The ionosphere (the ionised region of the atmosphere between about 60 km and 1000 km) affects all radio signals below ~5 GHz which pass through or travel via it. Some of the associated radio systems can only operate because of the ionosphere, but it can also degrade radio system operation. Sometimes the effects of the ionosphere are highly significant, sometimes they can all but be ignored. For high-frequency (HF) sky-wave propagation, the ionosphere is, of course, a prerequisite. If the ionosphere were stable in time and constant in space, it would be relatively easy to determine the effect of the ionisation on the radio propagation and hence on the radio system. Unfortunately, stability is not the norm, particularly in the high-latitude regions, and, as a consequence ionospheric, prediction methods and models are required to support system design, service planning and frequency management. These methods and models characterise the medium and estimate the system performance. Some operate in real (or close to real) time and they may even directly advise the radio operator on a course of action which would improve system performance.

Inspec keywords: HF radio propagation; ionospheric electromagnetic wave propagation

Other keywords: radio propagation; frequency management; service planning; HF sky-wave propagation; high frequency sky-wave propagation; atmosphere; radio system operation; system performance; ionised region; system design; ionospheric prediction; radio signal

Subjects: Ionospheric electromagnetic wave propagation; Radiowave propagation