# MCQ in Noise Part 3 | ECE Board Exam

(Last Updated On: April 25, 2020) This is the Multiples Choice Questions Part 3 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 3 of the Series

101. An amplifier operating over a 2 MHz bandwidth has a 80 ohms input resistance. It is operating at 27 degree Celsius, has a voltage gain of 200 and input signal of 6 microvolts rms. Calculate the output rms noise.

a. 325.6 millivolts

b. 0.326 millivolts

c. 32.55 microvolts

d. d. 0.3255 microvolts

View Answer:

Answer: Option B

Solution:

102. Man-made noise is caused by

a. Lightning discharge

b. Solar eruptions

c. Distant stars

d. Arc discharges in electrical machines

View Answer:

Answer: Option D

Solution:

103. Cosmic noise is produced by

a. Lightning discharge

b. Solar eruption

c. Distant stars

d. Industrial electrical discharges

View Answer:

Answer: Option C

Solution:

104. One of the following type of noise becomes of great importance in high frequencies. It is the

a. Shot noise

b. Random noise

c. Impulse noise

d. Transit-time noise

View Answer:

Answer: Option D

Solution:

105. Indicate the false statement

a. HF mixers are generally noisier than HF amplifiers

b. Impulse noise voltage is independent of bandwidth

c. Thermal noise is independent of the frequency at which it is measured

d. Industrial noise is usually of the impulse type

View Answer:

Answer: Option B

Solution:

106. The value of a resistor creating noise is doubled. The noise power generated is therefore

a. Halved

b. Quadrupled

c. Doubled

d. Unchanged

View Answer:

Answer: Option D

Solution:

107. One of the following is not useful for comparing the noise performance of receivers

a. Input noise voltage

b. Equivalent noise resistance

c. Noise temperature

d. Noise figure

View Answer:

Answer: Option A

Solution:

108. Indicate the noise whose source is in a category different from that

a. Solar noise

b. Cosmic noise

c. Atmospheric noise

d. Galactic noise

View Answer:

Answer: Option C

Solution:

109. Considered as the main source of an internal noise

a. Flicker

b. Thermal agitation

c. Device imperfection

d. Temperature change

View Answer:

Answer: Option B

Solution:

110. Convert noise factor of 4.02 to equivalent noise temperature. Use 300K for environmental temperature

a. 876K

b. 900K

c. 906K

d. 875K

View Answer:

Answer: Option C

Solution:

111. Atmospheric noise is less severe at frequencies above

a. 10 GHz

b. 30 MHz

c. 1 GHz

d. Audio level

View Answer:

Answer: Option B

Solution:

112. The most common unit of noise measurement in white noise voltage testing

a. NPR

b. dBrn

c. dBW

d. dBm

View Answer:

Answer: Option A

Solution:

113. What is the major cause of atmospheric or static noise?

a. Meteor showers

b. Sunspots

c. Airplanes

d. Thunderstorms

View Answer:

Answer: Option D

Solution:

114. Background noise is the same as the following EXCEPT

a. Impulse noise

b. Thermal noise

c. White noise

d. Gaussian noise

View Answer:

Answer: Option A

Solution:

115. Noise is caused by the thermal agitation of electrons in resistance

a. White noise

b. Thermal noise

c. Johnson’s noise

d. All of these

View Answer:

Answer: Option D

Solution:

116. The unit of noise power of psophometer

a. dBa

b. pWp

c. dBm

d. dBm0

View Answer:

Answer: Option B

Solution:

117. Extra-terrestrial noise is observable at frequencies from

a. 0 to 20 KHz

b. Above 2 GHz

c. 8 MHz to 1.43 GHz

d. 5 to 8 GHz

View Answer:

Answer: Option C

Solution:

118. What signal-to-noise ratio is required for satisfactory telephone services?

a. 50 dB

b. 30 dB

c. 40 dB

d. 20 dB

View Answer:

Answer: Option A

Solution:

119. A diode generator is required to produce 12 micro V of noise in a receiver with an input impedance of 75 ohms and a noise power bandwidth of 200 KHz. Determine the current through the diode in milliamperes.

a. 0.4 A

b. 298 mA

c. 0.35 A

d. 300 mA

View Answer:

Answer: Option A

Solution:

120. The equivalent noise temperature of the amplifier is 25K. What is the noise figure?

a. 0.4 A

b. 298 mA

c. 0.35 A

d. 300 mA

View Answer:

Answer: Option A

Solution:

121. The resistor R1 and R2 are connected in series at 300 K and 400 K temperature respectively. If R1 is 200 ohms and R2 is 300 ohms, find the power produced at the load (RL = 500 ohms) over a bandwidth of 100 KHz.

a. 0.05 nanowatts

b. 0.2 nanowatts

c. 0.5 femtowatts

d. 2.0 femtowatts

View Answer:

Answer: Option C

Solution:

122. The random unpredictable electric signals from natural causes, both internal and external to the system is known as

a. Distortion

b. Noise

c. Distortion

d. Interference

View Answer:

Answer: Option B

Solution:

123. Given a factor of 10, what is the noise figure in dB?

a. 20 dB

b. 10 dB

c. 50 dB

d. 40 dB

View Answer:

Answer: Option B

Solution:

124. The signal in a channel is measured to be 23 dBm while noise in the same channel is measured to be 23 dBm while noise in the same channel is measured to be 9 dBm. The signal to noise ratio therefore is

a. 32 dB

b. 5 dB

c. -14 dB

d. 14 dB

View Answer:

Answer: Option D

Solution:

125. If voltage is equal to twice its original value, what is its corresponding change in dB?

a. 3 dB

b. 6 dB

c. 9 dB

d. 12 dB

View Answer:

Answer: Option B

Solution:

