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Free-space Loss




Note: Free-space Loss is primarily caused by Beam Divergence , ''i.e.'', signal energy spreading over larger areas at increased distances from the source, and by the Inverse Square Law of Electromagnetic Radiation .

The equation for free-space loss is below where \lambda is the signal wavelength, f is the signal frequency, R is the distance or radius of the signal from the transmitter, and c is the speed of light in the signal transmission medium. Note that the units used should be consistent, e.g., \lambda and R in meters, and c in meters per second.

free\ space\ loss = \left ( rac{4\pi R}{\lambda} ight )^2 = \left ( rac{4\pi R f}{c} ight )^2

Source: from Federal Standard 1037C and from MIL-STD-188