PSD calculation using Matlab{help needed}

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qslazio

Joined: 23 May 2004
Posts: 194
Helped: 9

07 Oct 2006 14:08 calculate psd

I'm writing a Matlab m-file to calculate PSD of sinusoid signal.
However the output puzzle me a lot.

Below is the m-file:
------------------------------------------------------------------
fs =1e10;
fi =1e8;
amp =1;
nbpts =4e5;
t =[0:1/fs:nbpts/fs];
sig =amp*sin(2*pi*fi*t);
Hs = spectrum.periodogram('rectangular');
Hdsp2 = psd(Hs,sig,'Fs',fs,'NFFT',nbpts,'SpectrumType','onesided');
Pow = avgpower(Hdsp2,[0.9*fi,1.1*fi]);
plot(Hdsp2);
------------------------------------------------------------------

Here, I intended to calculate psd of this sinusoid of which the frequency is 100Meg Hz and amplitude is 1. I expected to see this 0.5*δ(w-100Meg) impulse on this one-sided PSD plot.
But instead, there is a impulse of which the amplitude is around -50dB, which I cannot explain it at all.

Can anyone tell me what's wrong with the m-file?
Thank in advance!!

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lassmat

Joined: 03 Sep 2006
Posts: 41
Helped: 2

20 Oct 2006 23:14 psd calculation

There is function in matlab call psd().This will calculate the psd of any signal you pass to it and plot it.Try help psd and will get all the details.You can even check the code of that function.