COMMS 6 - Trans line answers.doc

7/29/2019 COMMS 6 - Trans line answers.doc

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MITRC REFRESHER COURSE ANSWER KEY Transmission Lines

1. A system of conductors used to convey electric power or signalbetween two or more pointsa. Channelsb. Optical cablesc. Transmission linesd. Waveguides

2. These conductors are uniformly spaced by insulators. They havelow losses at low and medium frequencies and are economical toconstruct and maintaineda. Coaxial cablesb. Open-wire transmission linesc. Optical cablesd. Waveguides

3. To prevent radiation losses and interference from externalsources, the inner conductor of this transmission line is completelyenclosed with a metal sheath or braida. Coaxial cablesb. Open-wire transmission line

c. Optical cablesd. Waveguides

4. The term “balance line” means thata. Both conductors carry currents that flow in opposite directorsb. Conductors present equal capacitance to groundc. One conductor is connected to groundd. A and B above

5. The characteristic impedance of a transmission line is determinedby:a. Its operating frequencyb. Its length

c. Its physical size and arrangementd. The signal applied at the input terminal

6. The distributed parameters of the transmission line are: the seriesresistance; the series inductance; the shunt capacitance and theshunt conductance. What parameter was determined due todielectric losses?a. Series resistanceb. Series inductancec. Shunt capacitanced. Shunt conductance

7. Shunt capacitance was determined due to:

a. Conductors were closed to each otherb. The length and diameter of the conductorsc. Dielectric lossesd. Flux linkage

8. Series resistance was determined due to:a. Conductors were closed to each otherb. The length and diameter of the conductorsc. Dielectric lossesd. Flux linkages

9. At radio frequencies, a line is considered lossless because:a. Characteristic impedance is determined by its physical

structureb. Inductive reactance is much more than the resistancec. Capacitive reactance is much larger then the shunt

conductanced. B and C above

10. Determine the characteristic impedance of a transmission line which has a capacitance of 30pF/m and an inductance of 75nH/ma. 5 Ωb. 50 Ωc. 500 Ωd. 5 KΩ

11. The characteristic impedance of an open-wire balance line isdetermined from its physical structure. [ Zo = 276 log (2S/d) whereS is the center-to-center distance of the conductors and d is thediameter of the conductor ]. At what condition is the characteristicimpedance minimum?

a. S = db. S = 2dc. d = 2Sd. S >> d

12. If a change in the dielectric material decreases the capacitance,the characteristic impedance is:a. Kept constantb. Decreasedc. Increasedd. Halved

13. All power applied at the input of the line will be absorbed by theload if:

a. ZO > ZL

b. ZO < ZL

c. ZL = ZO

d. ZO = ZL

14. When ZL ≠ ZO, the power sent down the line toward the load iscalled thea. The incident powerb. The reflected powerc. The power dissipationd. The carrier power

15. When mismatch is great, this power actually cause damage to the

transmitter or the line itself.a. The incident powerb. The reflected powerc. The power dissipationd. The carrier power

16. A resultant wave due to the combination of incident and reflected wavea. Electromagnetic waveb. Sine wavec. Standing waved. Current

17. If the load impedance matches the characteristic impedance of theline, there are _____ standing wavesa. Moreb. Lessc. Nod. Ten (10)

18. A measure of the mismatch between line and load impedance iscalled asa. Reflection coefficientb. Standing wave ratioc. Lossd. Standing waves

19. At matched condition, SWR is equal toa. Zerob. Onec. 100d. Infinite

20. The ratio of the reflected voltage to the incident voltage on thetransmission line is termed asa. Reflection coefficientb. Standing wave ratio

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c. Lossd. Standing waves

21. A shorted or opened line will have a reflection coefficient ofa. Zerob. One

c. 100d. Infinite

22. The minimum voltage along a transmission line is 260V, while themaximum voltage is 390V. The SWR isa. 0.67b. 1.0c. 1.2d. 1.5

