# Communication Engineering (Test 2)

## Tancet Anna University : Ece Electronics And Communication Engineering

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Q.1
If R(τ) is the auto correlation function of a real, wide-sense stationary random process, then which of the following is NOT true
A. B. C. D. The mean square value of the process is R(0)
Explaination / Solution:
No Explaination.

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Q.2
A load of 50 Ω is connected in shunt in a 2-wire transmission line of Z0 = 50Ω as shown in the figure. The 2-port scattering parameter matrix (s-matrix) of the shunt element is A. B. C. D. Explaination / Solution: Workspace
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Q.3
A memory less source emits n symbols each with a probability p. The entropy of the source as a function of n
A. increases as log n
B. decreases as log(1/n )
C. increases as n
D. increases as nlogn
Explaination / Solution: Workspace
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Q.4
A white noise process X(t) with two-sided power spectral density 1 X 10-10  W/HZ is input to a filter whose magnitude squared response is shown below. A.

5 X 10-10  W

B.

1 X 10-6  W

C.

2 X 10-6  W

D.

1 X 10-5  W

Explaination / Solution:
No Explaination.

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Q.5

For a message signal and carrier of frequency fc which of thefollowing represents a single side-band (SSB) signal ?

A. B. C. D. Explaination / Solution: Workspace
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Q.6
Let X(t) be a wide sense stationary random process with the power spectral density SX(f) as shown in Figure (a), where f is in Hertz (Hz). The random process X(t) is input to an ideal low pass filter with frequency response As shown in Figure (b). The output of the lowpass filter is Y(t ). Let E be the expectation operator and consider the following statements.
I.   E( X(t)) = E(Y(t))
II.  E( X2(t)) = E(Y2(t))
III. E(Y2(t)) = 2
Select the correct option:
A. only I is true
B. only II and III are true
C. only I and II are true
D. only I and III are true
Explaination / Solution:  Workspace
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Q.7
The amplitude of a random signal is uniformly distributed between -5 V and 5 V.If the signal to quantization noise ratio required in uniformly quantizing the signal is 43.5 dB, the step of the quantization is approximately
A. 0.033 V
B. 0.05 V
C. 0.0667 V
D. 0.10 V
Explaination / Solution:  Workspace
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Q.8
A message signal m(t) = cos 200πt + 4cosπt  modulates the carrier c(t) = coe 2πfct where fc = 1MHz to produce an AM signal. For demodulating the generated AM signal using an envelope detector, the time constant RC of the detector circuit should satisfy
A. 0.5 ms < RC < 1 ms
B. 1 μs << RC < 0.5 ms
C. RC << μs
D. RC >> 0.5 ms
Explaination / Solution:

Highest frequency component in m(t) is Carrier frequency fc = 1 MHz
For Envelope detector condition Workspace
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Q.9
A dual trace oscilloscope is set to operate in the Alternate mode. The control input of the multiplexer used in the y-circuit is fed with a signal having a frequency equal to
A. the highest frequency that the multiplexer can operate properly
B. twice the frequency of the time base (sweep) oscillator
C. the frequency of the time base (sweep) oscillator
D. haif the frequency of the time base (sweep) oscillator
Explaination / Solution:
No Explaination.

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Q.10
A band-limited signal with a maximum frequency of 5 kHz is to be sampled. According to the sampling theorem, the sampling frequency in kHz which is not valid is
A. 5
B. 12
C. 15
D. 20