Quiznetik

Communication Engineering | Set 1

1. If the peak message signal amplitude is half the peak amplitude of the carrier signal, the signal is            modulated.

Correct : C. 50%

2. A percentage of modulation greater than

Correct : D. 100%

3. Single sideband AM systems occupy same bandwidth as of conventional AM systems.

Correct : B. false

4. How is the performance of SSB AM systems in fading channels?

Correct : A. poor

5. Which of the following is a disadvantage of tone-in-band SSB system?

Correct : D. generation and reception of signal is complicated

6. FFSR in AM systems stands for

Correct : A. feedforward signal regeneration

7. AM demodulation technique can be divided into            and            demodulation.

Correct : C. coherent, noncoherent

8. Non coherent detection requires the knowledge of transmitted carrier frequency and phase at the receiver.

Correct : B. false

9. A product detector in AM systems is also called

Correct : D. phase detector

10. AM system use only product detector for demodulation. They never use envelope detectors.

Correct : B. false

11. LCD uses

Correct : B. twisted nematic crystals

12. Which of the following stage is present in FM receiver but not in AM receiver?

Correct : A. amplitude limiter

13. Function of duplexer in a RADAR is to permit the use of same antenna for transmission and reception.

Correct : A. true

14. Single Sideband Modulation (SSB) is generally reserved for point-to-point communication.

Correct : A. true

15. For an AM transmitter, class C amplifier can be used after the modulation stage.

Correct : B. false

16. For which of the modulated system, the linear amplified modulated stage is used?

Correct : A. low level amplitude modulated system

17. When noise is passed through a narrow band filter, the output of filter should be?

Correct : D. sinusoidal

18. A narrow band noise can exist in

Correct : D. am and fm both

19. The upper and lower sideband frequencies for 5KHz amplitude modulation with a 30KHz carrier frequency will be?

Correct : A. 35khz and 25khz

20. Phase array radar can track many targets together.

Correct : A. true

21. A duplex arrangement use separate frequencies for transmission.

Correct : A. true

22. VSB modulation is used in televisions because it avoids phase distortion at low frequencies.

Correct : B. false

23. A cordless telephone that uses separate frequencies for transmission in base and portable units is called

Correct : B. duplex

24. Which polarization is used to reduce the depolarization effect on received waves?

Correct : A. circular polarization

25. Circular polarization involves critical alignment between transmitting and receiving antenna.

Correct : B. false

26. It is only the reflected color that decided the color of an object.

Correct : B. false

27. What do you understand by the term “carrier” in modulation?

Correct : C. voltage for which amplitude, phase or frequency can be varied

28. Carrier wave in modulation is a resultant wave.

Correct : B. false

29. For a low level AM system, amplifier modulated stage must have

Correct : B. linear devices

30. Which is the greatest disadvantage of Pulse Code Modulation?

Correct : D. large bandwidth is required for it

31. Inductance and capacitance of a line is 0.8

Correct : A. 158

32. Quantization noise occurs in

Correct : D. amplitude modulation

33. What the main advantage of PCM?

Correct : C. lower noise

34. In AM pilot carrier, transmission has

Correct : B. two side bands and a carrier

35. Quantization noise depends upon both sampling rate and number of quantization levels.

Correct : B. false

36. Which of the following frequency is not transmitted in AM transmission?

Correct : D. audio frequency

37. Companding is used in PCM transmitters to allow amplitude limiting in the receivers.

Correct : B. false

38. What is the use of Companding?

Correct : D. to protect small signals in pcm from quantizing distortion

39. 5 PSD MODULATORS AND DEMODULATORS

Correct : B. false

40. Which of the following is not an advantage of digital modulation?

Correct : D. less bandwidth requirement

41. The performance of modulation scheme is not measured in terms of

Correct : D. transmitted power

42. In digital communication system, in order to increase noise immunity, it is necessary to increase

Correct : A. signal power

43. Which of the following is the ratio of signal energy per bit to noise power spectral density?

Correct : C. power efficiency

44. Increasing the data rate implies the increase in pulse width of digital symbol.

Correct : B. false

45. Which of the following is the ratio of the throughput data rate per Hertz?

Correct : A. bandwidth efficiency

46. Which of the following is defined as the range of frequencies over which the signal has a non zero power spectral density?

Correct : D. absolute bandwidth

47. is equal to width of main spectral lobe.

Correct : A. null to null bandwidth

48. Half power bandwidth is also called

Correct : C. 3 db bandwidth

49. FM is a part of general class of modulation known as

Correct : A. angle modulation

50. Frequency modulated signal is regarded as the phase modulated signal in which the modulating wave is differentiated before modulation.

