water, it is possible for surface reflections to contribute to ionospheric propagation, with a consequent reduction in losses. The following method does not attempt to estimate this effect. 5.1 Derivation of foEs For a given time, set the percentage-time values used for interpolation or extrapolation. and p% p1 according to Table 1. p2, 1 Conditions for setting and p1 p2 time p% p1 p2 < 1% 0.1% 1% p 1% 10% 1% 10% ≤ p ≤ 10% < 10% 50% p For a given location, obtain and from the maps of exceeded for and time foEs1 foEs2 foEs p1 p2% respectively. Calculate exceeded for p% time using: foEs (MHz) (7) 5.2 Horizon elevation angles Additional attenuation can be caused by terrain obstruction at either terminal. For each terminals, find the terrain along the great-circle path from the terminal towards the other terminal with the highest elevation angle above the local horizontal as viewed from the terminal. The elevation angle of a given terrain point is given by: (radians) (8) where: distance to terrain point, km; dp: : height of terrain point, m above sea level; hp : height of terminal antenna, m above sea level. ha Perform this calculation twice, once for each terminal, to obtain the following: elevation angle to horizon at 1st, 2nd terminal, radians; εha,b: distance to horizon at 1st, 2nd terminal, km. dha,b: 5.3 Calculation for 1-hop propagation Obtain as calculated by equation (7) for the mid-point of the path to obtain the ionospheric loss foEs for one hop, using equation (3). Γ1, Calculate the slope path length: (km) (9) Free-space loss can now be calculated for the slope distance: (dB) (10) The ray take-off angle above the local horizontal at both terminals for 1 hop is given by:
water, it is possible for surface reflections to contribute to ionospheric propagation, with a consequent reduction in losses. The following method does not attempt to estimate this effect. 5.1 Derivation of foEs For a given p% time, set the percentage-time values used for interpolation or extrapolation. p1 and p2, according to Table 1. 1 Conditions for setting p1 and p2 p% time p1 p2 p < 1% 0.1% 1% 1% ≤ p ≤ 10% 1% 10% 10% < p 10% 50% For a given location, obtain foEs1 and foEs2 from the maps of foEs exceeded for p1 and p2% time respectively. Calculate foEs exceeded for p% time using: (MHz) (7) 5.2 Horizon elevation angles Additional attenuation can be caused by terrain obstruction at either terminal. For each terminals, find the terrain along the great-circle path from the terminal towards the other terminal with the highest elevation angle above the local horizontal as viewed from the terminal. The elevation angle of a given terrain point is given by: (radians) (8) where: dp: distance to terrain point, km; hp : height of terrain point, m above sea level; ha : height of terminal antenna, m above sea level. Perform this calculation twice, once for each terminal, to obtain the following: εha,b: elevation angle to horizon at 1st, 2nd terminal, radians; dha,b: distance to horizon at 1st, 2nd terminal, km. 5.3 Calculation for 1-hop propagation Obtain foEs as calculated by equation (7) for the mid-point of the path to obtain the ionospheric loss for one hop, Γ1, using equation (3). Calculate the slope path length: (km) (9) Free-space loss can now be calculated for the slope distance: (dB) (10) The ray take-off angle above the local horizontal at both terminals for 1 hop is given by:
R-REC-P.534-5-201202-I!!MSW-E.docx