Basic Qualification · B-007 Radio wave propagation · B-007-006-001
Observatories probe the ionosphere at vertical incidence. What term describes the highest frequency that a region can reflect at the time?
- ACritical frequency
- BMaximum usable frequency
- COptimum working frequency
- DDoppler frequency
Correct answer: A — Critical frequency. From the official ISED question bank, verified word for word.
Why
Critical frequency is the highest radio wave frequency that can bounce straight back to Earth when sent vertically into the ionosphere. The full explanation — and one for every question — is in Pro.
Practise this section
Radio wave propagation is section B-007 of the Basic exam: How signals travel: the ionosphere and its layers, skip, ground wave, sporadic E, and which bands work when.
Drill B-007 — free, no account