: straight-line distance between the source and points. s Note that, for = 2 and zero reflection coefficients, this should give the same results as the knife n edge diffraction loss curve shown in Fig 9. A MathCAD version of the UTD formulation is available from the Radiocommunication Bureau. 7 Guide to propagation by diffraction A general guide for the evaluation of diffraction loss corresponding to § 3 and 4 is shown in Fig 17. This flow chart summarizes the procedure to be adopted in each case. FIGURE 17 Guide to propagation by diffraction 1 1 Calculation of cylinder parameters The following procedure can be used to calculate the cylinder parameters illustrated in Figs 8c) and 14 for each of the terrain obstructions. Self-consistent are used, and all angles are in radians. The approximations used are valid for radio paths which are within about 5º of horizontal. 1 Diffraction angle and position of vertex Although not used directly as cylinder parameters, both the diffraction over the cylinder and the position of the vertex are required. The diffraction angle over the obstacle is given by: = + + (90) w z e where and are the angular elevations of points and above the local horizontal as viewed from x y w z points and respectively, given by: w z (91) (92) and is the subtended by the great-circle distance between points and given by: w z e (93) The distance of the vertex from point is calculated according to whether the obstruction is w represented by a single profile sample or by more than one. For a single-point obstruction:
s : straight-line distance between the source and points. Note that, for n = 2 and zero reflection coefficients, this should give the same results as the knife edge diffraction loss curve shown in Fig 9. A MathCAD version of the UTD formulation is available from the Radiocommunication Bureau. 7 Guide to propagation by diffraction A general guide for the evaluation of diffraction loss corresponding to § 3 and 4 is shown in Fig 17. This flow chart summarizes the procedure to be adopted in each case. FIGURE 17 Guide to propagation by diffraction 1 1 Calculation of cylinder parameters The following procedure can be used to calculate the cylinder parameters illustrated in Figs 8c) and 14 for each of the terrain obstructions. Self-consistent are used, and all angles are in radians. The approximations used are valid for radio paths which are within about 5º of horizontal. 1 Diffraction angle and position of vertex Although not used directly as cylinder parameters, both the diffraction over the cylinder and the position of the vertex are required. The diffraction angle over the obstacle is given by: = w + z + e (90) where w and z are the angular elevations of points x and y above the local horizontal as viewed from points w and z respectively, given by: (91) (92) and e is the subtended by the great-circle distance between points w and z given by: (93) The distance of the vertex from point w is calculated according to whether the obstruction is represented by a single profile sample or by more than one. For a single-point obstruction: