# MCQ in Noise Part 2 | ECE Board Exam

(Last Updated On: April 13, 2021) 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.

#### MCQ Topic Outline included in ECE Board Exam Syllabi

• MCQ in External Noise
• MCQ in Phase Noise
• MCQ in Noise Calculation and Measurements
• MCQ in Radio Interference

#### Continue Practice Exam Test Questions Part 2 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

View Answer:

Answer: Option D

Solution:

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

A. 8

B. 7

C. 9

D. 15

View Answer:

Answer: Option D

Solution:

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

View Answer:

Answer: Option A

Solution:

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

A. 90 dB

B. 90 dBm

C. -90 dB

D. -90 dBm

View Answer:

Answer: Option D

Solution:

55. Reference noise is ___________.

A. a 1000 Hz, -90 dBm tone

B. a noise that creates the same interfering effect as a 1000 Hz, –90 dBm tone

C. a noise that creates zero dBrn in a voice channel

D. B and C above

View Answer:

Answer: Option D

Solution:

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

A. positive

B. negative

C. imaginary

D. fractional

View Answer:

Answer: Option A

Solution:

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

A. -90 dBm

B. -82 dBm

C. -67 dBm

D. -85 dBm

View Answer:

Answer: Option D

Solution:

58. What is the reference tone level for dBrn?

A. -90 dBm

B. -82 dBm

C. -67 dBm

D. -85 dBm

View Answer:

Answer: Option A

Solution:

59. What is the reference tone level for dBa?

A. -90 dBm

B. -82 dBm

C. -67 dBm

D. -85 dBm

View Answer:

Answer: Option D

Solution:

60. Atmospheric noise becomes less severe at frequencies

A. above 30 MHz

B. below 30 MHz

C. above 3000 kHz

D. below 3000 kHz

View Answer:

Answer: Option A

Solution:

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

View Answer:

Answer: Option C

Solution:

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. Fluorescent lights are another source of man-made noise

View Answer:

Answer: Option C

Solution:

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

View Answer:

Answer: Option B

Solution:

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.

View Answer:

Answer: Option C

Solution:

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

A. halved

B. quadrupled

C. doubled

D. unchanged

View Answer:

Answer: Option D

Solution:

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.

View Answer:

Answer: Option B

Solution:

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

View Answer:

Answer: Option B

Solution:

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

View Answer:

Answer: Option B

Solution:

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 1 mV RMS. If the bandwidth of the amplifier is reduced to 5 kHz, 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

View Answer:

Answer: Option A

Solution:

70. The front-end of a television receiver, having a bandwidth of 7 Mhz, 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 500 Ω; for the mixer, these values are 2.2 kΩ and 13.5 kΩ 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

View Answer:

Answer: Option B

Solution:

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.

View Answer:

Answer: Option A

Solution:

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

View Answer:

Answer: Option C

Solution:

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

A. 39.4

B. 3.94

C. 394

D. 0.394

View Answer:

Answer: Option A

Solution:

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

A. 30.3

B. 3.03

C. 303

D. 0.303

View Answer:

Answer: Option A

Solution:

75. A receiver connected to an antenna whose resistance is 50 Ω has an equivalent noise resistance of 30 Ω. 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

View Answer:

Answer: Option B

Solution:

76. Most internal noise comes from

A. Shot noise

B. Transit-time noise

C. Thermal agitation

D. Skin effect

View Answer:

Answer: Option C

Solution:

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

A. Thermal agitation

B. Auto ignition

C. The sun

D. Fluorescent lights

View Answer:

Answer: Option A

Solution:

78. Noise can be reduced by

A. widening the bandwidth

B. narrowing the bandwidth

C. increasing temperature

D. increasing transistor current levels

View Answer:

Answer: Option B

Solution:

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

A. microvolts

B. milivolts

C. volts

D. kilo volts

View Answer:

Answer: Option A

Solution:

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

A. IF amplifier

B. Demodulator

C. AF amplifier

D. Mixer

View Answer:

Answer: Option D

Solution:

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

View Answer:

Answer: Option A

Solution:

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

A. MOSFET

B. Dual-gate MOSFET

C. JFET

D. MESFET

View Answer:

Answer: Option D

Solution:

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

A. 2.3 µV

B. 3.8 µV

C. 5.5 µV

D. 5.4 µV

View Answer:

Answer: Option C

Solution:

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

View Answer:

Answer: Option D

Solution:

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

View Answer:

Answer: Option A

Solution:

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

View Answer:

Answer: Option D

Solution:

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

View Answer:

Answer: Option A

Solution:

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

View Answer:

Answer: Option C

Solution:

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

A. Crosstalk

B. Quantizing noise

C. Reference noise

D. Tone interference

View Answer:

Answer: Option A

Solution:

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

View Answer:

Answer: Option D

Solution:

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

View Answer:

Answer: Option D

Solution:

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

A. Psophometer

B. Barometer

C. Reflectometer

D. Voltmeter

View Answer:

Answer: Option A

Solution:

93. External noise originating outside the solar system

A. Cosmic noise

B. Solar noise

C. Thermal noise

D. Lunar noise

View Answer:

Answer: Option A

Solution:

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

A. Solar noise

B. Thermal noise

C. Cosmic noise

D. Johnson Noise

View Answer:

Answer: Option A

Solution:

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

A. Noise density

B. Noise figure

C. Noise limit

D. Noise intensity

View Answer:

Answer: Option A

Solution:

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

View Answer:

Answer: Option D

Solution:

97. What is the primary cause of atmospheric noise?

A. Thunderstorm

B. Lightning

C. Thunderstorm and lightning

D. Weather condition

View Answer:

Answer: Option B

Solution:

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

View Answer:

Answer: Option B

Solution:

99. The major cause of atmospheric or static noise are

A. Thunderstorms

B. Airplanes

C. Meteor showers

D. All of these

View Answer:

Answer: Option A

Solution:

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

A. MOSFET

B. GASFET

C. MESFET

D. JFET

View Answer:

Answer: Option C

Solution:

#### Questions and Answers in Noise Series

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

MCQ in Noise
PART 1: MCQ from Number 1 – 50                        Answer key: PART 1
PART 2: MCQ from Number 51 – 100                   Answer key: PART 2
PART 3: MCQ from Number 101 – 150                 Answer key: PART 3
PART 4: MCQ from Number 151 – 200                 Answer key: PART 4
PART 5: MCQ from Number 201 – 250                 Answer key: PART 5

### Complete List of MCQ in Communications Engineering per topic

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