General exam question G9B07
Subelement G9, ANTENNAS AND FEED LINES· Group G9B
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?
- A.It steadily increases
- B.It steadily decreases (correct answer)
- C.It peaks at about 1/8 wavelength above ground
- D.It is unaffected by the height above ground
WhyA horizontal 1/2 wave dipole antenna's feed point impedance steadily decreases as the antenna height is reduced to 1/10 wavelength above ground. As a horizontal half-wave dipole is lowered from typical operating heights down toward 1/10 wavelength above ground, its feed point impedance steadily drops from the roughly 70-ohm free-space value toward much lower values as ground proximity increasingly loads the antenna, answer B. It doesn't steadily increase, doesn't peak partway down at 1/8 wavelength, and height clearly does affect the impedance, 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.
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