# MCQ Multiple Choice Questions Transmission Lines Communications Engineering

Below you can find MCQ’s or Multiple Choice Questions related to the Transmission Lines in the field of Communications Engineering. Correct answers are in red & bold font.

1. What determines the velocity factor in transmission line?

a) The termination impedance

b) The center conductor resistivity

c) Dielectrics in the line

d) The termination impedance

2. A transmission line has a capacitance of 25 pF / ft. and an inductance of 0.15 mH / ft. Determine the characteristic impedance of the line.

a) 100 W

b) 75 W

c) 77.5 W

d) 50 W

3. In a waveguide, the TE mode means that the:

a) none of the above

b) magnetic field is perpendicular to the direction of wave propagation

c) magnetic and electric field are perpendicular to each other

d) electric field is perpendicular to the direction of wave propagation

4. Determine the dB gain of a receiving antenna which delivers a microvolt signal to a transmission line over that of an antenna that delivers a 2 microvolt signal under identical circumstances.

a) 3 dB

b) 10 dB

c) 8 dB

d) 6 dB

5. How many cycles of a 1MHz wave can a 6-mile transmission line accommodate?

a) 16.67 cycles

b) 32.26 cycles

c) 6 cycles

d) 60 cycles

6.Power loss due to increased effective resistance of a conductor at microwave frequencies due to skin effect.

a) Conduction Loss

b) Dielectric Loss

d) Corona

7. What is the cut-off wavelength of a 6-cm x 3-cm waveguide? Assume the dominant mode of operation.

a) 20 cm

b) 18 cm

c) 15 cm

d) 12 cm

8. The ratio of incident and reflected voltage waves representing transmission and reflection coefficients used to characterize a linear microwave device.

a) Z Parameter

b) Y Parameter

c) S Parameter

d) H Parameter

9. What is the longest wavelength that a 2.5-cm wide waveguide will support in the dominant mode (m = 1)?

a) 3 cm

b) 5 cm

c) 6 cm

d) 1 cm

10. Who developed the Smith Chart?

a) James N. Smith b) Philip S. Chart

c) Philip H. Smith

d) Gunn Chart

11. What is the effect of standing waves on a transmission line?

a) increase in the power fed to antenna

b) a cooler operating line

c) prevention of arcing

d) decrease in the power fed to antenna

12. The _____ is a measure of the mismatch between a load and the transmission line.

a) Return Loss

b) SWR

c) Phase-shift constant

d) reflection coefficient

13. A very low-loss coaxial transmission line has 30 pF / ft. of distributed capacitance and 75 nH / ft. of inductance. What is its characteristic impedance?

a) 75 Ω

b) 100 Ω

c) 72.5 Ω

d) 50 Ω

14. What is meant by SWR of a transmission line?

b) Slope Waveguide Relation

c) Sitting Wave Ratio

d) Standing Wave Ratio

15. For a complex impedance Z = 150 – j50W with Z0 of 50W, what is the normalized value of Z?

a) 15 – j5 Ohms

b) 3 – j1 Ohms

c) 3 – j1

d) 15 – j5 Ohms

16. What is the impedance of most waveguide?

a) 300 ohms

b) 75 ohms

c) 600 ohms

d) 50 ohms

17. The outer conductor of a coaxial transmission line is always grounded at the

a) output only

b) input only

c) point of high SWR

d) input and output

18. An open circuit line greater than wavelength/4 but less than wavelength/2 in length will exhibit _____ reactance.

a) capacitive

b) minimum

c) inductive

d) maximum

19. An electronic equipment used to measure standing wave ratio.

a) Altimeter

c) Reflectometer

d) Wavemeter

20. What is a short (< l/4) length of transmission line, shorted at one end and attached at the appropriate distance from the load for the purpose of matching a complex load to the transmission line?

