General exam question G9B02
Subelement G9, ANTENNAS AND FEED LINES· Group G9B
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?
- A.Slope the radials upward
- B.Slope the radials downward (correct answer)
- C.Lengthen the radials beyond one wavelength
- D.Coil the radials
WhySloping the radials downward is a common way to adjust an elevated quarter-wave ground-plane vertical antenna's feed point impedance to approximately 50 ohms. Sloping a ground-plane vertical's radials downward from the feed point raises the antenna's feed point impedance from the roughly 20-25 ohms of perfectly horizontal radials up toward the 50 ohms a coax feed line expects, giving a convenient, hardware-free way to approach a good match, answer B. Sloping the radials upward, lengthening them beyond a wavelength, or coiling them don't produce this same practical impedance-raising effect, so A, C, and D are wrong.
Published 2026-08-28 · Last updated 2026-08-28 · Question text is verbatim from the 2023-2027 NCVEC Element 3 pool (public domain); the explanation above is original writing, see our methodology.
Related questions
- G9B01What is a characteristic of a random-wire HF antenna connected directly to the transmitter?
- G9B03Which of the following best describes the radiation pattern of a quarter-wave ground-plane vertical antenna?
- G9B04What is the radiation pattern of a dipole antenna in free space in a plane containing the conductor?
- G9B05How does antenna height affect the azimuthal radiation pattern of a horizontal dipole HF antenna at elevation angles higher than about 45 degrees?
- G9B06Where should the radial wires of a ground-mounted vertical antenna system be placed?