COMMS 2 - Antenna & Radio Wave Answers

MITRC REFRESHER COURSE Propagation & Antenna

Radiowave

ANSWER KEY

1. __________ is the amount of voltage induced in a wave by an electromagnetic wave a. Receive voltage b. Magnetic induction c. Field strength d. Power density

feedline loss, 4 dB duplexer and circulator loss, and 10 dB feedline antenna gain? a. 2000 W b. 126 W c. 317 W d. 260 W

2. a. b. c. d.

An electromagnetic wave consists of _____ Both electric and magnetic fields An electric field only A magnetic field only Non-magnetic field only

3. a. b. c. d.

What is the lowest layer of the ionosphere? F1 F2 E D

14. In a vacuum the speed of an electromagnetic wave a. Depends on its constant b. 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. Circular b. Horizontal c. Vertical d. Elliptical

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 of a. Ground waves b. Sky waves c. Surface waves d. Space waves 6. Electromagnetic waves are refracted when they __________ a. Pass into a medium of different dielectric constants b. 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.

a. b. c. d.

A changing magnetic field gives rise to Sound field Magnetic field Electric field Nothing in particular

17. a. b. c. d.

The index of refraction of a material medium Is greater than 1 Is less than 1 Is equal to 1 May be any of the above

18. As electromagnetic waves travel in free space, only one of the following can happen to them a. Absorption b. Attenuation c. Refraction d. Reflection 19. Groundwave communications is most effective in what frequency range? a. 300 kHz to 3 MHz b. 3 to 30 MHz c. 30 to 300 MHz d. Above 300 MHz

What is the thickest layer of the ionosphere F2 F1 D E

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

8. What is the highest frequency that can be sent straight upward and be returned to earth? a. MUF b. Skip frequency c. Critical frequency d. Gyro frequency 9.

16. a. b. c. d.

21. A microwave-transmitting antenna is 550 ft. high. The receiving antenna is 200 ft. high. The minimum transmission distance is a. 20 mi b. 33.2 mi c. 38.7 mi d. 53.2 mi

What is the unit of electric field strength? a. Volts per square meter b. Volt per square cm c. Volts per meter d. Millivolt per watt

10. Velocity of a radiowave in free space a. 186,000 miles per sec b. 300 x 106 meters per sec c. 162,000 nautical mile per sec d. All of the above

22. States that power density is inversely proportional to the distance from its source a. Principal or Reciprocity b. Inverse Square Law c. Huygen’s Principle d. Faraday’s Law

11. Refers to the direction of the electric field vector in space a. Polarization b. Directivity c. Radiation d. ERP

23. What is the primary cause of ionization in the atmosphere? a. Sun spot b. Cosmic rays c. Galactic disturbance d. Ultraviolet radiation

12. a. b. c. d.

24. a. b. c.

A TEM wave whose polarization rotates Vertically polarized Omnidirectional Horizontally polarized Circularly polarized

d.

13. What is the effective radiated power of a repeater with 200 W transmitter power output, 4 dB

Which layer does not disappear at night? D E F1 F2

25. The shortest distance measured along the earth’s surface that a skywave is returned to earth a. MUF

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MITRC REFRESHER COURSE Propagation & Antenna b. c.

d.

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Quarter-Wavelength Skip distance Skip zone

c.

d. 38. the a. b. c.

26. What do you call the gigantic emissions of hydrogen from the sun? a. Solar flares b. SIDs c. Kennely-Heaviside d. Sun spots

d.

Entropy Quantum If an antenna has a gain of 30 dB, it increases output of the transmitter by 10,000 times 1000 times 100 times 1 million times

39. Which does not use vertical polarization antenna? a. AM Broadcasting b. FM Broadcasting c. Mobile Communications d. Satellite Communications

27. Two directional antennas are pointed so that their beams intersect in the troposphere a. Skywave b. Surface wave c. Microwave d. Troposcatter

29. Two or more antennas are used separated by several wavelengths a. Space diversity b. Frequency diversity c. Hybrid diversity d. Polarization diversity

40. Which antenna radiates an omnidirectional pattern in the horizontal plane with vertical polarization? a. Marconi antenna b. Discone antenna c. Horn antenna d. Helical antenna 41. An antenna with very high gain and very narrow beamwidth a. Helical antenna b. Discone antenna c. Horn antenna d. Parabolic dish antenna

30. Two or more receivers are used using a single antenna a. Space diversity b. Frequency diversity c. Hybrid diversity d. Polarization diversity

42. _____ is the horizontal pointing angle of an antenna a. Azimuth b. Angle of elevation c. Right angle d. Beamwidth

31. Each point on a spherical waveform maybe a source of a secondary spherical wavefront a. Snell’s law b. Huygen’s principle c. Rayleigh’s principle d. De Morgan’s theorem

43. the a. b. c. d.

What is the estimated medium wind loading in Philippines for antenna tower design? 300 kph 100 kph 200 kph 250 kph

44. a. b. c. d.

_____ is an open-ended slot antenna Helical antenna Rhombic antenna Notch antenna Cassegrain antenna

28. a. b. c. d.

