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MITRC REFRESHER COURSE Radiowave Propagation & Antenna

MITRC REFRESHER COURSE ANSWER KEY Radiowave Propagation & Antenna

1. __________ is the amount of voltage induced in a wave by an electromagnetic wavea. Receive voltageb. Magnetic induction

c. Field strength

d. Power density

2. An electromagnetic wave consists of _____a. Both electric and magnetic fieldsb. An electric field only

c. A magnetic field only

d. Non-magnetic field only

3. What is the lowest layer of the ionosphere?a. F1b. F2

c. E

d. D

4. Who profounded electromagnetic radiation theory?a. Sir Edward Appleton

b. James Clerk Maxwell

c. Christian Huygens

d. Sir Isaac Newton 5. Frequencies in the UHF range propagate by means ofa. Ground wavesb. Sky waves

c. Surface wavesd. Space waves

6. Electromagnetic waves are refracted when they __________a. Pass into a medium of different dielectric constantsb. Are polarized at right angles to the direction of propagation

c. Encounter a perfectly conducting surface

d. Pass through a small slot in a conducting plane

7. What is the thickest layer of the ionosphere

a. F2b. F1c. D

d. E

8. What is the highest frequency that can be sent straight upward and be returned to earth?a. MUFb. Skip frequency

c. Critical frequency

d. Gyro frequency

9. What is the unit of electric field strength?a. Volts per square meterb. Volt per square cm

c. Volts per meter

d. Millivolt per watt

10. Velocity of a radiowave in free spacea. 186,000 miles per secb. 300 x 106 meters per sec

c. 162,000 nautical mile per sec

d. All of the above

11. Refers to the direction of the electric field vector in spacea. Polarization

b. Directivity

c. Radiation

d. ERP

12. A TEM wave whose polarization rotatesa. Vertically polarizedb. Omnidirectional

c. Horizontally polarized

d. Circularly polarized

13. What is the effective radiated power of a repeater with 200 W transmitter power output, 4 dB feedline loss, 4 dB duplexer and circulator loss, and 10 dB feedline antenna gain?a. 2000 Wb. 126 W

c. 317 W

d. 260 W

14. In a vacuum the speed of an electromagnetic wavea. Depends on its constantb. Depends on its wavelength

c. Depends on its electric and magnetic fields

d. Is a universal constant

15. When the magnetic field is perpendicular to the surface of the earth, what is the polarization of the TEM wave?a. Circularb. Horizontal

c. Vertical

d. Elliptical

16. A changing magnetic field gives rise toa. Sound field

b. Magnetic field

c. Electric field

d. Nothing in particular

17. The index of refraction of a material mediuma. Is greater than 1b. Is less than 1

c. Is equal to 1

d. May be any of the above

18. As electromagnetic waves travel in free space, only one of the following can happen to thema. Absorptionb. Attenuation

c. Refraction

d. Reflection

19. Groundwave communications is most effective in what frequency range?a. 300 kHz to 3 MHzb. 3 to 30 MHz

c. 30 to 300 MHz

d. Above 300 MHz

20. The ionosphere has its greatest effect on signals in what frequency range?a. 300 kHz to 3 MHz

b. 3 to 30 MHz

c. 30 to 300 MHz

d. Above 300 MHz

21. A microwave-transmitting antenna is 550 ft. high. The receiving antenna is 200 ft. high. The minimum transmission distance isa. 20 mib. 33.2 mi

c. 38.7 mi

d. 53.2 mi

22. States that power density is inversely proportional to the distance from its source a. Principal or Reciprocityb. Inverse Square Law

c. Huygens Principle

d. Faradays Law

23. What is the primary cause of ionization in the atmosphere?a. Sun spotb. Cosmic rays

c. Galactic disturbance

d. Ultraviolet radiation

24. Which layer does not disappear at night?a. D

b. E

c. F1

d. F2

25. The shortest distance measured along the earths surface that a skywave is returned to eartha. MUF

b. Quarter-Wavelength

c. Skip distance

d. Skip zone 26. What do you call the gigantic emissions of hydrogen from the sun?a. Solar flares

