Re: [Discuss-gnuradio] FFT block's use of sampling rate

[Marcus D. Leech]

On 04/18/2010 05:16 PM, David Barton wrote:

Hi,

In GRC I hooked up a signal source with a 100kHz sampling rate directly to a FFT sink. I accidentally listed the FFT sampling frequency as 200kHz. I noticed that it did not complain and all it did was shift the actual signal source frequency by a factor of 2. So my guess would be that the FFT block is not actually using the sampling rate parameter in the FFT calculations except to just scale the frequency axis. Is that accurate?

Thanks,
Dave

To a first approximation, yes.

The other thing I think the FFT graphical sink uses the sample rate for is to calculate the
  required "keep-one-in-N" for maintaining the desired screen update rate.

But the FFT itself onlys knows about a vector of samples, what they mean, in a temporal sense
  is rather outside the scope of the FFT calculation.

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