Tuesday, 8 November 2016

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EE AND ECE IMPORTANT MCQ-COMMUNICATION SYSTEMS PART TWO



ANSWER KEY-Correct answer is indicated by symbol (V) in options.
HINTS-In some questions options E-HINTS is indicating the hints of answer.

51) The modulation index is, if fm = 500 Hz, Δf = 2.25 kHz
A [ ]) 2.25
B [v]) 4.5
C [ ]) 9
D [ ]) 18
E [ ]) HINTS-Δf = 2.25 kHz, fm = 500 Hz ,Mi=Δf /fm

52) If D is mouth diameter of a paraboloid reflector, its directivity is proportional to
A [v]) D²
B [ ]) D
C [ ]) √D
D [ ]) D³
E [ ]) HINTS-Directivity of parabolic reflector = 6(D/λ)²

53) Directive gain is
A [v]) a power ratio
B [ ]) a current ratio
C [ ]) a voltage ratio
D [ ]) a distance ratio
E [ ]) HINTS-Directive gain is the ratio of power density radiated in a particular direction by the antenna to the power density that would be radiated by isotropic antenna.

54) Which of the following sampling frequencies is considered adequate in voice telephony?
A [ ]) 4 kHz
B [v]) 8 kHz
C [ ]) 16 kHz
D [ ]) 32 kHz
E [ ]) HINTS-Generally bandwidth of voice telephony is 4 kHz.Sampling frequency should be twice this value

55) Resonant circuits are used in
A [ ]) audio amplifiers
B [v]) RF amplifiers
C [ ]) both audio and RF amplifiers
D [ ]) none of the above

56) The requirements of carrier frequency are
A [ ]) precise frequency value
B [ ]) low frequency drift
C [v]) both (a) and (b)
D [ ]) neither (a) nor (b)

57) The received signal frequency at any time of a super-heterodyne receiver having IF =
456 kHz is 1 MHz. The corresponding image signal is
A [v]) within the medium band
B [ ]) outside the medium band
C [ ]) depend upon modulation index
D [ ]) depends on Modulating frequency
E [ ]) HINTS-Image signal frequency = Received signal frequency - 2 x Intermediate frequency.
fi= 1 MHz - 2 x 456kHz=1 MHz - 912 kHz =88 kHz ,which lies in medium bond.

58) For an ideal 3000 Hz channel, Nyquist rate is
A [ ]) 3000 bps
B [v]) 6000 bps
C [ ]) 9000 bps
D [ ]) 12000 bps
E [ ]) HINTS-Nyquist rate is twice

59) In the FM wave described by equation v = 15 sin (4 x 10² t + 3 sin 1100 t), the maximum frequency deviation is
A [ ]) 175 Hz
B [v]) 525 Hz
C [ ]) 3 Hz
D [ ]) 58.33 Hz
E [ ]) HINTS- fm=1100/2π=175Hz, Maximum frequency deviation = 3 x 175 = 525 Hz.

60) Consider the following statements about Rhombic antenna
1. It is non resonant
2.It is a broad band antenna
3.It is ideally suited for HF transmission
Which of the above are correct?
A [v]) 1, 2, 3
B [ ]) 1, 3 only
C [ ]) 2, 3 only
D [ ]) 1 only

61) The antenna diameter of a radar system is doubled. The maximum range will
A [v]) be doubled
B [ ]) become four times
C [ ]) be halved
D [ ]) decrease to one fourth

62) Quantizing error occurs in
A [ ]) TDM
B [ ]) FDM
C [v]) PCM
D [ ]) PWD

63) Which one of the following is non-resonant antenna?
A [ ]) Folded dipole
B [ ]) Broad side array
C [ ]) End fire array
D [v]) Rhombic antenna

64) The most suitable method for detecting a modulated signal g(t) = (3 to 6 cos 2πfmt) cos 2πfct is
A [v]) envelope detector
B [ ]) synchronous detector
C [ ]) ratio detector
D [ ]) both a and b
E [ ]) HINTS-Because it is an AM Signal

65) When the number of quantising levels is 16 in PCM, the number of pulses in a code group will be
A [ ]) 16
B [ ]) 8
C [v]) 4
D [ ]) 2
E [ ]) HINTS-Q=2^n ,16=2^n then n=4

66) In PCM, the biggest disadvantage as compared to AM is
A [v]) larger bandwidth
B [ ]) larger noise
C [ ]) inability to handle analog signals
D [ ]) incompatibility with time division multiplex systems

67) Kell factor is about
A [ ]) 5
B [ ]) 3
C [v]) 0.7
D [ ]) 0.2
E [ ]) HINTS-Kell factor indicates reduction in vertical resolution and varies from 0.65 to 0.85.

68) A Discone antenna is
A [v]) a combination of disk and cone in close approximate
B [ ]) a combination of disk and cone at λ/4 spacing
C [ ]) a combination of disk and cone far apart
D [ ]) a combination of disk and cone at λ/2 spacing

69) A balun provides an impedance transformation of
A [ ]) 16 : 1
B [v]) 4 : 1
C [ ]) 8 : 1
D [ ]) 2 : 1

70) Consider the draw backs
1.Slope overload
2.Serration noise
3.Granular noise
Which of these draw backs does Delta modulation have?
A [ ]) 1 and 2 only
B [ ]) 2 and 3 only
C [v]) 1 and 3 only
D [ ]) 1, 2, 3

71) Armstrong F.M. transmitter performs frequency multiplication in stages
A [ ]) to increase the overall S/N
B [ ]) For convenience
C [ ]) to reduce the bandwidth
D [v]) to find the desired value of carrier frequency with frequency deviation

