# Basic Question about the PSD

Started by February 21, 2006
```Hi

I am plotting the PSD using Wiener-Khintchin theorem (1).  I recall from
my signal processing course the the fourier transform is periodic with
peroiod of 2 pi. Should the PSD be periodic since the wiener-khintchin
theroem is essentialy a fourier transform?  What should the perido be in
general?

PSD(f)=4*Integral[cos(2*pi*f*t)*Autocorrelation from -inf, +inf]    (1)

thanks!!
```
```lebann wrote:
> Hi
>
> I am plotting the PSD using Wiener-Khintchin theorem (1).  I recall from
> my signal processing course the the fourier transform is periodic with
> peroiod of 2 pi. Should the PSD be periodic since the wiener-khintchin
> theroem is essentialy a fourier transform?  What should the perido be in
> general?

>
> PSD(f)=4*Integral[cos(2*pi*f*t)*Autocorrelation from -inf, +inf]    (1)

wrt to f

The PSD isn't in general periodic.  The Fourier Transform is not in
general periodic.

The Fourier transform of uniform sampled discrete time wave forms is
periodic.
>
> thanks!!
```
```>The PSD isn't in general periodic.  The Fourier Transform is not in
>general periodic.
>
>The Fourier transform of uniform sampled discrete time wave forms is
>periodic.

What do you mean by "uniform sampled dscrete time wave"?  I am samplying a
stochastic electric current every dt seconds...does that constitute what u
call a "uniform sampled time wave"?  thanks
```