Re: [Discuss-gnuradio] question about using FSK on noise

[Christopher Richardson]

Hi Abhinav,

This sounds really interesting!

Are you using RF or ultrasound out of interest, to grab emissions from the SMPS?

cheers

Chris

On Tue, Jun 7, 2016 at 6:35 AM, abhinav narain <address@hidden> wrote:

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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