Dictionary:Line of sight

{{#category_index:L|line of sight}} The straight-line distance from an object to an observer. High-frequency (short-wavelength) radio waves travel such raypaths so that the curvature of the Earth limits the range that can be achieved. Line-of-sight range R is given in terms of the height of transmitting and receiving antennas h_t and h_r:

$R=k(h_{t}^{\frac {1}{2}}+h_{r}^{\frac {1}{2}})$.

The constant k is 1.22 nautical miles when h is given in feet, 4.08 km when in meters. Refraction increases the effective range of radio waves depending on their wavelength; the sensitivity of the detecting system also affects the range; see radio earth.