General G9B: Dipoles, verticals and wire antennas
These are the 12 official questions in group G9B of the 2023–2027 General question pool, with the correct answer marked and a plain-English explanation of why it's right. The real exam asks one question from this group.
- G9B01Question 1
What is a characteristic of a random-wire HF antenna connected directly to the transmitter?
- AIt must be longer than 1 wavelength
- BStation equipment may carry significant RF current Correct
- CIt produces only vertically polarized radiation
- DIt is more effective on the lower HF bands than on the higher bands
Why: A random wire fed directly can put significant RF current on station equipment.
- G9B02Question 2
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?
- ASlope the radials upward
- BSlope the radials downward Correct
- CLengthen the radials beyond one wavelength
- DCoil the radials
Why: Sloping the radials downward raises the feed point impedance toward 50 Ω.
- G9B03Question 3
Which of the following best describes the radiation pattern of a quarter-wave ground-plane vertical antenna?
- ABi-directional in azimuth
- BIsotropic
- CHemispherical
- DOmnidirectional in azimuth Correct
Why: A quarter-wave ground-plane vertical is omnidirectional in azimuth.
- G9B04Question 4
What is the radiation pattern of a dipole antenna in free space in a plane containing the conductor?
- AIt is a figure-eight at right angles to the antenna Correct
- BIt is a figure-eight off both ends of the antenna
- CIt is a circle (equal radiation in all directions)
- DIt has a pair of lobes on one side of the antenna and a single lobe on the other side
Why: A free-space dipole radiates a figure-eight, broadside to the wire.
- G9B05Question 5
How does antenna height affect the azimuthal radiation pattern of a horizontal dipole HF antenna at elevation angles higher than about 45 degrees?
- AIf the antenna is too high, the pattern becomes unpredictable
- BAntenna height has no effect on the pattern
- CIf the antenna is less than 1/2 wavelength high, the azimuthal pattern is almost omnidirectional Correct
- DIf the antenna is less than 1/2 wavelength high, radiation off the ends of the wire is eliminated
Why: Below half a wavelength high, a dipole's high-angle pattern is almost omnidirectional.
- G9B06Question 6
Where should the radial wires of a ground-mounted vertical antenna system be placed?
- AAs high as possible above the ground
- BParallel to the antenna element
- COn the surface or buried a few inches below the ground Correct
- DAt the center of the antenna
Why: Ground radials go on the surface or a few inches underground.
- G9B07Question 7
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?
- AIt steadily increases
- BIt steadily decreases Correct
- CIt peaks at about 1/8 wavelength above ground
- DIt is unaffected by the height above ground
Why: As a dipole is lowered toward 1/10 wavelength, its feed impedance steadily decreases.
- G9B08Question 8
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?
- AIt steadily increases Correct
- BIt steadily decreases
- CIt peaks at about 1/8 wavelength from the end
- DIt is unaffected by the location of the feed point
Why: A dipole's impedance rises as the feed point moves from center toward the ends.
- G9B09Question 9
Which of the following is an advantage of using a horizontally polarized as compared to a vertically polarized HF antenna?
- ALower ground losses Correct
- BLower feed point impedance
- CShorter radials
- DLower radiation resistance
Why: Horizontal antennas have lower ground losses.
- G9B10Question 10
What is the approximate length for a 1/2 wave dipole antenna cut for 14.250 MHz?
- A8 feet
- B16 feet
- C24 feet
- D33 feet Correct
Why: 468 ÷ 14.25 ≈ 33 feet.
- G9B11Question 11
What is the approximate length for a 1/2 wave dipole antenna cut for 3.550 MHz?
- A42 feet
- B84 feet
- C132 feet Correct
- D263 feet
Why: 468 ÷ 3.55 ≈ 132 feet.
- G9B12Question 12
What is the approximate length for a 1/4 wave monopole antenna cut for 28.5 MHz?
- A8 feet Correct
- B11 feet
- C16 feet
- D21 feet
Why: 234 ÷ 28.5 ≈ 8 feet.