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MITRC REFRESHER COURSE ANSWER KEY

Microwaves

1. Referred to as a ferrite device that can be used inlieu of a duplexer to isolate a microwavetransmitter and receiver when both are connectedto the same antenna.a. Isolator

b. Circulatorc. Coupler d. Diode

2. What is the principal mode of a rectangularwaveguide?a. TEMb. TE11c. TE10d. TM11

3. What microwave device combines the advantagesof the klystron and the Traveling Wave Tube?

a. Striplineb. Microstripc. Cfad. Twystron

4. A microwave tube that uses a slow-wave structureas an input section that is isolated from anotherslow-wave section at its output.a. Klystronb. Magnetronc. Twystrond. TWT

5. A waveguide acts as a

a. LPFb. HPFc. BPFd. Resonator

6. Which of the following is a microwave frequency?a. 1.7 MHzb. 750 MHzc. 0.98 GHzd. 22 GHz

7. Which of the following permits a microwave signalto travel in one direction with virtually no loss but

severely attenuates any signal attempting to travelin the reverse direction?a. Isolatorb. Wave trapc. Tunnel dioded. Circulator

8. A waveguide has a cut-off frequency of 17 GHz.Which of the following signals will not pass thruthe waveguide?a. 15 GHzb. 18 Ghzc. 22 GHz

d. 255 GHz

9. When the electric field is perpendicular to thedirection of propagation, the mode is said to bea. Vertically polarizedb. Horizontally polarizedc. Transverse electricd. Transverse magnetic

10. Which of the following is not a microwave tube?a. TWT

b. CRTc. Klystrond. Magnetron

11. A measure of the reliability expressed as the

average number of hours between successivefailures.a. MTBFb. MTTRc. Downtimed. Outage time

12. A microwave band of 18 to 27 GHz is consideredas the ______ band.a. Cb. Xc. Qd. K

13. The radius in the circular zone is in the first fresnelzone when the reflected path is ______ longerthan the direct path.a. Half wavelengthb. Wavelengthc. Quarter wavelengthd. 2wavelengths

14. The microwave path wherein the microwave beamjust barely touches the obstruction.a. LOSb. Grazingc. Obstructed pathd. Direct path

15. A fade margin of 28 dB has a reliability ofa. 99%b. 99.9%c. 99.99%d. 99.999%

16. The velocity of a resultant wave as it travelsthrough the waveguide.a. Speed of lightb. Group velocityc. Phase velocityd. Incident velocity

17. The smallest free space wavelength that is justunable to propagate in the waveguide under givenconditions.a. Guideb. Phasec. Cut-off d. Group

18. Indicate which of the following cannot be followedby the word "waveguide".a. Ellipticalb. Flexible

c. Coaxiald. Ridge

19. Which of the following waveguide tuningcomponents is not easily adjustable?a. Screwb. Stubc. Irisd. Plunger

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20. What microwave component can sample part ofthe power traveling thru the waveguide?a. Directional couplerb. Magic teec. Circulatord. Isolator

21. A rectangular waveguide is 5.1 cm by 2.4 cm. Thecut-off frequency for the dominant mode isa. 2.94 GHzb. 6.25 GHzc. 664 MHzd. 57.7 GHz

22. If the MTBF of a communications circuit is 20,000hours and its MTTR is 5 hours, what is itsunavailability?a. 0.00025b. 99.975%c. 0.25%d. 0.975%

23. What would be the ERP, in watts, if the transmitteroutput is 30 dBm and the waveguide loss is 20 dBand the antenna connected to it has a power gainof 60 dB?a. 10000 wattsb. 1000 wattsc. 100 wattsd. 10 watts

24. A waveguide section used to couple a circular to arectangular waveguide.a. Taper b. Twist

c. Bendd. Tee

25. A waveguide section used to change the signalpolarizationa. Taper b. Twistc. Bendd. Tee

26. A waveguide section used to combine two or moresignalsa. Taper b. Twistc. Bendd. Tee

27. A signal propagated in a waveguide has a fullwave of electric field intensity change between twofurther walls and no component of the electric fieldin the direction of propagation. The mode isa. TE11b. TE10c. TM22d. TE20

28. A microwave transmission line constructed of a

center conductor suspended between parallelconductive ground planes is calleda. Microstripb. Coaxc. Striplined. Waveguide

29. The principal characteristic of tunnel diodesa. Negative resistance regionb. High forward current ratingc. Very high piv

d. High forward resistance

30. A metal wrapped around the parabolic antennaaperture to eliminate sidelobes interferin nearbystations.a. Radomeb. Shieldc. Shroudd. Bass drum

31. The region within the influence of the inductionfield of an antenna.a. Far fieldb. Near fieldc. Radiation fieldd. Radiation pattern

32. Which of the following is unlikely to be used as apulse device?a. TWTb. CFAc. BWO

d. Multicavity Klystron

33. The wavelength of microwaves at 100 GHz?a. 3 cmb. 0.3 cmc. 0.03 cmd. 0.3 m

34. The k factor under normal atmospheric conditionsin a microwave radio data profile calculation isa. 2/3b. 0c. 4/3

d. 1

35. To install an antenna with an LOS transmission ata distance of 75 miles, determine the height of areceiving antenna if the transmitting antenna is250 ft.a. 1385 ftb. 600 ftc. 400 ftd. 255 ft

36. Determine the gain of a 6 ft parabolic dishoperating at 1800 MHz.a. 30 dBb. 11.2 dBc. 15.5 dBd. 28.17 dB

37. What is the free space loss, in dB, between twomicrowave antennas 38 km apart operating at 7GHz?a. 145.6 dBb. 138.5 dBc. 135.5 dBd. 140.89 dB

