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# MCQ in Transmission Fundamentals Part 6 | ECE Board Exam

This is the Multiple Choice Questions Part 6 of the Series in Transmission Fundamentals 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 Transmission System
• MCQ in Transmission Medium
• MCQ in Velocity and Line Wavelength
• MCQ in Characteristics Impedance
• MCQ in Primary Line Constants and Propagation Constants
• MCQ in Standing Waves
• MCQ in Voltage Standing Wave Ratio
• MCQ in Telephone Lines and Cables
• MCQ in Wave Guides
• MCQ in Balanced and Unbalanced Lines
• MCQ in Twisted pair wire, Coaxial Cable
• MCQ in Decibel
• MCQ in Signal and Noise Fundamentals

#### Continue Practice Exam Test Questions Part 6 of the Series

Choose the letter of the best answer in each questions.

251. What is the characteristic impedance of a single wire with diameter d = 0.25 mm placed at the center between parallel planes separated by 1 mm apart? The wire is held by a material with a velocity factor of 0.75?

a. 75 ohms

b. 120 ohms

c. 100 ohms

d. 300 ohms

Solution:

252. There is an improper impedance match between a 30 W transmitter and the antenna and 5 W is reflected. How much power is actually transmitted?

a. 35 W

b. 25 W

c. 30 W

d. 20 W

Solution:

253. What is the actual length in feet of a one quarter-wavelength of a coax with a velocity factor of 0.69 at 40 MHz?

a. 6.15

b. 4.244

c. 5.904

d. 16.974

254. A quarter-wave line is connected to an RF generator and is shorted out at the far end. What is the input impedance to the line at the generator?

a. A low value of resistance

b. A high value of resistance

c. A capacitive reactance which is equal in value to the lineโs surge impedance

d. A value of resistance equal to the characteristic impedance of the line

Solution:

255. A coaxial cable has a capacitance of 90 pF/m and a characteristic impedance of 75 ohms. Find the inductance of a 2 m length.

a. 1.013 uH

b. 450 nH

c. 506.25 nH

d. 225 nH

Solution:

256. If the SWR on a transmission line has high value, the reason could be

a. An impedance mismatch between the line and the load

b. That the line is nonresonant

c. A reflection coefficient of zero at the load

d. A high degree of attenuation between the load and the position where the SWR is measured

Solution:

257. Calculate the velocity factor of a coaxial cable used as a transmission line with the characteristic impedance of 50 ohms; capacitance is 40 pF/m and an inductance equal to 50 microH/m.

a. 0.7450

b. 0.7504

c. 0.0745

d. 0.0475

258. If a quarter-wave transmission line is shorted at one end

a. There is minimum current at the shorted end

b. The line behaves as a parallel-tuned circuit in relation to the generator

c. The line behaves as a series tuned circuit in relation to the generator

d. There is a maximum voltage at the shorted end

Solution:

259. What is the velocity factor for a cable with a Teflon dielectric (relative permittivity = 2.1)?

a. 0.69

b. 0.476

c. 2.1

d. 1.449

Solution:

260. A 50-ohm transmission line is feeding an antenna which represents a 50-ohm resistive load. To shorten the line, the length must be

a. Any convenient value

b. An odd-multiple of three-quarters of a wavelength

c. An even multiple of a quarter of a wavelength

d. An odd multiple of an eight of a wavelength

Solution:

261. A feature of an infinite transmission line is that

a. Its input impedance at the generator is equal to the lineโs surge impedance

b. Its phase velocity is greater than the velocity of light

c. The impedance varies at different positions on the line

d. The input impedance is equivalent to a short circuit

Solution:

262. The outer conductor of the coaxial cable is usually grounded

a. At the beginning and at the end of the cable

b. Only at the beginning of the cable

c. Only at the end of the cable

d. The outer conductor must never be grounded

Solution:

263. What is the impedance of a balance 4-wire with a diameter of 0.25 cm and spaced 2.5 cm apart using an insulator with a dielectric constant of 2.56?

a. 100 ohms

b. 160.5 ohms

c. 88.93 ohms

d. 25.8 ohms

264. An attenuator has a loss of 26 dB. If a power of 3 W is applied to the attenuator, find the output power.

a. 1.65 watts

b. 7.54 milliwatts

c. 1194 watts

d. 5.459 watts

Solution:

265. When surge impedance of a line is matched to a load, the line will

a. Transfer maximum current to the load

b. Transfer maximum voltage to the load

c. Transfer maximum power to the load

d. Have a VSWR equal to zero

Solution:

266. A lossless line is terminated by a resistive load which is not equal to the surge impedance. If the value of the reflection coefficient is 0.5, the VSWR is

a. 2

b. 3

c. 1.5

d. 5

Solution:

267. The best insulation at UHF is

a. Black rubber

b. Bakelite

c. Paper

d. Mica

Solution:

268. Neglecting line losses, the RMS voltage along an RF transmission line having no standing waves

a. Is equal to the impedance

b. Is one-half of the surge impedance

c. Is the product of the surge impedance and the lien current

d. Varies sinusoidally along the line

Solution:

269. What length of standard RG-8/U coaxial cable would be required to obtain a 30 degree-phase shift at 250 MHz?

a. 0.792 m

b. 0.99 m

c. 0.066 m

d. 0.124 m

Solution:

270. Nitrogen is placed in transmission lines to

a. Improve the skin-effect of microwaves

b. Reduce arcing in the line

c. Reduce the standing wave ratio of the line

d. Prevent moisture from entering the line

Solution:

271. Referred to the fundamental frequency, a shorted stub line attached to the transmission line to absorb even harmonics could have a wavelength of

a. 1.41 wavelength

b. ยฝ wavelength

c. ยผ wavelength

d. 1/6 wavelength

Solution:

272. Nitrogen gas in concentric RF transmission lines is used to

a. Keep moisture out

b. Prevent oxidation

c. Act as insulator

d. Both A and B

Solution:

273. If a transmission line has a power loss of 6 dB per 100 feet, what is the power at the feed point to the antenna at the end of a 200 foot-transmission line fed by a 100 watt transmitter?

a. 70 watts

b. 50 watts

c. 25 watts

d. 6 watts

Solution:

274. Two adjacent minima on a slotted line are 20 cm apart. Find the wavelength assuming a velocity factor of 95 %.

a. 38 m

b. 43.7 m

c. 46 cm

d. 40 cm

Solution:

275. What would be the approximate series impedance of a quarter-wave matching line used to match a 600 ohm-feed to 70 ohm-antenna?

a. 205 ohms

b. 210 ohms

c. 25.88 ohms

d. 102.5 ohms

Solution:

276. Which of the following represents the best SWR?

a. 1:1

b. 1:2

c. 1:15

d. 2:1

Solution:

277. An optical domain reflectometer display shows a discontinuity 1.4 microseconds from the start. If the line has a velocity factor of 0.92, how far is the fault from the reflectometer?

a. 168 m

b. 193.2 m

c. 210 m

d. 386 m

Solution:

278. A high SWR creates losses in a transmission line. A high standing wave ratio might be caused by

a. Improper turns ratio between primary and secondary in the plate tank transformer

b. Screen grid current flow

c. An antenna electrically too long for its frequency

d. An impedance mismatch

Solution:

279. A properly connected transmission line

a. Is grounded at the transmitter end

b. Is cut to a harmonic of the carrier frequency

c. Is cut to an even harmonic of the carrier frequency

d. Has a standing wave ratio as near as 1:1 as possible

Solution:

280. If a ยพ wavelength transmission is shorted at one end, the impedance at the open will be

a. Zero

b. Infinite

c. Decreased

d. Increased

Solution:

281. The characteristic impedance of a transmission line does not depend upon its

a. Length

b. Conductor diameter

c. Conductor spacing

d. None of the above

Solution:

282. Which of the following is not a common transmission line impedance?

a. 50 ohms

b. 75 ohms

c. 120 ohms

d. 300 ohms

Solution:

283. A ratio expressing the percentage of incident voltage reflected on a transmission line is known as the

a. Velocity factor

b. Standing wave ratio

c. Reflection coefficient

d. Line efficiency

Solution:

284. A series tuned circuit operating at a frequency of 1 GHz is to be constructed from a shorted section of Teflon-dielectric coaxial cable. What length should be used? ( relative dielectric = 2.1)

a. 0.325 m

b. 0.10 m

c. 0.217 m

d. 0.143 m

Solution:

