propagation mode

Radio propagation is a term used to explain how radio waves behave when they are transmitted, or are propagated from one point on the Earth to another.In free space, all electromagnetic waves (radio, light, X-rays, etc) obey the inverse-square law which states that the power density of an electromagnetic wave is proportional to the inverse of the square of "r" (where "r" is the distance [radius] from the source) or:Doubling the distance from a transmitter means that the power density of the radiated wave at that new location is reduced to one-quarter of its previous value.
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The manner in which radio signals travel from a transmitting antenna to a receiving antenna, such as ground wave, sky wave, direct wave, ground reflection, or scatter. (188 )