Advanced Qualification · A-007 Feedlines and matching · A-007-007-005
When a half-wave dipole antenna is installed one-half wavelength above ground, the:
- Avertical or upward radiation is effectively cancelled
- Bradiation pattern changes to produce side lobes at 15 and 50 degrees
- Cside lobe radiation is cancelled
- Dradiation pattern is unaffected
Correct answer: A — vertical or upward radiation is effectively cancelled. From the official ISED question bank, verified word for word.
Why
When a half-wave dipole sits half a wavelength above the ground, the signal bouncing off the earth meets the direct signal going straight up exactly out of step, causing them to cancel each other out. The full explanation — and one for every question — is in Pro.
Practise this section
Feedlines and matching is section A-007 of the Advanced exam: Feedlines and matching at the advanced level: transmission line theory, impedance transformation, stubs and matching networks.
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