# Communication Engineering (Test 3)

## Tancet Anna University : Ece Electronics And Communication Engineering

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Q.1
If S(f) is the power spectral density of a real, wide-sense stationary random process, then which of the following is ALWAYS true?
A. S(0)≤S(f)
B. S(f)≥0
C. S(-f) = -S(f)
D. Answer : Option B
Explaination / Solution:
No Explaination.

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Q.2
The parallel branches of a 2-wire transmission line re terminated in 100Ω and 200Ω resistors as shown in the figure. The characteristic impedance of the line is Z0 = Ω and each section has a length of λ/4. The voltage reflection coefficient Γ at the input is A. -j-
B. -5/7
C. j-
D. 5/7
Answer : Option D
Explaination / Solution:  Workspace
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Q.3
A signal flow graph of a system is given below The set of equalities that corresponds to this signal flow graph is
A. B. C. D. Answer : Option C
Explaination / Solution: Workspace
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Q.4
The signal is
A. FM only
B. AM only
C. both AM and FM
D. neither AM nor FM
Answer : Option C
Explaination / Solution:
No Explaination.

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Q.5
The Nyquist sampling rate for the signal is given by
A. 400 Hz
B. 600 Hz
C. 1200 Hz
D. 1400 Hz
Answer : Option C
Explaination / Solution:

S(t) = sinc(500t) sinc(700t)
S(f ) is convolution of two signals whose spectrum covers f1 = 250 Hz and f2 = 350 Hz. So convolution extends
f = 25 + 350 = 600 Hz
Nyquist sampling rate
N = 2f = 2#600 = 1200 Hz

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Q.6
A half wavelength dipole is kept in the x-y plane and oriented along 45from the x-axis. Determine the direction of null in the radiation pattern for 0 ϕ π. Here the angle θ (0 θ π) is measured from the z-axis, and the angle ϕ (0 ϕ ≤ 2π) is measured from the x-axis in the x-y plane.
A. θ = 900, ϕ= 450
B. θ = 450, ϕ= 900
C. θ = 900, ϕ= 1350
D. θ = 450, ϕ= 1350
Answer : Option A
Explaination / Solution:

The null occurs along axis of the antenna which is θ = 900and  ϕ= 450

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Q.7
The maximum value of ᶿ until which the approximation sin ᶿ=ᶿ holds to within 10% error is
A. 10º
B. 18º
C. 50º
D. 90º
Answer : Option B
Explaination / Solution:

Here, as we know but for 10% error, we can check option (B) first so, the error is more than 10%. Hence, for error less than 10%, ᶿ = 18º can have the approximation

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Q.8
In the circuit shown below, the network N is described by the following Y matrix: the voltage gain (V2/V1)is A. 1/90
B. -1/90
C. -1/99
D. -1/11
Answer : Option D
Explaination / Solution:

From given admittance matrix we get Workspace
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Q.9
The fourier series expansion of the periodic signal shown below will contain the following nonzero terms A. B. C. D. Answer : Option D
Explaination / Solution:

⇒ it satisfies the half wave symmetry, so that it contains only odd harmonics.
⇒ It satisfies the even symmetry. So bn = 0

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Q.10
For a periodic signal the fundamental frequency in radians/s is
A. 100
B. 300
C. 500
D. 1500
Answer : Option A
Explaination / Solution:
No Explaination.

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