Very low frequency the bottom of the ionosphere called the D layer at 60 to 90 km (37 to 56 miles) altitude, which reflects VLF radio waves. The conductive ionosphere and the conductive Earth form a horizontal "duct" a few VLF wavelengths high, which acts as a waveguide confining the waves so they don't escape into space. The waves travel in a zigzag path around the Earth, reflected alternately by the Earth and the ionosphere, in TM (transverse magnetic) mode. VLF waves have very low path attenuation, 2-3 dB per 1000 km, with little of the "fading" experienced at higher frequencies, This is
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