Re: [Discuss-gnuradio] samples/symbols CPFSK

[Marcus Müller]

Hi Olivier,

as discussed, an FSK with 1 S/symbol is not really an FSK; so I can't really confirm that it does what you want (it does do some DPSK, in fact). 6 S/symbol mean that one symbol, ie. the duration for which the output frequency is held constant, is six samples, nothing more, nothing less.

When you decimate something by a factor of six, the resampler has to choose a filter that kills the upper 5/6 of the spectrum, inevitably damaging your signal, if your max deviation is more than 1/6 of the nyquist rate. So that's definitely not what you want to do! Even if the signal is all contained within 1/6 of the original bandwidth, you'd again end up with something that is not FSK.

As usual, I recommend adding frequency/time sinks at practically every point in your flow graph and check whether the signal there looks correct, according to your signal model.

It's still a bit hard to help you, not understanding what your signal *should* look like, and not being able to compare it to what it actually looks like – so I'd recommend testing every step as mentioned, and discussing the first point where things don't look like they should, using drawings (! this is important: it's most often much easier to discuss a technical problem with a minimal drawing) and screenshots of your displayed signals.

Best regards,

Marcus

On 21.07.2016 21:15, Olivier Goyette wrote:

Hi all !

I've been working on this flowgraph for a while now and I've been able to pinpoint what is not working, but I don't understand how to resolve this so, that's why i'm asking for your guidance.

Take a look at the flowgraph i've joined. The thing that doesn't seem to be working on this setup is the samples/symbol in th CPFSK mod block.

When I set this parameter to 1 i'm able to retrieve my message at the file sink. So it tells me that what I did is okay in some way.

What is not working is when I set the same parameter to 6. At the beginning I wasn't using the rational resampler and it wasn't working. So I thought I would need something to "divide" the number of samples to retrieve each symbols. I tried it with the rational resampler block and set decimation to 6, but then, Daaaaaah......not working again.

There is something I can't work around here because I do not have sufficient knowledge about this samples/symbol thing.

I'd like to hear from you pals if you could give me a bit of information about how to make this work properly.

thank you !

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