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TELE3113 Mid-Term Exam in T1 2022

Week 5: 14th March 2022


Name: ………………………
Student No: …………………



Instructions to Candidates
a) The time allowed: 60 minutes
b) Extra time to download, scan & upload: 30 minutes
c) Answer sheets should be uploaded via Midterm Exam
Answer Sheets Submission Link' on the Moodle
Course page
d) Deadline for uploading to Moodle: 10:30 am
e) Write your name and z-ID on this exam paper if you
are using a tablet/i-pad or on each answer sheet if
writing by hand
f) Answer all the questions. Total Marks = 20
g) Marks are as indicated. Questions do NOT have equal
marks.
h) All answers are to be written in the space provided on
this question paper or in blank sheets.
i) Trigonometric Identities, Fourier Transform table, and
Bessel function table are attached.
j) The paper consists of 2 questions, having three subparts
each.
k) This paper contains 22 pages in total, including this
page and six blank pages for doing rough work.
l) This exam contributes 20% to the total course
assessment.

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Question 1 (10 marks)
a) A message signal () = cos(2π40) +
1
2
cos(2π90) is transmitted using a
double sideband suppressed carrier (DSB-SC) modulation system with a sinusoidal
carrier signal having a frequency of and amplitude of . Sketch the spectrum
() of the transmitted DSB-SC signal () along with its phasor diagram. (3+2
marks)











































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Additional Space For Answering Q1a (Page 1 of 1)
















































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b) Now consider a message signal () = cos(200π) which is transmitted using
Amplitude Modulation (AM). Find the transmitted power and transmit
bandwidth for this AM modulated signal with underlying carrier amplitude
being = 10 and modulation index set as = 0.6. (2 marks)













































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c) A message signal () =
1
2
cos(2π70) +
1
3
cos(2π120) is fed as an input to the
square law modulator system, as shown in the figure below. Considering =
1 + 2
2 and a carrier angular frequency of = 2(10000) rad/s, find out
the centre frequency and bandwidth of the filter such that this system can produce
a standard AM signal. Also, determine the values of 1 and 2 when = 10 and
=
1
2
. (1+1+0.5+0.5 marks)

































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Additional Space For Answering Q1c (Page 1 of 2)










































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Additional Space For Answering Q1c (Page 2 of 2)







































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Question 2 (10 marks)
a) A tone-modulated Frequency Modulation (FM) signal with = 1 and = 100
Hz is applied to an ideal bandpass filter (BPF) with a passband of width = 250
Hz centred at = 500 Hz. Draw the spectrum, phasor diagram and envelope of
the output signal of this BPF. (2+2+2 = 6 marks)












































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Additional Space For Answering Q2a (Page 1 of 2)










































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Additional Space For Answering Q2a (Page 2 of 2)











































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b) Tone modulation is applied simultaneously to a frequency modulator and a
phase modulator, and the two output spectra are identical. Describe how
these two spectra will change when (a) the tone amplitude is increased or
decreased; (b) the tone frequency is increased or decreased; (c) the tone
amplitude and frequency are increased or decreased in the same proportion.
(1+1+1 = 3 marks)






































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Additional Space For Answering Q2b (Page 1 of 1)









































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c) What is the purpose of the Low Pass Filter (LPF) in the Frequency Modulation
(FM) detector with limiter system, as shown below? (1 mark)





















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(as a function of )
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(as a function of )
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Bessel Function Values Table