RADIO PROPAGATION FUNDAMENTALS 



605 



tion of three distances: di is the distance to the horizon from the lower 

 antenna, c?2 is the distance to the horizon from the higher antenna, and 

 ds is the distance beyond the hne-of-sight. In other woi'ds, the total dis- 

 tance between antennas, d = di -\- d-i -\- d-i . The distance to the horizon 

 over smooth earth is given by: 



c?i,2 = ■\/2kahi, 2 



(8) 



where /ii.s is the appropriate antenna height and ka is the effective earth's 

 radius. 



The preceding discussion assumes that the earth is a perfectly smooth 

 sphere and the results are critically dependent on a smooth surface and a 

 uniform atmosphere. The modification in these results caused by the 



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