 # MCQs in Noise Part II

(Last Updated On: December 8, 2017) This is the Multiples Choice Questions Part 2 of the Series in Noise 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 External Noise
• MCQs in Phase Noise
• MCQs in Noise Calculation and Measurements
• MCQs in Radio Interference
• MCQs in decibel (dB)

### MCQs in Noise Series

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

Noise 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

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

51. You are measuring noise at a -6 dB level point, using the Lenkurt 601A, F1A weighting network, and a flat meter. The meter reading is -59 dBm. This is _________ dBa0.

• A. 24
• B. 12
• C. 23
• D. 32

52. A measurement of -75 dBm, C-message weighted, would be _________ dBrnc.

• A. 8
• B. 7
• C. 9
• D. 15

53. Your Western Electric 3A test set meter reading is -23 dBm at at test point level of -8 dB. This is ______ dBrnc0.

• A. 75
• B. 29
• C. 30
• D. 31

54. At what power level does a 1 KHz tone cause zero interference (144 weighted)?

• A. 90 dB
• B. 90 dBm
• C. -90 dBm
• D. -90 dBm

55. Reference noise is ___________.

• A. a 1000 Hz, -90 dBm tone
• B. a noise that creates the same interfering effect as a 1000Hz, -90dBm tone
• C. a noise that creates zero dBrn in a voice channel
• D. B and C above

56. A practical dBrn measurement will almost always in a _______ number.

• A. positive
• B. negative
• C. imaginary
• D. fractional

57. What is the reference level for noise measurement, F1A weighted?

• A. -90 dBm
• B. -82 dBm
• C. -67 dBm
• D. -85 dBm

58. What is the reference tone level for dBrn?

• A. -90 dBm
• B. -82 dBm
• C. -67 dBm
• D. -85 dBm

59. What is the reference tone level for dBa?

• A. -90 dBm
• B. -82 dBm
• C. -67 dBm
• D. -85 dBm

60. Atmospheric noise becomes less severe at frequencies

• A. above 30 MHz
• B. below 30 MHz
• C. above 3000 kHz
• D. below 3000kHz

61. Indicate the noise whose sources are in category different from that of the other three?

• A. Solar noise
• B. Cosmic noise
• C. Atmospheric noise
• D. Galactic noise

62. Indicate the false statement.

• A. Industrial noise is usually of the impulse type
• B. Static is caused by lightning discharges in thunderstorms and other natural electric disturbances occurring in the atmosphere
• C. Distant stars are another source of man-made noise
• D. Flourescent lights are another source of man-made noise

63. Which of the following is not a source of industrial noise?

• A. Automobile ignition
• B. Sun
• C. Electric Motors
• D. Leakage from high voltage line

64. Indicate the false statement

• A. The noise generated in a resistance or the resistive component of any impedance is random.
• B. Random noise power is proportional to the bandwidth over which is measured
• C. A random voltage across the resistor does not exist
• D. All formula referring to random noise are applicable only to the value of such noise.

65. The value of the resistor creating thermal noise is doubled. The noise power generated is therefore.

• A. halved
• C. doubled
• D. unchanged

66. Indicate the false statement.

• A. HF mixer are generally noisier than HF amplifiers.
• B. Impulse noise voltage is dependent on bandwidth
• C. Thermal noise is independent of the frequency at which is measured.
• D. Industrial noise is usually of the impulse type.

67. An amplifier operating over the frequency range of 455 to 460 kHz has a 200 kΩ input resistor. What is the RMS noise voltage at the input to this amplifier if the ambient temperature is 17˚C ?

• A. 40 µV
• B. 4.0 µV
• C. 400 µV
• D. 4.0 mV

68. The first stage of a two-stage amplifier has a voltage gain of 10, a 600 Ω input resistor, a 1600Ω equivalent noise resistance and 27kΩ output resistor. For the second stage, these values are 25, 81kΩ, 19kΩ, and 1MΩ, respectively. Calculate the equivalent input-noise resistance of this two stage amplifier.

• A. 2,518 kΩ
• B. 2,518 Ω
• C. 251.8 Ω
• D. 12,518 Ω

69. The noise output of a resistor is amplified by a noiseless amplifier having a gain of 60 and a bandwidth of 20 kHz. A meter connected at the output of the amplifier reads 1mV RMS. If the bandwidth of the amplifier is reduced to 5kHz, its gain remaining constant, what does the meter read now?

• A. 0.5 mV
• B. 0.5 µV
• C. 5.0 mV
• D. 5.0 µV

70. The front-end of a television receiver, having a bandwidth of 7Mhz, and operating at a temperature of 27˚C , consists of an amplifier having a gain of 15 followed by a mixer whose gain is 20. The amplifier has a 300 Ω input resistor and a shot noise equivalent resistance of 500Ω; for the mixer, these values are 2.2kΩ and 13.5kΩ respectively, and the load resistance of the mixer is 470 kΩ. Calculate the equivalent noise resistance for this television receiver.

• A. 8760 Ω
• B. 875 Ω
• C. 8.76 Ω
• D. 0.876 Ω

71. One of the following is not a useful quantity for comparing the noise performance receivers.

• A. Input noise voltage
• B. Equivalent noise resistance
• C. Noise temperature
• D. Noise figure.

