# Plot the magnitude and phase by using Matlab

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Muhammad Rifqi Jafri Zain on 24 Jul 2021
Commented: Yazan on 24 Jul 2021 Yazan on 24 Jul 2021
Here is one way to get the spectrum.
clc, clear
% fundamental frequencies
f1 = 1/3;
f2 = 5/6;
% sampling frequency
fs = 50*max([f1, f2]);
% sampling period
Ts = 1/fs;
% Time span (5 periods)
T = 5*max([1/f1, 1/f2]);
% time axis
t = 0:Ts:T-Ts;
% frequency axis
f = -fs/2:fs/length(t):fs/2-fs/length(t);
% signal
x = 2 + cos(2*pi*f1*t) + 4*sin(2*pi*f2*t);
% fft
X = fftshift(fft(x));
% figure
fig = figure('Units', 'normalized', 'Position', [0.15 0.35 0.75 0.55]);
% plot signal in time
subplot(1, 3, 1), plot(t, x),
xlabel('Time (sec)'); ylabel('Amplitude');
title('Signal'); grid 'minor';
% plot fft magnitude
subplot(1, 3, 2), plot(f, abs(X)),
xlabel('Frequency (Hz)'), ylabel('Magnitude'),
title('Spectrum, magnitude'); grid 'minor';
% plot fft phase
subplot(1, 3, 3), plot(f, unwrap(angle(X))),
xlabel('Frequency (Hz)'); ylabel('Phase');
grid 'minor';
title('Spectrum, unwrapped phase'); ##### 2 CommentsShowHide 1 older comment
Yazan on 24 Jul 2021
The code is commented almost completely so that you can modify it easily. Just remove the first subplot! Any basic user should be able to do so.