FFT Frequency Range

Started by bashir siddiqui August 30, 2011
Hi,

I have one very simple question. I hope some one will clearify my doubts.

The range of frequencies covered in the output record from the FFT is 0 to
1/2 the sample rate of the acquired data record. For example, a sample rate
of 20 MS/s (megasamples per second) would give an FFT range of 0 to 10 MHz.

Does it mean I can only see the proper FFT peak of the signal with maximum
frequency 5 MHz ?

I appreciate your help.

-Tariq
Hi bashir,
Yes, if you are referring to an un-aliased signal, then 5MHz will be the
highest frequency at which the amplitude and phase can be properly computed.

If you consider undersampling, a phenomena where aliasing is
intentionally used, then the answer becomes much more complicated. See
here: http://en.wikipedia.org/wiki/Undersampling
-Brant

On Thu, Aug 11, 2011 at 3:14 AM, bashir siddiqui
wrote:

> **
> Hi,
>
> I have one very simple question. I hope some one will clearify my doubts.
>
> The range of frequencies covered in the output record from the FFT is 0 to
> 1/2 the sample rate of the acquired data record. For example, a sample rate
> of 20 MS/s (megasamples per second) would give an FFT range of 0 to 10 MHz.
>
> Does it mean I can only see the proper FFT peak of the signal with maximum
> frequency 5 MHz ?
>
> I appreciate your help.
>
> -Tariq
>
>

--
Brant Jameson
PhD Candidate
UC Santa Cruz Computer Engineering
http://people.ucsc.edu/~pheese