TELE3013 Mid-session QUIZ 1

Size: px

Start display at page:

Download "TELE3013 Mid-session QUIZ 1"

Bernard Horton
5 years ago
Views:

1 TELE3013 Mid-session QUIZ 1 Week 7 10 th April, 2006 Name: Student No: Instrutions to Candidates (1) Time allowed: 90 minutes or so (2) Answer all questions. Total Marks = 90. (3) Marks are as indiated. Questions do NOT have equal marks. (4) All answers are to written in the spae provided in this question paper. (5) This paper may not be retained by the andidate. (6) Trigonometri Identities, Fourier Transform table, and Bessel funtion table are attahed. (7) The paper onsist of 8 questions.

2 Question 1 (5 marks) a) Sketh a blok diagram showing a omplete ommuniation system. Inlude an enoder, modulator, transmitter, and their onverse funtional bloks. (3 marks) b) Explain the purpose of modulation. (2 marks)

3 Question 2 (16 marks) A arrier signal t) A os( ω t) ( = is modulated with a message, m( t) = 3 os + ( ω t) sin( ω t) The message frequeny is f = 100Hz, the arrier frequeny is f = 980kHz, and the arrier amplitude is m A = 20V. a) Express the message in the form m t ) = A ( ω t θ ) ( os m m. [Hint: reall the trigonometri identity, a os ( α ) + bsin( α ) a + b os α tan ( b a) m ( ) m.] (2 marks) b) Hene find the amplitude sensitivity fator, k a, needed to produe an AM s( t) = A 1+ k m( t) os ω t, with a modulation index of signal of the form [ ] ( ) 1 μ = 2. (2 marks) a ) Sketh a blok diagram of an AM modulator. (2 marks)

4 d) Sketh s(t), the modulated signal in the time domain. Show learly the maximum and minimum values of the arrier envelope on your diagram. (2 marks) e) Sketh the magnitude spetra of (i) the arrier, (ii) the message, and (iii) the AM signal. Show all numerial values on your axes that you an. (6 marks) f) What is the modulation effiieny of this AM signal? (2 marks)

5 Question 3 (12 marks) a) Under what onditions an an envelope detetor be used to demodulate an amplitude modulated signal? (2 marks) b) Draw a iruit diagram of an envelope detetor. (3 marks) ) With the aid of graphs, explain the priniples of operation of an envelope detetor. (5 marks) d) An envelope detetor is to be used to reover a message of bandwidth 5 khz from a arrier of frequeny 1 MHz. The resistor used in the RC iruit is to be 100 kω. Choose a suitable value for the apaitor. [Note: There is no unique answer here. Just pik a apaitor value within the range that will get the job done.] (2 marks)

6 Question 4 (14 marks) A message m(t) has the following spetrum; M(f) 2 4 f (khz) It is to be modulated onto a arrier of frequeny 1.2 MHz. a) Write a time domain expression for the DSB-SC signal for this message, in terms of m(t). (1 mark) b) Draw a blok diagram illustrating a simple DSB modulator. (2 marks) ) Sketh the spetrum of the DSB modulated signal. (2 marks) d) What is the bandwidth of the DSB modulated signal? (1 mark)

7 e) Write a time domain expression for the SSB-Upper Sideband modulated signal for this message, in terms of m(t), and the Hilbert transform of the message, m ˆ ( t). (2 marks) f) Draw a blok diagram for an SSB modulator, using the simple phase shift tehnique. (3 marks) g) Sketh the spetrum of the SSB-USB signal for this message. (2 marks) h) What is the bandwidth of the SSB signal for this message? (1 mark)

8 Question 5 (8 marks) a) Under what irumstanes is VSB a more pratial modulation tehnique than SSB? (1 mark) b) Draw a blok diagram of a VSB modulation system. (3 marks) ) A message of bandwidth 10 khz is to be modulated using VSB onto a arrier wave and sent down a hannel that has a bandwidth restrition of 900 khz to 915 khz. (i) Choose an appropriate arrier frequeny. (1 mark) (ii) Sketh a possible transfer funtion for the VSB shaping filter. (3 marks)

9 Question 6 (13 marks) a) Draw a blok diagram for a oherent detetor. (3 marks) b) Derive an expression for the output of the oherent detetor when the input is a DSB modulated signal arrying a message m(t). Denote the frequeny error of the loal osillator Δω and the phase offset θ. (5 marks)

10 ) Draw a blok diagram showing a Phase Loked Loop (PLL). (3 marks) d) Explain briefly why PLLs are so important in oherent detetors. (2 marks)

11 Question 7 (8 marks) a) Draw a blok diagram of a superheterodyne reeiver. (4 marks) b) A superheterodyne reeiver uses an intermediate frequeny of f IF = 455kHz. You wish to tune into a radio station with a arrier frequeny f = 1580 khz. Assuming high-side tuning, what is the frequeny of the loal osillator? (2 marks) ) What is the image frequeny in this ase? (2 marks)

12 Question 8 (14 marks) A single-tone message, m( t) = 2os( 2π 500t), is modulated onto a arrier of frequeny f = 92.9 MHz. The peak frequeny deviation of the modulated wave is Δf = 1kHz. a) What is the modulation index, β? (2 marks) b) Write a time domain expression for the FM modulated wave, assuming a arrier amplitude of 10 Volts. (3 marks) ) Is this Narrowband FM? (1 mark) d) What is the approximate bandwidth of this FM signal? (2 marks) e) Sketh the magnitude spetrum of this FM signal, showing the relative heights of the spetral omponents. (6 marks)

ENSC327 Communications Systems 4. Double Sideband Modulation. Jie Liang School of Engineering Science Simon Fraser University

ENSC327 Communications Systems 4. Double Sideband Modulation. Jie Liang School of Engineering Science Simon Fraser University ENSC327 Communiations Systems 4. Double Sideband Modulation Jie Liang Shool of Engineering Siene Simon Fraser University 1 Outline DSB: Modulator Spetrum Coherent Demodulator: Three methods Quadrature-arrier