Re: [Discuss-gnuradio] Demodulating digital signal (FSK?) from audio

[Marcus Müller]

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Hi Stefan,

this doesn't look like FSK, because then the amplitude of the
oscillations shouldn't change (only their frequency).
If I had to guess, it would be on-off-keying, and you could simply
detect that by squaring the signal, and using the integrate block on
that, with a integration length amounting to your symbol duration in
samples, which might be a little hard to guess from the signal you
posted, but maybe you know the symbol rate from elsewhere, or can
determine it by comparing signals from different battery states?

Greetings,
Marcus

On 16.07.2014 14:51, Stefan Oltmanns wrote:
> Hello,
> 
> I would like to write an application that checks the battery status
> of wireless microphones. The battery status is transmitted as a
> very low frequency (below 10 Hz) signal that is mixed in the normal
> audio. I was able to filter the signal out of the demodulated audio
> and display it (see image). AFAIK this modulation is called FSK. 
> The signal that is shown there should decode to data-blocks
> containing "11100000000" or something like that, are there any
> blocks in GnuRadio that can do that? Because the signal is derived
> from audio it is not complex but normal float, all GnuRadio
> demodulators seem to work only on complex data. Can somebody please
> help me?
> 
> Best regards, Stefan
> 
> 
> 
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