22. The auto eorelation function of white noise is
A. a delta function
B. a constant
C. Gaussian
D. exp (? I t ) with usual notation

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23. The spectral density of white noise is
A. exponential
B. uniform
C. Poisson
D. Gaussian

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24. The probability density function of the envelope of narrow band noise is
A. Uniform
B. Gaussian
C. Rayleigh
D. Rician

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25. The Fourier transform of a Gaussian time pulse is 1 z2 ? z
A. Uniform
B. a pair of impulses
C. Gaussian
D. Rayleigh

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26. The z-transform of a system is H(z)= z- 0.2 If the ROC is VI < 0.2, then impulse response of the system is
A. (0.2) u[n]
B. (0.2) u[-n -1]
C. -(0.2)" u(n)
D. ?(O.2)n u(-n -I)

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27. A causal LTI system is described by the difference equation 2yin] = ay[n -21- 2x[nl + 13x In -II The system is stable only if
A.a= 2 PI < 2
B. lal = 2 IRI > 2
C. u = 2, any value of 13
D. al = 2, any value of a

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28. The region of convergence of the z-transform of a unit step function is
A. IZI > 1
B. Z <1
C. (Real part of z) > 0
D. (Real part of z) < 0

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