B.E. / B.Tech.Degree Examinations, April / May 2010Regulations 2008
Fourth Semester
Electronics and Communication Engineering
EC2252 Communication Theory
Time: Three Hours Maximum: 100 Marks
Answer ALL Questions
Part A - (10 x 2 = 20 Marks)
1. How many AM broadcast stations can be accommodated in a 100 kHz bandwidth
if the highest frequency modulating a carrier is 5 kHz?
2. What are the causes of linear distortion?
3. Draw the block diagram of a method for generating a narrowband FM signal.
4. A carrier wave of frequency 100 MHz is frequency modulated by a signal20 sin (200 ¼ £ 103 t):
What is bandwidth or FM signal if the frequency sensitivity of the modulation is25kHz = V.
5. When i s a random process called deterministic?
6. A receiver connected to an antenna or resistance or 50 has an equivalent noise
resistance or 30 -. Find the receiver noise figure.
7. What are the characteristics of superheterodyne receivers?
8. What are the methods to Improve FM threshold reduction?
9. The ruin entropy function.
10. The ¯ ne Rate Bandwidth and Bandwidth e ± ciency.
Part B - (5 x 16 = 80 Marks)
11. (A) (i) Draw an envelope detector circuit used for Demodulation of AM and ex-plain its operation. (Marks 10)
(Ii) How SSB can be generated using Weaver's method? Illustrate with a neatblock diagram. (Marks 6)
OR
11. (B) (i) Discuss in detail about frequency translation and frequency division mul-tiplexing technique with diagrams. (Marks 10)
(Ii) compare Amplitude Modulation and Frequency Modulation.(6)
12. (A) (i) Using suitable Mathematical analysis show That Produces FM modulationin ¯ nite sideband. Also deduce an expression for the frequency modulatedoutput and its frequency spectrum. (Marks 10)
(Ii) How can you generate an FM from PM and PM from FM?(Marks 6)
OR
12. (B) (i) A 20 MHz is frequency modulated by a sinusoidal signal Such That the max-imum frequency deviation i s 100 kHz. Determine the modulation indexand approximate bandwidth of the FM signal for the following, modulatingsignal frequencies,
(1) 1 kHz (2) 100 kHz and (3) 500 kHz. (Marks 8)(Ii) Derive the time domain expressions or FM and PM signals.(8)
13. (A) (i) Give a random process, X (t) = Acos (wt + μ), where A and! are constantsand μ is a uniform random variable. That show X (t) i s ergodic in bothmean and auto correlation. (Marks 8)
(Ii) Write a short note on shot noise And also explain about power spectraldensity of shot noise. (Marks 8)OR
13. (B) Write the details about narrowband noise and the properties or quadraturecomponents or narrowband noise. (Marks 16)
14. (A) Derive an expression for SNR at Input (SNRC) and output or (SNRo) or acoherent detector. (Marks 16)OR
14. (B) (i) Explain pre-emphasis and de-emphasis in detail. (Marks 10)(Ii) compare the performances of AM and FM systems. (Marks 6)
15. (A) (i) Find the code words for ¯ ve symbols of the alphabet or a discrete memorysource with less probability f0.4, 0.2, 0.2, 0.1, 0.1g, using Hu ® man codingand determining the source entropy and average codeword length. (Marks 10)
(Ii) Discuss the source coding theorem. (Marks 6)
OR
15. (B) (i) Derive the channel capacity of a continuous band limited white Gaussiannoise channel. (Marks 10)
(Ii) Discuss about rate distortion theory. (Marks 6)
Fourth Semester
Electronics and Communication Engineering
EC2252 Communication Theory
Time: Three Hours Maximum: 100 Marks
Answer ALL Questions
Part A - (10 x 2 = 20 Marks)
1. How many AM broadcast stations can be accommodated in a 100 kHz bandwidth
if the highest frequency modulating a carrier is 5 kHz?
2. What are the causes of linear distortion?
3. Draw the block diagram of a method for generating a narrowband FM signal.
4. A carrier wave of frequency 100 MHz is frequency modulated by a signal20 sin (200 ¼ £ 103 t):
What is bandwidth or FM signal if the frequency sensitivity of the modulation is25kHz = V.
5. When i s a random process called deterministic?
6. A receiver connected to an antenna or resistance or 50 has an equivalent noise
resistance or 30 -. Find the receiver noise figure.
7. What are the characteristics of superheterodyne receivers?
8. What are the methods to Improve FM threshold reduction?
9. The ruin entropy function.
10. The ¯ ne Rate Bandwidth and Bandwidth e ± ciency.
Part B - (5 x 16 = 80 Marks)
11. (A) (i) Draw an envelope detector circuit used for Demodulation of AM and ex-plain its operation. (Marks 10)
(Ii) How SSB can be generated using Weaver's method? Illustrate with a neatblock diagram. (Marks 6)
OR
11. (B) (i) Discuss in detail about frequency translation and frequency division mul-tiplexing technique with diagrams. (Marks 10)
(Ii) compare Amplitude Modulation and Frequency Modulation.(6)
12. (A) (i) Using suitable Mathematical analysis show That Produces FM modulationin ¯ nite sideband. Also deduce an expression for the frequency modulatedoutput and its frequency spectrum. (Marks 10)
(Ii) How can you generate an FM from PM and PM from FM?(Marks 6)
OR
12. (B) (i) A 20 MHz is frequency modulated by a sinusoidal signal Such That the max-imum frequency deviation i s 100 kHz. Determine the modulation indexand approximate bandwidth of the FM signal for the following, modulatingsignal frequencies,
(1) 1 kHz (2) 100 kHz and (3) 500 kHz. (Marks 8)(Ii) Derive the time domain expressions or FM and PM signals.(8)
13. (A) (i) Give a random process, X (t) = Acos (wt + μ), where A and! are constantsand μ is a uniform random variable. That show X (t) i s ergodic in bothmean and auto correlation. (Marks 8)
(Ii) Write a short note on shot noise And also explain about power spectraldensity of shot noise. (Marks 8)OR
13. (B) Write the details about narrowband noise and the properties or quadraturecomponents or narrowband noise. (Marks 16)
14. (A) Derive an expression for SNR at Input (SNRC) and output or (SNRo) or acoherent detector. (Marks 16)OR
14. (B) (i) Explain pre-emphasis and de-emphasis in detail. (Marks 10)(Ii) compare the performances of AM and FM systems. (Marks 6)
15. (A) (i) Find the code words for ¯ ve symbols of the alphabet or a discrete memorysource with less probability f0.4, 0.2, 0.2, 0.1, 0.1g, using Hu ® man codingand determining the source entropy and average codeword length. (Marks 10)
(Ii) Discuss the source coding theorem. (Marks 6)
OR
15. (B) (i) Derive the channel capacity of a continuous band limited white Gaussiannoise channel. (Marks 10)
(Ii) Discuss about rate distortion theory. (Marks 6)
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