AP7 – 97 – Step 1: The receiving earth station may be operating with any satellite in the geostationary orbit above a minimum elevation angle, min, contained in Table 9. The maximum difference in longitude (b (degrees)) between the receiving earth station and its associated space station occurs at this minimum elevation angle, min, and is given by: cos(ζ)cos(ε)sin εarcsin arccos K min min b (103) where: : latitude of the receiving earth station, which is assumed to be the same as the transmitting earth station K: ratio of the radius of the satellite orbit to the radius of the Earth, equal to 6.62. Step 2: For each azimuth, , at the transmitting earth station: – determine the azimuth αr from the receiving earth station to the transmitting earth station: r = 180 for < 180 r = – 180 for 180 – for each azimuth r, determine the minimum angular separation, (r), between the receiving earth station main beam axis and the horizon at this azimuth using Case 1 in § 2 of Annex 3. For this evaluation, (r) is the minimum value of (r, 0, δ0), where the values of δ0 are between −δb and +δb in steps of 1° or less, making sure to include the end points. The minimum angular separation, φ(r), may be used with the gain pattern in § 3 of Annex 3 to determine the horizon gain for this azimuth, , unless a different gain pattern is referenced in Table 9. Figure 8 shows plots of the minimum angular separation between the horizon at zero degrees elevation on an azimuth r and a satellite on the geostationary orbit at an elevation above 3°. Plots are shown for a set of values of the station latitude, ζ, which is assumed to be the same for both transmitting and receiving earth stations. Figure 8 also provides a scale showing the corresponding azimuth, , of the transmitting earth station. Further information and an example may be found in the most recent version of Recommendation ITU-R SM.1448.