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Electronics and Communication Engineering - Exam Questions Papers

Exercise : Exam Questions Papers - Exam Paper 11
31.
{ x(n) } is a real-valued periodic sequence with a period N. x(n) and X(k) form N-point. Discrete Fourier Transform (DFT) pairs. The DFT Y(k) of the sequence. y(n) = x(r) X (n + r) is
|X(k)|2
X(r) X(k + r)
1
0
Answer: Option
Explanation:

Direct property

Convolution in time domain ↔ Multiplication in frequency domain.

32.
The signal x(t) is described by Two of the angular frequencies at which its fourier transform becomes zero are
p, 2p
0.5p, 1.5p
0, p
2p, 2.5p
Answer: Option
Explanation:

X(jω) = 1.e-jωt =

At ω = 0 X(j0) = 2

At ω = p X(jp) = 0

ω = 2p X(j2p) = 0

33.
(29)13 ÷ (29)12 x (29)x = (23)16 Find x
11
12
13
16
Answer: Option
Explanation:

(29)13 ÷ (29)12 x (29)x = (23)16

=> (35)10 , (33)10 x (29)x = (35)10

=> x(29)X = 35

∴ (29)x = (33)10 => X = 12.

34.
If the scattering matrix [S] of a two port network is then the network is
lossless and reciprocal
lossless but not reciprocal
not lossless but reciprocal
neither lossless nor reciprocal
Answer: Option
Explanation:

S11 ≠ S22 ≠ lossy [S]1 = [S] Reciprocal.

35.
Consider the frequency modulated signal 10 cos (2p x 105t + 5 sin (2p x 1500t) + 7.5 sin (2p x 1000t) with carrier frequency of 105Hz. The modulation index is
12.5
10
7.5
5
Answer: Option
Explanation:

Total frequency deviation = 5 x 1500 + 7.5 x 1000 = 15000

Thus modulation index = .

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