[Beginner] How to plot the resonance frequency with bandwidth

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.

Answer 1

[Star Strider]

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.

[Ben Cartwright]

Perfect, works a charm. Thanks very much!

[Star Strider]

As always, my pleasure!

[Simon Robinson]

Will be interesting to see how your's has worked Ben. I'm doing very much the same but can not convert this to my script using my data for Fr, Fh, Fl and I. Do not share until after hand in though :)