TRANSMEDIA Prelims Answers PDF

1. Determine the velocity of propagation for a given length of coaxial 16. A quarter-wave line is connected to an RF generator and is shorted out cable with distributed capacitance of 24 pF/m and distributed at the far end. What is the input impedance to the line at th...

1. Determine the velocity of propagation for a given length of coaxial 16. A quarter-wave line is connected to an RF generator and is shorted out cable with distributed capacitance of 24 pF/m and distributed at the far end. What is the input impedance to the line at the inductance of 484 nH/m. generator? A. 285.72 m/s A. A low value of resistance B. 276.15 m/s C. 293.41 m/s B. A high value of resistance D. 265.54 m/s C. A capacitive reactance which is equal in value to the line’s surge 2. An example of an unbalanced line is: impedance A. a coaxial cable D. A value of resistance equal to the characteristic impedance of the B. 300-ohm twin-lead TV cable line C. an open-wire-line cable 17. If the SWR on a transmission line has high value, the reason could be D. all of the above A. An impedance mismatch between the line and the load 3. When analyzing a transmission line, its inductance and capacitance are considered to be: B. That the line is nonresonant A. lumped C. A reflection coefficient of zero at the load B. equal reactances D. A high degree of attenuation between the load and the position C. distributed where the SWR is measured D. ideal elements 18. Calculate the velocity factor of a coaxial cable used as a transmission 4. As frequency increases, the resistance of a wire: line with the characteristic impedance of 50 ohms; capacitance is 40 A. increases pF/m and an inductance equal to 50 microH/m. B. stays the same C. decreases A. 0.7450 D. changes periodically B. 0.7504 5. The characteristic impedance of a cable depends on: C. 0.0745 A. the resistance per foot of the wire used D. 0.0475 B. the resistance per foot and the inductance per foot 19. If a quarter-wave transmission line is shorted at one end C. the resistance per foot and the capacitance per foot A. There is minimum current at the shorted end D. the inductance per foot and the capacitance per foot 6. For best matching, the load on a cable should be: B. The line behaves as a parallel-tuned circuit in relation to the A. lower than Z0 generator B. equal to Z0 C. The line behaves as a series tuned circuit in relation to the C. higher than Z0 generator D. 50 ohms D. There is a maximum voltage at the shorted end 7. The characteristic impedance of a cable: 20. What is the velocity factor for a cable with a Teflon dielectric (relative A. increases with length permittivity = 2.1)? B. increases with voltage C. increases with frequency A. 0.69 D. none of the above B. 0.476 8. The velocity factor of a cable depends mostly on: C. 2.1 A. the wire resistance D. 1.449 B. the inductance per foot 21. A feature of an infinite transmission line is that C. the dielectric constant A. Its input impedance at the generator is equal to the line’s surge D. all of the above impedance 9. The optimum value for SWR is: A. zero B. Its phase velocity is greater than the velocity of light B. as large as possible C. The impedance varies at different positions on the line C. one D. The input impedance is equivalent to a short circuit D. there is no optimum value 22. When surge impedance of a line is matched to a load, the line will 10. A non-optimum value for SWR will cause: A. Transfer maximum current to the load A. standing waves B. Transfer maximum voltage to the load B. higher voltage peaks on cable C. loss of power to load C. Transfer maximum power to the load D. all of the above D. Have a VSWR equal to zero 11. The impedance "looking into" a matched line: 23. A lossless line is terminated by a resistive load which is not equal to the A. is infinite surge impedance. If the value of the reflection coefficient is 0.5, the B. is the characteristic impedance VSWR is C. is zero A. 2 D. 50 ohms B. 3 12. Compared to a 300-ohm line, the loss of a 50-ohm cable carrying the same power: C. 1.5 A. would be less D. 5 B. would be the same 24. Neglecting line losses, the RMS voltage along an RF transmission line C. would be more having no standing waves D. cannot be compared A. Is equal to the impedance 13. A balanced load can be connected to an unbalanced cable: B. Is one-half of the surge impedance A. directly C. Is the product of the surge impedance and the line current B. by using a "balun" C. by using a filter D. Varies sinusoidally along the line D. cannot be connected 25. Nitrogen is placed in transmission lines to 14. There is an improper impedance match between a 30 W transmitter A. Improve the skin-effect of microwaves and the antenna and 5 W is reflected. How much power is actually B. Reduce arcing in the line transmitted? C. Reduce the standing wave ratio of the line A. 35 W D. Prevent moisture from entering the line B. 25 W 26. If a transmission line has a power loss of 6 dB per 100 feet, what is the C. 30 W power at the feed point to the antenna at the end of a 200 foot- D. 20 W transmission line fed by a 100 watt transmitter? 