How to plot Fourier transform of the signal from a text file (*.txt) ?

Hello all, I want to plot the fourier transform of the signal data content from my Text file. I want to see how the frequency content look like. Can someone help me for this problem ? Thank you very much.

Sampling rate: 30 second ( after 30 second, the system will update the new data samples)

I attached the DATA.txt file and here is the content:

4/14/2021 3:46:24 PM 64131.513381 5823.895335 7017.153421 6695.069373 7413.178682 6956.152618 5334.056631 6891.041994

4/14/2021 3:46:54 PM 15529.222786 13262.592256 15858.717263 14706.268907 15880.517662 14049.395919 10740.444064 13349.786401

4/14/2021 3:47:24 PM 9038.478136 8078.046143 8044.146001 8139.73422 8534.342051 8134.812117 7425.203919 7708.273828

4/14/2021 3:47:55 PM 54023.002964 5627.088249 4928.067327 5023.099482 5247.063935 5547.463894 5676.805973 5406.416953

4/14/2021 3:48:25 PM 3981.173038 4461.616278 3718.629479 3848.016262 3935.739398 4449.620843 4675.038159 4347.358983

4/14/2021 3:48:55 PM 222.834491 258.781016 241.129270 247.694552 234.340470 253.140926 241.834396 244.542956

4/14/2021 3:49:25 PM 262.118876 274.784863 249.400735 248.014927 257.641077 275.291502 259.727240 273.302197

4/14/2021 3:49:55 PM 262.692571 275.559723 248.383456 247.783959 257.559121 276.73419 260.770321 274.509192

4/14/2021 3:50:25 PM 232.912600 239.737332 224.359334 225.216150 237.390399 237.007778 230.602920 240.758061

4/14/2021 3:50:55 PM 106.386840 143.93250 128.857791 131.532550 123.547695 183.440745 119.321048 113.576651

4/14/2021 3:51:25 PM 233.294747 337.659466 257.007778 255.376101 552.373423 279.303465 268.600881 241.263624

[Walter Roberson]

How are we to interpret the data? You have 8 numeric values per line: is that 8 different signals, one per column? The rows are 30 seconds apart: is the implication that the columns are the same signal sampled at 8/30 = 0.26 Hz ?

[Dung Tran]

Yes, there is 8 different chanels, so we have 8 different signal, one per column.

About the sampling rate, we have 8 samples of signal in 1 row, each sample will be update in every 30 second.

so basicly the sampling rate ( samples per second) will be 8 / 30 = 0.26 Hz.

[Walter Roberson]

If the different columns correspond to different channels, then each signal updates every 30 seconds, so the frequency of each signal would be 1/30 Hz.

Answer 1

[Walter Roberson]

filename = 'https://www.mathworks.com/matlabcentral/answers/uploaded_files/614995/DATA.txt';
data = readtable(filename, 'readvariablename', false);
x = data{:,2:end};
f = fft(x - mean(x,1));
h = plot(abs(x));
size(h)

ans = 1×2

8 1

set(h, {'Marker'}, {'+', 'o', '*', '.', 'x', 'v', '^', '<'}.')
legend show