NVIS

NVIS Propagation

- overview, article, tutorial about NVIS, Near Vertical Incidence Skywave propagation used for radio communications and radio broadcasting.

NVIS, or Near Vertical Incidence Skywave propagation is a form of ionospheric radio propagation that can be used where radio communications links are needed to cover short distances. NVIS is particularly useful where radio communications coverage is required in regions where the ground is mountainous or rough because other modes relying on more direct coverage have significant areas where the radio signal is masked or shadowed. If MF or HF radio communications were used, the ground wave would be attenuated by the hills and mountains, and similarly line of sight radio communications using VHF or above would not be possible. Using Near Vertical Incidence Sky Wave (NVIS) it is possible to have a signal with a high angle of elevation that is not shielded by the terrain.

In view of this, NVIS is particularly suited to professional radio communications applications in geographical regions that are poorly served by land lines or line of sight repeaters, and it can provide a very useful and cost effective alternative to satellite links. It also has advantages over VHF radio in many applications for built up or forested regions as the buildings and trees introduce very significant levels of loss making line of sight VHF radio communications links virtually unworkable in many instances.