This is the Multiples Choice Questions Part 4 of the Series in Radiation and Wave Propagation 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 Electromagnetic Radiation
- MCQs in Radio Spectrum
- MCQs in Wave Propagation
- MCQs in Radiation Patterns
- MCQs in Wavelength Calculations
- MCQs in Radiation Resistance
- MCQs in Diversity Systems
MCQs in Radiation and Wave Propagation Series
Following is the list of multiple choice questions in this brand new series:
Continue Practice Exam Test Questions Part IV of the Series
151. What propagation condition is usually indicated when a VHF signal is received from a station 500 miles away?
- a. D-layer absorption
- b. Faraday rotation
- c. Tropospheric ducting
- d. Moonbounce
152. How does the bandwidth of the transmitted signal affect selective fading?
- a. It is more pronounced at wide bandwidths
- b. It is more pronounced at narrow bandwidths
- c. It is equally pronounced in both narrow and wide bandwidth
- d. The receiver bandwidth determines the selective fading effect
153. How much farther does the radio-path horizon distance exceed the geometric horizon?
- a. By approximately 15% of the distance
- b. By approximately twice the distance
- c. By approximately one-half the distance
- d. By approximately four times the distance
154. Determine the dB gain of a receiving antenna which delivers a microvolt signal to a transmission line over that of an antenna that delivers a 2 microvolt signal under identical circumstances.
- a. -6
- b. -3
- c. 6
- d. 3
155. What is transequatorial propagation
- a. Propagation between two points at approximately the same distance north and south of the magnetic equator
- b. Propagation between two points on the magnetic equator
- c. Propagation between two continent by way of ducts along the magnetic equator
- d. Propagation between any two station at the same latitude
156. Knife edge diffraction:
- a. Is the bending of UHF frequency radio waves around a building, mountain or obstruction
- b. Causes the velocity of wave propagation to be different than the original wave
- c. Both a and b above
- d. Attenuate UHF signal
157. The average range for VHF communications is
- a. 5 miles
- b. 15 miles
- c. 30 miles
- d. 100 miles
158. A 500 kHz radiates 500 W of power. The same antenna produces a field strength equal 10 1.5 mV/, If the power delivered by the antenna is increased to 1 kW, what would be the expected field intensity?
- a. 3 mV/m
- b. 1.732 mV/m
- c. 2.12 mV/m
- d. 1.456 mV/m
159. The earth’s layer is struck by a meteor; a cylindrical region of free electron is formed at what layer of the ionosphere?
- a. F1 layer
- b. E layer
- c. F2 layer
- d. D layer
160. What happens to a radio wave as it travels in space and collides with other particles
- a. Kinetic energy is given up by the radio wave
- b. Kinetic energy is gained by the radio wave
- c. Aurora is created
- d. Nothing happens since radio waves have no physical substance
161. Find the characteristic impedance of polyethylene, which has a dielectric constant of 2.4.
- a. 163.9 ohms
- b. 377 ohms
- c. 243 ohms
- d. 250 ohms
162. What is the maximum range for signals using transequatorial propagation
- a. About 1000 miles
- b. About 2500 miles
- c. About 5000 miles
- d. About 7500 miles
163. Calculate the electric field intensity in millivolts per meter at 30 kW from a 5 km source.
- a. 190 mV/m
- b. 95.49 uV/m
- c. 0.189 W/m
- d. 13.416 V/m
164. What is the index of refraction of a certain substance if light travels through the substance at 100 meters at a time it is 140 meter to air?