b. SIDsc. Kennely-Heaviside

d. Sun spots

27. Two directional antennas are pointed so that their beams intersect in the tropospherea. Skywaveb. Surface wave

c. Microwave

d. Troposcatter

28. Super refractiona. Ductingb. Troposcatter

c. Skywave

d. Space wave

29. Two or more antennas are used separated by several wavelengthsa. Space diversityb. Frequency diversity

c. Hybrid diversity

d. Polarization diversity

30. Two or more receivers are used using a single antennaa. Space diversity

b. Frequency diversity

c. Hybrid diversityd. Polarization diversity

31. Each point on a spherical waveform maybe a source of a secondary spherical wavefronta. Snells law

b. Huygens principle

c. Rayleighs principle

d. De Morgans theorem 32. Ducting occurs in which region of the atmosphere?a. Stratosphereb. Troposphere

c. Ionosphere

d. Ozone layer

33. Which ionosphere layer has an average height of 225 km at night?a. D layerb. E layer

c. F1 layer

d. F2 layer

34. In what range of frequencies are most omnidirectional horizontally polarized antennas used?a. VHF, UHF

b. VLF, LF

c. SH, EHF

d. MF, HF 35. What is the gain of the Hertzian dipole over isotropic antenna?a. 1.64 dB

b. 2.15 dB

c. 1.76 dB

d. 1.55 dB36. _____ is the measurement of a unilateral antenna properties of directivity a. Phase angle

b. Antenna gain

c. Beamwidth

d. Bandwidth 37. _____ is the amount of uncertainly in a system of symbolsa. Bandwidth

b. Enthalpy

c. Entropy

d. Quantum 38. If an antenna has a gain of 30 dB, it increases the output of the transmitter bya. 10,000 times

b. 1000 times

c. 100 times

d. 1 million times

39. Which does not use vertical polarization antenna?a. AM Broadcastingb. FM Broadcasting

c. Mobile Communications

d. Satellite Communications

40. Which antenna radiates an omnidirectional pattern in the horizontal plane with vertical polarization?a. Marconi antennab. Discone antenna

c. Horn antenna

d. Helical antenna41. An antenna with very high gain and very narrow beamwidtha. Helical antennab. Discone antenna

c. Horn antenna

d. Parabolic dish antenna

42. _____ is the horizontal pointing angle of an antennaa. Azimuthb. Angle of elevation

c. Right angle

d. Beamwidth

43. What is the estimated medium wind loading in the Philippines for antenna tower design?a. 300 kphb. 100 kph

c. 200 kph

d. 250 kph

44. _____ is an open-ended slot antennaa. Helical antennab. Rhombic antenna

c. Notch antenna

d. Cassegrain antenna

45. What is the radiation characteristic of a dipole antenna?a. Omnidirectionalb. Bidirectional

c. Unidirectional

d. Hemispherical

46. An antenna with unity gaina. Rhombicb. Half-wave dipole

c. Isotropic

d. Whip

47. An antenna which is one-tenth wavelength longa. Hertzian dipoleb. Loop antenna

c. Marconi antenna

d. Elementary doublet

48. What is the minimum number of turns a helix antenna must have?a. 3

b. 5

c. 4

d. 6

49. Which of the following improves antenna directivity?a. Driven element

b. Reflector element

c. Director element

d. Parasitic element

50. What is the front-to-back ratio of an antenna which radiates 500 watts in a northernly direction and 50 watts in a southernly direction?a. 25000 dB

b. 10 dB

c. 100 dB

d. 20 dB

51. The frequency of operation of a dipole antenna cut to a length of 3.4 ma. 88 MHzb. 44 MHz

c. 22 MHz

d. 11 MHz

52. Shortening effect of an antenna that makes it appear as if it were 5% longera. End effectb. Flywheel effect

c. Skin effect

d. Capture effect

53. A simple half-wavelength antenna radiates the strongest signala. At 45 degrees to its axisb. Parallel to its axis

c. At right angles to its axis

d. at 60 degrees to its axis54. If an antenna is too short for the wavelength being used, the effective length can be increased by addinga. Capacitance in seriesb. Inductance in series

c. Resistance in parallel

d. Resistance in series

55. Which of the following antennas is used for testing and adjusting a transmitter for proper modulation, amplifier operation and frequency accuracy?a. Elementaryb. Real

