Hi all, I am trying to make a covert communication channel using SMPS noise generated by the processor as a part of my research.
I see a change in frequency emitted by the processor when I run the following loop (http://pastebin.com/uRghLuLm) with message variable containing the message, and see the spectrogram ( http://postimg.org/image/g0ec0nvqj/full/), with fluctuating red points ~60kHz, indicating the change due to a loop and sleep executed on the processor. I want to decode the bits and I think I should use FSK, although I lack understanding to configure the details. The following is the current flowgraph where I have used bandpass filter to narrow down the signal to ~60kHz and using quadrature block to demodulate. Since the entity of interest is actual SMPS noise of the laptop adapter instead of a sinosoid, I have no clue how to write a clear decoder after looking at some tutorials of GNU Radio to know the symbol rate etc for the clock recovery algorithm. I would be grateful, if someone can guide me on how to proceed Thanks, Abhinav
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