Try this —
T1 = readtable('https://www.mathworks.com/matlabcentral/answers/uploaded_files/994895/fantest.xlsx%20-%20Sheet2.xlsx', 'VariableNamingRule','preserve')
VN = T1.Properties.VariableNames
L = size(T1,1);
% QQ1 = nnz(diff(T1{:,1}) ~= 1)
Ts = T1.hours(2) - T1.hours(1); % Sampling Interval
Fs = 1/Ts; % Sampling Frequency
Fn = Fs/2; % Nyquist Frequency
NFFT = 2^nextpow2(L); % For Efficiency
FT_T1 = fft(T1{:,2:end} - mean(T1{:,2:end}), NFFT)/L; % Fourier Transform (Mean Subtracted To Show Other Peaks More Clearly)
Fv = linspace(0, 1, NFFT/2+1)*Fn; % Frequency Vector
Iv = 1:numel(Fv); % Index Vector
figure
plot(Fv, abs(FT_T1(Iv,:))*2)
grid
xlabel('Frequency (hr^{-1})')
ylabel('Amplitude')
legend(VN{2:end}, 'Location','best')
NrSp = size(FT_T1,2);
figure
for k = 1:NrSp
subplot(NrSp,1,k)
plot(Fv, abs(FT_T1(Iv,k))*2)
grid
ylabel('Amplitude')
title(VN(k+1))
end
xlabel('Frequency (hr^{-1})')
.