a) quarter-wave transformer

b) stub

c) balun

d) network

21. To couple a coaxial line to parallel line, it is better to use a _____.

a) directional coupler

b) balun

c) slotted line

d) quarter-wave transformer

22. If a transmission line is terminated with a resistance equal to its characteristic impedance

a) the standing wave ratio will be minimum

b) the input impedance will be twice the terminating resistance

c) the reflection coefficient will be unity

d) the line loss will be maximum

23. In a waveguide, the TM mode means that the:

a) electric field is perpendicular to the direction of wave propagation

b) magnetic and electric fields are perpendicular to each other

c) none of the above

d) magnetic field is perpendicular to the direction of wave propagation

24. How can SWR be minimized?

a) using filters

b) using limiter

c) using Smith Chart

d) using stubs

25. In a transmission line, the characteristic impedance equals _____.

a) Zoc/Zsc

b) √ZocZsc

c) Zsc/Zoc

d) √Zsc/Zoc

26. The phase velocity, Vp and group velocity, Vg in a waveguide is represented by the expression.

a) Vp = C/Vg

b) C = (Vp)(Vg)

c) C = (VpVg)1/2

d) Vg = C2Vp

27. When does a transmission line terminated in a short look like a short to the source?

a) at less than l / 2

b) at quarter-wavelength

c) at less than l / 4

d) at half-wavelength

28. When a transmission line uses ground return, it is called a (n) _____ line.

a) ungrouped

b) unbalanced

c) balanced

d) grounded

29. Termination means

a) load connected to the output end of the transmission line

b) looking back impedance of a line with no load

c) result of cutting both ends of a conductor

d) result of disconnecting a line from a transmitter

30. A transmission line consisting of two conductors that have equal resistance per unit length.

a) Open-wire line

b) Balanced line

c) Coaxial line

d) Unbalanced line

31. Coaxial lines are used on those systems operating _____.

a) at 300 MHz

b) above 10 kHz

c) below 2 GHz

d) above 10 GHz

32. Which of the following determines the characteristics of a transmission line?

a) Physical dimensions

b) Length

c) Inductance

d) Capacitance

33. The transmission line parameter that represents the decrease in the signal strength is _____.

a) reflection coefficient

b) propagation constant

c) attenuation constant

d) phase-shift constant

34. What is the voltage reflection coefficient for a 75- Ω line with a terminating impedance of 50 Ω?

a) -0.5

b) 0.5

c) -0.2

d) 0.2

35. What is the meaning of the term velocity factor of a transmission line?

a) The velocity of the wave on the transmission line multiplied by the velocity of the wave of light in vacuum

b) The ratio of the characteristic impedance of the line to the terminating impedance

c) The index of shielding for coaxial cable

d) The velocity of the waves on the transmission line divided by the velocity of light in a vacuum

36. A waveguide can be considered as a _____.

a) LPF

b) BPF

c) HPF

d) BRF

37. A 5-GHz signal is to be propagated along a waveguide with a width of 3 cm. What is the largest value of m that can be accommodated by the waveguide? (0 correct answers)

a) m = 2

b) m = 0

c) m = 1

d) m = 3

38. Why is impedance matching of a transmission line to the antenna important?

a) for maximum power transfer

b) for minimum time delay

c) for maximum efficiency

d) for greater energy transformation

39. Would it be possible to produce a 70-W twin lead?

c) yes

d) no

40. A type of transmission line consisting of an inner conductor surrounded by, but insulated from an outer conductor.

a) strip line

b) Micro strip line

c) Coaxial cable

d) balanced line

41. A type of semiconductor bolometer is called _____.

a) Optocoupler

b) Thermistor

c) Galvanometer

d) Thyristor

42. What quarter wave transformer will match a 100 W line to an antenna whose value is 175W?

a) 150 Ohms

b) 132.29 Ohms

c) 137.5 Ohms

d) 16.58 Ohms

43. What is the distance between a voltage maximum and adjacent current maximum on a transmission line with standing waves?

