Recovery without a preamble

[rumpeltux]

First, thanks for this tool and the corresponding talk!
I guess I’m exactly the person you’re talking about, too little radio experience and completely thrown back by the scariness of the Gnuradio clock recovery blocks, which I guess wouldn’t work in my case anyways.

I’ve got this frequency modulated signal:

The base/modulation frequency seems to be 9.8kHz and the symbol rate 480Hz, thus the signal is clearly visible already in the FFT plot.
Your tool is usually doing a good job at recovering the symbol rate, but it’s also outputting gibberish data for the flatline part before the actual data starts.

Any advise on how to handle this?
I guess I could do some numpy magic to detect when the actual data starts, but I wonder if there’s a smarter way.

Thank you!

[hllhll]

I'm the exact same audience (security researcher with little DSP background), I'm using squelch / power squelch to shunt data before and after a burst, I guess it could work for you too.
Maybe 2 squelches, one for the rf part (i.e. the mess before the burst), and the second for the baseband (i.e. the silence before the data)
Use gnuradio for that

BTW, not related, If anyone have a clue how to turn wpcr into a 4 level one (4fsk), it would be awesome