# MCQs in Noise Part IV

Compiled MCQs in Noise Part 4 of the series as one topic in Electronic System and Technologies (Communications Engineering) in the ECE Board Exam.

This is the Multiples Choice Questions Part 4 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 IV of the Series

151. A current change that is equal to twice its original value will correspond to a change of

• a. 3 dB
• b. 9 dB
• c. 10 dB
• d. 6 dB

152. What does a power difference of –3 dB mean?

• a. A loss of one third of the power
• b. A loss of one-half of the power
• c. A loss of 3 watts of power
• d. No significant change

153. A gain of 60 dB is the same as a gain of

• a. 10 volts/volt
• b. 100 volts/volt
• c. 1000 volts/volt
• d. 10,000 volts/volt

154. ______ is mathematically equal to the logarithm to the base ten of the power ratio P1 over P2.

• a. bel
• b. dB
• c. bel/10
• d. dB/2

155. Noise that is produced by the active components within the receiver.

• a. Thermal
• b. External
• c. Internal
• d. White

156. Noise due to random variation in the arrival of charge carriers at the output electrode of an active device

• a. Shot
• b. Impulse
• c. Thermal
• d. Dynamic

157. A network has a loss of 20 dB. What power ratio corresponds to this loss

• a. 0.01
• b. 0.1
• c. 10
• d. 100

158. A receiver connected to an antenna whose resistance is 60 ohms has an equivalent noise resistance of 40 ohms. Calculate the receiver’s noise figure in decibels and its equivalent noise temperature.

• a. 1.67 & 194°K
• b. 2.23 & 194°K
• c. 1.67 & 174°K
• d. 2.23 & 194°K

159. _____ Noise is the most prevalent noise found in urban areas and is normally caused by the arc discharge from automobile or aircraft ignition systems, induction motors, switching gears, high voltage lines and the like.

• a. Industrial
• b. Johnson
• c. Flicker
• d. Mixer

160. The noise figure of a totally noiseless device is

• a. Unity
• b. Infinity
• c. Zero
• d. 100

161. Indicate the noise whose source is in a category different from that of the other three.

• a. Solar
• b. Cosmic
• c. Atmospheric
• d. Galactic

162. The ratio(in dB) of the power of a signal at point to the power of the same signal at the reference point.

• a. Transmission Level Point
• b. Noise Figure
• c. S/N Ratio
• d. Neper

163. A network has a power gain of –3 dB. If the input power is 100 watts, the output power is

• a. 50 watts
• b. 55 watts
• c. 60 watts
• d. 62 watts

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

• a. Shot
• b. Random
• c. Impulse
• d. Transmit time

165. The input current of a network is 190 ÂµA and the output is 1.3 ÂµA. The loss in decibels is

• a. 20.2
• b. 21.6
• c. 28.6
• d. 43.3

166. If a network connected in series have a gain of -0.5 dB, -0.3dB, -2dB and 6.8dB, the overall gain is

• a. 2 dB
• b. –2 dB
• c. 4 dB
• d. –4 dB

167. What is the gain, in dB, if the output to input ratio is 1000.

• a. 20
• b. 30
• c. 40
• d. 10

168. The following characteristics of noise except

• a. Unwanted energy
• b. Predictable in character
• c. Present in the channel
• d. Due to any cause

169. The equivalent noise temperature of the amplifier is 25 °K what is the noise figure?

• a. 10.86
• b. 1.086
• c. 0.1086
• d. 1.86

170. A receiver connected to an antenna whose resistance is 50 ohms has an equivalent noise resistance of 30 ohms. What is the receiver’s noise temperature?

• a. 464°K
• b. 754°K
• c. 400°K
• d. 174°K

171. A theoretical antenna has a gain of 1dB. Its gain in nepers is

• a. 8.686
• b. 0.1151
• c. 6.868
• d. 0.5111

172. What is the equivalent output of a circuit in dBm, if it has an output of 10 watts?

• a. 10 dBm
• b. 30 dBm
• c. 20 dBm
• d. 40 dBm

173. An amplifier with an input resistance of 1000 ohms is operating over a 4 MHz bandwidth. Calculate the rms voltage if the amplifier is operating at 27 °C.

