 MCQs in Noise Part III

(Last Updated On: September 10, 2019) 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.

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 III 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

102. Man-made noise is caused by

• a. Lightning discharge
• b. Solar eruptions
• c. Distant stars
• d. Arc discharges in electrical machines

103. Cosmic noise is produced by

• a. Lightning discharge
• b. Solar eruption
• c. Distant stars
• d. Industrial electrical discharges

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

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

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

• a. Halved
• c. Doubled
• d. Unchanged

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

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

109. Considered as the main source of an internal noise

• a. Flicker
• b. Thermal agitation
• c. Device imperfection
• d. Temperature change

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

• a. 876 K
• b. 900 K
• c. 906 K
• d. 875 K

111. Atmospheric noise is less severe at frequencies above

• a. 10 GHz
• b. 30 MHz
• c. 1 GHz
• d. Audio level

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

• a. NPR
• b. dBrn
• c. dBW
• d. dBm

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

• a. Meteor showers
• b. Sunspots
• c. Airplanes
• d. Thunderstorms

114. Background noise is the same as the following EXCEPT

• a. Impulse noise
• b. Thermal noise
• c. White noise
• d. Gaussian noise

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

116. The unit of noise power of psophometer

• a. dBa
• b. pWp
• c. dBm
• d. dBm0

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

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

• a. 50 dB
• b. 30 dB
• c. 40 dB
• d. 20 dB

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

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

• a. 0.4 A
• b. 298 mA
• c. 0.35 A
• d. 300 mA

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

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

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

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

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

126. NIF stand for

• a. Non-intrinsic noise figure
• b. Narrow interference figure
• c. Noise improvement factor
• d. Noise interference figure

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

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

• a. 800 Hz
• b. 1500 Hz
• c. 3400 Hz
• d. 1000 Hz

129. A three-stage amplifier is to have an overall noise temperature no greater than 70 K. 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

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

131. Which does not affect noise in a channel?

• a. None of these
• b. Bandwidth
• c. Temperature
• d. Quantizing level

132. Reference noise temperature

• a. 70 deg F
• b. 30 deg C
• c. 290 Kelvin
• d. 25 deg C

133. Industrial noise frequency is between

• a. 200 to 3000 MHz
• b. 15 to 160 MHz
• c. 0 to 10 kHz
• d. 20 GHz

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

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

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

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

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

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

140. Two resistors, R1 and R2 have temperatures of 300 K and 400 K, 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

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

• a. 6 nA
• b. 3 mA
• c. 12 nA
• d. 15 nA

142. The total noise power present in a 1 – Hz bandwidth

• a. Noise density
• b. Noise figure
• c. Noise limit
• d. Noise intensity

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

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

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

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

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

• a. 139 K
• b. 192 K
• c. 291 K
• d. 129 K

148. What is the primary cause of atmospheric noise?

• a. Thunderstorm
• b. Lightning
• c. Thunderstorm and lightning
• d. Weather condition

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

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

Complete List of MCQs in Communications Engineering per topic

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