# MCQs in Radiation and Wave Propagation Part VI

Compiled MCQs in Radiation and Wave Propagation Part 6 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 6 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 Wave Propagation
• MCQs in Wavelength Calculations
• MCQs in Diversity Systems

### MCQs in Radiation and Wave Propagation Series

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

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
PART 6: MCQs from Number 251 – 300                 Answer key: PART VI
PART 7: MCQs from Number 301 – 350                 Answer key: PART VII
PART 8: MCQs from Number 351 – 400                 Answer key: PART VIII

### Continue Practice Exam Test Questions Part VI of the Series

251. The curvature of the Earth presents a horizon to space wave propagation commonly called _________.

• a. Optical horizon
• c. Horizontal horizon
• d. Vertical horizon

252. Electromagnetic waves that are directed above the horizon level is called _________.

• a. direct waves
• b. sky waves
• c. space waves
• d. surface waves

253. The refracting and reflecting action of the ionosphere and the ground is called

• a. sliding
• b. skipping
• c. hopping
• d. boosting

254. An electrical energy that is escaped in free space

• a. Electrical signal
• b. Electromagnetic waves
• c. Magnetic waves
• d. Electromagnetism

255. The layer of the ionosphere which farthest from the sun

• a. D layer
• b. E layer
• c. F1 layer
• d. F2 layer

256. A condition which manifest itself in the form of double-image distortion

• a. running
• c. ghosting
• d. snowing

257. The D layer of the ionosphere absorbs _________ waves.

• a. LF and MF
• b. MF and HF
• c. HF and VHF
• d. VHF and UHF

258. The E layer of the ionosphere is sometimes called _________

• a. Kennely-Heavisides
• c. E-densed layer
• d. Kennely layer

259. It is defined as the higher frequency that can be propagated directly upward and still be returned to earth by the ionosphere

• a. critical angle
• b. maximum usable frequency
• c. critical frequency
• d. virtual height

260. The maximum vertical angle at which electromagnetic waves can be propagated and still be reflected back by the ionosphere

• a. numerical aperture
• b. incident angle
• c. critical angle
• d. refracted angle

261. It is defined as the plane joining all points of equal phase

• a. rays
• b. electromagnetic wave
• c. wavefront
• d. isotropic source

262. It is the height above Earth’s surface from which a reflected wave appears to have been reflected.

• a. virtual height
• b. maximum height
• c. vertical height
• d. horizontal height

263. It is the highest frequency that can be used for sky wave propagation between two specific points on Earth’s surface

• a. optimum working frequency
• b. maximum usable frequency
• c. critical frequency
• d. maximum frequency

264. The polarization of electromagnetic waves can be determined by the direction of the

• a. E field
• b. H field
• c. propagation
• d. both E and H field

265. 85 percent of the maximum usable frequency (MUF) is called _________.

• a. maximum usable frequency
• b. optimum working frequency
• c. critical frequency
• d. maximum frequency

266. It is defined as the minimum distance from the transmit antenna that a sky wave at a given frequency will be returned to earth.

• a. skip distance
• b. skip zone
• c. skip frequency distance
• d. skip zone frequency

267. At distance greater than the skip distance, two rays can take different paths and still be returned to the same point on Earth. The two rays are called lower rays and _________.

• a. Pedersen ray
• b. Light ray
• c. Huygen’s ray
• d. Miller’s ray

268. Undesired radiated energy from a radio transmitter or in another source.

• a. ESD
• b. EMI
• c. RFI
• d. ESI

269. The area between where the surface waves are completely dissipated and the point where the first sky wave returns to earth is called _________.

• a. skip distance
• b. skip distance zone
• c. optical horizon
• d. quiet zone

270. The undesired radiated energy that may cause interference with other electronic equipment in the vicinity.

• a. ESD
• b. EMI
• c. RFI
• d. ESI

271. It is defined as the loss incurred by an electromagnetic wave as it propagates in a straight line through a vacuum with no absorption or reflection of energy from nearby objects.

