fourrier analysis pwelch command

I am creating a signal and storing it as vector data [E] using a sample frequency of Fs=1/0.0005.

I would like to use pwelch to analyse the signal in the frequency domain and also plot a graph with the absolute values instead of in dB and frequencies of 0-200 Hz on the other axis. I have been stumbling around with this for some time, could you tell me the exact command i need?

Answer 1

[Youssef Khmou]

hi, Rune, you mean you want to use built-in spectrum , ok try this :

 Fs=1000;
 t=0:1/Fs:.3;
 x=cos(2*pi*t*200)+randn(size(t));
 Hs=spectrum.welch
 F=psd(Hs,x,'Fs',Fs);
 F
 figure, plot(F.Frequencies,F.Data)

the dspdata or "object" F is :

F =

                   Name: 'Power Spectral Density'
                   Data: [129x1 double]
           SpectrumType: 'Onesided'
    NormalizedFrequency: false
                     Fs: 1000
            Frequencies: [129x1 double]

The figure is not in dB in this case, but in case you want it as original then use semilogy :

 figure, semilogy(F.Frequencies,F.Data)
 % this is the same as : >>psd(Hs,x,'Fs',Fs)

[Youssef Khmou]

if you want to use several instructions with FFT , then you can try my submission : http://www.mathworks.com/matlabcentral/fileexchange/40002-psd-power-spectral-density-and-amplitude-spectrum-with-adjusted-fft