72. Indicate the false statement. Noise figure is defined as

• A. the ratio of the S/N power supplied at the input terminal of a receiver or amplifier to the S/N power supplied to the output or load resistor
• B. noise factor expressed in decibels
• C. an unwanted form of energy tending to interfere with the proper and easy reception and reproduction of wanted signals
• D. S/N of an ideal system divided by S/N at the output of the receiver or amplifier under test, both working at the same temperature over the same bandwidth and fed from the same source

73. Calculated the noise figure of the amplifier whose Req equals 2518Ω (RT=600Ω) if its driven by a generator whose output impedance is 50Ω.

• A. 39.4
• B. 3.94
• C. 394
• D. 0.394

74. Calculate the noise figure of the receiver whose RF amplifier has an input resistance of 1000Ω and an equivalent shot-noise resistance of 2000Ω, a gain of 25 and load resistance of 125 kΩ. Given that the bandwidth is 1.0MHz and the temperature is 20˚C, and that the receiver is connected to an antenna with an impedance of 75Ω.

• A. 30.3
• B. 3.03
• C. 303
• D. .303

75. A receiver connected to an antenna whose resistance is 50 Ω has an equivalent noise resistance of 30Ω. Calculate its equivalent noise temperature if the noise figure is equal to 1.6.

• A. 17.4 K
• B. 174 K
• C. 1.74 K
• D. 17 K

76. Most internal noise comes from

• A. Shot noise
• B. Transit-time noise
• C. Thermal agitation
• D. Skin effect

77. Which of the following is not a source of external noise?

• A. Thermal agitation
• B. Auto ignition
• C. The sun
• D. Fluorescent lights

78. Noise can be reduced by

• A. widening the bandwidth
• B. narrowing the bandwidth
• C. increasing temperature
• D. increasing transistor current levels

79. Noise at the input to the receiver can be as high as several

• A. microvolts
• B. milivolts
• C. volts
• D. kilo volts

80. Which circuit contributes most of the noise in a receiver?

• A. IF amplifier
• B. Demodulator
• C. AF amplifier
• D. Mixer

81. Which noise figure represents the lowest noise in receiver?

• A. 1.6 dB
• B. 2.1 dB
• C. 2.7 dB
• D. 3.4 dB

82. The transistor with the lowest noise figure in the microwave region is a

• A. MOSFET
• B. Dual-gate MOSFET
• C. JFET
• D. MESFET

83. What is the noise voltage across a 300Ω input resistance to a TV set with a 6MHz bandwidth and temperature of 30˚C?

• A. 2.3 µV
• B. 3.8 µV
• C. 5.5 µV
• D. 5.4 µV

84. Which of the following types of noise becomes of great importance at frequencies?

• A. Shot noise
• B. Random noise
• C. Impulse noise
• D. Transit-time noise

85. The solar cycle repeats the period of great electrical disturbance approximately every

• A. 11 years
• B. 10 years
• C. 9 years
• D. 8 years

86. The square of the thermal noise voltage generated by a resistor is proportional to

• A. its resistance
• B. its temperature
• C. the bandwidth over which it is measured
• D. All of the above

87. Noise occurring in the presence of signal resulting from a mismatch between the exact value of an analog signal and the closet available quantizing step in a digital coder.

• A. Quantizing noise
• B. Thermal noise
• C. Impulse noise
• D. Crosstalk

88. Noise consisting of irregular pulses of short duration and relatively high amplitude,

• A. Quantizing noise
• B. Tone interference
• C. Impulse noise
• D. Cross talk

89. Noise that occurs via capacitive or inductive coupling in a cable.

• A. Crosstalk
• B. Quantizing noise
• C. Reference noise
• D. Tone interference

90. Sources of impulse noise induced in communication channels.

• A. Erroneous digital coding bit caused by an error on a transmission facility
• B. Transients due to relay operation
• C. Crosstalk from dc signaling systems
• D. All of these

91. Crosstalk due to incomplete suppression of sidebands or to intermodulation of two or more frequency-multiplexed channels which is unintelligible is classified as

• A. Impulse noise
• B. Thermal noise
• C. Quantizing noise
• D. Miscellaneous noise

92. ___________ is device that measures the internal open circuit voltage of an equivalent noise generator having an impedance of 600Ω and delivering noise power to a 600 Ω load.

• A. Psophometer
• B. Barometer
• C. Reflectometer
• D. Voltmeter

93. External noise originating outside the solar system

• A. Cosmic noise
• B. Solar noise
• C. Thermal noise
• D. Lunar noise

94. A noise whose source is within the solar system.

• A. Solar noise
• B. Thermal noise
• C. Cosmic noise
• D. Johnson Noise

95. The total noise power present in a 1-Hz bandwidth .

• A. Noise density
• B. Noise figure
• C. Noise limit
• D. Noise intensity

96. Which of the following is not a way of minimizing if not eliminating noise?

• A. Use redundancy
• B. Increase transmitted power
• C. Reduce signaling rate
• D. Increase channel bandwidth

97. What is the primary cause of atmospheric noise?

• A. Thunderstorm
• B. Lightning
• C. Thunderstorm and lightning
• D. Weather condition

98. What do you call the noise coming from the sun and stars?

• A. Black-body noise
• B. Space noise
• C. Galactic noise
• D. All of these

99. The major cause of atmospheric or static noise are

• A. Thunderstorms
• B. Airplanes
• C. Meteor showers
• D. All of these

100. Which of the following low noise transistors is commonly used at microwave frequencies?

• A. MOSFET
• B. GASFET
• C. MESFET
• D. JFET

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