 # MCQs in Modulation Part II

(Last Updated On: December 8, 2017) This is the Multiples Choice Questions Part 2 of the Series in Modulation as one of the Communications Engineering topic. In Preparation for the ECE Board Exam make sure to expose yourself and familiarize in each and every questions compiled here taken from various sources including but not limited to past Board Examination Questions in Electronic System and Technologies, Communications Books, Journals and other Communications References.

### Online Questions and Answers Topic Outline

• MCQs in Amplitude Modulation
• MCQs in Phase Modulation
• MCQs in Sound Pressure Level
• MCQs in Frequency Modulation
• MCQs in Pulse Modulation

### MCQs in Modulation Series

Following is the list of multiple choice questions in this brand new series:

Modulation MCQs
PART 1: MCQs from Number 1 – 50                        Answer key: PART I
PART 2: MCQs from Number 51 – 100                   Answer key: PART II
PART 3: MCQs from Number 101 – 150                 Answer key: PART III
PART 4: MCQs from Number 151 – 200                 Answer key: PART IV
PART 5: MCQs from Number 201 – 250                 Answer key: PART V
PART 6: MCQs from Number 251 – 300                 Answer key: PART VI
PART 7: MCQs from Number 301 – 350                 Answer key: PART VII
PART 8: MCQs from Number 351 – 400                 Answer key: PART VIII
PART 9: MCQs from Number 401 – 450                 Answer key: PART IX
PART 10: MCQs from Number 451 – 500                 Answer key: PART X

### Continue Practice Exam Test Questions Part II of the Series

51. What will be the result of the gain level being too high for signals entering the modulator?

• A. Receiver noise
• B. Excessive volume of receiver output
• C. Oscillator disturbances
• D. Distortion and splatter

52. Amplitude modulation causes the amount of transmitter power to

• A. Increase
• B. Decrease
• C. Remain the same
• D. Double

53. When a carrier is modulated 100%, the total power increases by what percentage over that of the carrier alone?

• A. 25 %
• B. 50 %
• C. 75 %
• D. 100 %

54. When the amplitude of the modulating voltage is increased for AM, the antenna current will

• A. Increase
• B. Decrease
• C. Remain constant
• D. Decrease exponentially

55. An increase in transmitter power from 25W to 30W will cause the antenna current to increase from 700mA to

• A. 800 mA
• B. 750 mA
• C. 767 mA
• D. 840 mA

56. A second modulating tone having the same amplitude but a different frequency is added to the first at the input to the modulator. The modulation index will be increased by a factor of

• A. sq. root of 3
• B. sq. root of 2
• C. 2
• D. 3

57. A 1000 kHz carrier is modulated by a 2500Hz tone. One frequency component of the modulated signal is

• A. 1200 Hz
• B. 5000 Hz
• C. 1002.5 kHz
• D. 2500 Hz

58. A 1200 kHz carrier is amplitude-modulated by two tones of 500 Hz and 700 Hz. Which one is a frequency component of the modulated wave?

• A. 1195 kHz
• B. 1199.3 kHz
• C. 1199.7 kHz
• D. 1205 kHz

59. Identify a modulation method, or methods in use for a common-emitter configuration

• A. Base modulation
• B. Emitter modulation
• C. Collector modulation
• D. Both A and C

60. The RF signal injected into a balanced modulator is 10MHz and the modulating frequency is 1 kHz. Which frequency, or frequencies, will not appear in the output?

• A. 9.999 MHz
• B. 10 MHz
• C. 10.0001 MHz
• D. Both A and B

61. Unwanted sidebands in SSB equipment can be suppressed by one or more of the following methods.

• A. Phasing method
• B. Filter method
• C. Decoder method
• D. Both A and B

62. Envelope detection is concerned with the process of

• A. Mixing
• B. Heterodyning
• C. Modulation
• D. Rectification

63. Diagonal clipping in envelope detection will result in

• A. Distortion
• B. Phase reversal
• C. Reduced sensitivity
• D. Amplitude damage

64. Product detection requires the process of

• A. Rectification
• B. Heterodyning
• C. Decoding
• D. Phase shifting

65. A sine wave which is coherent with carrier has identical

• A. Amplitude
• B. Frequency
• C. Phase angle
• D. Both B and C

66. Frequency modulation and phase modulation are collectively referred to as

• A. Stereo
• B. Angle modulation
• C. High fidelity modulation
• D. FCC modulation

67. In FM, the change in carrier frequency is proportional to what attribute of the modulating signal?

• A. Angle
• B. Frequency
• C. Amplitude
• D. Tone

68. A louder sound, when generating the modulating waveform for FM, will cause a greater

• A. Carrier amplitude
• B. Angle amplitude
• C. Distortion at the receiver
• D. Frequency deviation

69. If a positive change in modulation signal level of 200 mW will cause a positive frequency deviation of 10 kHz, what will be the frequency deviation for a negative change of 10 mV in the level of the modulating signals?

