How to find the FFT of a variable frequency sinusoidal signal in Simulink

I generated a sinusoidal signal with 3 frequencies (5, 10, 15 Hz) using the following method:

I tried to find the FFT of this signal with:

but the spectrum was nothing like what it's supposed to be, so what is the correct the way to find it (is the generating method correct or is there a better way)?

Thanks.

[Mathieu NOE]

hello

I suspect your issues are because you forgot the fftshift block

see doc / example here

Transform Time-Domain Data into Frequency Domain - MATLAB & Simulink - MathWorks France

[Haider]

I tried using the fftshift, and I also replaced the clock with digital clock, but the results weren't better.

[Mathieu NOE]

I haven't used this demo example, but it's purpose is to do a single fft computation for a fixed frequency signal

I suppose that you want to create multiple fft spectra for a variable frequency signal (as you would do to plot a spectrogram), so you have to change a bit the logic