FFT, Periodogram difference, Power Spectral Density Representation and Effect of Hilbert Trasnform to PSD

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hans
hans 2013-11-9
回答： Youssef Khmou 2013-11-9
Hi,
My questions are;
1)Generally,FFT and periodogram do not show same thing! I want to get Power Spectral Density. If signal is real data and in time.
M=1533;fs=27; freqVector = (-(M-1)/2:(M-1)/2)/M*fs;
figure;plot(freqVector,20*log10(abs(fftshift(fft(hilbert(signal))))));
figure;periodogram((hilbert(signal)),[],'onesided',[],27*10^9,'power') why this above line needs abs of it ? why not support complex ?
figure;periodogram((hilbert(back_remvd(1:150,30))),[],'twosided',[],27*10^9,'power') why complex is ok for twosided ?
and the amplitude values btw fft and periodogram representation are not same. Why ?
Can you show me the right PSD and spectrum representation please ?
thanks in advance.

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Youssef Khmou
Youssef Khmou 2013-11-9
hans, If you are treating narrow band signals then FFT or pwelch as said by Andrew is sufficient, but for wideband signals, you need to use periodogram.
Periodogram of narrowband signal will show you a narrow line of fundamental frequency along the time axis, for FFT try this function :
http://www.mathworks.com/matlabcentral/fileexchange/40002-psd-power-spectral-density-and-amplitude-spectrum-with-adjusted-fft

更多回答（1 个）

Andrew
Andrew 2013-11-9
fft and periodogram are not the same things, read help. Try pwelch, it's better for me.

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