Advanced Qualification · A-007 Feedlines and matching · A-007-007-006
How does antenna height affect the horizontal (azimuthal) radiation pattern of a horizontal dipole HF antenna?
- A If the antenna is less than one-half wavelength high, radiation off the ends of the wire is eliminated
- B If the antenna is too high, the pattern becomes unpredictable
- C If the antenna is less than one-half wavelength high, reflected radio waves from the ground significantly distort the pattern
- D Antenna height has no effect on the pattern
Correct answer: C — If the antenna is less than one-half wavelength high, reflected radio waves from the ground significantly distort the pattern. From the official ISED question bank, verified word for word.
Why
When a horizontal dipole sits lower than half a wavelength above the ground, radio waves bouncing off the earth mix with the direct waves, creating peaks and nulls that warp the expected shape. The full explanation — and one for every question — is in Pro.
Practise this section
Feedlines and matching at the advanced level: transmission line theory, impedance transformation, stubs and matching networks.