Demodulating 4LFSK

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Joined: Sat Jan 12, 2019 9:17 pm

Demodulating 4LFSK

Post by [steven] » Sat Jan 12, 2019 9:41 pm

I'm trying to demodulate a Satelline tranceiver module at around 430Mhz using an RTL SDR with an R820T tuner.
I already have a lot of documentation about the data being transmitted, the data rate and the modulation type.
The modulation type is 4 level FSK, the bit rate is 9600bps (so the baud rate must be 4800) and the transmission power is 100mW.
When standing close to the transceiver I do see a few bursts at the expected frequency of around 430Mhz.
However, when listening in SDR# I simply hear silence when there is a tranmission (NFM mode) and then static noise again when the transceiver turns off.
Also analysing the demodulated transmission in Audacity only reveals a vague signal that doesn't look like a demodulated 4LFSK signal to me.

What am I doing wrong?

Video of the transmission:

Raw IQ file of the transmission: (transmission is at 429.838) ... sp=sharing
NFM signal.PNG
NFM signal.PNG (30.66 KiB) Viewed 135 times
spectrum.PNG (246.46 KiB) Viewed 135 times

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