The answer to practice questions in Genki I and II
wirting
anatomy review
MITRC REFRESHER COURSE ANSWER KEY
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Transmission Lines
A system of conductors used to convey electric power or signal between two or more points a. Channels b. Optical cables c. Transmission lines d. Waveguides
11. The characteristic impedance of an open-wire balance line is determined from its physical structure. [ Zo = 276 log (2S/d) where S is the center-to-center distance of the conductors and d is the diameter of the conductor ]. At what condition is the characteristic impedance minimum? a. S = d b. S = 2d c. d = 2S d. S >> d
These conductors are uniformly spaced by insulators. They have low losses at low and medium frequencies and are economical to construct and maintained a. Coaxial cables b. Open-wire transmission lines c. Optical cables d. Waveguides
12. If a change in the dielectric material decreases the capacitance, the characteristic impedance is: a. Kept constant b. Decreased c. Increased d. Halved
To prevent radiation losses and interference from external sources, the inner conductor of this transmission line is completely enclosed with a metal sheath or braid a. Coaxial cables b. Open-wire transmission line c. Optical cables d. Waveguides
13. All power applied at the input of the line will be absorbed by the load if: a. ZO > ZL b. ZO < ZL c. ZL = ZO d. ZO = ZL
The term “balance line” means that a. Both conductors carry currents that flow in opposite directors b. Conductors present equal capacitance to ground c. One conductor is connected to ground d. A and B above
14. When ZL ≠ ZO, the power sent down the line toward the load is called the a. The incident power b. The reflected power c. The power dissipation d. The carrier power
The characteristic impedance of a transmission line is determined by: a. Its operating frequency b. Its length c. Its physical size and arrangement d. The signal applied at the input terminal
15. When mismatch is great, this power actually cause damage to the transmitter or the line itself. a. The incident power b. The reflected power c. The power dissipation d. The carrier power
The distributed parameters of the transmission line are: the series resistance; the series inductance; the shunt capacitance and the shunt conductance. What parameter was determined due to dielectric losses? a. Series resistance b. Series inductance c. Shunt capacitance d. Shunt conductance
16. A resultant wave due to the combination of incident and reflected wave a. Electromagnetic wave b. Sine wave c. Standing wave d. Current
Shunt capacitance was determined due to: a. Conductors were closed to each other b. The length and diameter of the conductors c. Dielectric losses d. Flux linkage
17. If the load impedance matches the characteristic impedance of the line, there are _____ standing waves a. More b. Less c. No d. Ten (10)
Series resistance was determined due to: a. Conductors were closed to each other b. The length and diameter of the conductors c. Dielectric losses d. Flux linkages
18. A measure of the mismatch between line and load impedance is called as a. Reflection coefficient b. Standing wave ratio c. Loss d. Standing waves
At radio frequencies, a line is considered lossless because: a. Characteristic impedance is determined by its physical structure b. Inductive reactance is much more than the resistance c. Capacitive reactance is much larger then the shunt conductance d. B and C above
19. At matched condition, SWR is equal to a. Zero b. One c. 100 d. Infinite
10. Determine the characteristic impedance of a transmission line which has a capacitance of 30pF/m and an inductance of 75nH/m a. 5 Ω b. 50 Ω c. 500 Ω d. 5 KΩ
20. The ratio of the reflected voltage to the incident voltage on the transmission line is termed as a. Reflection coefficient b. Standing wave ratio 1
MITRC REFRESHER COURSE ANSWER KEY
c. d.
Transmission Lines
Loss Standing waves
31. Characteristic impedance and load impedance must be matched in order to transfer a. Maximum power to the load b. Maximum current to the load c. Maximum voltage to the load d. Maximum standing waves
21. A shorted or opened line will have a reflection coefficient of a. Zero b. One c. 100 d. Infinite
32. The ratio of reflected voltage to the forward or incident voltage is termed as a. Reflection coefficient b. SWR c. VSWR d. Propagation constant
22. The minimum voltage along a transmission line is 260V, while the maximum voltage is 390V. The SWR is a. 0.67 b. 1.0 c. 1.2 d. 1.5
33. A more common method of expressing the degree of mismatch between Zo and ZL is return loss. [Return Loss = 20 log (1/ reflection coefficient)]. Echoes may result if return loss is a. Too high b. Too low c. Zero d. Infinite
23. At UHF and microwave frequencies, transmission lines are commonly used as a. Antenna b. Coupler c. Resonant circuit d. Transformer
34. The points along the line where the incident and reflected voltages are in phase are points of a. Maximum voltage and maximum current b. Minimum voltage and minimum current c. Maximum voltage and minimum current d. Minimum voltage and maximum current
24. The time required for a wave to propagate on a transmission line will depend on the value of its a. Series resistance and shunt conductance b. Series inductance and shunt capacitance c. Series resistance and series inductance d. Shunt conductance and shunt capacitance
35. When incident and reflected voltages are out of phase, the voltages are a. Added b. Neutralized c. Multiplied d. Divided
25. The current (and voltage) distribution along a matched line vary _____ with distance a. Linearly b. Inversely c. Exponentially d. Logarithmically
36. If the distance of separation between centers of two parallel wires is increased, the characteristic impedance will a. Increased b. Decreased c. Be the same d. Doubled
26. a measure of how the voltage or current decreases with distance along the line a. Propagation constant b. Attenuation constant c. Phase constant d. SWR 27. The a. b. c. d.
37. Which statement is true? a. Increasing the length of the wire will increase the SWR b. Decreasing the length of the wire will increase the SWR c. Increasing the length of the wire will decrease the SWR d. Changing the length of the wire will have no effect on the SWR
value remains constant for any length of wire Characteristic impedance Inductance Capacitance Propagation constant
28. A measure of the difference in phase between the input and output current or voltage a. Attenuation constant b. Reflection constant c. Phase constant d. Characteristic impedance
38. The characteristic impedance of balance wire varies from a. 150 to 600 Ω b. 40 to 150 Ω c. 75 to 400 Ω d. 75 to 600 Ω 39. The characteristic impedance of coaxial cable varies from a. 150 to 600 Ω b. 40 to 150 Ω c. 75 to 400 Ω d. 75 to 600 Ω
29. To match a 300Ω transmission line to a 100Ω load, the impedance of the quarter-wave transformer is a. 1.732 KΩ b. 20 Ω c. 200 Ω d. 173.21 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 line impedance more closely equivalent to a pure resistance a. Amplifiers b. Transformer c. Equalizer d. Loading coils
30. An attenuation of 1 Neper is equal to _____ dB a. 8.686 x 10-3 b. 8.686 c. 4.343 d. 0.115
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MITRC REFRESHER COURSE ANSWER KEY
Transmission Lines
41. When the receiving end of the wire is an open circuit, it is a point of a. Maximum current and zero voltage b. Maximum voltage and zero current c. Zero current and zero voltage d. Maximum voltage and maximum current
c. d.
Waveguide Coax
52. Is a narrow, flat conductor on a single dielectric board whose opposite face is metallized, much like an ordinary printed-circuit board. It is also used in microwave circuits a. Stripline b. Microstrip c. Waveguide d. Coax
42. If a wire is terminated on a short circuit, the end of the wire is a point of a. Maximum current and zero voltage b. Maximum voltage and zero current c. Zero current and zero voltage d. Maximum voltage and maximum current
53. Can be placed at either end of a transmission line to convert between 72-Ω unbalanced line to a 300-Ω balance line a. Stub b. Resonant circuit c. Balun d. Coupler
43. The principal method of reducing noise and crosstalk to low value on open-wire lines a. Filter method b. Scrambling c. Feedback d. Transposing
54. Power loss due to increased effective resistance of a conductor at microwave frequencies due to skin effect. a. Conduction loss b. Radiation loss c. Dielectric loss d. Corona
44. Used for VHF antennas a. RG-214/U b. RG-59/U c. RG-11/U d. RG-58/U
55. When does a transmission line terminated in a short look like a short to the source? a. At quarter-wavelength b. At half-wavelength c. At less than λ/5 d. At less than λ/4
45. Which transmission line has the highest attenuation? a. RG-214/U b. RG-59/U c. RG-11/U d. Twin lead 46. Which transmission line has the lowest attenuation? a. RG-214/U b. RG-59/U c. RG-11/U d. Twin lead
56. How many cycles of a 1 MHz wave can a 6=mile transmission line accommodate? a. 60 cycles b. 6 cycles c. 16.67 cycles d. 32.26 cycles
47. A widely used transmission line, in which two stranded wires are separated by a flat continuous plastic insulators a. RG-214/U b. RG-59/U c. RG-11/U d. Twin lead
57. A transmission line has a capacitance of 25 pF / ft. and an inductance of 0.15 µh / ft. Determine the characteristic impedance of the line. a. 77.5 Ω b. 50 Ω c. 75 Ω d. 100 Ω
48. Used for TV antennas; cable TV; and HF antennas a. RG-214/U b. RG-59/U c. RG-11/U d. RG-58/U
58. 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. 1 d. 5
49. An open-wire line has an attenuation of 2.4 dB per 100 ft. The attenuation for 275 ft is a. 2.4 dB b. 3.3 dB c. 4.8 dB d. 6.6 dB
59. Two 2-mm-diameter wires held 6cm apart center-to-center has a characteristic impedance of______. a. 500 Ω b. 250 Ω c. 491 Ω d. 75 Ω
50. The ratio of velocity of propagation in the transmission line and the velocity of propagation in free space a. Wavelength constant b. Propagation constant c. Velocity factor d. Velocity of light
60. Does minimum or maximum VSWR indicate best matching of antenna to transmission line? a. Minimum b. Maximum c. Either a or b d. Neither a or b
51. This transmission line is used in microwave circuit. It consists of a narrow, flat conductor sandwiched between dielectric boards whose outside surfaces are coated with conductor a. Stripline b. Microstrip 3
MITRC REFRESHER COURSE ANSWER KEY
Transmission Lines
61. If two towers of a 1100-kHz array are separated by 120°, What is the tower separation in feet? a. 321 b. 48 c. 298 d. 412 62. What is the reflection coefficient of an open-circuited transmission line? a. 1 b. -1 c. 0 d. Infinity 63. The reflection coefficient on a transmission line is 1/3, what is the SWR? a. 0 b. 3 c. 2 d. 4 64. Indicate the false statement. The SWR on a transmission line is infinity: the line is terminated in a/an a. Short circuit b. Open circuit c. Pure reactance d. Complex impedance 65. Coaxial lines are used on those systems operating_______. a. Below 2 GHz b. At 300 MHz c. Above 10 kHz d. Above 10 Ghz 66. What is the SWR along a transmission line having a characteristic impedance of 75 Ω and a load impedance of 300 Ω? a. 0.25 b. 4 c. 2 d. 0.5 67. Who developed the Smith Chart? a. Philip H. Smith b. James N. Smith c. Philip S. Chart d. Gunn Chart 68. An electronic equipment used to measure standing wave ratio. a. Reflectometer b. Wavemeter c. Altimeter d. Multimeter 69. What is the phase shift corresponding to λ / 4 in standing wave pattern? a. 0° b. 40° c. 90° d. 180° 70. For a parallel resonant circuit, a λ / 4 stub must be_____ at the ends. a. Open b. Shorted c. Loaded d. complex
