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?
Last edited by [steven] on Fri Apr 05, 2019 10:53 am, edited 1 time in total.

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Joined: Tue Dec 27, 2016 11:00 pm

Re: Demodulating 4LFSK

Post by snn47 » Mon Jan 21, 2019 5:14 pm

What is a "Satelline tranceiver module"?
How do you conclude that the depicted Signals form a 4FSK. Frequency distribution of xFSK are in my understanding symetrical and of same amplitude unless there is additional modulation on the FSK signal itself. Two examples for 2 and 4 FSK are shown in the picture from 2FSK vs 4FSK | Difference between 2FSK modulation and 4FSK modulation ... ation.html Image

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