how to find FFT for pure sine wave in simulink?

i would like to find FFT for pure sine wave in simulink without using FFT spectrum, is it possible?

Answer 1

[Hari]

Hi Swarnalakshmi,

I understand that you want to compute the Fast Fourier Transform (FFT) of a pure sine wave in Simulink without using the “FFT Spectrum” block.

In order to find the FFT for a pure sine wave in Simulink without using the “FFT Spectrum” block, you can follow the below steps:

Generate the Sine Wave:

Use the “Sine Wave” block in Simulink to create a pure sine wave signal. Configure the frequency, amplitude, and sample time according to your requirements.

Buffer the Signal:

Use the “Buffer” block to collect a sequence of samples over a specified frame size. This is necessary because FFT operates on a block of data rather than a continuous stream.

Implement FFT Logic:

Use the “MATLAB Function” block to write a custom function that takes the buffered data as input and computes the FFT using MATLAB’s “fft” function.

function Y = computeFFT(u)
Y = fft(u); % Compute FFT
end

Calculate Magnitude:

Use the “Abs” block to calculate the magnitude of the FFT output. This gives the amplitude spectrum of the signal.

Visualize the Spectrum:

Use the “Scope” block to visualize the amplitude spectrum. Ensure the x-axis represents frequency by configuring the simulation parameters appropriately.

Refer to the documentation of “fft” function to know more about its usage:

• https://www.mathworks.com/help/matlab/ref/fft.html

Hope this helps!