• A. 0
• B. -5 kHz
• C. +5 kHz
• D. +0 kHz

70. A particular 15 kHz modulation tone results in a peak frequency deviation of 75 kHz. What is the modulation index?

• A. 5
• B. 15
• C. 75
• D. 3

71. A 15 kHz sine wave frequency modulates an 88 MHz carrier. A sideband frequency will be found at

• A. 87.970 MHz
• B. 87.985 MHz
• C. 88.015 MHz
• D. All of these

72. A device whose capacitance is deliberately made to be a function of the applied voltage

• A. Varactor diode
• B. UJT
• C. SAW
• D. Variable capacitor

73. A reactance modulator is one method of obtaining

• A. Indirect FM
• B. Direct FM
• C. Demodulation
• D. Low frequency filtering

74. A device, now available in IC form, is useful for direct FM and as one element in the phse-locked loop.

• A. AFC
• B. AGC
• C. VCO
• D. LPF

75. _____ is a frequency change process, whereby the phase deviation and frequency deviation are multiplied by some fixed constant.

• A. Translation
• B. Multiplication
• C. Division

76. A circuit that has the function of demodulating the frequency-modulated signal.

• A. AFC
• B. Envelope detector
• C. Decoder
• D. Foster-Seeley discriminator

77. The ratio detector is superior to the slope detector because

• A. It is less sensitive to phase modulation
• B. It is less sensitive to noise spikes
• C. It is less sensitive to interference causing AM
• D. Both B and C

78. One implementation of a pulse averaging discriminator is

• A. A free-running multivibrator
• B. A crystal-controlled oscillator
• C. A quartz crystal filter
• D. A triggered multivibrator

79. A 10% increase in the frequency of a constant-width pulse train should cause what change in its average value?

• A. –10 %
• B. –1 %
• C. +1 %
• D. +10 %

80. Two different signals can be coherent if they

• A. Have the same amplitude
• B. Are both sine waves of different frequencies
• C. Originate in the same physical equipment simultaneously
• D. Have the same frequency

81. A quadrature detector requires that

• A. Four gates bee provided
• B. The inputs are coherent
• C. The inputs are incoherent
• D. The inputs are identical

82. In a phase-locked loop, the VCO is the abbreviation for

• A. Variable coherent output
• B. VHF communication oscillator
• C. Voltage-controlled oscillator
• D. Vien-count oscillator (neutralized)

83. Identify an advantage, or advantages of a properly designed FM system.

• A. Relative immunity to atmospheric noise (lightning)
• B. Reduced bandwidth required
• C. No noise of any kind
• D. The noise figure is inversely proportional to the modulation index

84. The output of a balanced modulator

• A. LSB and USB
• B. LSB
• C. USB
• D. Carrier

85. If the modulation index of an AM wave is changed from 0 to 1, the transmitted power is

• A. Unchanged
• B. Halved
• C. Doubled
• D. Increased by 50%

86. Which of the following is not a baseband signal of modulation?

• A. Audio signal
• B. Video signal
• C. RF carrier
• D. Binary coded pulses

87. If the unmodulated level peak carrier amplitude is doubled in an AM signal, the perfect modulation is ________.

• A. 20
• B. 50
• C. 100
• D. 200

88. Balanced modulator circuit when inserted in the equivalent suppresses the ___________

• A. Carrier
• B. Upper sideband
• C. Lower sideband
• D. Baseband signal

89. The carrier of a 100% modulated AM wave is suppressed, the percentage power saving is __.

• A. 100 %
• B. 50 %
• C. 83 %
• D. 66.66 %

90. If the modulation index if an AM wave is doubled, the antenna current is also doubled, the AM system being used is

• A. H3E
• B. J3E
• C. C3F
• D. A3E

91. 100% modulation in AM means a corresponding increase in total power by _______.

• A. 100 %
• B. 50 %
• C. 75 %
• D. 25 %

92. A single-tone amplitude modulated wave has _______.

• A. 2 components
• B. 3 components
• C. 4 components
• D. 2n + 1 components

93. A carrier signal has ________.

• A. Constant peak amplitude
• B. Frequency range of 20 – 20,000 Hz
• C. A varying amplitude
• D. The information

94. The modulating system is _________ if the modulating frequency is doubled, the modulation index is halved, and the modulating voltage remains constant.

• A. Amplitude modulation
• B. Phase modulation
• C. Frequency modulation
• D. Pulse modulation

95. What is the modulation index of an FM signal if its modulating frequency is doubled?

• A. No effect
• B. Twice the original index
• C. Four times the original index
• D. One-half the original index

96. An AM transmitter is rated 1000 W at 100% modulation. How much power required for the carrier?

• A. 1000 W
• B. 666.6 W
• C. 333.3 W
• D. 866.6 W

97. Standard way of designating AM

• A. A3E
• B. B3E
• C. AHE
• D. C3F

98. _____ is the circuit used to detect frequency modulated signal.

• A. Discriminator
• B. Modulator
• C. Modem
• D. Detector

99. _____ is an information signal that is sent directly without modulating any carrier.

• A. C-band
• B. Q-band
• C. Baseband

100. Both frequency and phase modulation utilize ______ modulation.

• A. Digital
• B. Phase
• C. Amplitude
• D. Angle

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