FACULTY OF SCIENCE AND TECHNOLOGY
EXAMINATION FOR THE BSC (HONS) IN INFORMATION TECHNOLOGY; YEAR 2
ACADEMIC SESSION; 2012 SEMESTER 5
NET2204: TELECOMMUNICATIONS
FINAL- DECEMBER 2012 EXAM CYCLE
TIME: 2 HOURS + 10 MINUTES READING TIME
INSTRUCTIONS TO CANDIDATES
This question booklet contains two sections.
Section A: Answer the compulsory questions.
Section B: Answer two questions out of three questions
All answers must be written in the answer booklets provided using blue or black INK
IMPORTANT NOTES TO CANDIDATES
Materials Allowed
Standard Items :
Special Items :
Pen, Pencil, Eraser or Correction Fluid, Ruler
Non Programmable Calculators
It is your responsibility to ensure that you do NOT have in your possession any
unauthorised notes or any other means that would improperly help you in your work. If
you have any unauthorised materials with you, hand it to the invigilator BEFORE
reading any further.
DO NOT REMOVE THIS QUESTION PAPER FROM THE EXAMINATION HALL
[This paper contains FOUR questions printed on THREE pages]
Section A
Compulsory section
Question 1 (50 marks)
a)
Calculate the wavelength  of a 5.8 GHz communication signal.
(3 marks)
b)
A Rectangular waveform has a positive pulse width of 5 ms and a
duty cycle of 30 %, calculate its frequency.
(4 marks)
c)
Plot the following sine waveforms:i) a 1 kHz sine wave of 1V over a period of 2 ms.
(5 marks)
ii) a 2 kHz sine wave of 1V over a period of 1 ms.
(5 marks)
iii) a 1 kHz and 2 kHz sine waveforms of 1V together over a
period of 1 ms.
(5 marks)
iv) a 1 kHz sine wave of 1 V and a 1 kHz sine wave of 2V
together.
(5 marks)
d)
There are many different types of modulation. Name the three
common ones.
(3 marks)
e)
i) Give at least two reasons why the dB scale is useful in system
measurements and analysis.
(2 marks)
ii) Name one equipment that shows the pattern of an electrical
signal in the time domain.
(1 mark)
iii) Name one equipment to analyze the content of frequencies in
an electrical signal.
(1 mark)
iv) Draw a diagram of a signal waveform in the time and
frequency domains and explain the differences between them.
(4 marks)
f)
Network cables include twisted-pair, coaxial, and fiber optic
cable. For twisted-pair cable, why are wires twisted together?
What will happen if the number of the twists increases?
(4 marks)
g)
What is the output power, in watts, for the circuit shown in the
figure below?
(8 marks)
Loss = 0.2dB
Output
Input power =
-12dBm
Length = 8.2km
Loss = 2.4dB/km
Length = 150m
Loss = 3.0dB/km
Figure 1
NET2204: Telecommunications
(December 2012)
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Section B
Answer any TWO questions from this section.
Question 2 (25 marks)
a)
Fiber optic cable has several advantages over cables that use
wire. List three advantages of fiber optic cables.
(6 marks)
b)
An amplifier has a higher output power of 6mW compared to its
input power, which is 2mW. Determine the power gain of the
amplifier.
(4 marks)
c)
A silica optical fibre with a core diameter large enough to be
considered by ray theory analysis has a core refractive index of
1.60 and a cladding refractive index of 1.56. Determine;
i) The critical angle at the core-cladding interface
ii) The Numerical Aperture (NA) for the fiber
iii) The acceptance angle in air for the fiber
(5 marks)
(5 marks)
(5 marks)
Question 3 (25 marks)
a)
A pixel for digital TV uses 8 bits, how many levels of brightness
are there?
b)
Digital encoding schemes are used to convert the 0s and 1s of
digital data into the appropriate transmission form. Encode
“10001011” using the following digital encoding schemes:-
(5 marks)
i) NRZ-L.
(4 marks)
ii) NRZI.
(4 marks)
iii) Manchester.
(4 marks)
iv) Differential Manchester.
(4 marks)
v) Biploar-AMI.
(4 marks)
Question 4 (25 marks)
a)
b)
Explain the key principles of the following modulation:i) Amplitude Modulation (AM)
(3 marks)
ii) Frequency Modulation (FM)
(3 marks)
iii) Phase Modulation (PM)
(3 marks)
i) Express 200W as dBW and as dBm.
(2 marks)
NET2204: Telecommunications
(December 2012)
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c)
ii) A signal of 1.6 V that is amplified by 2.5 dB will become?
(2 marks)
iii) A signal that comes out the final stage of a 9-dB gain amplifier
with a measured value of 15 V must have had an original input
value of?
(2 marks)
i) Radar A produces 4000 W peak power, while radar B
produces 2000 W peak power. How many dB better is radar
A?
(2 marks)
(4 marks)
ii) Radar A has radio frequency (RF) component losses of 4.5 dB
(A loss is a negative gain - power is reduced). Radar B has
RF losses of 0.5 dB. Which radar is better in this respect?
What percentage of the power is lost by radar A? What
percentage of the power is lost in radar B?
(4 marks)
iii) Refer to (i) and (ii) above. Adjust the power of Radar A and
Radar B downward to reflect the losses for each of these two
radars. Which is more powerful after taking into account the
losses?
~ END OF PAPER ~
NET2204: Telecommunications
(December 2012)
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