Ground Wave Propagation

Mechanism. In ground-wave (or surface-wave) propagation, the radiated wave travels close to and essentially along the Earth's surface, its path bending very slightly to follow the curvature of the ground rather than continuing in a perfectly straight line out into space -- guided partly by diffraction around the curved, conducting Earth. This mode does not depend on the ionosphere at all.

Frequency range and why it is limited. Ground-wave propagation works well only for comparatively low frequencies -- up to roughly a couple of megahertz (the low- and medium-frequency bands), which is exactly the band used for local AM radio broadcasting. The reason it is confined to this range is that the conducting ground itself progressively absorbs the wave's energy as the wave travels along it, and this absorption becomes markedly stronger as the frequency rises; at higher frequencies the ground wave is attenuated so quickly that it becomes use …