MCQ in Microwave Communications Part 4 | ECE Board Exam

This is the Multiples Choice Questions Part 4 of the Series in Microwave Communications 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 Basic Principles of Microwave Communications
• MCQ in Electro-Optics
• MCQ in Photonics
• MCQ in Optoelectronics
• MCQ in Electromagnetics
• MCQ in Avionics, Aerospace, Navigational and Military Applications
• MCQ in Medical Electronics
• MCQ in Cybernetics
• MCQ in Biometrics

Continue Practice Exam Test Questions Part 4 of the Series

151. Attenuator is used in the travelling wave tube to

a. Help bunching

b. Prevent oscillations

c. Prevent saturation

d. Increase gain

152. The multicavity klystron

a. Is not a good low-level amplifier because of noise

b. Has a high repeller voltage to ensure a rapid transmit time

c. Is not suitable for pulsed operation

d. Needs a long transit time through the buncher cavity to ensure current modulation

153. What is the effective radiated power of a repeater with 450 W transmitting power output, 4 dB feedline loss, 6dB duplexer loss, and 7 dB circulator and feedline loss and antenna gain of 25 dB?

a. 2893.31 W

b. 2523.83 W

c. 2839.31 W

d. 2425.38 W

154. Magnetron oscillator are used for

a. Generating SHF signals

b. Multiplexing

c. Generating rich harmonics

d. FM demodulation

155. A microwave tube which has the advantage of having a high efficiency

a. Cross-field amplifier

b. Helix traveling wave tube

c. Klystron

d. Gridded tube

156. What term is used to describe the variation in a microwave oscillator frequency caused by power supply voltage or current changes?

a. Frequency pulling

b. Frequency pushing

c. Post-tuning drift

d. Tuning sensitivity

157. A rectangular waveguide has a width of 1.2 in and a height of 0.7 in. the waveguide will pass all signals above _____ GHz.

a. 4 GHz

b. 8.44 GHz

c. 10 GHz

d. 4.92 GHz

158. Waveguides are

a. A hollow tube that carries HF

b. Solid conductors of RF

c. Coaxial cables

d. Copper wire

159. A TWT is sometimes preferred to the multi-cavity klystron amplifier because the former

a. Is more efficient

b. Has a greater bandwidth

c. Has a higher number of modes

d. Produces a higher output power

160. Variation in oscillator frequency with changes in load SWR

a. Frequency pulling

b. Frequency pushing

c. Post-tuning drift

d. Tuning sensitivity

161. It is the frequency change of an electronically tuned oscillator at a specified time after it has reached its desired frequency

a. Frequency pulling

b. Frequency pushing

c. Post-tuning drift

d. Tuning sensitivity

162. What is the power level of the smallest signal that can be detected above the noise by a Schottky diode?

a. -20 dBm

b. 0 dBm

c. -60 dBm

d. -100 dBm

163. A line-of-sight radio link operating at a frequency of 6 GHz has a separation of 40 km between antennas. An obstacle in the path is located 10 km from the transmitting antenna. By how much must the beam clear the obstacle?

a. 11.6 m

b. 13.4 m

c. 19.34 m

d. 22.33 m

164. AM isolator

a. Acts a buffer between microwave oscillators coupled to a waveguide

b. Acts as a buffer to protect a microwave oscillator form variations in the load changes

c. Shields UHF circuits from RF transmitter

d. Both a and b

165. What is the effective earth’s radius when Ns = 300?

a. 8500 km

b. 9320 km

c. 5600 km

d. 4850 km

166. What is the power level of the largest signal that will still be in the square-law range of a Schottky diode?

a. -20 dBm

b. 0 dBm

c. -60 dBm

d. -100 dBm

167. A component that combines microwave signals from separate transmission lines into one common transmission line and allows no coupling between the separate lines

a. Isolator

b. Circulator

c. Directional coupler

d. Combiner

168. Telemetry is a microwave communications system which operates at

a. 600 MHz

b. 3.9 GHz

c. 4 GHz

d. 2 GHz

169. What is the maximum power that can be obtained from a microwave semiconductor?

a. 1 W

b. 500 mW

c. 10 W

d. 4 W

170. The cavity magnetron uses strapping to

a. Prevent mode-jumping

b. Prevent cathode back-heating

c. Ensure bunching

d. Improve the phase-focusing effect

171. As a result of reflections from a plane conducting wall, electromagnetic waves acquire an apparent velocity greater that the velocity of light in space. This is called the

a. Velocity of propagation

b. Normal velocity

c. Group velocity

d. Phase velocity

172. Which of the following is a method of modulating digital signals onto a microwave carrier?

a. FSK

b. Biphase

c. Quadraphase

d. All of the above

173. Suppose that the transmitter and receiver towers have equal height. How high would they have to be to communicate over a distance of 34 km?

a. 23.5 m

b. 28.47 m

c. 17 m

d. 8.47 m

174. In microwave communications system, for a carrier frequency of 6 GHz and a distance of 40 km, determine the free-space path loss in dB.