• a. 8.14 nV
• b. 8.14 uV
• c. 6.6 nV
• d. 6.6 uV

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

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

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

• a. Input noise voltage
• b. Equivalent noise resistance
• c. Noise temperature
• d. Noise figure

176. Any unwanted form of energy that tends to interfere with the wanted signal is called

• a. Noise
• b. Spectrum
• d. Absorption

177. The correct symbol for decibel is

• a. DB
• b. dB
• c. Db
• d. db

178. _____ is the noise created outside the receiver.

• a. Internal
• b. External
• c. Shot
• d. Industrial

179. _____ is the noise created by man.

• a. Solar
• b. Industrial
• c. Extraterrestrial
• d. Galactic

180. A voltage change that is equal to twice its original value correspond to a change of

• a. 3 dB
• b. 6 dB
• c. 9 dB
• d. 10 dB

181. Indicate the voltage level in dB with reference to one volt. This unit is used in video or TV measurement

• a. dBW
• b. dBk
• c. dBm
• d. dBV

182. which of the following is not an actual amount of power?

• a. dB
• b. dBm
• c. dBw
• d. dBk

183. In noise analysis, the reference temperature is

• a. 75 K
• b. 250 K
• c. 290 K
• d. 300 K

184. Noise from distant panels, stars, galaxies and other celestial objects are called

• a. Cosmic
• b. Extraterrestrial
• c. Galactic
• d. Black body

185. Indicate which one of the following types of noise does not occur in transistors

• a. Shot noise
• b. Flicker noise
• c. Partition noise
• d. Resistance noise

186. Which of the following is not a source of space noise

• a. Sun
• b. Star
• c. Lightning
• d. Black body

187. Noise that is due to the random and rapid motion of the charge carriers inside a resistive component.

• a. Johnson
• b. Thermal Agitation
• c. White
• d. All of the above

188. Indicate the false statement. The square of the thermal noise voltage generated by a resistor is proportional to

• a. Its resistance
• b. Its temperature
• c. Boltzmann’s Constant
• d. The bandwidth over which it is measured

189. In a communication system, noise is likely to affect the signal

• a. At the transmitter
• b. In the channel
• c. In the information source
• d. At the destination

190. The noise power generated by a resistor is proportional to

• a. Temperature
• b. Bandwidth
• c. a and b
• d. NOTA

191. Thermal noise is also known as

• a. Gaussian Noise
• b. White Noise
• c. Johnson noise
• d. All of the above

192. This type of noise has a power spectrum which decreases with increasing frequency. It is most important at low frequencies from 0 to about 100 Hz).

• a. Shot noise
• b. Flicker noise
• c. Diode noise
• d. BJT noise

193. Industrial noise extends up to what frequency?

• a. 500 MHz
• b. 500 GHz
• c. 500 THz
• d. 500 KHz

194. Impulse Noise is

• a. A function of current
• b. A shot duration pulse
• c. Dependent of frequency
• d. Dependent of temperature

195. When the power ratio of the output to input of a circuit is 200. What is the gain in dB?

• a. 23
• b. 46
• c. –23
• d. –46

196. What is the reference level for random noise measurement, FIA weighted?

• a. –82  dBm
• b. –90  dBm
• c. –85  dBm
• d. – 77 dBm

197. A 10 dB pad has an output level of -3 dBm. The level at the input is:

• a. 13 dBm
• b. -7 dBm
• c. 1 dBm
• d. 7 dBm

198. The sum of three signals of 45dBm each is ______ dBm.

• a. 45
• b. 135
• c. 20
• d. 50

199. It is characterized by high amplitude peaks of short duration in the total noise spectrum

• a. Intermodulation voice
• b. Impulse noise
• c. Dropout
• d. Phase hits

200. Originally was determined by measuring the interfering effect of noise in a Type 144 handset. A tone of 1 kHz, having a power level of 90 dBm was selected as the reference level.

• a. Noise figure
• b. S/N ratio
• c. Signal Figure
• d. Figure of Merit

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