Forum: GNU Radio Analysis_filterbank

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Sebastiaan H. (Guest)
on 2009-01-13 10:23
(Received via mailing list)

I managed to figure the connect mistakes that I made out.  Now there's
something different that's not working.  From what I understand about
the analysis_filterbank, it works as follows (in my case).

You send it a signal with a bandwidth of 4MHz.
You have a lowpass filter with fc = 70kHz and fs = 100kHz.
You tell it that you have 20 channels.

The result should be that you have 20 outputs corresponding to the
lowpass filtered signals at frequencies of
-2MHz,-1.8MHz,..,-200kHz,0,200kHz,...,1.8MHz (the order would just be
a bit mixed up because of the FFT).

The problem is that I tested this block by opening a file in Gnuradio
with a signal with a BW of 4MHz with carriers that are 200kHz apart.
Each carrier has a different bandwidth.  When I look at different
analysis_filterbank output, I should see each carrier in turn.

I only get a sensible output at channel 20 (output 19 of the
filterbank).  The rest don't make sense.

I'm thinking about writing my own block for this.  I already have
normal C++ and Matlab code that works.  Can someone please point me to
some examples that might be helpful?

What I need is a big polyphase filter and an FFT.  The input of the
block should be a single complex stream running at a high rate.  The
output should then be up to M channels each running at f_input/M.  I'm
struggling to find a nice example on how filter channel memory and the
variable number of outputs work.

Thank you.

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