285. A 75 ohm line is terminated in a 30 ohm resistance. Find the SWR.

a. 0.6

b. 0.429

c. 2.5

d. 0.4

Solution:

286. A generator sends 50 mW down a 50 ohm line. The generator is matched to the line but the load is not. If the coefficient of reflection is 0.6, how much power is reflected?

a. 18 mW

b. 20 mW

c. 30 mW

d. 32 mW

Solution:

287. At very high frequencies, transmission lines are used as

a. Tuned circuits

b. Antennas

c. Insulators

d. Resistors

Solution:

288. Transmission line shielding is grounded

a. At the input only

b. At both the input and output

c. At the output only

d. If the antenna is a Marconi design

Solution:

289. A shorted quarter-wave line at the operating frequency acts like a(an)

a. Series resonant circuit

b. Parallel resonant circuit

c. Capacitor

d. Inductor

Solution:

290. A transmitter is required to deliver 100 W to an antenna through 5 m of coaxial cable with a loss of 3 dB / 100 m. What must be the output power of the transmitter, assuming the line is matched?

a. 136 W

b. 153 W

c. 151 W

d. 116.815 W

Solution:

291. A generator sends 50 mW down a 50 ohm line. The generator is matched to the line but the load is not. If the coefficient of reflection is 0.25, how much power is dissipated in the load?

a. 46.9 mW

b. 37.5 mW

c. 3.125 mW

d. 12.5 mW

Solution:

292. Determine the Q of an antenna if it has a bandwidth of 0.06 MHz and is cut to a frequency of 30 MHz.

a. 50

b. 100

c. 150

d. 250

Solution:

293. The main disadvantage of the two-hole directional coupler is

a. Low directional coupling

b. Poor directivity

c. High SWR

d. Narrow bandwidth

Solution:

294. A shorted half-wave line at the operating frequency acts like a(an)

a. Capacitor

b. Inductor

c. Series resonant circuit

d. Parallel resonant circuit

Solution:

295. A load impedance of 100 + j25 ohms is normalized on a 100 ohm-line. The normalized value is

a. 2 + j0.5 ohms

b. 0.25 – j1 ohms

c. 0.94 – j24 ohms

d. 1 + 0.25 ohms

Solution:

296. A pattern of voltage and current variations along a transmission line not terminated in its characteristic impedance is called

a. Electric field

c. Standing waves

d. Magnetic field

Solution:

297. A 75-j50 ohms is connected to a coaxial transmission line of ZO = 75 ohms, at 10 GHz. The best method of matching consists in connecting

a. A short-circuited stub at the load

b. An inductance at the load

c. A capacitance at some specific distance from the load

d. A short-circuited stub at some specific distance from the load

Solution:

298. Calculate the impedance seen looking into a 75 ohm line 1 m long terminated in a load impedance of 100 ohms, if the line has a velocity factor 0f 0.8 and operates at a frequency of 30 MHz.

a. 72 – j21 ohms

b. 75 – j25 ohms

c. 40 – j30 ohms

d. 50 – j25 ohms

Solution:

299. The velocity factor of a transmission line

a. Depends on the dielectric of the material used

b. Increases the velocity along the transmission line

c. Is governed by the skin effect

d. Is higher for a solid dielectric than for air

Solution:

300. A transmitter supplies 50 W to a load through a line with an SWR of 4:1. Find the power absorbed by the load.

a. 44.4 W

b. 5.6 W

c. 32 W

d. 18 W

Solution:

#### Questions and Answers in Transmission Fundamentals Series

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

MCQ in Transmission Fundamentals
PART 1: MCQ from Number 1 โ 50                        Answer key: PART 1
PART 2: MCQ from Number 51 โ 100                   Answer key: PART 2
PART 3: MCQ from Number 101 โ 150                 Answer key: PART 3
PART 4: MCQ from Number 151 โ 200                 Answer key: PART 4
PART 5: MCQ from Number 201 โ 250                 Answer key: PART 5
PART 6: MCQ from Number 251 โ 300                 Answer key: PART 6
PART 7: MCQ from Number 301 โ 350                 Answer key: PART 7
PART 8: MCQ from Number 351 โ 400                 Answer key: PART 8
PART 9: MCQ from Number 401 โ 450                 Answer key: PART 9
PART 10: MCQ from Number 451 โ 500                Answer key: PART 10

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

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