EE AND ECE IMPORTANT MCQ-COMMUNICATION SYSTEMS PART FOUR

51) In spread spectrum technique
A [ ]) a modulated signal is modulated again
B [ ]) a modulated signal is modulated twice again
C [ ]) the power of a modulated signal is increased
D [v]) the noise component of a modulated signal is decreased

52) QAM stands for
A [ ]) Quasi-Amplitude Modulation
B [ ]) Quadrature Angle Modulation
C [v]) Quadrature Amplitude Modulation
D [ ]) None of the above

53) The bandwidth required for amplitude modulation is
A [ ]) half the frequency of modulating signal
B [ ]) equal to the frequency of modulating signal
C [v]) twice the frequency of modulating signal
D [ ]) four times the frequency of modulating signal

54) BPSK stands for
A [v]) Binary Phase Shifting Key
B [ ]) Broad Phase Shifting Key
C [ ]) Bit Phase Shifting Key
D [ ]) Binary Pulse Shifting Key

55) Top loading in an antenna increases
A [v]) effective height
B [ ]) beam width
C [ ]) input capacitance
D [ ]) bandwidth

56) In the stabilized reactance modulators AFC system
A [ ]) the discriminator must have a fast time constant to prevent demodulation
B [ ]) the higher discriminator frequency the better the oscillator frequency stability
C [ ]) the discriminator frequency must not be too low, or the system will fail
D [v]) phase modulation is converted into FM by the equalizer circuit

57) In a system using QASK and 4 bits to form a symbol, the required bandwidth is
A [ ]) same as BPSK
B [ ]) half of that in BPSK
C [v]) one-fourth of that in BPSK
D [ ]) none of the above

58) Which of the following terms is not applicable to Yagi-Uda array?
A [v]) High gain
B [ ]) Folded dipole
C [ ]) Parasitic elements
D [ ]) Good bandwidth

59) If transmission path, in PCM, is very long then
A [v]) repeater stations are used
B [ ]) pulse width may be increased
C [ ]) pulse amplitude is increased
D [ ]) pulse spacing is reduced

60) Bandwidth for practical PCM system is (where n is no. of channels, N length of PCM codes)
A [v]) 2n N fm Hz
B [ ]) 4n fm Hz
C [ ]) 2n fm
D [ ]) (N + 1)fm

61) Circuit switching, Message switching and Packet Switching Network belong to which of the following systems?
A [v]) Computer communication system
B [ ]) Electromechanical communication system
C [ ]) PBX system
D [ ]) EPBX system

62) The Shannon-Hartley law
A [v]) refers to noise
B [ ]) defines bandwidth
C [ ]) describes signalling rate
D [ ]) refers to distortion

63) Maximum undistorted power output of a transmitter is obtained when its modulation is__________ percent.
A [ ]) more than 100
B [v]) 100
C [ ]) less than 100
D [ ]) 50

64) Pulse modulation is used in
A [ ]) radio navigation
B [ ]) automatic landing equipment
C [ ]) data communications
D [v]) all of the above

65) In an amplitude modulated waveform, the amplitude of the sideband is
A [ ]) independent of the carrier amplitude
B [ ]) independent of the modulation index
C [ ]) carrier amplitude x modulation index
D [v]) 1/2 carrier amplitude x modulation index

66) In communication systems the frequency range used for voice is
A [ ]) 15 Hz to 150 Hz
B [ ]) 30 Hz to 1000 Hz
C [ ]) 100 Hz to 1500 Hz
D [v]) 300 Hz to 3800 Hz

67) A receiver has poor selectivity. It will also have poor
A [ ]) sensitivity
B [ ]) double spotting
C [v]) blocking
D [ ]) diversity reception

68) Ground wave can be used for communication upto
A [ ]) 5 kHz
B [ ]) 12 kHz
C [v]) 16 kHz
D [ ]) 25 kHz

69) A Marconi antenna
A [v]) is a grounded antenna with a length equal to λ/4
B [ ]) is an ungrounded antenna with a length equal to λ/4
C [ ]) has a length equal to 1
D [ ]) has a length equal to λ/2

70) The autocorrelation function of the white noise is
A [ ]) impulse function
B [ ]) step function
C [v]) constant
D [ ]) none of the above

71) If fs be the signal frequency and fi be the intermediate frequency then image frequency
is given by
A [ ]) fs + fi
B [ ]) fs ± fi
C [v ]) fs ± 2fi
D []) fs + 2fi

72) If k denotes Boltzmann’s constant, the rms value of thermal noise voltage is
proportional to
A [ ]) k²
B [ ]) k
C [v]) √k
D [ ]) (k)⅓

73) Vestigial sideband is most commonly used in
A [ ]) radio transmission
B [v]) television transmission
C [ ]) telephony
D [ ]) all of the above

74) A helical antenna is used for satellite tracking due to its
A [v]) good front to back ratio
B [ ]) broad bandwidth
C [ ]) circular polarization
D [ ]) both (a) and (b)

75) Costa’s receiver is used for
A [v]) coherent detection of AM-SC signal
B [ ]) asynchronous detection of AM-SC signal
C [ ]) amplitude modulation of signal
D [ ]) frequency modulation of signal