- a. 1.183
- b. 1.4
- c. 0.714
- d. 0.845
165. What s selective fading?
- a. A fading effect caused by small changes in beam heading at the receiving station
- b. A fading caused by phase difference between radio wave components of the same transmission as experienced at the receiving station
- c. A fading caused by large changes in the height of the ionosphere as experienced at the receiving station
- d. A fading effect caused by the time difference between the receiving and transmitting stations
166. To what distance is VHF propagation ordinarily limited?
- a. Approximately 100 miles
- b. Approximately 500 miles
- c. Approximately 1500 miles
- d. Approximately 2000 miles
167. Why does the radio path horizon distance exceed the geometric horizon?
- a. E-layer skip
- b. D-layer skip
- c. Auroral skip
- d. Radio waves may be bent
168. Determine the effective radiated power of 20kW TV broadcast transmitter whose antenna has a field gain of 2.
- a. 40 kW
- b. 80 kW
- c. 20 kW
- d. 10 kW
169. What is the major cause of selective fading?
- a. Small changes in beam heading at the receiving station
- b. Large changes in the height of the ionosphere as experienced in the receiving station
- c. Time difference between the receiving and transmitting station
- d. Phase differences between the radio waves components of the same transmission as experienced in the receiving station
170. Determine the critical frequency value of an HF signal if its maximum usable frequency is 7050.50 kHz at 35 degrees incidence.
- a. 4936.8 kHz
- b. 5775 kHz
- c. 4044 kHz
- d. 4908.75 kHz
171. What is the propagation effect called when phase difference between radio wave components of the same transmission are experiences at the recovery station?
- a. Faraday’s rotation
- b. Diversity reception
- c. Selective fading
- d. Phase shift
172. What is the best time for transequatorial propagation?
- a. Morning
- b. Noon
- c. Afternoon or early evening
- d. Transequatorial propagation only works at night
173. The dielectric strength of a certain medium is about 2.85 MV/m. what is the maximum power density of an electromagnetic wave in this medium?
- a. 23.9 GW/ sq. m
- b. 67.7 GW/ sq. m
- c. 21.5 GW/ sq. m
- d. 6.86 GW/ sq. m
174. What is the knife edge diffraction?
- a. Allows normally line-of-sight signals to bend around sharp edges, mountain ridges, building and other obstruction
- b. Arching in sharp bends of conductors
- c. Phase angle image rejection
- d. Line-of-sight causing distortion to other signals
175. The total power delivered to the radiator of an isotropic antenna is 200, 000 W. determine the power density at a distance of 100 meters
- a. 1.59 W/sq m
- b. 24.49 W/sq m
- c. 3.18 W/sq m
- d. 244.95 W/sq m
176. The bending of radio waves passing over the top of a mountain range disperse a weak portion of the signal behind the mountain is
- a. Eddy-current phase effect
- b. Knife-edge diffraction
- c. Shadowing
- d. Mirror refraction effect
177. A radio wave moves from air (er=1) to glass (er=7.8). Its angle of incidence is 20 degrees. What is the angle of refraction?
- a. 7 degrees
- b. 29 degrees
- c. 10.3 degrees
- d. 72.79 degrees
178. A dipole antenna requires to be feed with 20 kW of power to produce a given signal strength available with an input power of 11 kW. What is the dB gain obtained by the use of the reflector? (gain referred to this particular dipole)
- a. -2.6 dB
- b. 2.6 dB
- c. 5.19 dB
- d. -5.19 dB
179. What is a wavefront?
- a. A voltage pulse in a conductor
- b. A current pulse in a conductor
- c. A voltage pulse across a resistor
- d. A fixed point in an electromagnetic wave
180. What is meant by referring to electromagnetic waves as having circular polarization?
- a. The electric field is bent into a circular shape
- b. The electric field rotates
- c. The electromagnetic wave continues to circle the earth
- d. The electromagnetic wave has been generated by a quad antenna
181. An automobile travels at 90 km/h, find the time between fades if the car uses a cellphone at 800 MHz
- a. 11.2 ms
- b. 15 ms
- c. 7.5 ms
- d. 4.7 ms
182. When the electric field is parallel to the surface of the earth, what is the polarization of the electromagnetic wave?
