Basic Qualification · B-007 Radio wave propagation · B-007-005-011
What is the major cause of cyclical changes in HF propagation?
- A Jet stream cycle
- B Auroral cycle
- C Solar cycle
- D Magnetic pole drift cycle
Correct answer: C — Solar cycle. From the official ISED question bank, verified word for word.
Why
The Sun does not shine with the same strength every year; it goes through an eleven-year rhythm where its activity rises and falls, changing how the upper atmosphere reflects high-frequency radio waves. 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.