a. 80 dB

b. 84.2 dB

c. 140 dB

d. 144.2 dB

175. A microwave relay repeater that receives the modulated microwave carrier and obtains the baseband signal from it, and them modulates the baseband signal onto another carries and retransmit the new carrier with the baseband modulated onto it

a. Heterodyne repeater

b. Baseband repeater

c. RF repeater

d. Regenerative repeater

176. Which is the frequency range of the most common industrial microwave relay band?

a. 6.575 – 6.875 GHz

b. 3.7 – 4.2 GHz

c. 5.925 – 6.425 GHz

d. 10.7 – 11.7 GHz

177. When a particular mode is excited in a waveguide, there appears an extra electric component, in the direction of propagation. The resulting mode is

a. Transverse-electric

b. Transverse-magnetic

c. Longitudinal

d. Transverse-electromagnetic

178. Waveguide construction

a. Should not use silver plating

b. Should not use copper

c. Should not have short vertical runs

d. Should not have long horizontal runs

179. In a microwave system, the antenna sees a sky temperature of 120 K, and the antenna feedline has a loss of 3 dB. Calculate the noise temperature of the antenna/feedline system, referenced to the receiver input.

a. 205 K

b. 233.33 K

c. 182 K

d. 210 K

180. A choke flange may be used to couple two waveguides

a. To help in the alignment of the waveguides

b. Because it is simpler than any other join

c. To compensate for discontinuities at the join

d. To increase the bandwidth of the system

181. A PIN diode is

a. A metal semiconductor point-contact diode

b. A microwave mixer diode

c. Often used a microwave detector

d. Suitable for use as a microwave switch

182. For some applications, circular waveguides may be used preferred to rectangular ones because

a. The smaller cross section needed at any frequency

b. Lower attenuation

c. Freedom from spurious modes

d. Rotation of polarization

183. A circulator

a. Cools dc motors during heavy loads

b. Allows two or more antennas to feed one transmitter

c. Allows one antenna to feed two separate microwave transmitters and receivers at the same time

d. Insulates UHF frequencies on transmission lines

184. What is the free-space loss in dB between two microwave parabolic antennas 38 km apart operating at 7 GHz?

a. 85.10 dB

b. 80.90 dB

c. 140.90 dB

d. 145.10 dB

185. A ruby maser amplifier must be cooled

a. Because the maser amplification generates a lot of heat

b. To increase bandwidth

c. Because it cannot operate at room temperature

d. To improve the noise performance

186. The glass tube of a TWT may be coated with aquadag to

a. Help focusing

b. Provide attenuation

c. Improve bunching

d. Increase gain

187. An antenna covering that the transmitted or receives microwave power can pass through, used to protect the antenna and the antenna feed from weather

a. Shroud

b. Sub-reflector

c. Radome

d. Offset antenna

188. Waveguide are

a. Used exclusively in high frequency power supplies

b. Ceramic couplers attached to the antenna terminals

c. High-pass filters used at low radio frequencies

d. Hollow metal conductors used to carry high-frequency current

189. A microwave device which is unlikely to be used a pulsed device. It is based on the principle of operation of a traveling wave tube.

a. Multicavity klyston

b. Cross-field amplifier (CFA)

c. Backward wave oscillator (BWO)

d. Coaxial magnetron

190. A magnetic field is used in the cavity magnetron to

a. Prevent anode current in the absence of oscillations

b. Ensure that the oscillations are pulsed

c. Help in focusing the electron beam thus preventing spreading

d. Ensure that the electors will orbit around the cathode

191. In a micro wave communications system, if the minimum carrier-to-noise (C/N) requirements for a receiver with a 10MHz bandwidth is 22 dB, the minimum receive carrier power is…

a. -82 dB

b. 76 dBm

c. 84 dB

d. -82 dBm

192. A rectangular waveguide used for microwave transmission has a width of 1.4 inches and a height of 0.8 inches. All signals above ____ GHz will be passed by the waveguide.

a. 4.3 GHz

b. 2 GHz

c. 4.2 GHz

d. 5 GHz

193. A pyramidal horn has an aperture (opening) of 58 mm in the E plane and 78 mm in the H plane. It operates at 14 GHz. Calculate the gain in dBi.

a. 19.29

b. 24.14

c. 15.8

d. 19.31

194. A magnetron whose oscillating frequency is electronically adjustable over a wide range is called a

a. Coaxial magnetron

b. Dither-tuned magnetron

c. Frequency agile magnetron

d. VTM

195. Conductance takes place in a waveguide

a. By inter-electron delay

b. Through electrostatic field reluctance

c. In the same manner as a transmission line

d. Through electromagnetic and electrostatic fields in the walls of the waveguide

196. Indicate the false statement. Klystron amplifiers may use intermediate cavities to

a. Prevent the oscillations that occurs in two-cavity klystrons

b. Increase the bandwidth of the device

c. Improve power gain

d. Increase the efficiency of the klystron

197. The primary purpose of the helix in a traveling wave tube is to

a. Prevent the electron beam from spreading in the long tube

b. Reduce the axial velocity of the RF field

c. Ensure broadband operation

d. Reduce the noise figure

198. A microwave device which allows RF energy to pass through in one direction with very little loss, but absorbs RF power in the opposite direction

a. Circulator

b. Wave trap

c. Multiplexer

d. Isolator

199. A parametric amplifier must be cooled

a. Because parametric amplification generates a lot of heat

b. To increase bandwidth

c. Because it cannot operate at room temperature

d. To improve the noise performance

200. For low attenuation, the best transmission medium is

a. Flexible waveguide

b. Ridged waveguide

c. Rectangular waveguide

d. Coaxial line

Questions and Answers in Microwave Communications and Principles Series

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

Complete List of MCQ in Communications Engineering per topic