Fourth Semester B.Tech. Degree Examination, December 2009
(2003 Scheme)
03-403 : ANALOG COMMUNICATION (TA)
Time : 3 Hours Max. Marks : 100
PART – A
Answer all questions. Each question carries 4 marks. (4×10=40 Marks)
1. Explain the function of an echo suppressor in a telephone trunk circuit.
2. Define modulation index for sinusoidal AM. For standard AM transmission, the
maximum peak-to-peak volatge is 150 V, and minimum peak-to-peak volatge is 50 V.
Calculate the modulation index.
3. Compare DSB-SC modulation and standard AM with respect to transmitted power,
bandwidth and circuit complexity.
4. An AM broadcast receiver has an IF of 455 KHz and it is tuned to 1000 KHz. The
RF stage has one tuned circuit with a Q of 50. Find the image frequency, and image
rejection in dB.
5. Discuss the effect of frequency multiplication and frequency mixing on the frequency
deviation and centre frequency, in FM transmitters.
6. Explain how a varactor diode may be used to generate FM.
7. Explain the necessity of AFC in a direct FM transmitter.
8. Calculate the thermal noise power available from a resistance R at room temperature
(290°K) for a bandwidth of 2 MHz. Calculate the noise volatge given R = 50 ?? .
9. State the axioms of probability.
10. What do you mean by white noise ? Plot the autocorrelation function and power
spectral density of white noise.
PART – B
Answer any two questions from each Module. Each question carries 10 marks.
(10×6=60 Marks)
Module – I
11. Explain the architecture of a typical electronic digital switching machine for switching
PCM telephone channels. 10
12. a) Derive the frequency spectrum of a sinusoidally modulated AM wave. 5
b) A standard AM transmission sinusoidally modulated to a depth of 30% produces
sideband frequencies of 4.928 MHz and 4.914 MHz. The amplitude of each
sideband frequency is 75 volts. Determine the amplitude and frequency
of the carrier. 5
13. a) Describe the filter method of SSB generation. 6
b) Show mathematically that an SSB signal can be demodulated by a product
detector. What is the requirement on the locally generated carrier for demodulation ? 4
Module – II
14. Explain with relevant circuit diagram and theory, how a Foster-Seeley discriminator
may be used to detect FM waves. 10
15. a) Compare FM with PM. 4
b) Draw the circuit diagram of an amplitude limiter in an FM receiver and explain its
working. 6
16. Derive the figure of Merit for a DSB-SC receiver using coherent detection, assuming
sinusoidal modulation. 10
Module – III
17. a) State any two properties of power spectral density. 4
b) Define cross spectral densities of two random processes X(t) and Y(t).
Let Z(t) = X(t) + Y(t) be a sum random process with X(t) and Y(t) being random
processes of zero mean and individually wide sense stationary. Find the
Autocorrelation function and power spectral density of Z(t). 6
18. a) Derive an expression for narrow band noise in terms of the in-phase and
quadrature components. 5
b) Explain any two properties of the quadrature components of narrow band noise. 5
19. a) Define probability density function (pdf) and cumulative distribution function
(cdf) of a random variable and discuss its properties. 6
b) Define the pdf of a uniformly distributed random variable. Derive its mean value. 4
–––––––––––––––––––––––
(2003 Scheme)
03-403 : ANALOG COMMUNICATION (TA)
Time : 3 Hours Max. Marks : 100
PART – A
Answer all questions. Each question carries 4 marks. (4×10=40 Marks)
1. Explain the function of an echo suppressor in a telephone trunk circuit.
2. Define modulation index for sinusoidal AM. For standard AM transmission, the
maximum peak-to-peak volatge is 150 V, and minimum peak-to-peak volatge is 50 V.
Calculate the modulation index.
3. Compare DSB-SC modulation and standard AM with respect to transmitted power,
bandwidth and circuit complexity.
4. An AM broadcast receiver has an IF of 455 KHz and it is tuned to 1000 KHz. The
RF stage has one tuned circuit with a Q of 50. Find the image frequency, and image
rejection in dB.
5. Discuss the effect of frequency multiplication and frequency mixing on the frequency
deviation and centre frequency, in FM transmitters.
6. Explain how a varactor diode may be used to generate FM.
7. Explain the necessity of AFC in a direct FM transmitter.
8. Calculate the thermal noise power available from a resistance R at room temperature
(290°K) for a bandwidth of 2 MHz. Calculate the noise volatge given R = 50 ?? .
9. State the axioms of probability.
10. What do you mean by white noise ? Plot the autocorrelation function and power
spectral density of white noise.
PART – B
Answer any two questions from each Module. Each question carries 10 marks.
(10×6=60 Marks)
Module – I
11. Explain the architecture of a typical electronic digital switching machine for switching
PCM telephone channels. 10
12. a) Derive the frequency spectrum of a sinusoidally modulated AM wave. 5
b) A standard AM transmission sinusoidally modulated to a depth of 30% produces
sideband frequencies of 4.928 MHz and 4.914 MHz. The amplitude of each
sideband frequency is 75 volts. Determine the amplitude and frequency
of the carrier. 5
13. a) Describe the filter method of SSB generation. 6
b) Show mathematically that an SSB signal can be demodulated by a product
detector. What is the requirement on the locally generated carrier for demodulation ? 4
Module – II
14. Explain with relevant circuit diagram and theory, how a Foster-Seeley discriminator
may be used to detect FM waves. 10
15. a) Compare FM with PM. 4
b) Draw the circuit diagram of an amplitude limiter in an FM receiver and explain its
working. 6
16. Derive the figure of Merit for a DSB-SC receiver using coherent detection, assuming
sinusoidal modulation. 10
Module – III
17. a) State any two properties of power spectral density. 4
b) Define cross spectral densities of two random processes X(t) and Y(t).
Let Z(t) = X(t) + Y(t) be a sum random process with X(t) and Y(t) being random
processes of zero mean and individually wide sense stationary. Find the
Autocorrelation function and power spectral density of Z(t). 6
18. a) Derive an expression for narrow band noise in terms of the in-phase and
quadrature components. 5
b) Explain any two properties of the quadrature components of narrow band noise. 5
19. a) Define probability density function (pdf) and cumulative distribution function
(cdf) of a random variable and discuss its properties. 6
b) Define the pdf of a uniformly distributed random variable. Derive its mean value. 4
–––––––––––––––––––––––
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