MATLAB: Can anyone explain how the phase angle should look like for a square pulse with pulse width 1 that has undergone FFT in matlab

signals

What I have so far is the first attachment, after the frequency limit adjustment, I have the second attachment. I do not understand how the phase angle compares to the theoretical phase angle of the DFT. PLEASE HELP!

Best Answer

The phase of a symmetric square pulse is uniformly zero, because the Fourier transform is purely real:

syms w t 
FTpulse = int(1*exp(1j*w*t), t, -0.5, 0.5)
FTpulse =
(2*sin(w/2))/w

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MATLAB: How to make real and imaginary plot of the graph same color

Hi,

a fast and easy solution could be generate a triplette of RGB values randomly at each iteration and you use it as color for both plots, as you can see in the following code:

    RGB = rand(3,1);
    semilogx(imag(e),'--','Color',RGB)
    set(gca,'FontSize',20);
    set(gca,'Color','k');
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    xlabel('Frequency (Hz)','Fontsize', 40) ;
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    hold on
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I have defined RGB vector that I use as color property for both plots. In this way both plots have the same color.

An alternative you could define a matrix of RGB values in order to control which color you want at each iteration for both plots.

Hope this helps.

MATLAB: Taking DFT of Swept Sine Wave

Please do not use the acronym 'DFT' when you are using the 'FFT'

 close all,clear all, clc, plt = 0;  
    N = 48
    T = 3*pi
    dt = T/N
    t = dt*(0:N-1);
    Fs = 1/dt
    df = Fs/N
    f = df*(0:N-1);
    A =4
    y = A * sin(f .* t);
    plt=plt+1,figure(plt)
    hold on
    plot( t, y, 'LineWidth', 2)
    plot( t, zeros(1,N), 'k--',  'LineWidth', 2 )
    xlabel('Time (seconds)')
    ylabel('y(t)')
    title( 'SWEPT FREQUENCY TIME SIGNAL' )
    Y = fftshift(fft(y))/N;
    fb = f-Fs/2;
    realY = real(Y);
    imagY = imag(Y);
    absY = abs(Y);
    phaseY = angle(Y);
    plt=plt+1,figure(plt)
    subplot(2,2,1)
    hold on
    plot( fb, realY,  'LineWidth', 2 )
    plot( fb, zeros(1,N), 'k--', 'LineWidth', 2 )
    xlim( [ -Fs/2 Fs/2 ] )
    ylabel( ' REAL(Y) ' )
    title([ blanks(85) , ' SPECTRUM OF SWEPT FREQUENCY SIGNAL ' ] )
    subplot(2,2,2)
    hold on
    plot( fb, imagY,  'LineWidth', 2 )
    plot( fb, zeros(1,N), 'k--',  'LineWidth', 2 )
    xlim( [ -Fs/2 Fs/2 ] )
    ylabel( ' IMAG(Y) ' )
    subplot(2,2,3)
    hold on
    plot( fb, absY,  'LineWidth', 2)
    xlim( [ -Fs/2 Fs/2 ] )
    ylabel( ' AMPLITUDE(Y) ' )
    xlabel( ' FREQUENCY(HZ)  ' ) ; 
    subplot(2,2,4)
    hold on
    plot(fb,phaseY, 'LineWidth', 2)
    plot( fb, zeros(1,N), 'k--', 'LineWidth', 2 )
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Hope this helps.

Thank you for formally accepting my answer.

Greg

Best Answer

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