trying to take FFT of a signal but not getting the correct result

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zeshan chishti 2021-2-9

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https://ww2.mathworks.cn/matlabcentral/answers/740727-trying-to-take-fft-of-a-signal-but-not-getting-the-correct-result

评论： Star Strider 2021-2-10

采纳的回答： Star Strider

t1=load('201710h1.lvm'); %test 1

t2=load('201710h2.lvm'); %test 2

Fs = 100000; % frequency sample

x = t1 (:,1); % time for test 1

sin = t1 (:,2); % test 1 sesnor 1

plot(sin)

title('Sensor1')

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KALYAN ACHARJYA 2021-2-9

Have you checked here?

https://in.mathworks.com/help/matlab/ref/fft.html

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采纳的回答

Star Strider 2021-2-9

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Perhaps calling the fft function would get you closer.

Example —

t{1}=load('201710h1.lvm');  %test 1 
t{2}=load('201710h2.lvm');  %test 2
Fs = 100000; % frequency sample
for k = 1:numel(t)
    L = numel(t{k});
    Ts = 1/Fs;
    Fn = Fs/2;
    tv = linspace(0, L, L)*Ts;
    FTt = fft(t{k})/L;
    Fv = linspace(0, 1, fix(L/2)+1)*Fn;
    Iv = 1:numel(Fv);
    
    figure
    plot(tv, t{k})
    grid
    xlabel('Time (sec)')
    ylabel('Signal (Units)')
    title(sprintf('t_{%d} Time Domain',k))
    
    figure
    plot(Fv, abs(FTt(Iv))*2)
    grid
    xlabel('Frequency (Hz)')
    ylabel('Amplitude (Units)')
    title(sprintf('t_{%d} Frequency Domain',k))
end

Note that I loaded your signals into cell arrays to make the analysis easier.

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zeshan chishti 2021-2-10

Thank you i appreicte your help with this code it dose not recgnoise t1 as a variable. will have to change it around for it to work.

Star Strider 2021-2-10

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As always, my pleasure!

Change the first two lines back to:

t1 = load('201710h1.lvm');  %test 1 
t2 = load('201710h2.lvm');  %test 2

and the rest should work. (I changed my code to match your updated code, and forgot to change the ‘t1’ and ‘t2’ variables back to what they were originally.)

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