76) What is typical bandwidths of a 2-wire telephone line?
A [v]) 300 Hz to 3.4 kHz
B [ ]) 20 Hz to 4 kHz
C [ ]) dc to 4 kHz
D [ ]) 20 Hz to 20 kHz

77) In a FM signal, the modulation index increases, then the power
A [ ]) increases
B [ ]) decreases
C [v]) remains constant
D [ ]) none of the above

78) Higher order TDM levels are obtained by
A [ ]) forming super master groups
B [ ]) using A law
C [ ]) using μ law
D [v]) dividing pulse width

79) Limiter is not essential in the following detector
A [ ]) foster-Seeley
B [v]) ratio detector
C [ ]) balanced
D [ ]) none of the above

80) Which of the following is Doppler effect not used?
A [ ]) CW radar
B [ ]) FM radar
C [ ]) MTI system
D [v]) Moving target plotting on PPI

81) In pulse code modulation when the maximum frequency in the signal is fmax the
bandwidth required will be
A [ ]) ≤ p.fmax
B [v]) ≥ p.fmax
C [ ]) ≤ (p.fmax)²
D [ ]) ≥ (p.fmax)²

82) The main advantage of DM over PCM is
A [ ]) less bandwidth
B [ ]) less power
C [v]) simple circuit
D [ ]) better S/N ratio

83) Among the various modulation systems, the most favored from the point of linearity of modulation and efficiency is
A [v]) anode or collector modulation
B [ ]) central grid modulation
C [ ]) screen grid modulation
D [ ]) modulated oscillators

84) Multiplex techniques are used for
A [ ]) low density communications
B [ ]) low density point-to-point communications
C [v]) high-density point-to-point communications
D [ ]) all of the above

85) In delta modulation, the output signal to quantization noise ratio S0/Nq is (N is the
number of bits)
A [ ]) (3/π²)N²
B [v]) (3/π²)N³
C [ ]) (3/π)N³
D [ ]) NONE OF THESE

86) ISDN stands for
A [v]) Integrated Services Digital Network
B [ ]) Inter Services Digital Network
C [ ]) Inter Subscriber Digital Network
D [ ]) integrated Subscriber Digital Network

87) The relation between bandwidth B, modulating frequency fm and frequency deviation
Δf for a sinusoidally modulated FM signal is
A [ ]) B = Δf + fm
B [v]) B = 2(Δf + fm)
C [ ]) B = fm – Δf/
D [ ]) B = 2(fm – Δf)

88) In amplitude modulation, the magnitude of side bands is
A [v]) ma/2 times the carrier amplitude, Ec
B [ ]) ma times the carrier amplitude, Ec
C [ ]) 2ma times the carrier amplitude, Ec
D [ ]) 4ma times the carrier amplitude, Ec

89) If ω is the frequency of modulating voltage in FM, the modulation index is proportional to
A [ ]) ω
B [v]) 1/ω
C [ ]) √ω
D [ ]) 1/√ω

90) The baud rate is
A [ ]) not equal to signalling rate
B [ ]) always equal to bit transfer rate
C [v]) equal to twice the bandwidth of an ideal channel
D [ ]) equal to half the bandwidth of ideal channel

91) A better SNR can be obtained in a PCM by
A [ ]) increasing sampling rate above Nyquist rate
B [ ]) decreasing the code bits
C [ ]) reducing channel bandwidth
D [v]) increasing Quantization levels

92) Industrial noise has the frequency range of
A [ ]) 1 to 100 Hz
B [ ]) 200 to 5000 Hz
C [ ]) above 200 MHz
D [v]) 1 to 600 MHz

93) Line of sight transmission is used in
A [ ]) radio frequencies below 1 MHz
B [ ]) VHF only
C [ ]) audio signals only
D [v]) VHF and UHF

94) In phase modulation, the phase deviation is
A [ ]) proportional to the amplitude of the signal and varies with frequency
B [ ]) remains constant while amplitude and frequency of signal varies
C [v]) proportional to the amplitude of the signal and independent of the frequency
D [ ]) none of the above

95) The different channels in a TDM receiver are separated by
A [ ]) integration
B [ ]) differentiation
C [v]) AND gate
D [ ]) OR gate

96) An antenna operates effectively when its dimensions are
A [v]) of the order of magnitude of wavelength to be transmitted
B [ ]) very small than the magnitude of wavelength to be transmitted
C [ ]) very large than the magnitude of wavelength to be transmitted
D [ ]) either (a) or (b)

97) In FM and AM the ratio of signal to noise ratio at the detector output least depends upon
A [ ]) bandwidth
B [ ]) transmission
C [v]) carrier frequency
D [ ]) modulating frequency

98) Which of the following can provide two or more voice circuits with the same carrier?
A [ ]) SSB
B [v]) Carrier reinsertion
C [ ]) Lincompex
D [ ]) independent side band system

99) The FM broadcast band is from
A [ ]) 550 to 1600 kHz
B [ ]) 88 to 108 kHz
C [v]) 88 to 108 MHz
D [ ]) 1600 kHz to 59.75 MHz

100) The purpose of source coding is to
A [ ]) increase the information transmission rate
B [v]) decrease S/N ratio
C [ ]) decrease the information transmission rate
D [ ]) decrease probability of error

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