To find the frequency components in the data and make a frequency plot

I have a data which is a frequency modulated signal. I want to make a matlab code to find the frequency components in it using Fourier transform method and make a frequency plot? I tried fft(data(:,2)) but most of the time it is giving me wrong answers. I am attaching the data. The first column is time and the second column is the signal.

Answer 1

[Birdman]

Use the attached file with the following code:

filename='Test_Sample_edited.txt';
A=load(filename);
time=A(:,1);
signal=A(:,2);
h1=spectrum.welch;
set(h1,'Windowname','Hann');
Fs=1000;
set(h1,'OverlapPercent',66.7);
set(h1,'SegmentLength',2048);
myPsd=psd(h1,A(:,2)-mean(A(:,2)),'Fs',Fs)
semilogx(myPsd.Frequencies,myPsd.Data);xlabel('Frequency(rad/sec)');

[aneps]

Isn't it possible to use Fourier transform method (fft)? This code is working for this specific data but when I run for other similar data I get error:

Error using welchparse>segment_info (line 220)
The length of the segments cannot be greater than the length of the input signal.

Error in welchparse (line 32)
[L,noverlap,win] = segment_info(M,win,noverlap);

Error in welch (line 42)
    welchparse(x,esttype,varargin{:});

Error in pwelch (line 158)
[varargout{1:nargout}] = welch(x,esttype,varargin{:});

Error in spectrum.welch/thispsd (line 163)
      [Pxx, W] = pwelch(x,...

Error in spectrum.abstractspectrum/psd (line 132)
      [Pxx, W] = thispsd(this,x,opts);  % Produces spectrum with pos freq only!

Error in FourierTransform (line 17)
myPsd=psd(h1,A(:,2)-mean(A(:,2)),'Fs',Fs)

If I can plot the Fourier transform of the same data, it would be easy to know the frequency components in the data. Thank you.

[Birdman]

But this way you also obtain the frequency components of the data. Have you tried it?

[aneps]

Yes I tried. It work on the same data but when I try to run on another data it is giving error message (as it is in my previous comment). How can I make it to run for all data. All my data is in the same format. Only the values and size of the file changes.

[Birdman]

It will work if you change the following line accordingly:

set(h1,'SegmentLength',2048);

For your initial data, it is 2048 but if other data is smaller than this, than you have to change the value to 1024 or 512, to a reasonable value.

[aneps]

Yes... Thank you.