path loss: In a communication system, the attenuation undergone by an electromagnetic wave in transit between a transmitter and a receiver. Path loss may be due to many effects such as free-space loss, refraction, reflection, aperture-medium coupling loss, and absorption. Path loss is usually expressed in dB.
This can be calculated from the formula
Path loss (in dB) = 20 Log (F)+20 Log (D) +32.5
Where F= frequency in MHz D = distance in Km