Super refraction Ducting Troposcatter Skywave Space wave

32. Ducting occurs in which region of the atmosphere? a. Stratosphere b. Troposphere c. Ionosphere d. Ozone layer 33. 225 a. b. c. d.

45. What is the radiation characteristic of a dipole antenna? a. Omnidirectional b. Bidirectional c. Unidirectional d. Hemispherical

Which ionosphere layer has an average height of km at night? D layer E layer F1 layer F2 layer

46. a. b. c. d.

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 dB

An antenna with unity gain Rhombic Half-wave dipole Isotropic Whip

47. An a. b. c. d.

antenna which is one-tenth wavelength long Hertzian dipole Loop antenna Marconi antenna Elementary doublet

48. What is the minimum number of turns a helix antenna must have? a. 3 b. 5 c. 4 d. 6

36. _____ is the measurement of a unilateral antenna properties of directivity a. Phase angle b. Antenna gain c. Beamwidth d. Bandwidth

49. Which of the following improves antenna directivity? Driven element Reflector element Director element Parasitic element

37. _____ is the amount of uncertainly in a system of symbols a. Bandwidth b. Enthalpy

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MITRC REFRESHER COURSE Propagation & Antenna

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. cut a. b. c. d.

c. d.

Isotropic Whip

62. _____ is an antenna array which is highly directional at right angles to the plane of the array? a. Broadside array b. End-fire array c. Turnstile array d. Log-periodic array

The frequency of operation of a dipole antenna to a length of 3.4 m 88 MHz 44 MHz 22 MHz 11 MHz

63. The directivity pattern of an isotropic radiation is a. A figure – 8 b. A sphere c. A unidirectional cardioid d. A parabola

52. Shortening effect of an antenna that makes it appear as if it were 5% longer a. End effect b. Flywheel effect c. Skin effect d. Capture effect

64. The purpose of stacking elements on an antenna a. Sharper directional pattern b. Increased gain c. Improved bandpass d. All of these 65. Where are the voltage nodes in a half-wave antenna? a. At the ends b. Three–quarters of the way from the feed point toward the end c. One–half of the way from the feed point toward the end d. At the feed point

53. A simple half-wavelength antenna radiates the strongest signal a. At 45 degrees to its axis b. Parallel to its axis c. At right angles to its axis d. at 60 degrees to its axis 54. If an antenna is too short for the wavelength being used, the effective length can be increased by adding a. Capacitance in series b. Inductance in series c. Resistance in parallel d. Resistance in series

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 kHz b. 6545 kHz c. 436 kHz d. 6.546 kHz

55. Which of the following antennas is used for testing and adjusting a transmitter for proper modulation, amplifier operation and frequency accuracy? a. Elementary b. Real c. Isotropic d. Dummy

67. What is the gain of an antenna over a halfwavelength dipole when it has 6 dB gain over an isotropic radiator? a. 6.0 dB b. 8.1 dB c. 3.9 dB d. 10.0 dB

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 power a. 317 watts b. 158 watts c. 200 watts d. 400 watts

68. What is the usual electrical length of a driven element in an HF beam antenna? a. ¼ wavelength b. ¾ wavelength c. ½ wavelength d. 1 wavelength 69. Strong interference from one particular station can be eliminated by the use of a. Noise limiters b. Squelch circuits c. Negative feedback d. Wave traps in the antenna circuits

57. If the length of an antenna is changed from 2.5 meters to 2.8 meters, its resonant frequency will a. Increase b. Depend on the velocity factor so the resonant frequency can either be increased or decreased c. Will be unchanged d. Decrease

70. Good grounding is important for a. Horizontal antennas b. Broadside array antennas c. Vertical antennas d. Yagi-Uda antennas

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 coil b. ATU c. Counterpoise d. Earth mat

71. Which of the following antennas is best excited from a waveguide? a. Biconical b. Horn c. Helical d. Discone

59. What is the electrical wavelength of a 500 MHz signal? a. 60 centimeters b. 6 meters c. 0.06 meter d. 60 meters 60. a. b. c. d.

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ANSWER KEY

72. Not a reason for the use of an antenna coupler a. To make the antenna resistive b. To provide the output amplifier with the correct load impedance c. To discriminate against harmonics d. To prevent reradiation of the local oscillator

Actual height of antenna should be at least One wavelength Half wavelength Quarter wavelength Three-fourth wavelength

73. Which antenna is not a wideband? a. Discone b. Folded dipole c. Helical

61. Which antenna is not properly terminated? a. Resonant b. Non-resonant

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MITRC REFRESHER COURSE Propagation & Antenna d.

Radiowave

Marconi

74. _____ is an antenna made up of a number of full wavelengths a. Elementary doublet b. Log-periodic c. Long wire d. Whip 75. Which antenna does not use the ground? a. Marconi b. 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 pattern b. Polarization c. Beamwidth d. Sidelobes 77. In a turnstile antenna, the crossed dipoles are excited with voltages a. 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 factor

a. b. c. d.

θ cos θ sin θ csc θ sec

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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