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

# FFT Frequency Range

Started by ●August 30, 2011

Reply by ●September 2, 20112011-09-02

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

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