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I am fairly new to GNU Radio and the SDR world. I am currently trying to reverse engineer a signal from my Logitech wireless keyboard. Besides the knowledge I gained from my electrical engineering education, I have used various guides to assist me with this project ([1],[2],[3]).

I have been able to record a sample of the keyboard and am able to play it back so that the computer with the receiver thinks it is seeing a keyboard, so I know I have a signal at least. Demodulating the signal is where I am having problems. I know from FCC ID research and the radio chip it uses that the modulation is GFSK, but when I try to do any sort of demodulation in GNU Radio, I am unable to find any usable data.

I have been poking around at this problem for a few months now, and haven't been able to solve it. Any assistance would be greatly appreciated.

[1] Radio to Data: http://www.inguardians.com/pubs/GRC_signal_analysis_InGuardians_v1.pdf

[2] keysweeper: http://samy.pl/keysweeper/

[3] Keyfob hack: http://blog.kismetwireless.net/2013/08/playing-with-hackrf-keyfobs.html

Jonathan Leffler
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Paccachu
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1 Answers1

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I don't know if this really is a good answer from a StackOverflow Perspective, but I'll try nevertheless:

Whilst GNU Radio has a demod for GFSK signals, it's hard to guess GFSK parameters. You might be a little better off sufficiently oversampling your signal, and having a look at a waterfall visualization of it. Can you see the different FSK subcarriers?

Assuming you do, simply appropriately filter that signal into the FSK subcarriers, and compare their energy.

Marcus Müller
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