# 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