23. At UHF and microwave frequencies, transmission lines arecommonly used asa. Antennab. Coupler

c. Resonant circuitd. Transformer

24. The time required for a wave to propagate on a transmission line will depend on the value of itsa. Series resistance and shunt conductanceb. Series inductance and shunt capacitancec. Series resistance and series inductanced. Shunt conductance and shunt capacitance

25. The current (and voltage) distribution along a matched line vary _____ with distancea. Linearly

b. Inverselyc. Exponentiallyd. Logarithmically

26. a measure of how the voltage or current decreases with distancealong the linea. Propagation constantb. Attenuation constantc. Phase constantd. SWR

27. The value remains constant for any length of wirea. Characteristic impedance

b. Inductancec. Capacitanced. Propagation constant

28. A measure of the difference in phase between the input and outputcurrent or voltagea. Attenuation constantb. Reflection constantc. Phase constantd. Characteristic impedance

29. To match a 300Ω transmission line to a 100Ω load, the impedanceof the quarter-wave transformer isa. 1.732 KΩb. 20 Ωc. 200 Ωd. 173.21 Ω

30. An attenuation of 1 Neper is equal to _____ dBa. 8.686 x 10-3

b. 8.686c. 4.343d. 0.115

31. Characteristic impedance and load impedance must be matched inorder to transfera. Maximum power to the loadb. Maximum current to the loadc. Maximum voltage to the loadd. Maximum standing waves

32. The ratio of reflected voltage to the forward or incident voltage istermed asa. Reflection coefficientb. SWRc. VSWRd. Propagation constant

33. A more common method of expressing the degree of mismatchbetween Zo and ZL is return loss. [Return Loss = 20 log (1/reflection coefficient)]. Echoes may result if return loss isa. Too highb. Too lowc. Zero

d. Infinite

34. The points along the line where the incident and reflected voltagesare in phase are points ofa. Maximum voltage and maximum currentb. Minimum voltage and minimum currentc. Maximum voltage and minimum currentd. Minimum voltage and maximum current

35. When incident and reflected voltages are out of phase, thevoltages area. Addedb. Neutralized

c. Multipliedd. Divided

36. If the distance of separation between centers of two parallel wiresis increased, the characteristic impedance willa. Increasedb. Decreasedc. Be the samed. Doubled

37. Which statement is true?a. Increasing the length of the wire will increase the SWRb. Decreasing the length of the wire will increase the SWR

c. Increasing the length of the wire will decrease the SWRd. Changing the length of the wire will have no effect on theSWR

38. The characteristic impedance of balance wire varies froma. 150 to 600 Ωb. 40 to 150 Ωc. 75 to 400 Ωd. 75 to 600 Ω

39. The characteristic impedance of coaxial cable varies froma. 150 to 600 Ωb. 40 to 150 Ωc. 75 to 400 Ωd. 75 to 600 Ω

40. Often inserted in telephone lines at spacing as close as 1 (1.6km),to counteract the capacitance of the line and thus make the lineimpedance more closely equivalent to a pure resistancea. Amplifiersb. Transformerc. Equalizerd. Loading coils

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41. When the receiving end of the wire is an open circuit, it is a pointofa. Maximum current and zero voltageb. Maximum voltage and zero currentc. Zero current and zero voltaged. Maximum voltage and maximum current

42. If a wire is terminated on a short circuit, the end of the wire is apoint ofa. Maximum current and zero voltageb. Maximum voltage and zero currentc. Zero current and zero voltaged. Maximum voltage and maximum current

43. The principal method of reducing noise and crosstalk to low valueon open-wire linesa. Filter methodb. Scramblingc. Feedbackd. Transposing

44. Used for VHF antennasa. RG-214/Ub. RG-59/Uc. RG-11/Ud. RG-58/U

45. Which transmission line has the highest attenuation?a. RG-214/Ub. RG-59/Uc. RG-11/Ud. Twin lead

46. Which transmission line has the lowest attenuation?a. RG-214/Ub. RG-59/Uc. RG-11/Ud. Twin lead

47. A widely used transmission line, in which two stranded wires areseparated by a flat continuous plastic insulatorsa. RG-214/Ub. RG-59/Uc. RG-11/Ud. Twin lead

