CHAPTER 4 (54-117)

54. An isotropic antenna is a:

• a. hypothetical point source
• b. infinitely long piece of wire
• c. dummy load
• d. half-wave reference dipole

55. As the length of a "long-wire" antenna is increased:

• a. the number of lobes increases
• b. the number of nodes decreases
• c. efficiency decreases
• d. none of the above

56. For high-frequency operation, which of the following antenna polarization patterns is preferred?

• a. vertically polarized
• b. spherically polarized
• c. elliptically polarized
• d. horizontally polarized

57. To lower the resonant frequency of an antenna, the operator should:

• a. shorten it
• b. lengthen it
• c. ground one end
• d. centre feed it with TV ribbon feeder

58. Omnidirectional transmission is obtained from which of the following antennas?

• a. elliptically polarized
• b. horizontal half-wave
• c. vertical half-wave
• d. each of the above

59. If a slightly shorter parasitic element is placed 0.1 wavelength away from an HF dipole antenna, what effect will this have on the antenna's radiation pattern?

• a. a major lobe will develop in the horizontal plane, parallel to the two elements
• b. a major lobe will develop in the horizontal plane, toward the parasitic element
• c. a major lobe will develop in the vertical plane, away from the ground
• d. the radiation pattern will not be affected

60. Which of the following describes a half-wave dipole?

• a. it is the type of resonant antenna with total nominal length of quarter wave at the carrier frequency
• b. a bidirectional antenna
• c. it has an impedance of 288 ohms
• d. all of these

61. With an antenna height of 40 feet and a transmitter frequency of 50 megahertz, which of the following antenna radiation patterns is best for transmitting over bodies of water?

• a. vertically polarized
• b. spherically polarized
• c. elliptically polarized
• d. horizontally polarized

62. If a slightly longer parasitic element is placed 0.1 wavelength away from an HF dipole antenna, what effect will this have on the antenna's radiation pattern?

• a. a major lobe will develop in the horizontal plane, parallel to the two elements
• b. a major lobe will develop in the vertical plane, away from the ground
• c. a major lobe will develop in the horizontal plane, away from the parasitic element, toward the dipole
• d. the radiation pattern will not be affected

63. Which of the following describes a log periodic antenna?

• a. wideband antenna
• b. bidirectional antenna
• c. an array consisting of same lengths and relative spacing, fed from a two wire line which is transposed between each adjacent pair dipoles
• d. all of these