75 lines
3.4 KiB
Markdown
75 lines
3.4 KiB
Markdown
G9B – Basic dipole and monopole antennas
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- [[G9B01]] (B)
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What is a characteristic of a random-wire HF antenna connected directly to the transmitter? #card
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- A. It must be longer than 1 wavelength
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- B. Station equipment may carry significant RF current
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- C. It produces only vertically polarized radiation
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- D. It is more effective on the lower HF bands than on the higher bands
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- [[G9B02]] (B)
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Which of the following is a common way to adjust the feed point impedance of an elevated quarter-wave ground-plane vertical antenna to be approximately 50 ohms? #card
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- A. Slope the radials upward
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- B. Slope the radials downward
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- C. Lengthen the radials beyond one wavelength
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- D. Coil the radials
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- [[G9B03]] (D)
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Which of the following best describes the radiation pattern of a quarter-wave ground-plane vertical antenna? #card
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- A. Bi-directional in azimuth
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- B. Isotropic
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- C. Hemispherical
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- D. Omnidirectional in azimuth
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- [[G9B04]] (A)
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What is the radiation pattern of a dipole antenna in free space in a plane containing the conductor? #card
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- A. It is a figure-eight at right angles to the antenna
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- B. It is a figure-eight off both ends of the antenna
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- C. It is a circle (equal radiation in all directions)
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- D. It has a pair of lobes on one side of the antenna and a single lobe on the other side
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- [[G9B05]] (C)
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How does antenna height affect the azimuthal radiation pattern of a horizontal dipole HF antenna at elevation angles higher than about 45 degrees? #card
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- A. If the antenna is too high, the pattern becomes unpredictable
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- B. Antenna height has no effect on the pattern
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- C. If the antenna is less than 1/2 wavelength high, the azimuthal pattern is almost omnidirectional
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- D. If the antenna is less than 1/2 wavelength high, radiation off the ends of the wire is eliminated
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- [[G9B06]] (C)
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Where should the radial wires of a ground-mounted vertical antenna system be placed? #card
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- A. As high as possible above the ground
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- B. Parallel to the antenna element
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- C. On the surface or buried a few inches below the ground
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- D. At the center of the antenna
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- [[G9B07]] (B)
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How does the feed point impedance of a horizontal 1/2 wave dipole antenna change as the antenna height is reduced to 1/10 wavelength above ground? #card
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- A. It steadily increases
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- B. It steadily decreases
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- C. It peaks at about 1/8 wavelength above ground
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- D. It is unaffected by the height above ground
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- [[G9B08]] (A)
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How does the feed point impedance of a 1/2 wave dipole change as the feed point is moved from the center toward the ends? #card
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- A. It steadily increases
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- B. It steadily decreases
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- C. It peaks at about 1/8 wavelength from the end
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- D. It is unaffected by the location of the feed point
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- [[G9B09]] (A)
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Which of the following is an advantage of using a horizontally polarized as compared to a vertically polarized HF antenna? #card
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- A. Lower ground losses
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- B. Lower feed point impedance
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- C. Shorter radials
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- D. Lower radiation resistance
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- [[G9B10]] (D)
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What is the approximate length for a 1/2 wave dipole antenna cut for 14.250 MHz? #card
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- A. 8 feet
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- B. 16 feet
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- C. 24 feet
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- D. 33 feet
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- [[G9B11]] (C)
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What is the approximate length for a 1/2 wave dipole antenna cut for 3.550 MHz? #card
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- A. 42 feet
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- B. 84 feet
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- C. 132 feet
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- D. 263 feet
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- [[G9B12]] (A)
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What is the approximate length for a 1/4 wave monopole antenna cut for 28.5 MHz? #card
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- A. 8 feet
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- B. 11 feet
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- C. 16 feet
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- D. 21 feet
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