ACHARYA INSTITUTE OF TECHNOLOGYDepartment of Mechatronics

Subject: COMMUNICATION SYSTEMSub Code: 10MT665

QUESTION BANK

Chapter 1

1 With a neat block diagram explain the basic building blocks of a communication system.

2 Write a note on different channels used for Communication System.

3 Define modulation? Explain the need for modulation.

4 Find the fourier transform of i) Ac Cos 2 Π fct ii) m (t) Cos 2 Π fct. Write its equivalent frequency spectrum.

5 Mention the Significance of Fourier Series and Fourier Transform in communication system..

6 Give the significance of Channel encoder and Source encoder.

7 Give the Significance of Repeater in Transmission of signal.

8 Give the Characteristics of Following channel i) Satellite ii) OFC

9 Mention the advantages of OFC over Telephone and Coaxial cable.

10 Give difference between Analog and Digital communication.

Chapter 2

11 Write a note on thermal noise. And mentions properties of thermal noise voltage 12 Define noise figure .derive noise figure of a two part device.

13 Write a note on SHOT noise and thermal noise.

14 Give the classification of NOISE

15 Explain internal and External Noise.

16 Derive the Equation for Equivalent noise temperature.

17 Mention the draw back of Noise Figure.

18

Chapter 3

19 Briefly explain the generation of AM using square law modulator giving relevant waveforms

20 Explain generation of AM using Switching Modulator.

21 Explain Demodulation of information using Square law Demodulator.

22 Explain Demodulation of information using Envelope Detector.

23 Write a note on generation of DSBSC using ring modulator.

24 A transmitter radiates 35kw,when μ=85, calculate the carrier power & power of each SB.

25 Explain in detail detection of DSBSC using COSTAs receiver.

26 An audio frequency b/g 10 sin [2 X105t] . assume the modulation index 0.2. calculate the side band frequency, amplitude of each side band, bandwidth & total power delivered through a load of 600 .

27 Derive equations for modulation index, efficiency and total power carried for a single tone amplitude modulation. 28Explain generation of AM using switching modulator 29 Consider message s/g met = 20 cos 2μt and carrying s/g c(t) =50 los 100nt. Give the time 30 domain expression resulting conventional AM wave for 75% modulation. Find the power developed. Across load of 100η developed due to this AM wave.31 Explain in detail detection of DSBSC using COSTAs receiver

32 Explain in detail detection of AM using envelop detector.

33 An audio frequency b/g 10 sin [2 X105t] . assume the modulation index 0.2. calculate the side band frequency, amplitude of each side band, bandwidth & total power delivered through a load of 600 .

32. Derive equations for modulation index, efficiency and total power carried for a single tone amplitude modulation.

33.Explain generation of AM using switching modulator

34.Consider message s/g met = 20 cos 2μt and carrying s/g c(t) =50 los 100nt. Give the time domain expression resulting conventional AM wave for 75% modulation. Find the power developed. Across load of 100η developed due to this AM wave.

35. A broadcast AM transmitter radiates 50 kW of carrier power. What will be the radiated power at 85 percent modulation?

36. A certain AM transmitter has an unmodulated RF carrier power of 1 kW. Determine the total power, the power in each sideband, and the peak power for each of the following modulation percentages using single-tone modulation: a) 25%, b) 50%, and c) 100%.

37. When the modulation percentage is 75, an AM transmitter produces 10 kW. How much of this is the carrier power? How much is the power per sideband? What would be the percentage power saving if the carrier and one of the sidebands were suppressed before transmission took place?

38. At what depth of modulation can an AM transmitter save 90% of power if the carrier and one sideband are suppressed?

39. The antenna current of an AM transmitter is 8 A when only the carrier is sent, but it increases to 8.93 A when the carrier is sinusoidally modulated. Determine the antenna current when the depth of modulation is 0.8.

40. When a broadcast AM transmitter is 50% modulated, its antenna current is 12 A. What will the current be when the modulation depth is increased to 0.9?

41. The input impedance at the base of a certain 10 kW commercial broadcasting station antenna is 50Ω resistive. For single-tone modulation, the rms ammeter at the base of the antenna reads 16 A. Determine the percentage of modulation.

42. A certain transmitter radiates 9 kW with the carrier unmodulated, and 10.125 kW when the carrier is sinusoidally modulated. Calculate the modulation index. If another sine wave, corresponding to 40 percent modulation, is transmitted simultaneously, determine the total radiated power.

43. The antenna current of an AM broadcast transmitter modulated to a depth of 40% by an audio sine wave, is 11 A. It increases to 12 A as a result of simultaneous modulation by another audio sine wave. What is the modulation index due to this second wave?

