ated by equations 7.73 to 7.77. c=G(Z++Z,+Z1+Z2)-R(Z)-R(Z,)-20 (7.73) (7.74) =0.058Z-10logZ (7.75) Z 2000:R(Z)=0.058Z-33 (7.76) Z > 2000:R(Z)=G(Z) = (7.77) The calculation does not allow for the roughness of the terrain and as a result the loss of signal on the path is usually overestimated. A better result is obtained from an interpola- tion between this and the knife edge calculation. The form of interpolation can be deter- mined by obtaining a best fit with a set of measured data. In the United Kingdom, it was found that an averaging of losses, expressed in decibels, gave good results. Approximating a Single Hill to a Wedge Shape On a land path with one diffraction edge, a prediction can be made by assuming a wedge- shaped profile. This wedge has its peak at the diffraction edge and surfaces that clear the terrain on both sides of the profile, as shown in Figure 7.22, with an angle between the horizon lines of O. Fig. 7.22 Geometry for a wedge diffraction calculation. Chapter 7 Electromagnetic Waves The angles between the wedge surfaces and these horizon lines are Q and . The dif- fraction loss is given by equations 7.78 to 7.83, where F is given in equations 7.24. (7.78) V1=0u (7.79) U2=(A+2Q)u (7.80) U3=(A+24)u (7.81) (7.82) (7.83) The simulated reflection coefficients Pr and Pt depend on how the actual profile deviates from the wedge surface, and the values should range from about -0.9 for a very smooth wedge-like profile to about -0.1 for a rough, "peaky" edge. Attenuation by Buildings and Trees Significant attenuation is caused by buildings and trees. For television reception with rooftop antennas (about 10 m above ground level), the attenuation can be obtained by reasonably simple methods without specific details of buildings and trees. A clutter loss ACL is given approximately by Table 7.1. However, today the ability to predict for lower antennas has become increasingly important. This is the case for receivers in cars and for the mobile phone industry. For predictions to lower receivers, it is necessar