15. What is the actual length in feet of a one quarter-wavelength of a coax A. 70.31 watts with a velocity factor of 0.69 at 40 MHz? B. 50.31 watts A. 6.15 C. 25.31 watts B. 4.244 D. 6.31 watts C. 5.904 D. 16.974 27. What would be the approximate series impedance of a quarter-wave 39. A shorted half-wave line at the operating frequency acts like a(an) matching line used to match a 600 ohm-feed to 70 ohm-antenna? A. Capacitor A. 205 ohms B. Inductor B. 210 ohms C. Series resonant circuit C. 25.88 ohms D. Parallel resonant circuit D. 102.5 ohms 40. A load impedance of 100+j25 ohms is normalized on a 100 ohm-line. 28. Which of the following represents the best SWR? The normalized value is A. 1:1 A. 2+j0.5 ohms B. 1:2 B. 0.25-j1 ohms C. 1:15 C. 0.94-j24 ohms D. 2:1 D. 1+j0.25 ohms 29. A high SWR creates losses in a transmission line. A high standing wave 41. A pattern of voltage and current variations along a transmission line not ratio might be caused by terminated in its characteristic impedance is called A. Improper turns ratio between primary and secondary in the plate A. Electric field tank transformer B. Radio waves B. Screen grid current flow C. Standing waves C. An antenna electrically too long for its frequency D. Magnetic field D. An impedance mismatch 42. A transmitter supplies 50 W to a load through a line with an SWR of 4:1. 30. A properly connected transmission line Find the power absorbed by the load. A. Is grounded at the transmitter end A. 32 W B. Is cut to a harmonic of the carrier frequency B. 5.6 W C. Is cut to an even harmonic of the carrier frequency C. 44.4 W D. Has a standing wave ratio as near as 1:1 as possible D. 18 W 31. The characteristic impedance of a transmission line does not depend upon its 43. Category of media with some form of conductor that provides a A. Length conduit in which electromagnetic signals are contained. A. Guided B. Conductor diameter B. Balanced C. Conductor spacing C. Unguided D. None of the above D. Unbalanced 32. Which of the following is not a common transmission line impedance? 44. A kind of wave where the displacement is in the direction of the A. 50 ohms propagation. B. 75 ohms A. Transverse C. 120 ohms B. Longitudinal C. Reverse D. 300 ohms D. Perpendicular 33. A ratio expressing the percentage of incident voltage reflected on a 45. The desirable SWR on a transmission line is transmission line is known as the A. 0 A. Velocity factor B. 1 B. Standing wave ratio C. 2 C. Reflection coefficient D. Infinity D. Line efficiency 46. A kind of wave where the direction of displacement is perpendicular to the direction of propagation. 34. A 75 ohm line is terminated in a 30 ohm resistance. Find the SWR. A. Transverse A. 0.6 B. Longitudinal B. 0.429 C. Reverse C. 2.5 D. Perpendicular D. 0.4 47. A short circuited half-wavelength line acts like a 35. A generator sends 50 mW down a 50 ohm line. The generator is A. Parallel resonant circuit B. Series resonant circuit matched to the line but the load is not. If the coefficient of reflection is C. Inductor 0.6, how much power is reflected? D. Capacitor A. 18 mW 48. Determine the characteristic impedance for a parallel wire, air B. 20 mW dielectric with ratio of the spacing between conductors and the C. 30 mW diameter of 3. D. 32 mW A. 250 ohms 36. At very high frequencies, transmission lines are used as B. 210 ohms C. 180 ohms A. Tuned circuits D. 215 ohms B. Antennas 49. Currents that flow in opposite direction in a balanced wire pair is C. Insulators called D. Resistors A. Longitudinal circuit currents 37. A shorted quarter-wave line at the operating frequency acts like a(an) B. Reverse circuit currents A. Series resonant circuit C. Transverse circuit currents B. Parallel resonant circuit D. Metallic circuit currents 50. In transmission lines, it refers to the woven stranded mesh or C. Capacitor braid that surround some types of coaxial cables. D. Inductor A. Grounding 38. A generator sends 50 mW down a 50 ohm line. The generator is B. Shielding matched to the line but the load is not. If the coefficient of reflection is C. Degaussing 0.25, how much power is dissipated in the load? D. Protecting A. 46.9 mW 51. Type of twisted pair wire cable that consists of two copper wires where each wire is separately encapsulated in PVC insulation. B. 37.5 mW A. Shielded twisted pair C. 3.125 mW B. Twin lead D. 12.5 mW C. Unshielded twisted pair D. Open wire line 52. A circuit device used to connect a balanced transmission line to an 65. If the length of short-circuited stub is greater than quarter unbalanced load wavelength but less than half-wavelength, the stub behaves as A. Slotted lines A. Parallel resonant circuit B. Stub B. Series