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Re: [Discuss-gnuradio] Half band decimator/interpolator

From: CEL
Subject: Re: [Discuss-gnuradio] Half band decimator/interpolator
Date: Tue, 23 Apr 2019 16:24:09 +0000

Hi Albin,

I'm very very tired right now, but me and Felix came to the following
conclusions on our *Whiteboard Of Wisdom, Smarts, Expertise,
Rationality and Science* (WOWSERS):

1. A Nyquist-M bandpass filter, esp. a halfband, has zeros on every
other tap – except for the one center tap, which is at the maximum of
the sinc that you window your prototype filter with. 
2. you'd thus implement that filter as polyphase filter with two
different polyphase components:
  1. one polyphase component that contains all the zeros, and the
     single center tap that's not
  2. one component that contains all the non-zero taps
3. you'd thus need to "deinterleave" your input stream into two:
  1. Delay by half the number of taps (and multiply by the maximum
  2. filter with all the non-zero taps
4. sum up the results

So, for all this, we already have blocks – yay!

Best regards,

On Tue, 2019-04-23 at 17:45 +0200, Albin Stigö wrote:
> Just checking before I write one, is there a half band decimator/interpolator 
> in gnuradio I haven't been able to find...
> Optimized like this:
> http://liquidsdr.org/doc/resamp2/
> Or is there an even better option for interpolation by 2?
> --Albin
> _______________________________________________
> Discuss-gnuradio mailing list
> address@hidden
> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio

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