# Tie to frequency using F

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Karl Zammit on 17 May 2021
Commented: Karl Zammit on 17 May 2021
Hi, I am trying to perform a fft on a series of runs of a vibration analysis with the following code. An empty plot seems to show up, any ideas?
%Frequency Analysis
time = xlsread('Lab-2ciii.xlsx','A1:A300');; % Time Vector
signal = xlsread('Lab-2ciii.xlsx','B1:B300');; % Signal data in Time-Domain
N = length(signal); % Number Of Samples
Ts = mean(diff(time)); % Sampling Interval
Fs = 1/Ts; % Sampling Frequency
Fn = Fs/2; % Nyquist Frequency
FT_Signal = fft(signal)/N; % Normalized Fourier Transform Of Data
Fv = linspace(0, 1, fix(N/2)+1)*Fn; % Frequency Vector (For ‘plot’ Call)
Iv = 1:length(Fv); % Index Vector (Matches ‘Fv’)
figure(1)
plot(Fv, abs(FT_Signal(Iv))*2)
grid

Geoff Hayes on 17 May 2021
Karl - are you reading the correct columns? For example, on my Mac, the time array
is empty, and the signal array
has just a handful of elements
signal =
0.0807
68.4870
0.0002
-0.1851
NaN
68.2636
0.0027
-0.0607
Both correspond to the first and second columns of your spreadsheet. I suspect you want columns E (which seems to correspond to time) and either H, K, or N...all of which have 300 elements.
Karl Zammit on 17 May 2021
My bad for not commenting that the problem was solved. Thanks a lot nonetheless