ULTRA-SHORT-WAVE TRANSAilSSION 



509 



a boundary with an irregular surface is carried past the reflection zone 

 by the normal motion of the atmosphere.) A further increase in 

 transmitter distance and the "5" or residual curve drops out of the 

 picture leaving only the "A'' curve and, presumably, fairly steady 

 signal amplitude conditions. The location of these zones of undis- 

 turbed and disturbed signal will vary from day to day as: (1) the 

 reflection coeflacient and height of the layer change, (2) the effective 

 radius of the earth changes. The effect of the height of the layer is 

 shown in Fig. 16. 



OQ 20 



10 



-10 



-20 



60 80 100 120 140 160 



DISTANCE FROM TRANSMITTER IN KILOMETERS 



180 



Fig. 15 — Calculated curves for air boundary reflected and earth refracted- 

 diffracted radiation components, in both vertical and horizontal polarization. 

 Short doublet antennas, 1 kw. power radiated, wave-length 4.7 meters, o- = 5 X 10~^^ 

 (E.M.U.) and e = 80 for sea water. Height of transmitter, antenna 42 meters, of 

 receiver antenna 5 meters, air boundary height 1500 meters, effective radius of earth 

 8500 kilometers. 



Since the major lobe of the polar characteristic of any simple an- 

 tenna, such as ours, is directed forward and away from the earth, the 

 signal intensity at the reflecting boundary surface will be comparatively 

 high and will, in some measure, make up for a small reflection coeffi- 

 cient. For longer waves, such as broadcast waves, the high level of the 

 " 5 " curve will move the disturbed zone so far out that the low residual 

 signal level and the Kennelley-Heaviside layer reflections will conceal 



