Directional antenna for GSM phone tracking?

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orbit308
Posts: 2
Joined: Wed Dec 14, 2016 12:15 am

Directional antenna for GSM phone tracking?

Post by orbit308 » Wed Dec 14, 2016 12:19 am

Can a directional antenna and SDR be used to triangulate direction of a gsm phone? I am trying to come up with something to determine if there are any phones nearby (very rural area), and their direction. I'm not worried about intercepting signals, just trying to find any phones that are on.

AD5NL
Posts: 34
Joined: Fri Sep 16, 2016 7:00 pm

Re: Directional antenna for GSM phone tracking?

Post by AD5NL » Wed Dec 14, 2016 4:55 pm

A few random thoughts:

1. I know that RDF at VHF is usually done with small yagis. These do not have the greatest directionality (three element yagi has a main lobe that is something like 90 degrees wide). But that is sufficient to get a rough direction, particularly when multiple antennas are used.

2. For GSM you might want you use a log-periodic because GSM spans several bands. There are some printed-circuit LPDA designs that can be gotten affordably that might work well here. These should also be light enough such that you could use an inexpensive servo to rotate them.

3. Another consideration is that you might want to do something with cross or circular polarization, since phone antennas are typically going to be in "random" orientations. Might want to get two LPDAs or yagis and cross them (connect them 1/4 wave out-of-phase). I guess you could also make a helical antenna, possibly out of inexpensive material like PVC and wire and maybe a copper-clad PCB as the base.

Link to LPDA on PCB: http://www.wa5vjb.com/products1.html
I've bought these less-expensively at an electronic shop in the Dallas area (Tanner Electronics in Carrolton) rather than buying straight from WA5VJB direct. I've owned the smallest of these; they were out of stock on the bigger ones at the time. They also had some printed circuit patch antennas as well.

orbit308
Posts: 2
Joined: Wed Dec 14, 2016 12:15 am

Re: Directional antenna for GSM phone tracking?

Post by orbit308 » Wed Dec 14, 2016 6:35 pm

Thanks for the info, looks like that's the way I need to go. Any idea what range one of these can pick up a cell signal? The area is a bit wooded, not really line of sight.

Would something like this work?
http://www.ebay.com/itm/US-STOCK-Extern ... SwGvhT~ixu

AD5NL
Posts: 34
Joined: Fri Sep 16, 2016 7:00 pm

Re: Directional antenna for GSM phone tracking?

Post by AD5NL » Thu Dec 15, 2016 7:41 pm

It might work.

As for range... I'm not really sure. Never worked with GSM.

I will say that an LPDA with somewhere around 5 elements will add somewhere around 6 db to your link budget. So roughly twice as far as you'd be able to receive with a dipole.

More elements, more gain. Each 6 db gain is roughly a doubling of line-of-site distance.

AD5NL
Posts: 34
Joined: Fri Sep 16, 2016 7:00 pm

Re: Directional antenna for GSM phone tracking?

Post by AD5NL » Thu Dec 15, 2016 7:44 pm

Although fwiw you have to knock off 3 db if you cross-polarize two LPDAs. It's counterintuitive (two antennas actually gets less gain than just one) but such is life.

The tradeoff though is that instead of polarization losses between 0 and 20 dB (depending on orientation of the remote antenna), you only have a constant loss of 3db. In most cases that is a worthwhile tradeoff.

(That is why a lot of FM broadcast antennas use circular/cross polarization so that their signal is good regardless of how your receiver is oriented).

Username
Posts: 507
Joined: Sun Oct 09, 2016 7:27 am

Re: Directional antenna for GSM phone tracking?

Post by Username » Tue Dec 20, 2016 3:35 pm

:D are you aware of IMSI Catcher?

The "problem" with GSM is the Burst is 1/2 second or shorter so its extremely hard to track anyone that way.


AD5NL
Posts: 34
Joined: Fri Sep 16, 2016 7:00 pm

Re: Directional antenna for GSM phone tracking?

Post by AD5NL » Sat Dec 24, 2016 5:55 pm

Hmm, phased monopoles. Not a bad idea.

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