Basic Qualification · B-007 Radio wave propagation · B-007-006-004
Why is communication possible between two continents at a frequency above the local critical frequency?
- A Ionization is not uniform around the globe
- B A higher frequency cuts through absorption more easily
- C The signal enters the ionosphere at an oblique (inclined) angle
- D The sun's relative position differs between the two locations
Correct answer: C — The signal enters the ionosphere at an oblique (inclined) angle. From the official ISED question bank, verified word for word.
Why
When a radio wave hits the ionosphere at a slant, or oblique angle, it travels a longer path through the charged layers before bending 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.