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Engineering Services (Main)
Examination - 2025 farsa DETACHABLE
ELECTRONICS AND TELECOMMUNICATION
ENGINEERING
Paper II
Time Allowed : Three Hours Maximum Marks : 300
QUESTION PAPER SPECIFIC INSTRUCTIONS
Please read each of the following instructions carefully before attempting questions.
There are EIGHT questions divided in TWO Sections.
Candidate has to attempt FIVE questions in all.
Questions No. 1 and 5 are compulsory and out of the remaining, any THREE are to be attempted
choosing at least ONE question from each Section.
The number of marks carried by a question/part is indicated against it.
Wherever any assumptions are made for answering a question, they must be clearly indicated.
Diagrams/Figures, wherever required, shall be drawn in the space provided for answering the
question itself.
Unless otherwise mentioned, symbols and notations have their usual standard meanings.
Attempts of questions shall be counted in sequential order. Unless struck off, attempt of a question
shall be counted even if attempted partly.
Any page or portion of the page left blank in the Question-cum-Answer Booklet must be clearly
struck off.
Answers must be written in ENGLISH only.
1 NESP-T-ENTE
1.(a)
1.(b)
1.(c)
1.(d)
1:6)
1.(f)
SECTION ‘A’
A random process Y(t) is obtained by multiplication of a stationary process X(t)
with a sinusoidal wave cos(27f,t+@) where the phase @ is a random variable
that is uniformly distributed over the interval [0, 27].
Express the power spectral density of random process Y(¢) in terms of power
spectral density of X(¢). Assume that random variable 0 is independent of X(t).
10
Consider the system shown below :
jee
R(s) E(s) C(s)
G(s) G,(s) =.
Here G,(s)= 100(s +5)
s+2
5
G. =
- Als) s(s+4)
Determine the steady state error due to unit step input and a step disturbance of
10 unit. 10
Find out the time complexity of the following code segment :
for (i = n/2; i < n; i++)
for (kK = 1; k <i; k* = 2)
count + =n *n; 10
>
Determine the divergence of the vector field 4 and evaluate them at the specified
point :
Py : A 2 A
A=pzsing ap+3pz° cosh ag at (5, 7/2, 1). 5+5=10
Use Euler path method to find out optimal gate ordering for the stick diagram and
layout of CMOS implementation of the Boolean expression 4(B+C)+DE. 10
A bit stream 10011101 is received (LSB is received first). The transmitter is
using standard CRC method with the generator polynomial x° + 1. Show the actual
bit stream transmitted. Show that the error is detectable at the receiver’s side.
5x2=10
' NESP-T-ENTE 2
2.(a)
2.(b)
2.(c)
3.(a)()
3.(a)(ii)
3.(b)(i)
3.(b)(ii)
3.(c)
Consider that, two input signals of a Binary Phase Shift Keying (BPSK) receiver
are +sin 27f,t (where ‘f,’ is carrier frequency). Draw the functional block diagram
of a BPSK receiver to recover the bit stream of ‘0’ and ‘1’. Give the necessary
mathematical interpretation of the signals. 20
Show that the maximum phase lead of a lead compensator occurs at frequency Jab,
where (—a) and (—b) are the locations of zero and pole respectively of the lead
compensator. 20
A system has 512 mega bytes of main memory and 128 kilo bytes of cache
memory. Memory is word addressable with 32 bit word size. Cache memory is
8-way associative with 128 byte block size. Calculate the number of tag bits
required for this set associative cache mapping scheme. 20
Amplitude Modulation (AM) transmitter with a carrier power of 900 W, transmits
a power of 1-1 kW, when modulated with a single sine wave. Calculate the
percentage of modulation.
If the same carrier is simultaneously modulated with one more sine wave of 50%
modulation, calculate the total transmitted power. 4+6=10
Frequency modulation (FM) broadcast system is having a maximum frequency
deviation of 75 kHz and modulating frequency of 15 kHz. Calculate the modulation
Index and the required bandwidth using Carson’s rule. Discuss whether this FM
broadcast system is narrowband or wideband. Justify your answer. 10
The forward path transfer function of a negative unity feedback system is given by
G(s) = . Determine the values of K and TJ such that all the roots of
s(s+T)
characteristic equation are in the left-half plane of the vertical line passing through
S=-a. 10
A negative feedback control system has the forward path transfer function
K(s+05
Gy = 5) )
s°(s+12)
breakaway points. 10
and feedback transfer function H(s) = 1. Find the value of K at the
An embedded system for a plant control uses two processes P1 and P2. High
priority process P1 reads temperatures from two sensors at regular interval t and
updates the latest temperature values in two fixed memory locations 71 and 72
sequentially. Low priority process P2 uses the values stored in locations 71 and 72
to calculate the average of this set of values. If the average of any set of values
happens to be more than 50, then P2 calls a function to sound an alarm. The loop
time of P2 is variable, but is ensured to be always less than t.
(i) Write an indicative pseudocode describing the above situation and mention
what can go wrong in this case.
(ii) Suggest appropriate operating system mechanism for solving the possible
code problem with appropriate modifications in the pseudocode for part (i)
above. 10+10
3 NESP-T-ENTE
4.(a)(i)
4.(a)(ii)
4.(b)
4.(c)
5.(a)
5.(b)
Plot the entropy function of a Binary Memoryless Source (BMS). List the
important observations from the drawn plot. 10
Plot the curve of transition probability versus Channel capacity for a Binary
Symmetric Channel (BSC). List the significant observation from the drawn plot.
