ELEVATED LAYERS ON THE ILLINOIS PATH 



251 



0.5 I 5 10 30 50 70 90 95 99 99.5 99.9 



PERCENT OF TIME VALUE EXCEEDS ORDINATE 



0.1 0.5 I 5 10 30 50 70 90 95 99 915 99.9 



PERCENT OF TIME VALUE EXCEEDS ORDINATE 



Figure 6.13. Distribution of hourly median field strengths with different radiosonde 



profile conditions. 



not only as a feature occasionally producing high field strengths, but also 

 as a mechanism which, in less intense form, partly determines the strength 

 of the weaker fields observed for large percentages of the time. 



6.2.5. The Effect of Elevated Layers on the Illinois Path 



The influence of elevated layers of VHF transmission beyond the 

 horizon has been studied by several workers [21, 22, 28, 34, 35, 36, 37]. 

 However, few investigations have contained any detailed comparisons of 

 theory and experimental results. The following analysis presents such 

 a comparison, using simple models of the elevated layer for the four 

 Illinois paths. 



