Dead zone
A radio hole / radio shadow is a spatial area in which a connection between a transmitter and a receiver is not possible. We speak of dead spots in radio and television reception , in mobile communications when the mobile phone is outside the range of broadcasting stations, in positioning via satellite, and in amateur radio and professional radio in aviation and shipping.
Dead spots occur behind obstacles (unfavorable geographical location) or through electromagnetic interference , but also in buildings, tunnels or parking garages with navigation devices in cars. Due to the quasi-optical propagation of the radio waves or due to excessive interference, a useful signal can no longer be received at these points.
In the case of terrestrial radiation, the shadowing is heavily dependent on the frequency used. In principle, the lower its frequency, the better a radio wave is bent. In the medium wave range it can follow the curvature of the earth, in the VHF range it can be bent at edges and in the UHF range it can be stopped by a few damp leaves. See path loss .
In the case of terrestrial broadcasting of radio and television signals, converters or filler transmitters are often used to avoid dead spots if there is insufficient local transmitter coverage .
