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Re: [Discuss-gnuradio] resampler block (DRM ok!)

From: Eric Blossom
Subject: Re: [Discuss-gnuradio] resampler block (DRM ok!)
Date: Sat, 8 Oct 2005 18:59:15 -0700
User-agent: Mutt/1.5.6i

On Fri, Oct 07, 2005 at 11:44:27PM +0200, Stephane Fillod wrote:
> > > In the case of the 512kS/s to 48kS/s ddc, would the gr_rational_resampler
> > > be able to replace gr_freq_xlating_fir_filter ?
> Ok no.
> IOW, the gr_rational_resampler does not do frequency translation,
> and the USRP cannot decimate above 256. I used a decim rate
> below 128 because I heard there's gain problems above.

Yes.  If you need more decimation, just use gr.fir_filter_xxx.  
The first argument is the decimation factor.

> So it looks like freq_xlating_fir_filter_ccf must be used.

No, only if you want to decimate AND frequency translate.  If you just
want to decimate, use gr.fir_filter_xxx.  If you just want to
frequency translate, use a complex sinusoid LO and gr.multiply_cc.  
If you want both, use freq_xlating_fir_filter_ccf.

> This is still ok, the whole ddc python script takes less than 
> 9% on a 1GHz AMD CPU. Still, I wished it would be less, because 
> I hope to eventually have several of them running in parallel,
> plus a point and click waterfall, and some demodulating clients
> around.

> Patchs available on demand, comments welcome!

Cool stuff.  Looking forward to getting a chance to play with all of it.


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