL
INPUT box and set the
(or the RDF41/42's calibration) 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.
mentioned, RDF-Mapper can upload your bearings and download
bearings from other RDF stations to present them on your screen, using
These options are highly self-explanatory but Jonathan and I will help out if you encounter any problem.
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
Obviously, the transmitter is likely to be very close to or even in the
crossing area of all bearing lines.
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,
a mobile station can collect a number of bearings which reveil the
can see lines emerging from the highway I drove on, and after some time
them cross the area in the circle, which I added by hand for
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.
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
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.
after a few seconds driving into the new direction, the GPS heading
calculation becomes accurate again and so does any bearing that is sent
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.
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