Basic Qualification · B-007 Radio wave propagation · B-007-004-006
What can be done to continue HF communications during a sudden ionospheric disturbance (SID)?
- A Try the other sideband
- B Try a different antenna polarization
- C Try a different frequency shift
- D Try a higher frequency band
Correct answer: D — Try a higher frequency band. From the official ISED question bank, verified word for word.
Why
A sudden ionospheric disturbance, caused by solar flares, knocks out lower HF frequencies by absorbing their signals in the lower atmosphere. 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.