a) wavelength/4

b) wavelength/2

c) wavelength/8

d) wavelength

44. Which tester is used to measure SWR?

a) Spectrum analyzer

b) Reflectometer

d) Multimeter

45. How wide must a waveguide be?

a) over wavelength/2

b) over wavelength/4

c) less than wavelength/4

d) less than wavelength/2

46. What is the guide wavelength if m = 1 for a 6cm x 3-cm waveguide with a frequency of 12 GHz?

a) 4.5 cm

b) 5 cm

c) 2.55 cm

d) 2 cm

47. Characteristic impedance of a transmission line is the impedance measured at the _____ when its length is infinite.

a) midsection

b) output

c) shorted end of the line

d) input

48. What is the dominant mode in a rectangular waveguide?

a) TE02

b) TM11

c) TM01

d) TE10

49. For an ideal transmission line, the best possible conductor to use is _____.

a) Iron

b) Silver

c) Gold

d) Copper

50. Referred to as a ferrite device that can be used in lieu of a duplexer to isolate a microwave transmitter and receiver when both are connected to the same antenna.

a) Isolator

b) Coupler

c) Circulator

d) Diode

51. What is the input impedance of a shorted lossless line of length wavelength/4?

a) Z0

b) infinity

c) 0

d) complex

52. Does minimum or maximum VSWR indicate best matching of antenna to transmission line?

a) either a or b

b) minimum

c) either a nor b

d) maximum

53. What is the main frequency determining element of a klystron?

a) resonant cavity

b) accelerating voltage

c) repeller voltage

d) mode of operation

54. The mode at which a waveguide operates is determined by the:

a) shape of the waveguide

b) method used to couple the signal into the waveguide

c) length of the waveguide

d) impedance of the waveguide

55. When does a transmission line have an SWR equal to 1?

a) ZL = a

b) ZL = Z0

c) ZL = 0

d) G = 1

56. For a parallel-resonant circuit, a l / 4 stub must be _____ at the ends.

a) shorted

b) open

c) complex

57. In a transmission line, if the maximum current to minimum current ratio is 2:1, what is the ratio of the maximum voltage to minimum voltage?

a) 1:2

b) 1:4

c) 2:1

d) 4:1

58. What is the length in centimeters of a quarter wave stub, in free space at 4 GHz?

a) 19 m

b) 18.75 m

c) 19 cm

d) 1.875 cm

59. Best choice of transmission line component to couple a coaxial line to a parallel wire line.

a) Balun

b) Directional coupler

c) Shorting

d) Slotted line

60. A matching stub should be placed _____.

a) midway between load and transmitter

c) nearest to transmitter

d) anywhere

61. What would be the SWR of a transmission line if power is being delivered to a 100-Ω load by a line with a characteristic impedance of 50 W?

a) 4

b) 2

c) 5.5

d) 3

62. A quarter-wave stub shorted at the end has high impedance:

a) at the shorted end

b) wavelength/4 back from the short

c) wavelength/2 back from the short

d) at the center

63. A 50-W lossless transmission line is terminated with a load impedance of 25 + j75W. What is the input impedance at a distance of 0.5l from the load?

a) 15.5 + j31.6W Ohms

b) 30 +j15W Ohms

c) 50 Ohms

d) 25 + j75W Ohms

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

a) length

b) conductor diameter

c) conductor spacing

65. A 300-W line is terminated is a load impedance of 100 + j200W. What is the reflection coefficient for this line?

a) 0.85<212.1°

b) 0.632<108°

c) 0.35<61.5°

d) 0.75<120°

66. A flat transmission line delivers 5 kW at 10 A. What is its impedance?

a) 50 Ohms

b) 20 Ohms

c) 200 Ohms

d) 500 Ohms

67. What must be the ratio of outer conductor diameter to center conductor diameter, for a 75- Ω Teflon coaxial transmission line?

