### Online Questions and Answers Topic Outline

- MCQs in Transmission System
- MCQs in Transmission Medium
- MCQs in Velocity and Line Wavelength
- MCQs in Characteristics Impedance
- MCQs in Primary Line Constants and Propagation Constants
- MCQs in Standing Waves
- MCQs in Voltage Standing Wave Ratio
- MCQs in Telephone Lines and Cables
- MCQs in Wave Guides
- MCQs in Balanced and Unbalanced Lines
- MCQs in Twisted pair wire, Coaxial Cable
- MCQs in Decibel
- MCQs in Signal and Noise Fundamentals

### MCQs in Transmission Fundamentals Series

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

**Transmission Fundamentals MCQs**

**MCQs from Number 1 – 50**Answer key:

**PART I**

**MCQs from Number 51 – 100**Answer key:

**PART II**

**MCQs from Number 101 – 150**Answer key:

**PART III**

**MCQs from Number 151 – 200**Answer key:

**PART IV**

**MCQs from Number 201 – 250**Answer key:

**PART V**

**MCQs from Number 251 – 300**Answer key:

**PART VI**

**MCQs from Number 301 – 350**Answer key:

**PART VII**

**MCQs from Number 351 – 400**Answer key:

**PART VIII**

**MCQs from Number 401 – 450**Answer key:

**PART IX**

**MCQs from Number 451 – 500**Answer key:

**PART X**

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

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

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

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 line’s surge impedance
- d. A value of resistance equal to the characteristic impedance of the line

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

- a. 1.013 uH
- b. 450 nH
- c. 506.25 nH
- d. 225 nH

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

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

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

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

261. A feature of an infinite transmission line is that

- a. Its input impedance at the generator is equal to the line’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

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

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

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

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

267. The best insulation at UHF is

- a. Black rubber
- b. Bakelite
- c. Paper
- d. Mica

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

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

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

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. ½ wavelength
- c. ¼ wavelength
- d. 1/6 wavelength

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

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

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

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

276. Which of the following represents the best SWR?

- a. 1:1
- b. 1:2
- c. 1:15
- d. 2:1

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

- a. 168 m
- b. 193.2 m
- c. 210 m
- d. 386 m

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

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

280. If a ¾ wavelength transmission is shorted at one end, the impedance at the open will be

- a. Zero
- b. Infinite
- c. Decreased
- d. Increased

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

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

- a. 50 ohms
- b. 75 ohms
- c. 120 ohms
- d. 300 ohms

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

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. 0.325m
- b. 0.10 m
- c. 0.217 m
- d. 0.143 m

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

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

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

- a. Tuned circuits
- b. Antennas
- c. Insulators
- d. Resistors

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

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

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

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

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

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

- a. Low directional coupling
- b. Poor directivity
- c. High SWR
- d. Narrow bandwidth

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

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

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

- a. Electric field
- b. Radio waves
- c. Standing waves
- d. Magnetic field

297. A 75-j50 ohms is connected to a coaxial transmission line of Z_{O }= 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

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

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

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. 32 W
- b. 5.6 W
- c. 44.4 W
- d. 18 W

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