MATLAB: Plotting power Vs frequency graph

frequencyfrequency response matlab

Hi all,

I have loaded some data from the oscilloscope and I need to plot power vs frequency graph for my data. I usually use pwelch to plot the frequency response but it seems for this data it wont give me good frequency respose. anyone can help please.

Fs=10e9. L=1000000

Best Answer

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)')

Related Solutions

MATLAB: Ask help to do the fft on the ‘untreatable’ data

Try this:

D = load('data.txt');
t = D(:,1);
s = D(:,2);
L = numel(t);
Ts = mean(diff(t));
Fs = 1/Ts;
Fn = Fs/2;
FTs = fft(s-mean(s))/L;
Fv = linspace(0, 1, fix(L/2)+1)*Fn;
Iv = 1:numel(Fv);
[pks,locs] = findpeaks(abs(FTs(Iv))*2, 'MinPeakProminence',0.001);
figure
plot(t, s)
grid
xlabel('Time (s)')
ylabel('Amplitude')
title('Time Domain')
figure
plot(Fv, abs(FTs(Iv))*2)
hold on
plot(Fv(locs), abs(FTs(locs))*2, '^r', 'MarkerFaceColor','r')
hold off
grid
xlabel('Frequency (Hz)')
ylabel('Amplitude')
title('Frequency Domain')
xlim([0 1500])

Make necessary changes to get the result you want.

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: Ask help to do the fft on the ‘untreatable’ data

MATLAB: Single sided spectrum of vector y obtained using fft

Related Question