Basic Qualification · B-007 Radio wave propagation · B-007-005-007
When sunspot numbers are high, how is propagation affected?
- A Frequencies up to 40 MHz or even higher become usable for long-distance communication
- B High frequency radio signals are absorbed
- C Frequencies up to 100 MHz or higher are normally usable for long-distance communication
- D High frequency radio signals become weak and distorted
Correct answer: A — Frequencies up to 40 MHz or even higher become usable for long-distance communication. From the official ISED question bank, verified word for word.
Why
When sunspot numbers are high, the Sun's increased radiation strengthens the ionosphere, the upper atmospheric layer that reflects radio waves back to Earth. 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.