a) 4.8

b) 6.12

c) 4

d) 3.2

68. A type of transmission line where the two conductors carry equal current.

a) unbalanced

b) balanced

c) strip line

d) waveguide

69. A waveguide acts as a _____.

a) LPF

b) Resonator

c) HPF

d) BRF

70. To connect coaxial line to a parallel-wire, _____ is the best to use.

a) balun

b) directional coupler

c) slotted line

d) quarter-wave transformer

71. One of the following microwave diodes is suitable for very low-power oscillators only.

a) IMPATT

b) Tunnel

c) TWT

d) LSA

72. Which of the following is not a microwave vacuum tube?

a) BWO

b) Gunn

c) Klystron

d) Magnetron

73. What is meant by a voltage node?

a) high impedance

b) voltage minima

c) current minima

d) voltage maxima

74. What is the name of the microwave transmission line that is used with printed circuits?

a) coax

b) microstrip

c) ferrite loop

d) waveguide

75. The use of stub-matching network eliminates standing waves on _____.

a) transmitter side of stub

b) both sides of stubs

c) all of the above

76. Two 2-mm-diameter wires held 6 cm apart center-to-center has a characteristic impedance of _____. (0 correct answers)

a) 75 Ohms

b) 250 Ohms

c) 491 Ohms

d) 500 Ohms

77. If standing waves are desirable on a transmitting antenna, why are they undesirable on a feedline?

a) it decreases the length

b) it limits the life of the antenna

c) it increases power loss

d) it shortens the feeding life

78. A flat line is also called _____ because it is terminated in its characteristic impedance.

a) Capacitive

b) Non-resonant

c) Resonant

d) Inductive

79. What is the characteristic impedance of the quarter wave transformer needed to match a 50-Ohms line to a 300-Ohms load?

a) 122 200 Ohms

b) Ohms

c) 312Ohms

d) Ohms

80. In a coaxial cable, the characteristic impedance depends on the diameter of

a) inner conductor

b) both a and d

c) none of the above

d) outer conductor

81. Distance travelled by a wave in the time of one cycle.

a) Crest

b) Wavelength

c) Frequency

d) Hop

82. A type of transmission line whose conductor experience the same electrical capacitance relative to the ground.

a) Strip Line

b) Waveguide

c) Balanced Line

d) Coax

83. The characteristic impedance will _____, if the spacing between the wires of a balanced transmission line is increased.

