Communication Engineering (Test 4)

Tancet Anna University : Ece Electronics And Communication Engineering

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Communication Engineering

Communication Engineering
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Q.1
In delta modulation, the slope overload distortion can be reduced by
A. decreasing the step size
B. decreasing the granular noise
C. decreasing the sampling rate
D. increasing the step size
Answer : Option D
Explaination / Solution:
No Explaination.


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Q.2
A λ/2 dipole is kept horizontally at a height of λ0/2 above a perfectly conducting infinite ground plane. The radiation pattern in the lane of the dipole ( plane) looks approximately as
A.
B.
C.
D.
Answer : Option B
Explaination / Solution:



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Q.3
A rectangular waveguide of internal dimensions (a = 4 cm and b = 3 cm) is to be operated in TE11 mode. The minimum operating frequency is
A. 6.25 GHz
B. 6.0 GHz
C. 5.0 GHz
D. 3.75 GHz
Answer : Option A
Explaination / Solution:



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Q.4
A speed signal, band limited to 4 kHz and peak voltage varying between +5 V and -5 V, is sampled at the Nyquist rate. Each sample is quantized and represented by 8 bits. If the bits 0 and 1 are transmitted using bipolar pulses, the minimum bandwidth required for distortion free transmission is
A. 64 kHz
B. 32 kHz
C. 8 kHz
D. 4 kHz
Answer : Option B
Explaination / Solution:



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Q.5
X(t) is a stationary process with the power spectral density Sx(f)>0, for all f . The process is passed through a system shown below

Let Sy (f ) be the power spectral density of Y(t). Which one of the following statements is correct
A. Sy (f ) > 0 for all f
B. Sy (f ) = 0 for |f| > 1 kHz
C. Sy (f ) = 0 for f = nf0, f0 = 2 kHz kHz, n any integer
D. Sy (f ) = 0 for f = (2n + 1) f= 1 kHz, n any integer
Answer : Option D
Explaination / Solution:



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Q.6
Consider the signal  where  denotes the Hilbert transform of m(t) and the bandwidth of m(t) is very small compared to fcThe signal s(t) is a
A. high-pass signal
B. low-pass signal
C. band-pass signal
D. double side-band suppressed carrier signal
Answer : Option C
Explaination / Solution:

We have the signal,

Here, s(t) represents SSB - Lower side band, and thus a band pass signal.

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Q.7
The bit rate of a digital communication system is R kbits/s. The modulation used is 32-QAM. The minimum bandwidth required for ISI free transmission is
A. R/10 Hz
B. R/10 Hz
C. R/10 Hz
D. R/5 kHz
Answer : Option B
Explaination / Solution:

In ideal Nyquist Channel, bandwidth required for ISI (Inter Symbol reference) free transmission is
 
Here, the used modulation is 32 - QAM (Quantum Amplitude modulation
 


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Q.8
A four-phase and an eight-phase signal constellation are shown in the figure below.

For the constraint that the minimum distance between pairs of signal points be d for both constellations, the radii r1, and r2 of the circles are
A. r1 = 0.707d, r2 = 2.782d
B. r1 = 0.707d, r2 = 1.932d
C. r1 = 0.707d, r2 = 1.545d
D. r1 = 0.707d, r2 = 1.307d
Answer : Option D
Explaination / Solution:

Four phase signal constellation is shown below 

d2 = r12 + r12
d2 = 2r12

r1 = d/√2 = 0.707d




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Q.9
The steady state error of a unity feedback linear system for a unit step input is 0.1. The steady state error of the same system, for a pulse input r(t) having a magnitude of 10 and a duration of one second, as shown in the figure is

A. 0
B. 0.1
C. 1
D. 10
Answer : Option A
Explaination / Solution:



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Q.10
A continuous random variable X has a probability density function  is
A. 0.368
B. 0.5
C. 0.632
D. 1.0
Answer : Option A
Explaination / Solution:
No Explaination.


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ECE Electronics and Communication Engineering