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function specan(filename)
% Spectrum analyser
%
% Analyse and plot the frequency spectrum of a waveform
% given by a tab-separated value (TSV) file.
%
% The following column headers for the TSV are assumed:
% time, v1, v2, v3, i1, i2, i3
%
% Time measurements are assumed to be in milliseconds.
% All voltages and currents are assumed to be given
% in Volts and Amperes, respectively.
data = readtable(filename, FileType="text", Delimiter="\t");
L = length(data.time);
% Assumes data is sampled at regular intervals.
T = 1e-3*(data.time(end)-data.time(1))/(L-1);
fs = 1/T;
% Frequency axis for plotting.
f = fs/L*(0:L-1);
Y1 = abs(fft(data.v1)/L);
Y2 = abs(fft(data.v2)/L);
Y3 = abs(fft(data.v3)/L);
Y4 = abs(fft(data.i1)/L);
Y5 = abs(fft(data.i2)/L);
Y6 = abs(fft(data.i3)/L);
figure(1);
subplot(2, 1, 1);
hold on;
plot(f, Y1, "r", LineWidth=2);
plot(f, Y2, "g", LineWidth=2);
plot(f, Y3, "b", LineWidth=2);
title("Frequency Spectrum of Voltage Measurements");
xlim([0 1e3]);
xlabel("Frequency, $f$ (Hz)", Interpreter="latex");
ylabel("$\left|\mathcal{F}(V)\right|$ (V)", Interpreter="latex");
legend("V_1", "V_2", "V_3");
subplot(2, 1, 2);
hold on;
plot(f, Y4, "r", LineWidth=2);
plot(f, Y5, "g", LineWidth=2);
plot(f, Y6, "b", LineWidth=2);
title("Frequency Spectrum of Current Measurements");
xlim([0 1e3]);
xlabel("Frequency, $f$ (Hz)", Interpreter="latex");
ylabel("$\left|\mathcal{F}(I)\right|$ (A)", Interpreter="latex");
legend("I_1", "I_2", "I_3");
end
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