- a. Vertical
- b. Horizontal
- c. Circular
- d. Elliptical
183. At what speed do electromagnetic waves travel in space?
- a. Approximately 300 million meters per second
- b. Approximately 468 million meters per second
- c. Approximately 186, 300 feet per second
- d. Approximately 300 million miles per second
184. The maximum number of free electrons in a certain ionospheric layer is 3.256x 10 ^ 13 per cu m. the critical frequency is
- a. 51.355 MHz
- b. 17.118 MHz
- c. 34.237 MHz
- d. 5.706 MHz
185. What are electromagnetic waves?
- a. Alternating currents in the core of an electromagnet
- b. A wave consisting of two electric fields at right angles to each other
- c. A wave consisting of an electric field and a magnetic field at right angles to each other
- d. A wave consisting of two magnetic fields at right angles to each other
186. When the electric field is perpendicular to the surface of the earth, what is the polarization of the electromagnetic wave?
- a. Circular
- b. Vertical
- c. Horizontal
- d. Elliptical
187. Determine the refractive index of an ionospheric layer with 1.567×10^6 free electrons per cu m. The frequency of the radio wave is 32 kHz.
- a. 0.999
- b. 0.936
- c. 0.956
- d. 0.987
188. What is meant by electromagnetic waves as horizontally polarized?
- a. The electric field is parallel to the earth
- b. The magnetic field is parallel to the earth
- c. Both the electric and magnetic field are horizontal
- d. Both the electric and magnetic field are vertical
189. Why do electromagnetic waves not penetrate a good conductor to any great extent?
- a. The electromagnetic field induces currents in the insulator
- b. The oxide on the conductor surface acts as a shield
- c. Because of eddy currents
- d. The resistivity of the conductor dissipates the field
190. A transmitter has a power output of 250 W at a carrier frequency of 325 MHz. it is connected to an antenna with a gain of 12 dBi. The receiving antenna is 10 km away and has a gain of 5 dBi. Calculate the power delivered to the receiver, assuming free-space propagation. Assume that there are no losses or mismatches in the system.
- a. 404 nW
- b. 2.04 nW
- c. 960 nW
- d. 680 nW
191. What is the frequency to use for skywave propagation if the critical frequency is 15 MHZ and the angle of radiation is 60 degrees?
- a. 17.32 MHz
- b. 30 MHz
- c. 25.5 MHz
- d. 14.722 MHz
192. When the magnetic field is parallel tot eh surface of the earth, what is the polarization of the electromagnetic field?
- a. Circular
- b. Horizontal
- c. Elliptical
- d. Vertical
193. What is the index of refraction of a certain medium if the velocity of propagation of a radio wave in this medium is 1.527×10^8 m/s?
- a. 0.509
- b. 0.631
- c. 0.713
- d. 1.965
194. When the magnetic field is perpendicular to the surface of the earth, what is the polarization of the electromagnetic field?
- a. Circular
- b. Horizontal
- c. Elliptical
- d. Vertical
195. Frequencies most affected by knife-edge refraction are
- a. Low and medium frequencies
- b. High frequencies
- c. Very high and ultra high frequencies
- d. 100 kHz to 3 MHz
196. The ionosphere causes radio signals to be
- a. Diffused
- b. Absorbed
- c. Refracted
- d. Reflected
197. To increase the transmission distance of a UHF signal, which of the following should be done?
- a. Increase antenna gain
- b. Increase antenna height
- c. Increase transmitter power
- d. Increase receiver sensitivity
198. A receiver-transmitter station used to increase the communications range of VHF, UHF and microwave signals is called a(an)
- a. Transceiver
- b. Remitter
- c. Repeater
- d. Amplifier
199. A taxi company uses a central dispatcher with an antenna at the top of a 25 m tower, to communicate with the taxicabs. The taxi antennas are on the roofs of the cars, approximately 1.5 m above the ground. Calculate the maximum communication distance between the dispatcher and a taxi.
- a. 25.7 km
- b. 8.8 km
- c. 21 km
- d. 10.1
200. Microwave propagate by means of
- a. Direct wave
- b. Sky wave
- c. Surface wave
- d. Standing wave