Aliasing (Fourier Transform)

  • #1
Hi. I have been given a plot for 1 Hz, sampled at 0.2 sec. And, 4 Hz and 11 Hz has also been plotted. So, from the plot, I can see that its really hard to distinguish between the signals after digitalization. My question is how do I find the next higher frequency which, when sampled at 0.2 secs, will look like a 1 Hz wave ?
 

Answers and Replies

  • #2
Low-Q
Gold Member
284
8
Hi. I have been given a plot for 1 Hz, sampled at 0.2 sec. And, 4 Hz and 11 Hz has also been plotted. So, from the plot, I can see that its really hard to distinguish between the signals after digitalization. My question is how do I find the next higher frequency which, when sampled at 0.2 secs, will look like a 1 Hz wave ?
Do you mean 0.2s duration of sampling (with a given sampling frequency), or do you mean one sample every 0.2s (5Hz sampling frequency)?

Vidar
 
  • #3
I mean one sample every 0.2 seconds
 
  • #4
Low-Q
Gold Member
284
8
I mean one sample every 0.2 seconds

In general you need at least two samples per cycle. You have a sampling frequency of 5Hz. Sampling 1Hz with this is not a problem - however very coarse plot. Using the same sampling frequency when you have 4 and 11Hz input would not provide any results at all.
According to Nyquist theorem, the minimum sampling frequency is twice the frequency you are trying to sample. Below you see a link to a PDF explaining this.

http://redwood.berkeley.edu/bruno/npb261/aliasing.pdf


Vidar
 

Related Threads on Aliasing (Fourier Transform)

  • Last Post
Replies
4
Views
9K
Replies
6
Views
1K
  • Last Post
Replies
3
Views
3K
  • Last Post
Replies
5
Views
8K
Replies
7
Views
12K
Replies
4
Views
8K
  • Last Post
Replies
1
Views
3K
Top