PAGER

Decoding FLEX pager data

-----------------------------------------------------------------------------

Using GQRX and multimon-ng

Open GQRX from the applications menu and select your radio from the drop-down device list.
Your device string should look something like 'rtl=0' for rtlsdr or 'hackrf=256f17' for hackrf.

Locate a FLEX transmission and demodulate using NBFM. In my area there are several channels located between 929MHz and 931 MHz. After tuning to the desired frequency and setting filter width between 12.5k and 17.5k, press the UDP button at the bottom of the audio panel to stream the raw audio data on port 7355.

Next open a terminal and enter the following command:
nc -l -u -p 7355 | sox -t raw -esigned-integer -b 16 -r 48000 - -esigned-integer -b 16 -r 22050 -t raw - | multimon-ng -t raw -a FLEX -f alpha -

There's a few things going on here. First, we're using net cat to listen on port 7355 for UDP connections
nc -l -u -p 7355

and piping that data into sox to resample the stream from GQRX output of 48000 to what multimon-ng is looking for, 22050.
sox -t raw -esigned-integer -b 16 -r 48000 - -esigned-integer -b 16 -r 22050 -t raw -

finally, sending that on to multimon-ng to decode the FLEX data
multimon-ng -t raw -a FLEX -f alpha -

New data should appear in the terminal as it is received and decoded.

-----------------------------------------------------------------------------

Using rtl_fm and multimon-ng

For rtlsdr only.
Open a terminal and enter the following command:
rtl_fm -f 929.6236M -s 12500 | sox -t raw -esigned-integer -b 16 -r 12500 - -esigned-integer -b 16 -r 22050 -t raw - | multimon-ng -t raw -a FLEX -f alpha -

Alternatively, using a wider bandwidth, multimon-ng can be fed directly from rtl_fm:
rtl_fm -f 929.6236M -s 22050 | multimon-ng -t raw -a FLEX -f alpha -

-----------------------------------------------------------------------------

Using CubicSDR or GQRX and PDW

Start CubicSDR or GQRX and select your radio. If using GQRX select Virtual_Sink from the audio device drop-down menu before hitting OK. Tune to desired frequency, set filter width and demodulation, making sure squelch is turned off. If using CubicSDR set audio output to default and set system sound to Virtual_Sink using Menu>Settings>Sound>Output.

Next, start PDW from the applications menu. To pipe audio we need to tell PDW monitor the Virtual_Sink.
Open 'PulseAudio Volume Control' from the applications menu or from the command line using:
pavucontrol

Select the recording tab and set the drop-down menu for PDW to 'Monitor Virtual_Sink'.

The decoded messages should start to appear in the PDW output window.
Adjusting the audio gain in the receiver application can help achieve a better output.