MATLAB: [Beginner] How to plot the resonance frequency with bandwidth

bandwidthcircuitscurrentelectricalfrequencygraphsplotresistance

Been looking for ages and struggling to find how to plot a bandwidth line onto a graph for an AC circuit. I've managed to gather the resonance frequency, bandwidth and current. How would I go about plotting these into the graph? Image shows what I'm looking for. Thanks in advance.

Best Answer

Try this:

f = linspace(0, 10);                                        % Create Data: Frequency
h = exp(-(f-5).^2);                                         % Create Data: Transfer Function
[hmax,idx] = max(h);                                        % Maximum
dB3 = hmax * 10^(-3/20);                                    % -3 dB Amplitude
f_lower3dB = interp1(h(1:idx), f(1:idx), dB3);              % Lower -3 dB Frequency
f_upper3dB = interp1(h(idx+1:end), f(idx+1:end), dB3);      % Upper -3 dB Frequency
figure(1)
plot(f, h, '-r')
hold on
plot(xlim, [1 1]*hmax, '-k')
plot(xlim, [1 1]*dB3, '-k')
plot([1 1]*f_lower3dB, [0 dB3], '-b')
plot([1 1]*f_upper3dB, [0 dB3], '-b')
plot([1 1]*f(idx), [0 hmax], ':b')
hold off
text(7, hmax, ' 0 dB', 'HorizontalAlignment','left', 'VerticalAlignment','bottom')
text(7, dB3, '-3 dB', 'HorizontalAlignment','left', 'VerticalAlignment','bottom')
text(f_lower3dB, 0.3, '\leftarrow', 'HorizontalAlignment','left', 'VerticalAlignment','middle')
text(f_upper3dB, 0.3, '\rightarrow', 'HorizontalAlignment','right', 'VerticalAlignment','middle')
text(5.2, 0.3, '\itB\rm', 'HorizontalAlignment','right', 'VerticalAlignment','middle')
axis([xlim    [0  1.1*hmax]])

Experiment to get the result you want.

Related Solutions

MATLAB: How to add a vertical line in a plot that corresponds to a maximum

Changing part of your code to draw the vertical lines, and the text label in figure(2):

%__________________________________________________Focus
idx =  F >= 0 & F <= 1000;         %Focusing 0-1000 Hz
zoomX = F(idx);
zoomY = phase1(idx);
subplot(2,1,2);
plot(zoomX, zoomY);
title('Amplitude Spectrum of Signal');
xlabel('Frequency (Hz)');
ylabel('Absolute Amplitude of Frequencies (dB)');
[pks1,locs1] = findpeaks(zoomY, 'MinPeakProminence',0.002, 'MinPeakDistance',100);      % Identify Prominent Peaks ...
hold on
ylv = ylim;
plot([1;1]*zoomX(locs1), ylv(:)*ones(size(pks1')))                                      % ... & Plot Vertical Lines Through Them
hold off
%________________________________________Fundamental Frequency
[maxValue, f1] = max(Y);
idx2 =  F >= 80 & F <= 120;        %Focusing 80-120 Hz  
zoomX2 = F(idx2);
zoomY2 = phase1(idx2);
figure;
plot(zoomX2, zoomY2);
title('Amplitude Spectrum of Signal');
xlabel('Frequency (Hz)');
ylabel('Absolute Amplitude of Frequencies (dB)');
[pks2,locs2] = max(zoomY2);                                                             % Identify Prominent Peak ...
hold on
plot([1;1]*zoomX2(locs2)', ylv(:)*ones(size(pks2')))                                    % ... & Plot Vertical Line Through It
text(zoomX2(locs2), pks2/2, sprintf('\\leftarrow %.1f Hz = Fundamental Frequency',zoomX2(locs2)), 'HorizontalAlignment','left')

I wasn’t certain if you also wanted the vertical lines in the lower subplot, so I used findpeaks to add them as well. The peak in figure(2) kist needs max, since ther is only one peak.

Experiment to get the result you want.

MATLAB: How to plot x-axis only

This comes close:

figure
xlim([-4.2 4.2])
plot((rand(1,20)-0.5)*3, zeros(1,20), '+r')
text(min(xlim), 0.025, '\leftarrow', 'HorizontalAlignment','left', 'VerticalAlignment','middle', 'FontSize',18)
text(max(xlim), 0.025, '\rightarrow', 'HorizontalAlignment','right', 'VerticalAlignment','middle', 'FontSize',18)
set(gca, 'XAxisLocation','origin', 'YColor','none')

Experiment to get the result you want.

Best Answer

Related Solutions

MATLAB: How to add a vertical line in a plot that corresponds to a maximum

MATLAB: How to plot x-axis only

Related Question