Thursday, July 31, 2014

Triangulation of a VHF signal

Locating the source of a signal

Privacy and security is a big topic in today's society. With the advances made in technology, the commercial and military techniques of the past is suddenly becoming available for everyone. 
With almost everything being wireless today anything and anyone can be tracked.

With this in mind I decided to try and track a signal with easy to buy equiptment.
I started with a cheap TV tuner known as RTL-sdr and the the stock/cheap supplied antenna.
Scanning the VHF band I noticed a strong permanent encrypted signal. Judging from the Norwegian frequency plan this looks to belong to either "Norwegian Directorate for Civil Protection" or the local police that is known to operate in the same area provides an interesting subject for this exercise. The signal strength was higher than commercial FM radio stations in the area suggesting the transmitter would be very close by.

Equipment used:
  • RTL-SDR TV dongle (
  • GPS receiver (NMEA or GPSd compatible)
  • rtlsdr-scanner (
Using the software and data collecting from a 15 min ride in my car I was able to track the source of the digital signal broadcasting with reasonably accuracy. The signal originates from a modern residential area. For security reasons this test is done with a cheap antenna and a low sampling rate. Enough to show the approximate area, but will not show what building.

Heatmap overlayed on Google Earth


  1. Hi! Can you please share some info on how your produced the map? It looks great! Thanks,

    1. This comment has been removed by the author.

    2. Assuming you have the following:
      Using Debian Linux
      This Program installed
      GPSD installed
      RTL-SDR dongle
      GPS that is compatable with GPSD (use xgps or cgps to check to see if its working ok, troubleshoot as needed)

      If all is working in the Scanner set your freq range
      Then under "Mode" choose "Continuous"
      Under "Dwell" choose a lower number I used 32ms

      then click start and drive around

      After you find a safe spot to pull over it STOP

      Then File and Export to MAP
      This will save a file that GoogleEarth can read.
      Open it in GoogleEarth just by File and OPEN

      it should automatically overlay the heat map on it assuming again that you have an internet connection that will load the terrain.

      Hope this helps.


  2. Interesting article, my compliments!