Essentials
In essence the calculation is based upon the sum of two other calculations.
Link Loss = free space loss + terrain loss.
The LR contribution relates to the derivation of an empirical formula for the terrain loss based
upon terrain profile, resistivity, climatic variability. The vegetation is not explicitly accounted for.
Free Space Loss
The simplest part is the free space loss calculation formulated by Harald T Friis.
Where
Pr = Link loss in db to the receiver.
Gt = Transmitter antenna gain.
Gt = Receiver antenna gain.
&lambda = Wavelength in m.
R = isotropic radios. ie: distance between Tx and Rx in m.
Pt = Polarisation gain.
Polarisation gain
The antennae are generally polarised, vertical, horizontal, circular, elliptical. The miss alighnment of the polarisation will create a loss.
Note: LR take polarisation in the terrain calculation.
Note: Also a parabolic antenna will be polarised, unless driven by a circular waveguide or helix.
Where
PL = The polarisation gain less than 1.
ϕ = The miss alignment angle.