Radio atmospheric In the case of the ionospheric D-layer, it depends, in addition, on time of day, season, latitude, and the geomagnetic field in a complicated manner. VLF propagation within the Earth–ionosphere waveguide can be described by ray theory and by wave theory. When distances are less than about 500 km (depending on frequency), then ray theory is appropriate. The ground wave and the first hop (or sky) wave reflected at the ionospheric D layer interfere with each other. At distances greater than about 500 km, sky waves reflected several times at the ionosphere must be added. Therefore, mode theory is here
Coast earth station Earth station (article 1.63) Coast earth station Coast earth station, also called the coast earth radio station is – according to "article 1.76" of the International Telecommunication Union´s (ITU) ITU Radio Regulations (RR) – defined as «"An earth station in the fixed-satellite service or, in some cases, in the maritime mobile-satellite service, located at a specified fixed point on land to provide a feeder link for the maritime mobile-satellite service".» Each "radio station" shall be classified by the "service" in which it operates permanently or temporarily. In accordance with "ITU Radio Regulations" (article 1) this type of "radio station" might