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Re: [Discuss-gnuradio] Decode Frequency Modulated Signal

From: Gerhard
Subject: Re: [Discuss-gnuradio] Decode Frequency Modulated Signal
Date: Tue, 31 May 2016 20:20:51 +0200

Hello Franz, hello Marcus, hello list!

Thanks for your answers!

Yes, Marcus, after decoding the signal with quadrature demod the "long
period" is a 1 and the "short period" is a 0. (Although it is not really
a period. More like period/2.) Maybe you are right with your assumption
that this is just a FSK within a FSK.

You can find the GRC flowgraph I used to extract the waveform from the
last mail in the appended image. The signal was recorded with a 4MHz
sample rate at a frequency around 170MHz. I also know that the baudrate
of this signal is 2400.

I will try to make the double FSK setup to work. Whether is using
quadrature demod, WBFM demod, or something like this. However, if there
is any best practice on how to decode a signal like this, I'm happy if
you tell me how. ;)

Best regards

On 05/29/2016 10:24 AM, Franz Dworschak wrote:
> Hi Gerhard,
> I see no demodulation in your pictures, it seems you just filtered the
> signal. I would need some background information.
> What is the sample rate and the input signal frequency. If the sample
> rate is much higher, just measure the pulse length by measuring the
> amplitude and use a comparator.
> Or you can use the WBFM demodulator or you place your frequency band on
> the edge of a filter for demodulation.
> There are many possibilites, so I would need more information.
> Regards
> Franz
> Am 28.05.2016 um 21:21 schrieb Gerhard:
>> Hello!
>> I want to decode a signal that slightly varies in Frequency. Therefore I
>> used "Quadrature Demod" block. After this, its waveform looks like the
>> appended image "baudline-waveform.jpg". Although it's a bit fuzzy I
>> already can decode it with my eyes. Have a look at the appended picture
>> "decoded-signal.jpg".
>> My Questions:
>> * How do I decode the signal to ones and zeros?
>> * Is the signal O.K. the way I demodulated it, or is it to fuzzy?
>> Any help is appreciated!
>> Cheers
>>    Gerhard
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