Basic Qualification · B-007 Radio wave propagation · B-007-004-001
What effect does the D region of the ionosphere have on lower frequency HF waves in the daytime?
- A It bends the radio waves out into space
- B It refracts the radio waves back to Earth
- C It distorts the waves
- D It absorbs the waves
Correct answer: D — It absorbs the waves. From the official ISED question bank, verified word for word.
Why
During the day, sunlight creates the D region, a lower layer of the ionosphere filled with many free electrons that act like a sponge for lower frequency HF 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.