Basic Qualification · B-007 Radio wave propagation · B-007-007-011
What effect is responsible for propagating a VHF signal over 800 km?
- A Ionospheric refraction
- B Tropospheric ducting
- C Faraday rotation
- D D-region refraction
Correct answer: B — Tropospheric ducting. From the official ISED question bank, verified word for word.
Why
Tropospheric ducting occurs when layers of air in the lower atmosphere act like a pipe, trapping VHF signals and guiding them hundreds of kilometres beyond the normal horizon. The full explanation — and one for every question — is in Pro.
Practise this section
How signals travel: the ionosphere and its layers, skip, ground wave, sporadic E, and which bands work when.