Communication Systems Question Paper

Communication Systems

Course:Bachelor Of Telecommunication And Information Engineering

Institution: Kenyatta University question papers

Exam Year:2009

KENYATTA UNIVERSITY
UNIVERSITY EXAMINATIONS 2009/2010
FIRST SEMESTER EXAMINATION FOR THE DEGREE OF BACHELOR OF
SCIENCE IN TELECOMMUNICATION AND INFORMATION TECHNOLOGY

SPH 405:
COMMUNICATION SYSTEMS

DATE:
Tuesday, 22nd December, 2009 TIME: 2.00 p.m. – 4.00 p.m.

INSTRUCTIONS:
Answer question ONE and any other TWO questions. Question ONE carries 30 marks.
The rest of the questions carry 20 marks each.

Q.1
a)
Define and describe the terms step index and graded index bringing out
their
differences
clearly.
(3
marks)

b)
The core and the cladding of an optical fibre have refractive indices of
1.515 and 1.524 respectively. Calculate the critical angle of refraction.
What transpires to a light ray that is incident at the core – cladding
interface
at
this
angle? (3
marks)

c)
What is the meaning of the term acceptance angle and how is it related to
the critical angle in (b)
above? (3
marks)

d)
Compute the maximum acceptance angle using the parameters obtained in
(b)
and
(c)
(3
marks)

e)
Draw a block schematic of a conventional communication system.
i)
Explain the functions of the elements of the system
ii)
What would happen if you found the output of an antenna in open?
(3 marks)
Page 1 of 4

f)
Express in DBm the following power levels.
i)
1 Watt
ii)
1 mill watt (mW)
iii)
1 microwatt ( µ W)
(3 marks)

g)
i)
Give briefly the operation principles of a basic radar systems.
ii)
What
factors
determine the range of radar set?

(3 marks)

h)
Assuming the probabilities of weather conditions to be:- 0.25, 0.125,
0.125 and 0.5 respectively, determine the source entropy and information
rate

(3 marks)

i)
Explain why microwaves are used for multi-channel point – to – point
communications
(3
marks)
j)
Explain Doppler effect
Q.2 a) i) Explain
the
operation of a radar beacon
ii)
Explain how two telephone subscribers may be connected
together via a local GSC and TSC switching centers

(4 marks)

b)
i)
State the causes of fading of ionospheric signals in
reference to radio wave propagation
(2 marks)
ii)
Explain
the
following
as applied to radio receivers
a)
Fidelity
b)
Sensitivity
(2 marks)
c)
i)
Define
population
inversion in reference to LASERS

ii)
With the aid of a well labeled diagram explain the principle
of
operation
of
LASERS

(4 marks)

Q.3 a) i) State
and
explain the Merits of carrier operating in long distance
Telephony
(3
marks)
Page 2 of 4

ii)
With the aid of a well annotated block diagram explain the
operation of a 12-channel carrier telephone system

(6 marks)

b)
i)
What is meant by the term channel as applied to communication
sytem

(2 marks)
ii)
Differentiate
between
base band transmission and band pass
transmission

(4
marks)

c)
i)
Explain the terms:
a)
Entropy
b)
Redundancy
c)
Information source
(3 marks)

ii)
Calculate the amount of information if it is given that P(Xi) = ¼

(2 marks)

Q.4
a)
Explain the following terms as used in information theory:
i)
Channel capacity
ii)
Coding
iii)
Signal to Noise ration bandwidth trade-off
(6 marks)

b)
A channel has bandwidth of 5 kHz and a sign al to noise power ratio of 63.
Determine the bandwidth needed if the power ratio is reduced to 31. What
will be the signal power required if the channel bandwidth is reduced to 3
kHz?

(8 marks)

c)
What do you understand by the following terminology used in radio
navigation system
i)
LORAN
ii)
DME
iii)
PAR
(6 marks)

Page 3 of 4

Q.5 a) Explain
the
following:-
i)
Multiplexing
ii)
TDM and FDM
(4 marks)

b)
A discrete source emits one of the five symbols once every millisecond
with probabilities ½, ¼, ?, 1/16, and 1/16 respectively. Determine source
entropy
and
information
rate.
(10
marks)
Page 4 of 4

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