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[Discuss-gnuradio] Port flowgraph from Python to C++

From: Stefan Oltmanns
Subject: [Discuss-gnuradio] Port flowgraph from Python to C++
Date: Tue, 29 Jul 2014 23:53:49 +0200
User-agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:24.0) Gecko/20100101 Thunderbird/24.0

I was able to create a flowgraph in GRC to demodulate a signal
(low-frequency battery telegram of wireless microphones). Now I started
to port the generated code from Python to C++.
I had to realize that some blocks are Python-only, like the FM
Demodulator. I was able to rebuild the FM Demodulator in C++, for one
exception: The FM demodulator uses optfir, which is implemented in
Python, so it cannot be used in C++. So I replaced it with firdes (I
noticed the parameter difference in transition band end and transition
band width).
Another thing is that the Frequency-Xlating-Filter uses a complex
lowpass, but in C++ I could only find a complex band-pass, so I used a
band-pass with lower frequency 0, is that the same?

Also it works, the signal is a lot noisier and the result cannot be
decoded in many cases. I think the reason are the different filters.
Could that be the reason?
As I understood, both optfir and firdes create just a bunch of numbers
and that´s it. As my program is not going change the filter parameters
they could be hardcoded in my program, right?

Best regards

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