Radio Direction Finders and Direction Finding Systems
Doppler Radio Direction Finders and Direction Finding Equipment
Doppler Systems helps find culprit jamming aircraft transmissions
December 01, 2016
Recently someone made hoax calls to pilots, causing a passenger flight to
abort landing as it approached Melbourne Airport in Australia. In total there
were 15 unauthorized transmissions on aircraft frequencies in the Melbourne area
article here). The Australian Communications and Media Authority
deployed a Doppler Systems radio direction finder to assist the Australian
Federal Police in finding the culprit. Thankfully he was found and has
Antenna Placement in a Mobile Installation
September 30, 2016
Frequently we are asked "What antenna spacing should I use for my mobile
antennas?" This is a good question because many people think that antenna
spacing would be critical for good performance and people are surprised when our
answer is "Somewhere between an 1/8 and 1/4 wavelength." In this
post I'm going to present to you the results from the detailed model of our
antennas to show the effect on error of antenna spacing and also antenna gain
and phase errors. I'm also going to make some recommendations not only on
spacing but on placement of the antennas on the vehicle.
Figure 1 below shows the effect on bearing error due to antenna spacing.
Results for both the 4 element and 8 element antenna are shown. Notice
that the curve is fairly flat from 0.125 wavelength to 0.35 wavelength and then
it increases rapidly. This is really good news if you are going to be
operating over a relatively large portion of the band since you don't want to
have to jump out and change the spacing when you change frequency.
Another source of error in the DF is mismatch in the gain of the antennas. Figure 2 illustrates this effect.
You may ask why do we care about this since all the antennas are identical?
The answer is that the antenna's ground plane has an effect on the gain of the
antenna. Therefore it is important to have adequate ground plane around
all of the antennas. Typically we suggest at least a 1/4 wavelength of
ground plane around each antenna.
In conclusion use a spacing somewhere between 1/8 and 1/3 of a wavelength but
try to make sure that each antenna has at least 1/4 wavelength of ground plane
all around it. The table below is a good reference
Frequency Range (MHz)
Mounting a DF Antenna to the Side of a Tower
September 06, 2016
Over the years many of our customers have asked about mounting the DF antenna
on the side of a tower or mast. Will it work? The short answer is not very well.
We've posted the results of some extensive
modeling we've done to predict the error associated with side mounting the DF
array on a tower. To achieve a less than 5 degree peak error at 150 MHz the
array must be mounted over 8 feet from the tower. To achieve less than 2 degree
peak error the array must be 75 feet from the tower.
The conclusion is that for best performance the DF antenna array must be top mounted
on the tower or mast and away from any significant RF transmtters. Please
contact us if you have any questions.
Improved Mapping in TargetTrack
September 02, 2016
We released TargetTrack 3.2.0 last week. Several of our users had requested that we improve our bitmap based mapping functions. The previous versions of TargetTrack limited the map file size and the level of zooming. The new version allows for much larger file sizes and considerably more zoom levels. We've also added some more map like zooming and panning tools.
The bitmap mapping facility in TargetTrack allows our users to make their own custom maps using screenshots or scans of physical maps. Use our MapFix utility and you then have the map that you want.
We also have our Great Map function so that you can use online mapping data from several different mapping data providers e.g.OpenStreetMap, Google, Bing.
Download the latest version of TargetTrack from our Downloads page and let us know what you think.
Welcome to our Blog
September 01, 2016
Welcome to the Doppler Systems blog. Our blog will give us the opportunity to keep you up to date on our latest products and software releases as well as offer helpful hints to enable you to use our products more effectively.
Thank you for visiting and contact us if we can be of any assistance