## Variance of a t-realization of a stochastic process

Hello everyone!

Suppose we have a stochastic process N that is stationary in the wide sense (WSS), and we're sampling this process every T seconds.

Also suppose that the mean of the process is given to be 0. Now I know that the random variable N(kT) should be zero-mean, but what is its variance?

In the book, there is a relation between the spectrum of N, $S_N (f)$ and the variance of the sample, but I can't seem to track it down!

Any help would be appreciated!