# Spectral Density and Autocorrelation

This set of Digital Communications Multiple Choice Questions & Answers (MCQs) focuses on “Spectral Density and Autocorrelation”.

1. Power spectral density function is a?

a) Real and even function

b) Non negative function

c) Periodic**d) All of the mentioned**

2. Energy spectral density defines

a) Signal energy per unit area**b) Signal energy per unit bandwidth**

c) Signal power per unit area

d) Signal power per unit bandwidth

3. Power spectrum describes distribution of _________ under frequency domain.

a) Mean**b) Variance**

c) Gaussian

d) None of the mentioned

4. How can power spectral density of non periodic signal be calculated?

a) By integrating**b) By truncating**

c) By converting to periodic

d) None of the mentioned

5. What is Wiener-Khinchin theorem?

a) Spectral density and auto-covariance makes a fourier transform pair**b) Spectral density and auto-correlatioon makes a fourier tranform pair**

c) Spectral density and variance makes a fourier tranform pair

d) None of the mentioned

6. According to Parseval’s theorem the energy spectral density curve is equal to?

a) Area under magnitude of the signal**b) Area under square of the magnitude of the signal**

c) Area under square root of magnitude of the signal

d) None of the mentioned

7. Spectogram is the graph plotted against?

a) Frequency domain**b) Time domain**

c) Frequency & Time domain

d) None of the mentioned

8. Autocorrelation is a function which matches

a) Two same signals

b) Two different signal**c) One signal with its delayed version**

d) None of the mentioned

9. Autocorrelation is a function of

a) Time

b) Frequency**c) Time difference**

d) Frequency difference

10. Autocorrelation is maximum at _______

a) Unity**b) Origin**

c) Infinite point

d) None of the mentioned

11. Autocorrelation function of periodic signal is equal to _______

a) Energy of the signal**b) Power of the signal**

c) Its area in frequency domain

d) None of the mentioned

12. Autocorrelation is a _______ function.

a) Real and even

b) Real and odd**c) Complex and even**

d) Complex and odd

13. Autocorrelation function of white noise will have?

a) Strong peak

b) Infinite peak**c) Weak peak**

d) None of the mentioned