Correct : B. false

51. Frequency modulation index defines the relationship between the              and bandwidth of transmitted signal.

Correct : B. amplitude of message signal

52. Which of the following are two methods for generating FM signal?

Correct : C. direct method, indirect method

53. In indirect method, the carrier frequency is directly varied in accordance with the input modulating signal.

Correct : B. false

54. Which of the following is used to vary the frequency of the carrier frequency in accordance with the baseband signal amplitude variations in direct method of FM generation?

Correct : D. voltage controlled oscillators

55. Frequency demodulator is a frequency to amplitude converter circuit.

Correct : A. true

56. Which of the following is not a technique for FM demodulation?

Correct : C. product detector

57. Which of the following FM demodulator is sometimes known as pulse averaging discriminator?

Correct : B. zero crossing detection

58. PLL in FM detection stands for

Correct : A. phase locked loop

59. In angle modulation, signal to noise ratio before detection is a function of

Correct : D. if filter bandwidth

60. FM can improve the receiver performance through adjustment of transmitted power.

Correct : B. false

61. De-emphasis circuit is used

Correct : B. after detection

62. Why frequency fogging is used in a carrier system?

Correct : B. to reduce cross talk

63. For a phase modulated signal, the frequency deviation is proportional to

Correct : B. amplitude only

64. The frequency deviation is proportional to frequency in phase modulated signal.

Correct : B. false

65. Which of the following is not necessarily an advantage of FM over AM?

Correct : C. higher bandwidth is required

66. What is number of possible outputs if there is 7 line digital input?

Correct : D. 128

67. What is the frequency of the stereo sub carrier signal in FM broadcasting?

Correct : D. 38 khz

68. What is the bandwidth required in SSB signal?

Correct : A. fm

69. One of the advantage of using a high frequency carrier wave is that it dissipates very small power.

Correct : A. true

70. The antenna current is 10A. Find the percentage of modulation when the antenna current increases to 10.4A?

Correct : C. 28.5%

71. Find the total power, if the carrier of an AM transmitter is 800W and it is modulated to 50%?

Correct : D. 900w

72. Spread spectrum is used for

Correct : C. encrypting & hiding signal

73. Which is a quantization process?

Correct : C. rounding & truncation

74. Quantization is a            process.

Correct : C. many to few mapping

75. Which conveys more information?

Correct : B. low probability event

76. If the channel is noiseless information conveyed is        and if it is useless channel information conveyed is

Correct : D. 1,0

77. The mutual information between a pair of events is

Correct : D. all of the mentioned

78. 2 QUANTIZATION

Correct : B. false

79. The output of an information source is

Correct : A. random

80. When the base of the logarithm is e, the unit of measure of information is

Correct : C. nats

81. Flat top sampling of low pass signals

Correct : A. gives rise to aperture effect

82. In a delta modulation system, granular noise occurs when the

Correct : D. modulating signal remains constant

83. A PAM signal can be detected using

Correct : A. low pass filter

84. Coherent demodulation of FSK signal can be performed using

Correct : A. matched filter

85. The use of non uniform quantization leads to

Correct : C. increase in snr for low level signals

86. A PWM signal can be generated by

Correct : B. a monostable multi vibrator

87. TDM is less immune to cross-talk in channel than FDM.

Correct : B. false

88. In an ideal TDM system, the cross correlation between two users of the system is

Correct : B. 0

89. TDM requires

Correct : B. transmission of data samples

90. Which waveforms are also called as line codes?

Correct : A. pcm

91. When pulse code modulation is applied to non binary symbols we obtain waveform called as

Correct : C. m-ary

92. Examples of PCM waveforms are

Correct : D. all of the mentioned

93. Which type is used and preferred in digital logic circuits?

Correct : A. nrz-l

94. Which method is called as differential encoding?

Correct : B. nrz-m

95. Which method is preferred in magnetic tape recording?

Correct : B. nrz-m

96. NRZ-S is complement of

Correct : B. nrz-m

97. The return to zero waveform consists of

Correct : D. all of the mentioned

98. Phase encoded group consists of

Correct : D. all of the mentioned

99. In which waveform logic 1 is represented by half bit wide pulse and logic 0 is represented by absence of pulse?

Correct : A. unipolar rz

100. In which waveform logic 1 and logic 0 are represented by opposite one half bit wide pulses?

Correct : B. bipolar rz