Marconi's law

Marconi's law is an empirical rule that radio transmission range increases roughly with the square root of antenna height, under comparable conditions.

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Radio horizon: The farthest line-of-sight distance between a transmitting antenna and a receiving antenna, limited by Earth’s curvature. Antenna height raises the geometric horizon and helps explain the range increase.
Guglielmo Marconi: An Italian inventor and engineer who developed practical long-distance wireless telegraphy. The empirical rule is named for his work extending wireless range.
Radio link budget: An accounting of gains and losses that predicts received signal power in a radio link. It tests whether added antenna height yields a usable signal at the predicted range.
Friis transmission equation: An equation estimating received power in free space from transmitted power, antenna gains, wavelength, and distance. It relates signal power to distance rather than asserting a height-based range law.
Antenna height: The vertical distance of an antenna above its reference surface, usually ground or sea level. It is the variable whose square root predicts range in Marconi's law.
Wireless telegraphy: The transmission of telegraph signals by radio waves rather than wires. Marconi's law emerged from efforts to extend this technology's operating distance.
Line-of-sight propagation: Radio transmission along a path unobstructed by terrain or structures. Marconi's square-root rule is most intuitive when geometric visibility limits the link.
Longley–Rice model: A terrain-sensitive model for predicting radio signal propagation over irregular ground. It accounts for terrain and propagation conditions omitted from Marconi's empirical rule.
Radio propagation: The transmission of radio waves through space, air, or other materials. The empirical rule summarizes how propagation distance responds to antenna elevation.
Marconi transatlantic transmission: The radio transmission received by Guglielmo Marconi in Newfoundland from Cornwall in December 1901. It exemplified the long-distance communication problem that made antenna height matter.