• a. free-space path loss
• b. free space loss
• c. path loss
• d. any of these

272. To increase the transmission distance of a UHF signal, which of the following should be done?

• a. increase the antenna gain
• b. increase antenna height
• c. increase transmitter power

273. For a carrier frequency of 6 GHz and a distance of 50 km, determine the free-space path loss

• a. 132 dB
• b. 123 dB
• c. 142 dB
• d. 152 dB

274. A microwave-transmitting antenna is 550 ft. high. The receiving antenna is 200 ft. high. The maximum transmission distance is

• a. 20 mi
• b. 33.2 mi
• c. 38.7 mi
• d. 53.2 mi

275. Indicate which one of the following term applies to troposcatter propagation

• a. SIDs
• c. Atmospheric storms

276. Line-of-sight communications is not a factor in which frequency range?

• a. VHF
• b. UHF
• c. HF
• d. Microwave

277. VLF waves are used for some types of services because

• a. of the low powers required
• b. the transmitting antenna are of convenient size
• c. they are very reliable
• d. affected by the solar cycle

278. Microwave signals propagate by way of the

• a. direct wave
• b. sky wave
• c. surface wave
• d. standing wave

279. Indicate which of the following frequencies cannot be used for reliable beyond-the-horizon terrestrial communications without repeaters:

• a. 20 kHz
• b. 15 MHz
• c. 900 MHz
• d. 12 GHz

280. The type of radio wave responsible for long-distance communications by multiple skips is the

• a. ground wave
• b. direct wave
• c. surface waves
• d. sky wave

281. High-frequency waves are

• a. absorbed by the F2 layer
• b. reflected by the D layer
• c. capable of use for long-distance communications on the moon
• d. affected by the solar cycle

282. The ionosphere has its greatest effect on signals in what frequency range?

• a. 300 kHz to 3 MHz
• b. 3 to 30 MHz
• c. 30 to 300 MHz
• d. above 300 MHz

283. Distances near the skip distance should be used for sky-wave propagation

• a. to avoid tilting
• b. to prevent sky-wave and upper ray interference
• c. to avoid Faraday effect
• d. so as not to exceed the critical frequency

284. Ground-wave communications is most effective in what frequency range?

• a. 300 kHz to 3 MHz
• b. 3 to 30 MHz
• c. 30 to 300 MHz
• d. above 300 MHz

285. The ionosphere causes radio signals to be

• a. diffused
• b. absorbed
• c. refracted
• d. reflected

286. Helical antenna are often used for satellite tracking at VHF because of

• a. troposcatter
• b. superrefraction
• c. ionospheric refraction

287. A ship-to-ship communication system is plagued by fading. The best solution seem to use of

• a. a more directional antenna
• c. frequency diversity
• d. space diversity

288. It is defined as the ratio of the electric field intensity of the reflected wave to that of the incident wave

• a. refractive index
• b. numerical aperture
• c. reflection coefficient
• d. absorption coefficient

289. It is the measure of energy received per unit time, per unit area, per unit frequency interval.

• a. solar intensity
• b. sunspot
• c. solar flare
• d. solar flux

290. A long period with lack of any solar activity

• a. El NiÃ±o
• b. La NiÃ±a
• c. Maunder period
• d. Sunspots

291. As a ground-wave signal moves away from the transmitter, the ground wave eventually disappears due to the

• a. absorption
• b. tilting
• c. refraction
• d. diffraction

292. It is the lowest layer of the atmosphere where all weather disturbances takes place

• a. D layer
• b. Stratosphere
• c. Ionosphere
• d. Troposphere

293. It is the lower limit of the range of frequencies that provide useful communication between two given points by the way of the ionosphere.

• a. MUF
• b. LUF
• c. OWF
• d. MMF

294. It is the area that lies between the outer limit of the ground-wave range and the inner edge of energy return from the ionosphere

• a. skip distance
• b. skip zone
• c. virtual height
• d. optical horizon

295. Variations brought about by the rotation of the earth around its axis.

• a. cyclical rotation
• b. seasonal variation
• c. diurnal variation
• d. weather variation

296. Ionospheric irregularity caused by solar flares, which are gigantic emissions of hydrogen from the sun.

• a. Sudden ionospheric disturbances
• d. Any of these

298. Radio horizon is _________ greater than the optical horizon.

• a. one-third
• b. four-third
• c. two-third
• d. twice

299. An increase in temperature with height which gives rise to superrefraction or ducting is known as _________.

• a. height inversion
• b. depth inversion
• c. temperature inversion
• d. ionospheric inversion

300. A region in which superrefraction occurs which is formed in the troposphere when the layer of cool air becomes trapped underneath a layer of warmer air.

• a. duct
• b. dielectric area
• c. gateway
• d. window

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

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