a) none of the above

b) increase

c) decrease

d) remain the same

84. Find the input impedance, in ohms, for a 50- Ω lossless transmission line, 3.5l long, if the load is 20 + j75 Ω.

a) 7 + j8 Ω

b) 20 + j75 Ω

c) 6.25 – j12.5 Ω

d) 12.5 – j6.25 Ω

85. A single conductor running from the transmitter to the antenna.

a) RG-8 / U

b) Single line wire

c) Microstrip

86. Transmission lines are either balanced or unbalanced with respect to _____.

a) ground

b) input

c) positive terminal

d) negative terminal

87. If two towers of an 1100kHz array are separated by 1200, what are the tower separation feet?

a) 412

b) 321

c) 298

d) 48

88. Skin effect describes the tendency of:

a) ac conductors to carry the circuit current on their surface

b) both a nor c

c) dc conductors to carry the circuit current on their surface

d) both a and c

89. A major and basic advantage for the used of a klystron.

a) High power

b) Lesser noise

c) Efficiency

d) Cheaper

90. A transmission line capable of handling high-powered signal is _____.

a) coax

b) waveguide

c) micro strip line

d) stripline

91. What physical length corresponds to 0.25wavekerh at 500 MHz for cable with a propagation velocity of 0.68C?

a) 0.102 m

b) 0.102 m

c) 1.02 m

d) 2.01 m

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

a) 120 ohms

b) 50 ohms

c) 650 ohms

d) 75 ohms

93. When does an open transmission line look a short to the source?

a) at half-wavelength

b) at less than l / 4

c) at quarter-wavelength

d) at less then l / 5

94. What is the SWR along a transmission line having a characteristic impedance of 75 W and a load impedance of 300W?

a) 4

b) 0.5

c) 2

d) 0.25

95. What is the SWR for a 100-Ohms characteristic line and a 300-Ohms load?

a) 0.33

b) 3

c) 2

d) 4

96. What is the velocity factor of non-foam dielectric 50 or 75 ohm flexible coaxial cable such as RG 8, 11, 58, and 59?

a) 0.10

b) 0.66

c) 2.70

d) 0.30

97. Referred to the dielectric constant of a transmission line material.

b) Velocity factor

c) Characteristic impedance

d) Propagation velocity

98. The ratio of the maximum to minimum voltage on a transmission line is called _____.

a) Smax

b) Reflection Coefficient

c) SWR

d) Propagation Constant

99. The aspect ratio of a standard rectangular waveguide is _____.

a) 1:2

b) 4:3

c) 3:4

d) 2:1

100. A type of transmission line used in gamma match.

a) strip line

c) micro strip line

d) coaxial

101. A shorted transmission line less than l / 4 in length will exhibit _____ reactance.

a) capacitive

b) inductive

c) minimum

d) maximum

102. The cut-off frequency in a waveguide signifies

a) longer wave will not propagate significantly

b) the frequency at which no transmission takes place

c) the dimension of the waveguide

d) all of the above

103. Which of the following is not a method of coupling into or out of a waveguide?

a) Probe

b) Loop

c) Holes

d) Slot

104. Name a use for a circular waveguide.

b) telephony

c) TV transmitter

105. A convenient method of determining antenna impedance.

a) Smith Chart

b) Reactance circle

c) Trial and error

d) Stub matching

106. What type of coupling is used between helical resonators?

a) loop

b) probe

c) mechanical

d) slot

107. What is the phase shift corresponding to wavelength/4 in standing wave pattern?

a) 180°

b) 40°

c) 0°

d) 90°

108. For a transmission line giving a maximum rms voltage reading of 50 V at one point and a minimum rms voltage reading 25 V at another point. What is the VSWR of the line?

a) 2

b) 4

c) 5

d) 1

109. What should be the SWR into a dummy antenna?

a) a

b) 1:2

c) 0

d) 1:1

110. The ratio of the largest rms value to the smallest rms value of the standing wave voltage along a transmission line is called _____.

a) attenuation constant

b) propagation constant

c) SWR

d) reflection coefficient

111. Indicate the false statement. The SWR on a transmission line is infinity: the line is terminated in a (n)

a) pure reactance

b) open circuit

c) complex impedance

112. Transmission line must be matched to the load to

b) transfer maximum current to the load

c) transfer maximum power to the load

d) transfer maximum voltage to the load

113. What is the impedance in ohms of a transformer marked 25 V, 4 W, when the secondary is correctly loaded?

a) 165 Ohms

b) 150 Ohms

c) 156 Ohms

d) 160 Ohms

114. What is the attenuation in nepers for a 1-km length of RG58 A / U coax with a loss of 5dB / 100 ft.?

a) 86.86 Np

b) 68.68 Np

c) 18.88 Np

d) 8 Np

115. A wire conductor experiences the following characteristics:

a) b and

b) Resistance increases with wire length

c) Resistance increases with a decrease in wire diameter

d) none of these

116. What is the function of a resistive pyramid or vane at the end of a waveguide section?

a) reflector

c) termination

d) absorber

117. Energy that has neither been radiated into space nor completely transmitted.

a) Standing waves

b) Captured waves

c) Incident waves

d) Modulated waves

118. Transmission lines when connected to antenna have

a) resistive load whose resistance is less than characteristic impedance

c) resistive load at the resonant frequency

d) resistive load whose resistance is greater than the characteristic impedance of the line

119. What is the characteristic impedance of twin lead?

a) 600 W

b) 50 W

c) 300 W

d) 70 W

120. The standing wave ratio is equal to _____ if the load is properly matched with the transmission line.

a) 10

b) 50

c) 1

d) 2

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