Re: [Discuss-gnuradio] Channelizing

[Colby Boyer]

On Thu, Jun 23, 2011 at 8:32 PM, Marcus D. Leech <address@hidden> wrote:

I'm working on a multi-channel radiometer, based on USRP2 with the
dual-DDC feature.

I'm trying to come up with channelizing structure that won't overwhelm
my CPU--I'm using
 a 6-core Phenom II 1055T, with 4GB of 1333MHz memory.

I need to be able to carve-off 4 channels, with widths between 100KHz
and 500Khz, anywhere within
 25MHz of the center frequency.

I've tried a single 25MHz input channel, then carving it up with 4 FIR
filters.  That produces massive
 'O', no matter how sloppy I make the channel filters.

I've tried a pair of 12.5MHz channels (using the dual-DDC feature that's
relatively new). That produces
 massive 'O'.

Since ultimately, I'm mostly interesting in channel power estimates, I
might just FFT it, and pick off
 the bin(s) that correspond to my channels.

Is one or two polyphase filter banks going to be cheaper?  And how do I
compute the taps?  There
 doesn't appear to be a helper function for that in GRC :-(


--
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org



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Hi Marcus,

Check out a pfb channelizer! 

gnuradio-core/src/python/gnuradio/blks2impl/pfb_channelizer.py is a nice python wrapper for the class and gr_pfb_channelizer_ccf is the C++ name.

Also if you need to carve out a a shifted part of the spectrum, use the gr_freq_xlating_fir_filter_*** block.

These are polyphase implementations so they should be computationally efficient. Lastly, if you need even more efficiency you can see if they are doing the fft implementation of filtering (not sure if they are vs standard computation). As you know, there is the difference between NlogN and N^2

--Colby