126. NIF stand for

a. Non-intrinsic noise figure

b. Narrow interference figure

c. Noise improvement factor

d. Noise interference figure

View Answer:

Answer: Option C

Solution:

127. Two resistors rated 5 ohms and 10 ohms are connected in series and are at 27 degrees Celsius. Calculate their combined thermal noise voltage for a 10 KHz bandwidth.

a. 0.05 millivolts

b. 0.5 millivolts

c. 0.05 microvolts

d. 0.005 microvolts

View Answer:

Answer: Option C

Solution:

128. What is the reference frequency of CCITT psophometric noise measurement?

a. 800 Hz

b. 1500 Hz

c. 3400 Hz

d. 1000 Hz

View Answer:

Answer: Option A

Solution:

129. A three-stage amplifier is to have an overall noise temperature no greater than 70K. The overall gain of the amplifier is to be at least 45 dB. The amplifier is to be built by adding a low-noise first stage with existing characteristics as follows: stage 2 has 20 dB power gain and 3 dB noise figure. Stage 3 has 15 dB power gain and 6 dB noise figure. Calculate the maximum noise figure (in dB) that the first stage can have.

a. 0.267 dB

b. 0.56 dB

c. 1.235 dB

d. 0.985 dB

View Answer:

Answer: Option B

Solution:

130. A transistor has measured S/N power of 60 at its input and 19 at its output. Determine the noise figure of the transistor.

a. 5 dB

b. 10 dB

c. 2.5 dB

d. 7.5 dB

View Answer:

Answer: Option A

Solution:

131. Which does not affect noise in a channel?

a. None of these

b. Bandwidth

c. Temperature

d. Quantizing level

View Answer:

Answer: Option D

Solution:

132. Reference noise temperature

a. 70°F

b. 30°C

c. 290K

d. 25°C

View Answer:

Answer: Option C

Solution:

133. Industrial noise frequency is between

a. 200 to 3000 MHz

b. 15 to 160 MHz

c. 0 to 10 kHz

d. 20 GHz

View Answer:

Answer: Option B

Solution:

134. Noise from random acoustic or electric noise that has equal per cycle over a specified total frequency band

a. Thermal noise

b. White noise

c. Gaussian noise

d. All of these

View Answer:

Answer: Option D

Solution:

135. A transistor amplifier has a measured S/N power of 100 at its input and 20 at its output. Determine the noise figure of the transistor.

a. 14 dB

b. 7 dB

c. -6 dB

d. -3 dB

View Answer:

Answer: Option B

Solution:

136. What does the noise weighing curve show?

a. Noise signals measured with a 144 handsets

b. Power levels of noise found in carrier systems

c. The interfering effect of other frequencies in a voice channel compared with a reference frequency of one kilohertz

d. Interfering effects of signals compared with a 3-KHz tone

View Answer:

Answer: Option C

Solution:

137. The signal power of the input to an amplifier 100 microW and the noise power is 1 microW. At the output, the signal power is 1 W and the noise power is 40 mW. What is the amplifier noise figure?

a. -6 dB

b. 9 dB

c. 6 dB

d. -3 dB

View Answer:

Answer: Option C

Solution:

138. In measuring noise in a voice channel at a -4 dB test point level, the meter reads -70 dBm (F1A weighted), convert the reading into pWp.

a. 53

b. 93

c. 63

d. 83

View Answer:

Answer: Option C

Solution:

139. An amplifier with 20 dB gain is connected to another with 10 dB gain by means of a transmission line with a loss of 4 dB. If a signal with a power level of -14 dBm were applied to the system, calculate the power output.

a. 14 dBm

b. -12 dB

c. -20 dB

d. 12 dBm

View Answer:

Answer: Option D

Solution:

140. Two resistors, R1 and R2 have temperatures of 300K and 400K, respectively. What is the noise power if the two resistors are connected in series at 10 MHz bandwidth?

a. 96.6 fW

b. 55.2 fW

c. 41.4 fW

d. 88.36 fW

View Answer:

Answer: Option A

Solution:

141. Determine the shot noise for a diode with a forward bias of 1.40 mA over an 80 kHz bandwidht. (q = 1.6 x 10^-9 C)

a. 6 nA

b. 3 mA

c. 12 nA

d. 15 nA

View Answer:

Answer: Option A

Solution:

142. 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:

143. An amplifier with an overall gain of 20 dB is impressed with a signal whose power level is 1 watt. Calculate the output power in dBm.

a. 50 dBm

b. 150 dB

c. 80 dBm

d. 100 dBm

View Answer:

Answer: Option A

Solution:

144. What is the effect on the signal to noise ratio of a system (in dB) if the bandwidth is doubled considering all other parameters to remain unchanged except the normal thermal noise only. The S/N will be

a. Increased by a factor of 2

b. Decreased by ½ its value

c. Increased by a factor of 4

d. Decreased to ¼ its value

View Answer:

Answer: Option B

Solution:

145. Express the ratio in decibels of noise power ratio 50 is to 10 watts.

a. 7 dB

b. 21 dB

c. 14 dB

d. 3.5 dB

View Answer:

Answer: Option A

Solution:

146. 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:

147. A satellite has a noise figure of 1.6 dB. Find its equivalent noise temperature.

a. 139K

b. 192K

c. 291K

d. 129K

View Answer:

Answer: Option D

Solution:

148. 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:

149. In a microwave communications system, determine the noise power in dBm for an equivalent noise bandwidth of 10 MHz.

a. -104 dBm

b. -114 dBm

c. -94 dBm

d. -174 dBm

View Answer:

Answer: Option A

Solution:

150. The solar cycle repeats the period if great electrical disturbance approximately every

a. 11 years

b. 10 years

c. 9 years

d. 8 years

View Answer:

Answer: Option A

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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