44. A 360-W carrier is simultaneously modulated by two audio waves with modulation percentages of 55 and 65, respectively. What is the total sideband power radiated?

45. The output current of a 60% modulated AM generator is 1.5 A. To what value will this current be if the generator is modulated additionally by another audio wave whose modulation index is 0.7? What will be the percentage power saving if the carrier and one of the sidebands are now suppressed?

46. A 60 dB AM transmitter is to be modulated simultaneously by two audio waves of indices 0.5 and 0.7. What is the total current if the antenna resistance is 75Ω?

47. An SSB transmission contains 80 kW. It is required that the system be replaced by a standard amplitude-modulated signal with the same power content. Determine the power content of each of the sidebands in the new system if the percentage modulation is 80%.

48. The antenna current of an AM broadcast transmitter modulated to a depth of 38.5% by an audio wave is 10.5 amperes. It increased by 4% as a result of simultaneous modulation caused by another wave. Determine the percent modulation caused by the second wave.

49. At a certain depth of modulation, the power used is 22% of the total power when the carrier is suppressed. If another simultaneous wave is added and the carrier and one of the sidebands are suppressed, the power saved is 85%. What are the modulation indices?

50. For a modulating signal of maximum bandwidth 20kHz and a carrier frequency of 2Mhz calculate the minimum and maximum frequencies when the signals are amplitude modulated by the following methods

a. DSB-AM

b. DSB-SC

c. SSB-AM

51. Calculate the modulation index of a carrier waveform of amplitude 10V and a sinusoidal modulating signal of 3.5V

52. Describe the diode demodulator and explain the function of each component. Why cannot a normal diode such as the 1N4148 be used as a demodulator?

53. Describe the operation of the ring modulator. What will happen if the diodes are mismatched? Draw diagrams how the AM waveforms are produced.

54. A square wave of amplitude 2V will be Amplitude modulated with a carrier waveform of amplitude 6V. Calculate the resultant modulation index.

55. Explain how message signal can be detected from AM wave using Super heterodyne receiver.

56. Give Time Domain and frequency domain Equation for AM.

57. Derive Time and frequency Domain Equation For DSBSC

Chapter 4

58. Explain the non linearity modulation in FM

59. Explain FM stereo multiplexing.

60. Give the CARSON’s rule for finding BW in FM

61. Write a note on generation of FM signal using Direct method.

62. Write a note on generation of FM signal using indirect method.

63. Write Time domain Equation of Narrowband FM

64. Write Time domain Equation of Wideband FM

65. Write Frequency domain Equation of Narrowband FM

66. Write Frequency domain Equation of Wideband FM

67. Give the Difference between Narrow band and Wideband FM

Chapter 5

68. Explain Detection of message signal from FM signal using PLL.

69. Explain Detection of message signal from FM signal using indirect method.

70. Explain Slope detector method of finding Message signal from modulated signal.

Chapter 6

71. Explain TDM in detail. 72. Discuss in brief working PCM.73. Show that quantization SNR for sinusoidal s/g is 1.8 + 6N.

74. A 10 khz sinusoidal with amplitude IV peak is quantized to have SNR of about 45db. Find

the number of both required/sample, bit rate and B.W.

75. A telephone s/g with B.W 4KHZ is digitized into an 8 – bit PCM Sampled at nyquist rate. Calculate PCM transmission B.W .

76. Explain the delta modulation.

77. Write a note on Quantization noise

78. Find the Signal to quantization noise ratio for Sinusoidal message signal.

79. Give the difference between uniform and non uniform quantization.

80. Show that quantization SNR for sinusoidal s/g is 4.8 + 6N.

81. Give the difference between midtread and mid raiser Quantization.

82. Explain A-Law and U- Law

83. Give the Drawback of uniform Quantization.

84. Encode the bits 11001011 using i) Manchester code ii) NRZ-R

85. Explain Robust Quantization.

Chapter 7

86. Find the Probability error of BASK

87. Find the Probability error of BFSK

88. Find the Probability error of BPSK

89. Find the Probability error of BQPSK

90. Explain the Transmitter and Receiver of BASK

91. Explain the Transmitter and Receiver of BPSK

92. Explain the Transmitter and Receiver of BFSK

93. Explain the Transmitter and Receiver of BQPSK

Chapter 8

94. What is RADAR? Explain in brief with block diagram blocks present in RADAR.

95. With a neat block diagram explain monochrome TV transmitter & receiver.

96. Give the RADAR Range Equation.

97. Explain the Working concept of RADAR

98. Explain Color TV transmitter and Receiver

99. Explain RADAR Transmitter .

100.Explain RADAR Receiver.