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N CLIMATOLOGY 



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Figure 4.52. Geometry of the shadow zone loss region. 



For the maximum midspring ducting conditions (fig. 4.49) and the 

 100-m-thick duct, recalling do = 83 km, the antenna is to be located 



90 



83 = 7 km 



beyond the onset point of the shadow zones. For the 200-m duct, the 

 antenna is located 



90 - 72 = 18 km 



beyond point A of figure 4.52. From figure 4.44, the half-length traveled 

 by a ray in a 100-m duct under maximum midspring ducting conditions 

 is 30.5 km. Thus, as described above, the distance used in figure 4.49 

 to find h is 



30.5 - 7.0 = 23.5 km 



because at 25 km the ray is still sloping dov/nward and hence is on the 

 lefthand side of point B of figure 4.52. From figure 4.44, dht = 43 km 

 for a 200-m duct; therefore, the distance used in figure 4.49 is 



43 



18 = 25 km. 



Similarly, utilizing figures 4.45 and 4.46 for mean ducting and minimum 

 ducting conditions for a 100-m and 200-m duct: 



Figure 4.50 distance to be used for the 100-m duct = 45 km, 

 Figure 4.50 distance to be used for the 200-m duct = 56 km, 

 Figure 4.51 distance to be used for the 100-m duct ^ 191 km. 

 Figure 4.51 distance to be used for the 200-m duct = 262 km. 



