 # Blake: MCQ in Transmission Lines

(Last Updated On: January 9, 2018)

This is the Multiple Choice Questions in Chapter 14: Transmission Lines from the book Electronic Communication Systems by Roy Blake . If you are looking for a reviewer in Communications Engineering this will definitely help. I can assure you that this will be a great help in reviewing the book in preparation for your Board Exam. Make sure to familiarize each and every questions to increase the chance of passing the ECE Board Exam.

### Start Practice Exam Test Questions

Choose the letter of the best answer in each questions.

MULTIPLE CHOICE

1. SWR stands for:

• b. Sine Wave Response
• c. Shorted Wire Region
• d. none of the above

ANS: D

2. TDR stands for:

• a. Total Distance of Reflection
• b. Time-Domain Reflectometer
• c. Time-Domain Response
• d. Transmission Delay Ratio

ANS: B

3. An example of an unbalanced line is:

• a. a coaxial cable
• b. 300-ohm twin-lead TV cable
• c. an open-wire-line cable
• d. all of the above

ANS: A

4. When analyzing a transmission line, its inductance and capacitance are considered to be:

• a. lumped
• b. distributed
• c. equal reactances
• d. ideal elements

ANS: B

5. As frequency increases, the resistance of a wire:

• a. increases
• b. decreases
• c. stays the same
• d. changes periodically

ANS: A

6. The effect of frequency on the resistance of a wire is called:

• a. I2R loss
• b. the Ohmic effect
• c. the skin effect
• d. there is no such effect

ANS: C

7. As frequency increases, the loss in a cable’s dielectric:

• a. increases
• b. decreases
• c. stays the same
• d. there is no loss in a dielectric

ANS: A

8. The characteristic impedance of a cable depends on:

• a. the resistance per foot of the wire used
• b. the resistance per foot and the inductance per foot
• c. the resistance per foot and the capacitance per foot
• d. the inductance per foot and the capacitance per foot

ANS: D

9. For best matching, the load on a cable should be:

• a. lower than Z0
• b. higher than Z0
• c. equal to Z0
• d. 50 ohms

ANS: C

10. The characteristic impedance of a cable:

• a. increases with length
• b. increases with frequency
• c. increases with voltage
• d. none of the above

ANS: D

11. The velocity factor of a cable depends mostly on:

• a. the wire resistance
• b. the dielectric constant
• c. the inductance per foot
• d. all of the above

ANS: B

12. A positive voltage pulse sent down a transmission line terminated in a short-circuit:

• a. would reflect as a positive pulse
• b. would reflect as a negative pulse
• c. would reflect as a positive pulse followed by a negative pulse
• d. would not reflect at all

ANS: B

13. A positive voltage pulse sent down a transmission line terminated with its characteristic impedance:

• a. would reflect as a positive pulse
• b. would reflect as a negative pulse
• c. would reflect as a positive pulse followed by a negative pulse
• d. would not reflect at all

ANS: D

14. A positive voltage-pulse sent down a transmission line terminated in an open-circuit:

• a. would reflect as a positive pulse
• b. would reflect as a negative pulse
• c. would reflect as a positive pulse followed by a negative pulse
• d. would not reflect at all

ANS: A

15. The optimum value for SWR is:

• a. zero
• b. one
• c. as large as possible
• d. there is no optimum value

ANS: B

16. A non-optimum value for SWR will cause:

• a. standing waves
• b. loss of power to load
• c. higher voltage peaks on cable
• d. all of the above

ANS: D

17. VSWR stands for:

• a. variable SWR
• b. vacuum SWR
• c. voltage SWR
• d. none of the above

ANS: C

18. The impedance "looking into" a matched line:

• a. is infinite
• b. is zero
• c. is the characteristic impedance
• d. 50 ohms

ANS: C

19. A Smith Chart is used to calculate:

• a. transmission line impedances
• b. propagation velocity
• c. optimum length of a transmission line
• d. transmission line losses

ANS: A

20. Compared to a 300-ohm line, the loss of a 50-ohm cable carrying the same power:

• a. would be less
• b. would be more
• c. would be the same
• d. cannot be compared

ANS: B

21. A balanced load can be connected to an unbalanced cable:

• a. directly
• b. by using a filter
• c. by using a "balun"
• d. cannot be connected

ANS: C

22. On a Smith Chart, you "normalize" the impedance by:

• a. assuming it to be zero
• b. dividing it by 2π
• c. multiplying it by 2π
• d. dividing it by Z0

