Path loss
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Path loss: In a communication system, the attenuation undergone by an electromagnetic wave in transit between a transmitter and a receiver.

Note 1: Path loss may be due to many effects such as free-space loss, refraction, reflection, aperture-medium coupling loss, and absorption.

Note 2: Path loss is usually expressed in dB. Synonym path attenuation.

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

The original article can be found at: http://en.wikipedia.org/wiki/Path_loss.
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