Decoding FLEX pagers using RTL-SDR and Linux

Superkuh2 demonstrates how to decode FLEX pager radio traffic. He uses gr-pager and zarya’s implementation of it on the Linux platform with the RTL-SDR dongle.

This script runs at a 250 KS/s sample rate and decodes one 12.5 KHz channel only. Internally it uses gnuradio’s optfir to generate low pass taps stopping at 12.5 KHz to use witih a frequency xlating FIR filter. It then passes what’s left to gr-pager’s flex_demod.

Here I show such an activity with the osmocom gr-fosphor visualization tacked on to patchvonbraun’s gnuradio multimode receiver for context.

For more detail on this process, visit SuperKuh’s website.

This entry was posted in digital radio data, Linux, RF, SDR and tagged , , , .


  1. Darren says:

    I was decoding flex last night on windows. I found v2, VB Audio and PDW worked very well.

  2. superkuh says:

    PDW is really nice, I agree. I just couldn’t get the audio piping to it working on linux under Wine. zarya’s script decodes only one channel at a time like PDW but there are other gr-osmocom + gr-pager gnuradio scripts that decode all FLEX channels in the band at once, like mothran’s FLEX_hackrf. There should be a version of these adapted for the max rtl-sdr bandwidth soon.

  3. tty7 says:

    the video is gone, and i can’t find too much other underpinning data, as i’d like to do this. any hints? thx.

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