KrakenSDR: Finding Multiple GSM Base Station Transmit Towers with the Multi-VFO Feature
If you weren't already aware, KrakenSDR is our 5-channel coherent radio based on RTL-SDRs, and it can be used for applications like radio direction finding. KrakenSDR is in stock and can be purchased from CrowdSupply or Mouser. More information is also available on our website at krakenrf.com.
Last month we used the KrakenSDR to find the location of a low power FM transmitter. Now in this video we're using KrakenSDR to find the location of GSM base station transmit towers for four frequencies. We're also using the multi-vfo feature to capture the bearing data of these four frequencies simultaneously which can save us some search time.
Once we've found the first transmit tower, we already have some logged bearing data that can be used to help us find the second tower faster. Then the third and fourth towers are even faster to find due to even more data having already been collected.
Interestingly, it also turns out that the first frequency we search for is actually being used by another tower that we pass along the way back. The location of this tower was picked up on the drive back to the first tower. It's possible that these two towers which are a few kilometers apart are covering different areas with directional antennas.
Also note that the first two transmitter searches use the "auto-zoom" map camera feature, which will automatically zoom the screen to show both the vehicle and estimated transmitter location. The second half uses the standard free camera mode.
This is on a new build of the App which is currently in testing, so some things may look slightly different to the currently released version. The new app version will have some minor feature improvements.
Hey! Great article! Just a question about the VFO. The frequencies need to be close or we can space them in the spectrum? Still waiting my kraken…
GSM usually used at least a three sector cell site so it’s not unusual to see the BCCH reused within a reasonable spatial distance. The lower the freq, the less frequently it will be reused due to distance, but sectoring is a great way to get better coverage and better frequency reuse from a smaller number of sites.
This is a cool article. I’d love to know the location of all the cell sites around me.
Cell tower locations are public in many countries – and if not, opencellid.org can give you a good hint on the estimated location of most towers. By most – those that are in areas where people have been gathering and sharing data.
That will generally give good coverage – except in restricted areas where the public is not allowed – like that ‘secret’ military base in the desert.
In the USA, all radio transmitters have to have a registration. But, tying tower registrations to actual cell sites is a bit harder. The tower registry may have some frequencies listed and some ownership info. But that leaves taking the frequency info and trying to determine the service/company using it. The towers are often owned by a different company than the cellular providers and they just lease the towers to the cell providers. Even worse, they may lease space on the tower to multiple carriers which makes the listings even harder to parse.
If someone has found a way to parse the FCC database and get out a cell map, that’s wonderful. Also, having a registration for a frequency at a particular tower doesn’t mean the cell site is operational nor is it always actively using all of those frequencies.
Ground truth is much harder to come by. When I worked for a cellular provider, the engineering teams would always have big maps stuck up to the walls that they updated pretty regularly. It was a lot of work for even them to keep track of what sites are using what frequencies. And this was a bit before the addition of macro and nano cells where you may have multiple layers of cells using different frequency ranges specific to their tasks–500-700 MHz for wide area coverage, 1-2GHz for smaller cells and >2GHz for tiny cells. So, a ‘coverage chart’ isn’t as simple to compile as it used to be as there are at least three layers of cells covering any particular area. Maybe even more with femto cells and other venue specific installations.