Sub-model 2. Anomalous propagation
Use the method given in Appendix D to calculate basic transmission loss not exceeded for p% time due to anomalous propagation, Lbm2:
dB (4.2.1)
where Lba is given by equation (D.8.1) and Agsur, the total gaseous attenuation for a surface path, appears in Table 3.1.
Sub-model 3. Troposcatter propagation
Use the method given in Appendix E to calculate the troposcatter basic transmission loss Lbs as given by equation (E.17).
Calculate the attenuation A2 exceeded for q% time over the troposcatter scatter path.
Perform the preliminary rain/sleet calculations in Appendix C, § C.2 for the transmitter to common-volume path segment with the following inputs:
degrees (4.3.1a)
degrees (4.3.1b)
masl (4.3.1c)
masl (4.3.1d)
km (4.3.1e)
Save the value of Fwvr calculated in § C.2 and call it Fwvrtx:
Calculate the precipitation fade for the transmitter to common-volume path segment using:
dB (4.3.2)
Perform the preliminary rain/sleet calculations in § C.2 for the receiver to common‑volume path segment with the following inputs:
degrees (4.3.3a)
degrees (4.3.3b)
masl (4.3.3c)
masl (4.3.3d)
km (4.3.3e)
Save the value of Fwvr calculated in § C.2 and call it Fwvrrx:
Calculate the precipitation fade for the receiver to common-volume path segment using:
dB (4.3.4)
For both path segments Aiter(q) is the iterative function described in Appendix I.
In Appendix I the function Aiter(q) uses a function Qiter(A) where A takes trial values. Function Qiter(A) is defined for troposcatter path segments by:
(4.3.5)
where Qcaftropo(A) is defined in Appendix B, § B.5, and function Qrain(A) is defined in § C.3. Q0ra is as calculated in the preceding preliminary calculations in § C.2.
A2 is now given by:
dB (4.3.6)
Use the method given in Appendix F, § F.3, to calculate the gaseous attenuations due to oxygen, and for water vapour under both non-rain and rain conditions, for a troposcatter path. This will give values to Aos, Aws and Awrs as calculated by equations (F.3.3a) to (F.3.3c).
The total gaseous attenuation under non-rain conditions is given by:
dB (4.3.7)
Calculate the sub-model 3 basic transmission loss not exceeded for p% time:
dB (4.3.8)
where Fwvrtx and Fwvrrx are the saved values for the transmitter and receiver path segments as described following equations (4.3.1e) and (4.3.3e).
4.4 Sub-model 4: Sporadic-E
Ionospheric propagation by sporadic-E may be significant for long paths and low frequencies.
Use the method in Appendix G to calculate basic transmission loss not exceeded for p% time due to sporadic-E scatter, Lbm4:
dB (4.4.1)
where Lbe is given by equation (G.4.1). Note that at higher frequencies and/or for short paths, Lbe may be very larger.