Re: [Discuss-gnuradio] RFNoc and data rates

[Marcus D. Leech]

On 09/23/2015 06:13 PM, Simon Olvhammar wrote:
> What would be a good choice for N in this case?
> However, this seems very promising and I thank you for your help!
>
> Cheers
> Simon
Whatever rate you're comfortable receiving integrated FFTs at. You'd 
adjust the 'alpha' value for the IIR filter and N appropriately.

Let's say you're running the FFT input at full bandwidth--200Msps, and 
you have an FFT size of 2048.  That's 97.7e3 FFTs/second
  being produced in the FFT machinery in RFNoC, including the 
complex-to-mag part.  Run that through a single-pole-IIR filter with
  an alpha value of, let's say, 0.01 (or the integer/fixed-point 
equivalent).  Then set your 'N' in keep-one-in-N to be about 100. You'll get
  roughly 97.7e1 FFTs/second into your host instead of 97.7e3 
FFTs/second.  At those low rates, even a purely-Python-based secondary
  long-term integrator should be able to keep up just fine.


> On 09/23/2015 11:40 PM, Marcus D. Leech wrote:
> > On 09/23/2015 04:19 PM, Simon Olvhammar wrote:
> > > Hi Marcus,
> > > No, we also have some spectrometers for atmospheric measurements.
> > >
> > > Regarding the keep 1 in N. It occurs to me then that by using this I 
> > > would loose (N-1)/N percent of the FFT data for a given amount of 
> > > observation time? Or am I missing something?
> > > Simon
> > Since you're integrating prior to decimation here, there should be no 
> > loss of information.
> >
> >
> > > Den 2015-09-23 kl. 21:40, skrev Marcus D. Leech:
> > > > On 09/23/2015 03:06 PM, Marcus D. Leech wrote:
> > > > > On 09/23/2015 02:49 PM, Simon Olvhammar wrote:
> > > > > > Hello,
> > > > > > Thank you for your answers.
> > > > > > Yes we do alot of averaging to expose the signal, in some 
> > > > > > applications we even average over several months.
> > > > Are these astronomical spectral features?   They usually aren't 
> > > > that wide, even with doppler spreading.
> > > >
> > > >
> > > >
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