612 



THE BELL SYSTEM TECHNICAL JOURNAL, MAY 1957 



Effects of Nearby Hills — Particularly on Short Paths 



The experimental results on the effects of hills indicate that the shadow 

 losses increase with the frecjuency and with the roughness of the terrain.^^ 



An empirical summary of the available data is shown on Fig. 11. The 

 roughness of the terrain is represented bj^ the height H shown on the 

 profile at the top of the chart. This height is the difference in elevation 

 between the bottom of the valley and the elevation necessary to obtain 

 line of sight from the transmitting antenna. The right hand scale in Fig. 

 11 indicates the additional loss above that expected over plane earth. 

 Both the median loss and the difference between the median and the 10 

 per cent values are shown. For example, with variations in terrain of 500 

 feet, the estimated median shadow loss at 450 mc is about 20 db and the 



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