According to ITU-R Rec. P.526-2, the diffraction loss L_p (d) can be derived by the received field strength E referred to the free space E₀:

(Eq. 220)

with:

is the normalized radio path between transmitter and receiver

is the normalized antenna height of the transmitter

is the normalized antenna height of the receiver

where:

is a parameter derived from the earth admittance factor K: =1 for > 20 MHz.

is the frequency in MHz

is the equivalent earth radius in km (definition see below)

is the distance in km

is the antenna height above ground in m with =1 or 2 for the transmitter or receiver, respectively

The distance-dependent term is given by the semi-empirical formula:

(Eq. 221)

The antenna height gain is given by the formula set:

(Eq. 222)

for

for

for

for

where is the normalized earth surface admittance factor (see ITU-R Rec. P.526), default value 10e-5:

All frequencies used attenuation due to diffraction have the unit MHz in contrast to the attenuation due to atmosphere where GHz is applied.

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