I am given a task to do sampling on the function
$$f(t) = 1.3 \sin(2\pi \cdot 10 \cdot t)$$
with sampling frequency 4 Hz and start at time
t_start = 0.0877s, so there should be aliasing and in the frequency spectrum, the amplitude should be at the perceived frequency.
The perceived frequency is 2 Hz as the folding frequency.
I chose to take $N=128$ data points.
Then after completing FFT with sampled $f(t)$, I wanted to plot frequency spectrum, however I have a peak of 1.815 at 2 Hz, however the height of peak should be around 1.3. Here I attached this spectrum.
Is there any explanation to this? Usually due to the leakage, the peak should be less than the actual amplitude, however I got higher peak. It seems quite strange for me.
Here is also a Matlab code, if you find it more convenient to check.
t = 0.0877:0.25:32.087; signal = 1.3.*sin(2.*pi.*10.*t); y = fft(signal); %65th data point corresponds to fft at 2 Hz abs(y(65))/(numel(t)/2)
Thank you in advance.