410 PROPAGATION THROUGH THE STANDARD ATMOSPHERE 
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FicureE 37. eh: = eu versus sd = gy. Points eh,sd, lying to right of dotted line corresponding to eh; for a given trans- 
mitter indicate that the points lie in the diffraction region of the transmitter, ord > dz. Diffraction region dielectric earth 
— curve parameter: 20 log A = 20 log A — 20 log h, — 20 log g,. 
the gain is approximately the exponential value 
3k 
= 1A (zen) 
ANNI 
aS a consequence of refraction giving a value k 
greater than 4/3. For k = 12, and sd; = 5, the gain 
would be about 140 db at some point near dz’ = 3dz, 
at heights h; and he such that 
dy! = V2ka (Why + Vie ) 
and such that fz is well within the diffraction region. 
For given transmitter height hy and distance d, the 
effect of increasing k is to lower the lowest lobe 
roughly by the amount by which the line-of-sight 
