What kind of modulation?

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royb
Posts: 4
Joined: Fri Feb 21, 2020 12:24 pm

What kind of modulation?

Post by royb » Tue Feb 25, 2020 1:36 pm

I have identified a signal I am trying to hack as some sort of FSK / GFSK or 2-FSK modulation.
When using FSK demodulation this is the resulting spectrogram I am getting:
Signals.png
Signals of receiver
Signals.png (418.88 KiB) Viewed 2480 times
What I find peculiar about this signal is that when I would interpret it as 2-FSK the frequency never shifts just 1 space from "00" to "01" or from "10" to "11", it only moves either 2 or 3 bands, or 1 band between "01" and "10" leaving me to think that this signal is not actually 2-FSK.

Anybody has any idea?

royb
Posts: 4
Joined: Fri Feb 21, 2020 12:24 pm

Re: What kind of modulation?

Post by royb » Tue Feb 25, 2020 10:10 pm

So in the end it turned out to be just GFSK with a "slow" gaussian filter, making it seem like 2 bit. This explains why we always see an upward movement ending up in the top half of the band and a downward movement to the lower half of the band.

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