Basic Qualification · B-007 Radio wave propagation · B-007-004-008
What causes selective fading?
- A Large changes in the height of the ionosphere at the receiving station ordinarily occurring shortly before
- B Phase differences between radio wave components of the same transmission, as experienced at the receiving station
- C Small changes in directional antenna heading at the receiving station
- D Time differences between the receiving and transmitting stations
Correct answer: B — Phase differences between radio wave components of the same transmission, as experienced at the receiving station. From the official ISED question bank, verified word for word.
Why
Selective fading happens when different parts of the same radio signal arrive at your antenna at slightly different times, causing them to cancel each other out or boost each other depending on their alignment. 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.