# Frequency domain and Shannon limit

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long le on 12 Oct 2020
Answered: Robert U on 12 Oct 2020
Hi all,
I am a newbie in MATLAB coding. I have some questions related to frequency domain.
I have an sine wave equation as below:
x1= A1*sin(2*pi*f1*t+phi)
With A1 = 1; phi = pi/2
My question is.
How to represent x1 in frequency domain for different values of f1 and different value of fs (how to make sure Shannon limit is repected in this case).
Thank you all.

Robert U on 12 Oct 2020
Hi long le,
Matlab documentation is quite nice since it provides several examples on key topics. One possibility to transform time dependent signal into frequency domain is the fast fourier transform (short: fft). Matlab has an inbuilt function for that. How to use it is described in the documentation: https://de.mathworks.com/help/matlab/ref/fft.html
Whether the Shannon-limit is respected or not, you can question using an if-statement before the domain transformation (https://de.mathworks.com/help/matlab/ref/if.html)
Kind regards,
Robert