ANS: D

23. The radius of the circle you draw on a Smith Chart represents:

• a. the voltage
• b. the current
• c. the impedance
• d. none of the above

ANS: D

24. The center of the Smith Chart always represents:

• a. zero
• b. one
• c. the characteristic impedance
• d. none of the above

ANS: C

25. A TDR is commonly used to:

• a. measure the characteristic impedance of a cable
• b. find the position of a defect in a cable
• c. replace a slotted-line
• d. all of the above

ANS: B

COMPLETION

1. A cable that lacks symmetry with respect to ground is called ____________________.

ANS: unbalanced

2. Parallel lines are usually operated as ____________________ lines since both wires are symmetrical with respect to ground.

ANS: balanced

3. Normally, a transmission line is terminated with a load equal to its ____________________ impedance.

ANS: characteristic

4. Twisted-pair cables are transmission lines for relatively ____________________ frequencies.

ANS: low

5. To analyze a transmission line, it is necessary to use ____________________ parameters instead of lumped ones.

ANS: distributed

6. The increase of a wire’s resistance with frequency is called the ____________________ effect.

ANS: skin

7. The increase of a wire’s resistance with frequency is caused by the ____________________ field inside the wire.

ANS: magnetic

8. Dielectrics become more ____________________ as the frequency increases.

ANS: lossy

9. The inductance and capacitance of a cable are given per unit ____________________.

ANS: length

10. Characteristic impedance is sometimes called ____________________ impedance.

ANS: surge

11. A cable that is terminated in its characteristic impedance is called a ____________________ line.

ANS: matched

12. A pulse sent down a cable terminated in a short-circuit will reflect with the ____________________

polarity.

ANS: opposite

13. The apparently stationary pattern of waves on a mismatched cable is called a ____________________ wave.

ANS: standing

14. SWR stands for ____________________-wave ratio.

ANS: standing

15. The ideal value for SWR is ____________________.

ANS: one

16. Transmission line impedances can be found using a ____________________ chart.

ANS: Smith

17. Short transmission-line sections called ____________________ can be used as capacitors or inductors.

ANS: stubs

18. Any cable that radiates energy can also ____________________ energy.

ANS: absorb

19. A ____________________-dB loss in a cable means only half the power sent reaches the load.

ANS: 3

20. It is often best to measure SWR at the ____________________ end of a cable.

21. Besides heat from I2R, the power a cable can carry is limited by the ____________________ voltage of its dielectric.

ANS: breakdown

22. To normalize an impedance on a Smith Chart, you divide it by ____________________.

ANS: Z0

23. The ____________________ of a Smith Chart always represents the characteristic impedance.

ANS: center

24. A ____________________ wavelength transmission line can be used a transformer.

ANS: one-quarter

25. A slotted line is used to make measurements in the ____________________ domain.

ANS: frequency

1. A transmission line has 2.5 pF of capacitance per foot and 100 nH of inductance per foot. Calculate its characteristic impedance.

ANS:

Z0 = 200 ohms

2. Two wires with air as a dielectric are one inch apart. The diameter of the wire is .04 inch. Calculate, approximately, its characteristic impedance.

ANS:

386 ohms

3. If a coaxial cable uses plastic insulation with a dielectric constant ∈r = 2.6 , what is the velocity factor for the cable?

ANS:

0.62

4. If a cable has a velocity factor of 0.8, how long would it take a signal to travel 3000 kilometers along the cable?

ANS:

12.5 ms

5. If a cable has a velocity factor of 0.8, what length of cable is required for a 90° phase shift at 100 MHz?

ANS:

0.6 meters

6. A cable has a VSWR of 10. If the minimum voltage along the cable is 20 volts, what is the maximum voltage along the cable?

ANS:

200 volts

7. A lossless line has a characteristic impedance of 50 ohms, but is terminated with a 75-ohm resistive load. What SWR do you expect to measure?

ANS:

1.5

8. If a cable has an SWR of 1.5, what will be the absolute value of its voltage coefficient of reflection?

ANS:

0.2

9. A generator matched to a line with a voltage coefficient of reflection equal to 0.2 transmits 100 watts into the line. How much power is actually absorbed by the load?

ANS:

96 watts

10. Using a Smith Chart to analyze a 50-ohm cable, what would be the normalized value of an impedance equal to 200 + j50 ohms?

ANS:

4 + j1

### Complete List of MCQs in Electronic Communication Systems by Blake

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