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ECE Objective Questions { Digital Communication System }



71. Two orthogonal signals s1(t) and s2(t) satisfy the following relation :
A. 0 si (t) s2 (t) dt = 0 s1 (t)
B.s2 (t) dt = 1 si (t)
C.s2 (t) dt = co s1 (t)
D.s2 (t) dt =71

72. In communication, the sampling technique leads to
A. higher efficiency
B. higher speed of communication
C. cheaper equipment
D. all of the above

73. For a periodic function, the spectral density and the auto-correlation functions are
A. Fourier transform pair
B. Laplace transform pair
C. One and the same thing
D. None of the above

74. The channel capacity C of a band limited Gaussian channel equals, where B is the channel bandwidth
A. B log2(1 --)
B.B log2 (-) 1
C.log2 (S/N)
D. ? lo2g (1B

75. Spectral density of white noise
A. varies with frequency
B. is constant
C. varies with bandwidth
D. none of the above

76. A random process is defined as ergodic if
A. All types of ensemble averages are not changeable
B.All types of ensemble averages are constant
C. All types of ensemble average are interchangeable
D. None of above

77. Auto correlation function of a random process is defined as
A. R (t1 t2) = E (X, ) = ffx y p (x, y) dX dY
B. E (X, Y)= fx2 y2 dX dY
C. R t2) = ix2 y2 dX dY
D. none of the above

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