Decoding Pocsag Pagers With The HackRF

HackRF Tutorials

Decoding Pocsag Pagers With The HackRF

Postby admin » Fri Aug 16, 2013 10:34 am

Remember evesdropping on pagers may be illegal in your country do so at your own risk.

This is another quick tutorial on things you can do with the HackRF. I was lucky enough to get one as part of the beta, it is a great piece of hardware and it is my hope that with these tutorials I can do my part in getting more people interested and we can get massive community built around the HackRF. Today I am going to be talking about decoding pocsag pager messages, for this I will assume you are using the great ubuntu live cd for the hackrf.

First thing to do is get gqrx going and tune around the 137 - 160 ish mhz range - You will be looking for a signal like this:

gqrx.png
gqrx.png (268.29 KiB) Viewed 5317 times

You can atually see three pocsag channels in this image.

Ok now you have found the stream we need a way to decode it, it took me a bit of fiddling to get this to work so hopefully this will save you some time.
First thing we need to do is install some tools so in a terminal run:

sudo apt-get install pavucontrol


Next we need to download a program called Multimon-NG from here, Log in or register to see all links ,click on download zip on the right hand side. Once this is downloaded unzip its contents to any directory.

Cd in to the directory where you extracted Multimon-NG and enter the following:

mkdir build
cd build
qmake ../multimon-ng.pro
make
sudo make install


Now start Multimon-NG with this command:

padsp multimon-ng -a POCSG512 -f alpha

You will need to adjust -a depending on what your are decoding, anyway at this point you should have something that look like below:

pocsag.png
pocsag.png (186.75 KiB) Viewed 5317 times


Now that this is running we need to pipe the audio from gqrx to multimon and this is were we use little pulse audio magic, In a new command line enter this command:

pavucontrol


You should now be looking at a window like the one below. What you need to do now is click on the recording tab and you should see listed "Multimon-NG recording from" in the box next to this make sure "Monitor of audio adapter" is selected. *Note you only need to do this once it will remember in the future.

pavucontol.png
pavucontol.png (303.71 KiB) Viewed 5317 times


Thats it when the next page comes through it should be decoded like you can see on the screen below, If you wondering why alot of this is blurred out its because these message often conatain a lot of personal information such as names, phone numbers and address's. Anyway thats all for today stay safe and have fun.

decoded.png
decoded.png (457.39 KiB) Viewed 5316 times
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