c. Isotropic

d. Dummy

56. The power fed to a two-bay turnstile antenna is 100 watts. If the antenna has a 2dB power gain, what is the effective radiated powera. 317 wattsb. 158 watts

c. 200 watts

d. 400 watts

57. If the length of an antenna is changed from 2.5 meters to 2.8 meters, its resonant frequency willa. Increase

b. Depend on the velocity factor so the resonant frequency can either be increased or decreased

c. Will be unchanged

d. Decrease 58. It is an array of metallic conductors buried beneath the antenna, which is used to improve the conductivity of the natural earth a. Loading coilb. ATU

c. Counterpoise

d. Earth mat

59. What is the electrical wavelength of a 500 MHz signal?a. 60 centimetersb. 6 meters

c. 0.06 meter

d. 60 meters

60. Actual height of antenna should be at leasta. One wavelengthb. Half wavelength

c. Quarter wavelength

d. Three-fourth wavelength 61. Which antenna is not properly terminated?

a. Resonant

b. Non-resonant

c. Isotropic

d. Whip

62. _____ is an antenna array which is highly directional at right angles to the plane of the array?a. Broadside arrayb. End-fire array

c. Turnstile array

d. Log-periodic array

63. The directivity pattern of an isotropic radiation isa. A figure 8 b. A sphere c. A unidirectional cardioid

d. A parabola

64. The purpose of stacking elements on an antennaa. Sharper directional patternb. Increased gain

c. Improved bandpass

d. All of these

65. Where are the voltage nodes in a half-wave antenna?a. At the endsb. Threequarters of the way from the feed point toward the end

c. Onehalf of the way from the feed point toward the end

d. At the feed point

66. A Hertz antenna is operating on a frequency of 2182 kHz and consists of a horizontal wire that is hanged between two towers. What is the frequency of its third harmonic?a. 727 kHzb. 6545 kHz

c. 436 kHz

d. 6.546 kHz

67. What is the gain of an antenna over a half-wavelength dipole when it has 6 dB gain over an isotropic radiator?a. 6.0 dBb. 8.1 dB

c. 3.9 dB

d. 10.0 dB

68. What is the usual electrical length of a driven element in an HF beam antenna?a. wavelengthb. wavelength

c. wavelength

d. 1 wavelength69. Strong interference from one particular station can be eliminated by the use ofa. Noise limitersb. Squelch circuits

c. Negative feedback

d. Wave traps in the antenna circuits

70. Good grounding is important fora. Horizontal antennasb. Broadside array antennas

c. Vertical antennas

d. Yagi-Uda antennas

71. Which of the following antennas is best excited from a waveguide?a. Biconicalb. Horn

c. Helical

d. Discone

72. Not a reason for the use of an antenna couplera. To make the antenna resistiveb. To provide the output amplifier with the correct load impedance

c. To discriminate against harmonics

d. To prevent reradiation of the local oscillator

73. Which antenna is not a wideband?a. Disconeb. Folded dipole

c. Helical

d. Marconi

74. _____ is an antenna made up of a number of full wavelengthsa. Elementary doubletb. Log-periodic

c. Long wire

d. Whip

75. Which antenna does not use the ground?a. Marconib. Yagi

c. Hertz

d. Rhombic

76. It is a measure of the microwave power radiated from an antenna as a function of angular direction from the antenna axis

a. Antenna patternb. Polarization

c. Beamwidth

d. Sidelobes

77. In a turnstile antenna, the crossed dipoles are excited with voltagesa. In phase with each other

b. 360 out of phase with each other

c. 90 out of phase with each other

d. 180 out of phase with each other

78. It is described as the MUF factora. sec

b. cos

c. sin

d. csc

79. Known as the technique for adding a series inductor at or near the center of an antenna element in order to cancel the capacitive reactance of an antenna

a. Dipole

b. Center loading

c. Reflector

d. Loading coil

80. At the ends of a half-wave antenna, what values of current and voltage exist compared to the remainder of the antenna?

a. Minimum voltage and minimum current

b. Equal voltage and current

c. Minimum voltage and maximum current

d. Maximum voltage and minimum current

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