72) The use of SSB
A [v]) halves the bandwidth required for transmission
B [ ]) does not affect the bandwidth for transmission
C [ ]) decreases the bandwidth required for transmission by 25%
D [ ]) decreases the bandwidth required for transmission by 66.6%

73) Video signals are transmitted through
A [v]) amplitude modulation
B [ ]) frequency modulation
C [ ]) either amplitude or frequency modulation
D [ ]) neither amplitude nor frequency modulation

74) Beam width of an antenna is expressed in
A [ ]) metres
B [v]) degrees
C [ ]) ratio of two powers
D [ ]) ratio of two angles

75) In broadcast television, the number of lines per frame is chosen to be odd number to
A [ ]) reduce the required bandwidth
B [ ]) improve resolution
C [ ]) reduce peak power requirement
D [v]) make interlacing easier

76) In a picture tube, the video signal is applied to
A [v]) cathode
B [ ]) grid
C [ ]) any anode
D [ ]) either cathode or grid

77) Full duplex operation
A [ ]) requires modems at both ends of circuit
B [ ]) requires two pairs of cables
C [ ]) can transfer data in both directions simultaneously
D [v]) all of the above

78) Which of the following antennas is circularly polarized?
A [ ]) Yagi-Uda
B [ ]) Parabolic reflector
C [ ]) Small circular loop
D [v]) Helical

79) In a communication receiver, a squelch circuit is normally inserted
A [ ]) before detector
B [v]) after detector
C [ ]) before mixer
D [ ]) after power amplifier

80) In PCM, the information lies
A [ ]) in one or two properties of the pulse
B [ ]) in absence of pulse
C [ ]) in presence of pulse
D [v]) in presence or absence of pulse

81) The discone antenna is
A [v]) used in UHF range
B [ ]) circularly polarized
C [ ]) used in radar
D [ ]) used as a direction finding antenna

82) In PCM the amplitude levels are transmitted in a 7 unit code. Sampling frequency is 10 kHz. The bandwidth should be
A [ ]) 5 kHz
B [ ]) 30 kHz
C [v]) 35kHz
D [ ]) 5 MHz
E [ ]) HINTS-Bandwidth = 1/2(10 x 7) = 35 kHz.

83) In a circuit the value of resistor is made four times. The noise voltage generated by this resistance will
A [v]) be doubled
B [ ]) be increased four times
C [ ]) remain the same
D [ ]) become half
E [ ]) HINTS-Noise voltage ∝ √R.

84) In a satellite system circular polarization is to be obtained. The antenna used is
A [ ]) parabolic
B [ ]) horn
C [ ]) log periodic
D [v]) helical

85) To prevent overloading in the last IF amplifier one should use
A [v]) variable sensitivity
B [ ]) squelch
C [ ]) double conversion
D [ ]) None

86) In a communication system, noise is most likely to affect the signal
A [ ]) at the receiver
B [ ]) at the transmitter
C [ ]) at the information source
D [v]) in the channel

87) The simplest method of suppression of unwanted side band in AM is
A [v]) filter method
B [ ]) phase shift method
C [ ]) third method
D [ ]) both (a) and (b)

88) For attenuation of low frequencies we should use
A [ ]) shunt capacitance
B [v]) series capacitance
C [ ]) shunt inductance
D [ ]) series inductance

89) Which one of the following is true?
A [ ]) Characteristic impedance of twin wire feeder and coaxial cable are nearly the. same
B [ ]) The characteristic impedance of coaxial cable is more than that of twin wire cable
C [v]) The characteristic impedance of twin wire cable is more than that of coaxial cable
D [ ]) The characteristic impedance of a twin wire feeder may be more or less than that of coaxial cable

90) In cellular telephone each cell is designed to handle
A [v]) 45 two way communications
B [ ]) 90 two way communications
C [ ]) 45 one way communications
D [ ]) 180 two way communications

91) It is desired to couple a coaxial line to a two parallel wire line. It is best to use
A [ ]) quarter wave transformer
B [v]) balun
C [ ]) slotted line
D [ ]) slotted line

92) The effective length of antenna is different from actual length due to
A [ ]) top loading
B [ ]) end effects
C [v]) both (a) and (b)
D [ ]) none of the above

93) Noise can be measured by
A [ ]) D.C. voltmeter
B [v]) A.C. voltmeter
C [ ]) either of the above
D [ ]) none of the above

94) In FM, as bandwidth increases
A [ ]) distortion increases
B [v]) distortion decreases
C [ ]) distortion remains unaffected
D [ ]) all

95) To separate channels in FDM receiver we have to use
A [ ]) integration
B [ ]) AND gate
C [v]) band pass filter
D [ ]) differentiation

96) UHF range is
A [ ]) 3 to 30 MHz
B [ ]) 30 to 300 MHz
C [v]) 300 to 3000 MHz
D [ ]) 3000 to 30000 MHz

97) In asynchronous TDM, for n signal sources, each frame contains m slots, where m is usually
A [ ]) Less than n
B [ ]) 2n
C [ ]) n
D [v]) greater than 2n

 98) Noise which assumes great importance at high frequencies is
A [ ]) flicker noise
B [ ]) Johnson noise
C [v]) transit-time noise
D [ ]) shot noise

99) Which one is Analog Continuous modulation technique?
A [v]) AM
B [ ]) PAM
C [ ]) DM
D [ ]) PCM

100) AM transmitter employing low level modulation
A [ ]) uses class C amplifier for amplification
B [ ]) requires higher audio power
C [v]) has a poor efficiency
D [ ]) has a higher efficiency
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