How to see a part of my FFT plot in magnified size in other window?

I have drawn a FFT plot for my data and now I want to show a particular part of my plot in zoom. How to do it , Please guide me?

Answer 1

[Wayne King]

You can simply use

>>zoom on

Or you can set your xlim and/or ylim properties appropriately:

Fs = 1000;
t = 0:1/Fs:1;
x = cos(2*pi*100*t)+randn(size(t));
xdft = fft(x);
plot(abs(xdft))
% now do the following
set(gca,'xlim',[0 200])

You can do the same for the 'ylim' as well if you like.

Or finally, you can just plot the relative portion of the output of fft() to begin with:

plot(abs(xdft(1:201)))

[Deepika]

Sorry Mr. Wayne King. But this is not what I want. I have to mark an area of the plot and den show it into some window. I am attaching a plot here. You may then understand my need. Kindly help me out.

Answer 2

[Wayne King]

You can do something like that with subplot

Fs = 1000;
t = 0:1/Fs:1-1/Fs;
x = cos(2*pi*100*t)+randn(size(t));
xdft = fft(x);
xdft = xdft(1:length(x)/2+1);
df = Fs/length(x);
freqvec = 0:df:Fs/2;
subplot(211)
plot(freqvec,abs(xdft)); xlabel('Hz');
subplot(212)
plot(freqvec(1:201),abs(xdft(1:201)));
xlabel('Hz');

Why do you need to have that callout graphic like you show in your document. You can do that, but it is much more complicated and what purpose does it serve?

[Deepika]

Mr. Wayne King, Thanks for the reply. But the method you suggested is not needed. I show you the way I want the plot in attached document. So, please help me out. I have a plot which shows disturbed harmonics and I have to it sinusoidal nature so I need the zoomed portion of a particular part of a plot to prove it.