SignalsEverywhere: Driving around with KerberosSDR and Locating a P25 Transmitter

On this weeks episode of SignalsEverywhere, host Corrosive tests out our KerberosSDR coherent RTL-SDR unit for radio direction finding. If you didn't already know KerberosSDR is our experimental 4x Coherent RTL-SDR product. With it, coherent applications like radio direction finding (RDF) and passive radar are possible. Together with the KerberosSDR direction finding Android app it is possible to visualize the direction finding data produced by a KerberosSDR running on a Pi3/Tinkerboard.

In the video Corrosive uses the KerberosSDR together with the recently updated companion Android app to determine the location of a P25 control channel. By driving around with the app constantly collecting data he's able to pinpoint the location within about 15 minutes.

If this interests you, we also have some more driving demo videos available here.

In addition to his video, Corrosive has also created a very useful calculator that can be used to calculate the required antenna spacing for a circular or linear direction finding array that can be used with the KerberosSDR.

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This is a great video as it also shows some of the issues using pseudo doppler systems. I have used a variety of them over the years from the first one being a Ramsey kit that I built to actual professional DopSys and others. A few important lessons learned: 1) Take all other antennas off the vehicle including your AM/FM radio (you can leave GPS and Sat Radio), 2)do not transmit in close proximity (HT inside vehicle should be okay but a mobile is a no-go), 3) the noise you are hearing is the tone created by the pseudo rotation of the antennas. I found that using attenuators and band pass filters greatly improved accuracy.


This video is amazing. I have a KerberosSDR on a Tinkerboard-S and another on a RasPi 3+ and they are the cutting edge for RDF. Our club bought 4 KerberosSDR’s for hunting down some bad actors in our area who are intentionally jamming repeaters. We have been using an app called SigTrax to create a team of mobile DF stations. Is there anyway to make the KerberosSDR compatible with SigTrax so that we could automatically ‘network’ our mobile DF stations? It would help us to find the bad actors much quicker.