Radio Propagation

- Overview

The range of a radio communications link is defined as the farthest distance that the receiver can be from the transmitter and still maintain a sufficiently high signal-to-noise ratio (SNR) for reliable signal reception. The received SNR is degraded by a combination of two factors: beam divergence loss and atmospheric attenuation. Beam divergence loss is caused by the geometric spreading of the electromagnetic field as it travels through space. As the original signal power is spread over a constantly growing area, only a fraction of the transmitted energy reaches a receiving antenna. For an omnidirectional radiating transmitter, which broadcasts its signal as an expanding spherical wave, beam divergence causes the received field strength to decrease by a factor of 1/r², where r is the radius of the circle, or the distance between transmitter and receiver.