Basic Qualification · B-007 Radio wave propagation · B-007-001-002
What does near vertical incidence sky-wave (NVIS) propagation enable?
- A Continent-wide communications
- B Medium range HF communications, especially in difficult terrain
- C Multi-hop HF worldwide communications
- D Regional communications above the critical frequency
Correct answer: B — Medium range HF communications, especially in difficult terrain. From the official ISED question bank, verified word for word.
Why
Near vertical incidence sky-wave, or NVIS, sends radio signals almost straight up so they bounce off the ionosphere and return to Earth nearby, filling the gap between ground wave and long-distance sky wave. 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.