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Fee 421: Telecommunications And Electroacoustics A Question Paper
Fee 421: Telecommunications And Electroacoustics A
Course:Electrical And Communication Engineering
Institution: University Of Nairobi question papers
Exam Year:2011
UNIVERSITY OF NAIROBI
SPECIAL/SUPPLEMENTARY EXAMINATIONS 2010/2011
FOURTH YEAR EXAMINATIONS FOR THE DEGREE OF BACHELOR OF SCIENCE
IN ELECTRICAL & ELECTRONIC ENGINEERING
FEE 421: TELECOMMUNICATIONS AND ELECTROACOUSTICS A
DATE: 18TH OCTOBER, 2011 TIME: 2.00 P.M. – 4.00 P.M.
INSTRUCTIONS
1. Attempt any THREE questions
2. All questions carry equal marks
SOME USEFUL IDENTITIES AND CONSTANTS
1. Assume one-sided PSD of AWGN, N W Hz o 5 10 / -9 = ×
2. cos cos cos( ) cos( ) 2
1
2
A B = 1 A + B + A - B ; sin sin cos( ) cos( ) 2
1
2
A B = 1 A - B - A + B
3. cos sin sin( ) sin( ) 2
1
2
A B = 1 A + B - A - B ; sin cos sin( ) sin( ) 2
1
2
A B = 1 A + B + A - B
4.
+¥
=¥
sin ( ) = 1 2 c x dx ;
+¥
=¥
sin c (x) dx = 1
TABLE OF BESSEL FUNCTION VALUES
Jn(b)
b 0 0.2 0.5 1 2 3 4 5 6 8 10 12 15
n
0 1.00 0.990 0.9385 0.7652 0.2239 – 0.2601 – 0.3971 – 0.178 0.1506 0.1717 – 0.2459 0.0477 – 0.01
1 - 0.100 0.2423 0.4401 0.5767 0.3391 – 0.0660 – 0.328 – 0.2767 0.2346 0.0435 – 0.2234 0.21
2 0.005 0.0306 0.1149 0.3528 0.4861 0.3641 0.047 – 0.2429 – 0.1130 0.2546 – 0.0849 0.04
3 - 0.0026 0.0196 0.1289 0.3091 0.4302 0.365 0.1148 – 0.2911 0.0584 0.1951 – 0.19
4 0.0002 0.0025 0.0340 0.1320 0.2811 0.391 0.3576 – 0.1054 – 0.2196 0.1825 – 0.12
5 - 0.0002 0.0070 0.0430 0.1321 0.261 0.3621 0.1858 – 0.2341 – 0.0735 0.13
6 - 0.0012 0.0114 0.0491 0.131 0.2458 0.3376 – 0.0145 – 0.2437 0.21
7 0.0002 0.0025 0.0152 0.053 0.1296 0.3206 0.2167 – 0.1703 0.03
8 - 0.0005 0.0040 0.018 0.0565 0.2235 0.3179 0.0451 – 0.17
9 0.0001 0.0009 - 0.0212 0.1263 0.2919 0.2304 – 0.22
10 - 0.0002 0.0070 0.0608 0.2075 0.3005 – 0.09
11 - 0.0020 0.0256 0.1231 0.2704 0.10
12 0.0005 0.0096 0.0634 0.1953 0.24
13 0.0001 0.0033 0.0290 0.1201 0.28
14 - 0.0010 0.0120 0.0650 0.25
15 - - 0.03 0.18
16 0.01 0.12
NB: J-n(b) = (-1)nJn(b); ½ [J0(b)]2 + [J1(b)]2 + [J2(b)]2 + ….. = ½
QUESTION ONE
(a) Classify the following signals, with justification, according to the five categories.
(i)
(ii)
[8 marks]
(b) Classify the following systems, with justification, according to the six categories. is the system
input and is the system output.
(i)
(ii)
[12 marks]
QUESTION TWO
Given the signals
(a) Sketch the two signals, indicating all salient points [4 marks]
(b) Obtain the Fourier Transform of x(t) [4 marks]
(c) Obtain the Fourier Series representation of xp(t) [4 marks]
(d) Determine the total energy of x(t) [2 marks]
(e) Determine the average power in xp(t) [2 marks]
(f) Determine the expression for the Fourier Transform of xp(t) [4 marks]
QUESTION THREE
(a) A certain DSB waveform of single tone modulation has a peak amplitude of 2.75V at and
the immediately succeeding minimum amplitude of 0.5V at . If within that interval
there are 12.5 cycles of the waveform, determine
(i) the frequency of the modulating signal
(ii) the frequency of the carrier
(iii) the percentage modulation
(iv) the transmission power efficiency
(v) the time domain expression for the DSB waveform
(vi) and sketch the frequency spectrum of the waveform
[15 marks]
(b) Using suitable diagrams explain how pre-emphasis leads to an improvement in the noise performance
of FM
[5 marks]
QUESTION FOUR
The carrier signal is angle modulated by a signal of variable amplitude,
. In observing the frequency spectrum of the modulated signal, it is
found that as is varied from 0V, the first time the carrier component is missing from the
spectrum is when V.
(a) Assuming that the waveform is FM
(i) determine the value of the frequency sensitivity factor of the modulator in V/Hz
(ii) determine the expression for the modulated signal
[5 marks]
(b) Assuming that the waveform is PM
(i) determine the value of the phase sensitivity factor of the modulator in V/rad.
(ii) determine the expression for the modulated signal
[5 marks]
(c) Given that the Bessel function of the first kind, order n at b, is given by
(i) show that the PM wave in (b) above may be represented as
(ii) sketch the one-sided magnitude spectrum of the signal for V, giving at least
10 spectral lines and their amplitudes
[10 marks]
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