48. Used for TV antennas; cable TV; and HF antennasa. RG-214/Ub. RG-59/Uc. RG-11/Ud. RG-58/U

49. An open-wire line has an attenuation of 2.4 dB per 100 ft. Theattenuation for 275 ft isa. 2.4 dBb. 3.3 dBc. 4.8 dBd. 6.6 dB

50. The ratio of velocity of propagation in the transmission line and thevelocity of propagation in free spacea. Wavelength constantb. Propagation constantc. Velocity factord. Velocity of l ight

51. This transmission line is used in microwave circuit. It consists of anarrow, flat conductor sandwiched between dielectric boards

whose outside surfaces are coated with conductora. Stripline

b. Microstripc. Waveguided. Coax

52. Is a narrow, flat conductor on a single dielectric board whoseopposite face is metallized, much like an ordinary printed-circuit

board. It is also used in microwave circuitsa. Striplineb. Microstripc. Waveguided. Coax

53. Can be placed at either end of a transmission line to convertbetween 72-Ω unbalanced line to a 300-Ω balance linea. Stubb. Resonant circuitc. Balund. Coupler

54. Power loss due to increased effective resistance of a conductor at

microwave frequencies due to skin effect.a. Conduction lossb. Radiation lossc. Dielectric lossd. Corona

55. When does a transmission line terminated in a short look like ashort to the source?a. At quarter-wavelengthb. At half-wavelengthc. At less than λ/5d. At less than λ/4

56. How many cycles of a 1 MHz wave can a 6=mile transmission lineaccommodate?a. 60 cyclesb. 6 cyclesc. 16.67 cyclesd. 32.26 cycles

57. A transmission line has a capacitance of 25 pF / ft. and aninductance of 0.15 µh / ft. Determine the characteristic impedanceof the line.a. 77.5 Ωb. 50 Ωc. 75 Ω

d. 100 Ω

58. For a transmission line giving a maximum rms voltage reading of50 V at one point and a minimum rms voltage reading 25 V atanother point. What is the VSWR of the line?a. 2b. 4c. 1d. 5

59. Two 2-mm-diameter wires held 6cm apart center-to-center has acharacteristic impedance of______.a. 500 Ωb. 250 Ωc. 491 Ωd. 75 Ω

60. Does minimum or maximum VSWR indicate best matching ofantenna to transmission line?a. Minimumb. Maximumc. Either a or bd. Neither a or b

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61. If two towers of a 1100-kHz array are separated by 120°, What isthe tower separation in feet?a. 321b. 48c. 298d. 412

62. What is the reflection coefficient of an open-circuited transmissionline?a. 1b. -1c. 0d. Infinity

63. The reflection coefficient on a transmission line is 1/3, what is theSWR?a. 0b. 3c. 2d. 4

64. Indicate the false statement. The SWR on a transmission line isinfinity: the line is terminated in a/ana. Short circuitb. Open circuitc. Pure reactanced. Complex impedance

65. Coaxial lines are used on those systems operating_______.a. Below 2 GHzb. At 300 MHzc. Above 10 kHzd. Above 10 Ghz

66. What is the SWR along a transmission line having a characteristicimpedance of 75 Ω and a load impedance of 300 Ω?a. 0.25b. 4c. 2d. 0.5

67. Who developed the Smith Chart?a. Philip H. Smithb. James N. Smithc. Phil ip S. Chartd. Gunn Chart

68. An electronic equipment used to measure standing wave ratio.a. Reflectometerb. Wavemeterc. Altimeterd. Multimeter

69. What is the phase shift corresponding to λ / 4 in standing wavepattern?a. 0°b. 40°c. 90°d. 180°

70. For a parallel resonant circuit, a λ / 4 stub must be_____ at theends.a. Openb. Shortedc. Loadedd. complex

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COMMS 6 - Trans line answers.doc