Montag, 29. September 2014

Receiving FLEX Pager with the HackRF and GNU Radio 3.7

This weekend I was browsing through the RF spectrum with my HackRF and found some pretty strong FSK signals:

FLEX Pager in GQRX
They showed up frequently and on various channels. My first thought was: POCSAG pagers. It turned out that I was wrong, not POCSAG but FLEX pagers. After some more research it seems like TELUS is using FLEX pagers here on Vancouver Island (

I also found an example GNU Radio script from Parker Thompson ( He is pointing out that it is a modification of the original script from Johnathan Corgan, who wrote the GNU Radio blocks for FLEX. Unfortunately it was incompatible with GNU Radio 3.7, so I had to change some pieces.

Here can you find my modified version:

Except for some scrambled messages it works like a charm ;) See for yourself:

running the script to receive pager messages. Somebody spilled urine ^^
As you can see, there are also lots of bit errors... I might have to work on the tuning. Also the error correction mechanism isn't implemented in the GNU Radio FLEX blocks yet.

But nevertheless, I had some fun ;) Hope someone finds this useful. Feel free to leave a comment!

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