MATLAB: Plotting frequency response of data in matlab

frequencyfrequency responseplottingtime

Hi all,

I am trying to plot frequency response for the attached data. I can plot its time domain, However I am not able to plot the frequency response. Can anyone help please.

Regards

Shirin

Best Answer

There is only one column of data, that I assume are the independent variable. You cannot plot its frequency response without an associated time vector (vector of sampling instants). This is important with respect to knowing if the sampling intervals are constant (they can be resampled to constnt samplilng intervals if not), since that is required for all signal processing applications, including the Fourier transform. The time vector is required in order to calculate the frequency vector (independent variable) in the fft plot.

Related Solutions

MATLAB: Plotting power Vs frequency graph

I am not certain what the probme is with pwelch. It appears to give the correct result when I plot it.

Alternatively, try this:

s = readmatrix('Sumof3MIMOsDATASET1afterDACFs10G200K512eros.csv');
Fs=10e9;
L=numel(s);
t = linspace(0, L, L)/Fs;
Ts = 1/Fs;
Fn = Fs/2;
t = linspace(0, L, L)*Ts;
ms = mean(s);
FTs = fft(s)/L;
Fv = linspace(0, 1, fix(L/2)+1)*Fn;
Iv = 1:numel(Fv);
figure
plot(t, s)
grid
xlabel('Time (s)')
ylabel('Amplitude (Units)')
figure
semilogy(Fv, abs(FTs(Iv))*2)
grid
xlabel('Frequency (Hz)')
ylabel('Amplitude (Units)')
figure
plot(Fv, mag2db(abs(FTs(Iv))*2))
grid
xlabel('Frequency (Hz)')
ylabel('Power (Units^2)')

MATLAB: Single sided spectrum of vector y obtained using fft

The way I usually calculate and plot it:

t = linspace(0, 1, 1E+4);
s = sum(sin([0; 100; 200; 300]*2*pi*t*10)) .* randn*10;
Ts = mean(diff(t));                                         % Sampling Interval
Fs = 1/Ts;                                                  % Sampling Frequency
Fn = Fs/2;                                                  % Nyquist Frequency
L1 = numel(t);
FTs1 = fft(s)/L1;                                           % FFT Of Original Signal
Fv1 = linspace(0, 1, fix(L1/2)+1)*Fn;                       % Frequency Vector

Iv1 = 1:numel(Fv1);                                         % Index Vector

L2 = 2^nextpow2(L1);
FTs2 = fft(s,L2)/L1;                                        % FFT Of Zero-Padded Signal
Fv2 = linspace(0, 1, fix(L2/2)+1)*Fn;                       % Frequency Vector
Iv2 = 1:numel(Fv2);                                         % Index Vector
figure
subplot(2,1,1)
plot(Fv1, abs(FTs1(Iv1))*2)
title('FFT of Original Signal')
xlabel('Frequency (Hz)')
ylabel('Amplitude')
grid
subplot(2,1,2)
plot(Fv2, abs(FTs2(Iv2))*2)
title('FFT of Zero-Padded Signal')
xlabel('Frequency (Hz)')
ylabel('Amplitude')
grid

This also demonstrates a way to increase the frequency resolution of the fft result by zero-padding it.

Best Answer

Related Solutions

MATLAB: Plotting power Vs frequency graph

MATLAB: Single sided spectrum of vector y obtained using fft

Related Question