38. How many receiving antenna(s) are used with

frequency diversity?a. 1b. 2c. 3d. 4

39. A type of diversity reception, where the output ofthe transmitter is fed to two or more antennas thatare physically separated by an appreciablenumber of wavelengths.a. Frequency

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MITRC REFRESHER COURSE ANSWER KEY

Microwaves

b. Spacec. Angled. Polarization

40. Which of the following is used as a high power

microwave oscillator?a. Thyratronb. Magnetronc. Klystrond. Twystron

41. A microwave communications system space losscalculation formulaa. 94.2 + 20 log F + 20 log Db. 92.4 + 20 log F + 20 log Dc. 94.2 + 10 log F + 20 log Dd. 92.3 + 10 log F + 20 log D

42. Which of the following frequency bands fall underthe microwave band?a. UHF and SHFb. SHF and EHFc. UHF, SHF and EHFd. VLF, LF and MF

43. Find the cut-off frequency for a waveguide in theTE21 mode if the dimensions of the guide are 3 by1.5 cm with wall thickness of 0.08 cm.a. 14.14 GHzb. 5 GHzc. 5.28 GHzd. 15.39 GHz

44. The progressive decrease of signal strength withincreasing distancea. Radiationb. Attenuationc. Modulationd. Propagation

45. A magnetic field is introduced into the waveguideby aa. probeb. dipolec. striplined. capacitor

46. Varactor and step recovery diodes are widely usedin what type of circuit?a. Amplifierb. Oscillatorc. Frequency multiplierd. Mixer

47. The optimum clearance from an obstacle in amicrowave system is accepted as ________ of thefirst fresnel zone radius.a. 0.6b. 0.5

c. 0.9d. 1.5

48. A range of microwave frequencies more easilypassed by the atmosphere than the othersa. Windowb. Critical frequencyc. Gyro frequencyd. Resonant

49. When microwave signals follow the curvature ofthe earth, this is known asa. Faraday effectb. Ductingc. Troposcatter

d. Ionospheric reflection

50. A waveguide mode in which there is nocomponent of electric field in the direction ofpropagation given in the British Europeanstandardsa. H modeb. E modec. TE moded. TM mode

51. The subscript which indicates the number of halfwavelengths along the waveguide heighta. mb. nc. ad. b

52. Which of the following microwave tubes uses theprinciple of velocity modulation?a. TWTb. CFAc. Magnetrond. klystron

53. An X band radar operates in which frequencyband?a. 1 - 2 GHz

b. 2 - 4 GHzc. 4 - 8 GHzd. 8 - 12 GHz

54. Calculate the cut-off wavelength, the guidewavelength and the characteristic impedance of acircular waveguide whose internal diameter is 4cm for a 10 GHz signal propagated in it in thedominant mode. (kr = 1.84)a. 6.83 cm, 3 cm, 420 ohmsb. 3 cm, 6.83 cm, 420 ohmsc. 6.83 cm, 3.34 cm, 420 ohmsd. 6.83 cm, 3.34 cm, 338 ohms

55. A wave is propagated in a parallel planewaveguide. The frequency is 6 GHz and the planeseparation is 3 cm. The cut-off wavelength for thedominant mode, the group and phase velocitiesarea. 5 cm, 166 Mm/sec, 543 Mm/secb. 6 cm, 166 Mm/sec, 543 Mm/secc. 6 cm, 543 Mm/sec, 166 Mm/secd. 5 cm, 543 Mm/sec, 166 Mm/sec

56. The following are negative resistance amplifiersexcept

a. Tunnelb. Gunnc. IMPATTd. PIN diode

57. A cross between the TWT and the magnetron inits operationa. CFAb. BWOc. EIAd. Twystron

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58. Diodes designed to store energy in theircapacitance during forward bias and generatesharmonics in the reverse biasa. Step recoveryb. Gunnc. APDd. IMPATT

59. Topographical maps are maps used for microwavecommunications systems design because

_________ are shown, thereby elevations areknown.a. Latitudesb. Longitudesc. Contour linesd. Scales

60. Surface Acoustic Waves propagate ina. GaAsb. Indium Phosphidec. Stripline

d. Quartz crystal

61. What do you call the process of speeding up andslowing down the beam of electrons in the vacuumtube?a. Velocity modulationb. Logitudinal velocityc. Gyrofrequencyd. Group frequency

62. What is the name of the microwave transmissionline that is used with printed circuits?a. Ferrite loop

b. Coaxc. Waveguided. Microstrip

63. The output of a LASER is monochromatic; thismeans that it isa. Infraredb. Narrow beamc. Polarizedd. Single frequency

64. The attenuator is used in the TWT toa. Help bunchingb. Prevent oscillationc. Prevent saturationd. Increase gain

65. The angle between electric and magnetic fields ina waveguide isa. 90 degreesb. 0 degreesc. 180 degreesd. 360 degrees

66. Materials generally preferred for waveguides area. Brass and aluminumb. Cast iron and steel

c. Non-metallic solidsd. High carbon steel and vanadian steel

67. Waveguide feeders are pressurized toa. Reduce lossb. Reduce noisec. Detect faultsd. Prevent ingress of moisture

68. In order to reduce cross-sectional dimension,which of the following waveguides is preferred?

a. Flexibleb. Rectangularc. Circular d. Ridged

69. A low noise, low power, narrow band microwaveamplifier utilizing a varactor to achieve gaina. Parametric amplifierb. LNAc. SAWd. CFA

70. Which of the following uses buncher and catchercavities?a. magnetronb. klystronc. TWTd. Stripline

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