Basic Qualification · B-007 Radio wave propagation · B-007-002-009
What is the main reason the 160-metre and 80-metre bands tend to be useful only for short-distance communications during daylight hours?
- A Because of signal scattering
- B Because of E region ionization
- C Because of E region absorption
- D Because of D region absorption
Correct answer: D — Because of D region absorption. From the official ISED question bank, verified word for word.
Why
During daylight, the Sun creates a lower layer in the ionosphere called the D region, which acts like a sponge that soaks up radio energy on the 160-metre and 80-metre bands before it can travel far. 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.