resonant circuit C. Balun C. Inductor D. Quarter wave lines D. Capacitor 53. What is the characteristic impedance of a coaxial line, air 66. A pulse is transmitted down a cable that has a velocity of dielectric with a ratio of the diameter and inner conductor equal propagation of 0.8c. The reflected signal is received 1 us later. to 1.5? How far down the cable is the impairment? A. 24.3 ohms A. 240 m B. 25.6 ohms B. 15 m C. 13.2 ohms C. 60 m D. 18.2 ohms D. 120 m 54. A pattern of voltage and current variations along the transmission 67. A flat conductor sandwich between two ground planes. line not terminated in its characteristic impedance is called A. Stripline A. Electric field B. Microstrip B. Radio waves C. Waveguide C. Standing waves D. Coaxial cable D. Magnetic field 68. A flat conductor separated from a ground plane by an insulating 55. A shorted quarter-wave line at the operating frequency acts like dielectric material A. Series resonant circuit A. Stripline B. Parallel resonant circuit B. Microstrip C. Capacitor C. Waveguide D. Inductor D. Coaxial cable 56. An open-circuited quarter-wavelength line acts like 69. Indicate the false statement. The SWR on a transmission line is A. Parallel resonant circuit infinity, the line is terminated in B. Series resonant circuit A. A short circuit C. Capacitor B. A complex impedance D. Inductor C. An open circuit 57. The mismatch between the antenna and transmission line D. A pure reactance impedances cannot be corrected by 70. The velocity factor of a transmission line A. Using an LC matching network A. Depends on the dielectric constant of the transmission line B. Adjusting antenna length B. Increases in velocity along the transmission line C. Using a balun C. Is governed by the skin effect D. Adjusting the length of transmission line D. Is higher for a solid dielectric than for air 58. A type of twisted-pair wherein its wires and dielectric are 71. Impedance inversion may be obtained with enclosed in a conductive metal sleeve called a foil. A. A short-circuited stub A. STP B. An open-circuited stub B. Twin lead C. A quarter-wave line C. UTP D. A half-wave line D. Unshielded twin lead 72. The most desirable reflection coefficient 59. A type of coaxial cable that has a tubular outer conductor A. 0 surrounds the center conductor coaxially and the insulating B. 0.5 material is air. C. 1 A. Rigid air coaxial cable D. Infinity B. Gas-filled coaxial cable 73. Short circuited stubs are preferred to open-circuited stub because C. Solid coaxial cable the latter are D. Flexible coaxial cable A. More difficult to make and connect 60. If the length of an open circuited stub is less than quarter B. Made of transmission line with different characteristic wavelength but greater than zero, the stub behaves as impedance A. Parallel resonant circuit C. Liable to radiate B. Series resonant circuit D. Incapable of giving a full range of reactance C. Inductor 74. Transmission line must be matched to the load to D. Capacitor A. Transfer maximum voltage to the load 61. For matched condition, what is the relationship of load and B. Transfer maximum current to the load characteristic impedance? C. Reduce the load current A. Greater than D. Transfer maximum power to the load B. Less than 75. A transmission line consisting of two conductors that have equal C. Equal resistance per unit length D. Impossible to say A. Unbalanced line 62. Delay line is a function of what two parameters? B. Open-wire line A. Resistance and capacitance C. Balanced line B. Resistance and susceptance D. Coaxial line C. Inductance and resistance 76. What is the capacitance per meter of a 75-ohm cable that has an D. Inductance and capacitance inductance of 60 nH/m? 63. When current flows through a conductor, the loss introduced as a A. 15.65 pF/m function of resistance and current is called B. 12.75 pF/m A. Conductor loss B. Dielectric heating C. 10.67 pF/m C. Radiation loss D. 11.78 pF/m D. Corona 77. Calculate the characteristic impedance of an open-wire 64. The difference in potential between two conductors of a metallic transmission line consisting of two wires with diameter 1 mm and transmission line causes separation 1 cm. A. Conductor loss A. 180 ohms B. Dielectric heating B. 76 ohms C. Radiation loss D. Corona C. 193 ohms D. 359 ohms 78. Calculate the characteristic impedance of a coaxial line with a polyethylene dielectric (k=2.27) if the diameter of the inner conductor is 3 mm and the inside diameter of the outer conductor is 10 mm. A. 72 ohms B. 32 ohms C. 75 ohms D. 48 ohms 79. A forward voltage of 3V propagates from the source to a mismatched load producing a reflecting voltage to the source of 1.2 V. What is the reflection coefficient? A. 0.2 B. 0.3 C. 0.4 D. 0.5 80. What is the transmission line reflection coefficient if the maximum and minimum voltage of the standing wave is 5V and 1.5V respectively? A. 0.67 B. 0.75 C. 0.54 D. 0.13