Basic Qualification · B-007 Radio wave propagation · B-007-006-002
What causes the maximum usable frequency to vary?
- A The temperature of the ionosphere
- B The speed of the winds in the upper atmosphere
- C The type of weather just below the ionosphere
- D The amount of radiation received from the sun
Correct answer: D — The amount of radiation received from the sun. From the official ISED question bank, verified word for word.
Why
The maximum usable frequency changes because the sun's radiation constantly alters how dense the ionosphere becomes, which in turn determines the highest radio signal that can bounce 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.