The band normally used for Aeronautical Mobile Service (AMS) voice communication is defined between 118.000 and 136.975 MHz.
The Aeronautical Mobile Service refers to VHF and HF voice communication. VHF is amplitude modulated direct (line of sight) waves - practically straight-line propagation. Therefore, the VHF propagation characteristics are ideal for short-distance terrestrial communication. When, due to shadowing (e.g. by a hill), VHF communication is not possible, it is still possible to communicate using the upper part of the HF band where the surface wave is of little use.
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