POCSAG is an asynchronous protocol used to transmit data to pagers.
The family of POCSAG protocols can operate at three speeds, 512 bits per second (the original specification speed) is the base standard.
1. Hardware
– One computer running Ubuntu
– 1 DVB-T USB receiver (usually used to receive HD TV on computers)
2. Software
– OS : Ubuntu 16.04.1 LTS
– Driver : Rtl-sdr
– Software defined radio receiver (SDR) : Gqrx
– Decoder : Multimon-ng
3. Installation
3.1 Preparation
Let’s install first all the tools that we’ll need :
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sudo apt-get update sudo apt-get upgrade sudo apt-get -y install git cmake build-essential libusb-1.0 libusb-1.0-0-dev qt4-qmake libpulse-dev libx11-dev |
3.2 Driver : Rtl-sdr
Clone it from git, compile and install :
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git clone git://git.osmocom.org/rtl-sdr.git cd rtl-sdr mkdir build cd build cmake ../ -DINSTALL_UDEV_RULES=ON make sudo make install sudo ldconfig cd ~ sudo cp ./rtl-sdr/rtl-sdr.rules /etc/udev/rules.d/ sudo reboot |
3.3 Software defined radio receiver (SDR) : Gqrx
On Ubuntu, it’s really easy to install Gqrx :
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sudo apt-get update sudo apt-get install gqrx-sdr |
3.4 Decoder : Multimon-ng
Clone it from git, compile and install :
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sudo apt-get update mkdir multimon-ng cd multimon-ng mkdir build cd build qmake ../multimon-ng.pro make sudo make install |
4. Gqrx
You can start Gqrx and then :
– Start DSP processing (in red)
– Adjust frequency to a POCSAG frequency (in blue)
– Start UDP streaming (in green)
– Adjust parameters as below (in pink)
The short burst of data are POCSAG data. Let’s decode it !
4. Multimon-ng
Here is the command to decode the POCSAG messages :
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nc -l -u 7355 | sox -t raw -esigned-integer -b16 -r 48000 - -esigned-integer -b16 -r 22050 -t raw - | multimon-ng -t raw -a SCOPE -a POCSAG512 -a POCSAG1200 -a POCSAG2400 -f alpha - |
Then, when you’ll hear a POCSAG data, you should be able to read the decoded data in the terminal :
This doesn’t work. When the command is run, a blank screen pops up and nothing is decoded in the terminal. Any ideas?
The standard UDP port has moved at least in the Ubuntu 18.04 GQRX ppa to 65535. If you change the port number it will work.