10
(i) Sketch the polar plot for G(s) H(s) = 7 I ;
s'(s+2)
(ii) How do you count the number of encirclements of the
(A) Origin
(B) (-1 +0)
points ? Use examples to justify the answer. 12+4x2=20
A demand paged virtual memory system uses 4 page frames. Consider following
string of memory references : :
1 2 4 0 5 7 4 3 4 0
Indicate the page frames for the reference string and determine the number of page
faults for
(i) FIFO (First In First Out) page replacement algorithm
(ii) LRU (Least Recently Used) page replacement algorithm 10+10
SECTION ‘B’
Consider a telephone channel having a bandwidth of 3 kHz and the channel capacity
of 30 kbps. Calculate the Signal-to-Noise ratio of this digital telephone communi-
cation system. 10
Figure approximately represents a differentiator. Its transfer function
OY) asi Neat -°- SOs.
R(s) s(ts+1)+K 130, Ke R(s)
Find the step, ramp and parabolic error constants for this system, where the ideal
system is assumed to be a differentiator.
R(s) + K
> C(s)
= 10
NESP-T-ENTE 4
5.(c)
5.(d)
5.(e)
5.(f)
6.(a)
Draw precedence graph for the schedule of transactions X, Y, and Z shown below
and find if the schedule is conflict serializable ?
X Y Z
Read (A)
Write (B) ;
Read (C) | me
Write (A)
Write (C)
Commit
Read (B)
Write (A)
Commit
Write (A)
Commit 10
Find the maximum effective area of a A/2 wire dipole operating at 300 MHz.
How much power is received with an incident plane wave of strength 2 mV/m?
5+5=10
Show that the accumulator is the inverse system of a backward difference system.
10
A double-heterojunction InGaAsP light emitting diode (LED) used in a Fiber
optic communication system emitting a peak wavelength of 1310 nm has radiative
and non radiative recombination times of 30 ns and 100 ns respectively. The drive
current is 40 mA.
Calculate :
(i) Bulk recombination life time
(ii) Internal Quantum efficiency
(iii) Internal power of the LED 3+3+4=10
The z-component of magnetic field for the dominant mode propagating in air-filled
waveguide in the z-direction at 10 GHz is given by the following expression :
Hx, 2) = 10 cos(43-74 x) e/P:2, Alm
Find :
(i) the cutoff wave number
(ii) the broader dimension of the guide
(iii) the phase velocity
(iv) the wave impedance 5+5+5+5=20
5 NESP-T-ENTE
6.(b)
6.(c)(i)
6.(c)(ii)
7.(a)
7.(b)
7.(c)
Using overlap add method of block filtering find the output of a filter with impulse
2, 2, 0, 0.... . 7 ‘Ss
response h[n]= tr and input x[n]= \f hy delete af
Take L(value of nonoverlapping blocks) = 3. 20
The loss computed for a single-mode optical fiber cable is given as 0-25 dB/km.
Determine the optical power at a distance 100 km from a light source of 0-1 mW.
10
Consider that 6 GHz is the receiving frequency at satellite transponder from
the earth station and 4 GHz is the output frequency of the satellite transponder.
Draw the block diagram of the satellite transponder and explain the functionality
of each block. 10
Given a uniform plane wave in air as
i,
E; = 40 cos(wt— B2) ay +30 sin(wt— Bz)4,, Vim.
+
Find H; . If the wave encounters a = Detecny conducting plate normal to the z-axis
at z=0, find the reflected wave E. and H,. Assume ¢€,= 1. 20
A light bulb Z tums ON and OFF depending on the positions of two switches
P and Q. P and Q never change positions simultaneously. L is OFF when P is in
OFF position irrespective of the position of switch Q. L turns ON when Q toggles
its position while P is in ON position, and then remains ON until P goes to
OFF position.
Design an asynchronous circuit to implement the above logic. Derive the
minimal-sum Boolean expressions for the output and next state variables in terms
of the inputs and present state variables. 20
Find the shortest path tree from every node to node | for the graph of figure shown
using the Bellman-Ford and Dijkstra algorithms.
10+10=20
NESP-T-ENTE 6
t
8.(a)(i)
8.(a)(ii)
8.(b)
8.(c)(i)
8.(c)(ii)
Two A/4 transformers in tandem are to connect a 50Q line to a 75Q load as
given below :
A
___4
Z,=502 Zs Za 75.2
|
i]
i
———
|
oA a
40 Sy
I i}
Determine the characteristic impedance Z,, if Z,.= 30 Q and there is no reflected
wave to the left of A. 10
A distortionless transmission line operating at 250 MHz has R=30 Q/n,
L=200 nH/m and C= 80 pF/m. After how many meters travelling along the line,
will the voltage wave get reduced to 30% of its initial value. 10
A data byte read from port 0 of 8051 microcontroller is to be sent out serially from
bit 0 of port 1. Each bit duration for serial transmission is 2 milliseconds and least
significant bit goes out first. Write assembly language program using timer 0 for
the delay. Assume crystal clock frequency to be 12 MHz. 20
The downlink of a satellite communication operated at 4 GHz, the receiving antenna
is a parabolic reflector with a diameter of 3-6 m and efficiency is 0-7. Calculate the
gain of the receiving antenna in dB. 10
The numerical aperture of an optical fiber is 0-3. Calculate the acceptance angle
for the meridional rays. Further calculate the acceptance angle for the skew rays
which change direction by 90° at each reflection.
(Assume that refractive index, n, of air is 1) 10
7 NESP-T-ENTE
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