INTRODUCTION 



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 1950 1951 1952 



Figure 6.3. Comparison of the monthly median basic transmission loss and refradivity 

 gradient for KIXL-FM, Dallas, Tex., recorded at Austin, Tex. 



The development of prediction techniques is especially difficult in the 

 case of: 



(a) any path with terminals just v/ithin or just beyond the normal 

 horizon, and 



(b) signal enhancements which occur for small percentages of the time. 

 Section 6.2 therefore includes some discussion of propagation charac- 

 teristics on VHF paths for which considerable radio and meteorological 

 data are already available. The results obtained are particularly relevant 

 to an understanding of the large differences observed between median 



