• Support PF! Buy your school textbooks, materials and every day products Here!

Fourier transform power dependent on frequency

  • #1

Homework Statement


this is something i noticed doing homework rather than homework itself. I plot fft output from different frequency signals, i am not sure why power changes with increasing frequency?

Homework Equations



if i take (with matlab notation):

time = 0:0.01:10
y = fft(sin(2*pi*f*time))

with f = 5
then the maximum amplitude of the fft output is about 498.

with f = 10
the maximum amplitude of fft output is 492.

3. My attempt at a solution

I understand the amplitude is 'halved' in both cases because this fft is ambiguous so the energy is spread over two peaks. But why is the energy less when the frequency increases? I have more cycles in the case with more frequency, but I suppose this means I have less samples. Is it usual to normalise this in some way? It seems like this is something you wouldn't want if you were dealing were plotting energy return from doppler shifts.
 

Answers and Replies

  • #2
18,086
7,507
Thanks for the post! This is an automated courtesy bump. Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post?
 

Related Threads on Fourier transform power dependent on frequency

  • Last Post
Replies
4
Views
9K
  • Last Post
Replies
2
Views
4K
Replies
7
Views
1K
Replies
5
Views
778
Replies
2
Views
6K
Replies
0
Views
5K
  • Last Post
Replies
2
Views
527
  • Last Post
Replies
3
Views
1K
  • Last Post
Replies
1
Views
670
  • Last Post
Replies
5
Views
1K
Top