SURVEY OF PROPAGATION 



9 



t^'pe (3) are given. These illustrate the effects of 

 frequencj^, polarization, and transmitter height. 



A comparison of Figures 9 and 10 shows the effect 

 of frequency. As the frequency increases, the lobes 

 become more numerous, narrower, and lower. 

 Another effect is exhibited along the surface. For 

 the higher frequency the corresponding decibel lines 

 come in closer to the transmitter. This illustrates the 

 fact that for the higher frequency the shadow effect 

 is more pronounced along the surface of the earth. 



A comparison of Figures 10 and 11 shows that 

 for horizontal polarization the nulls are deeper but 

 the lobes extend out farther. Along the line of sight, 

 vertical polarization gives the higher field strength, 

 while well within the diffraction region the field 



strength is about the same. The last observation 

 holds for all frequencies greater than 300 mc, the 

 greater the frequency the less difference in the 

 diffraction region between the two polarizations. 



A comparison of Figures 9 and 12 shows the effect 

 of the height of the transmitting antenna. As the 

 antenna height is increased, the lobes are narrower 

 and depressed toward the horizon. The range is 

 improved. However, there are broad nulls for the 

 higher antenna in which detection will fail. Below 

 the horizon, the corresponding decibel contours are 

 pushed to the right so that point-to-point com- 

 munication is improved. It should be observed that 

 the effect of height upon the lobe structure is similar 

 to that of frequency. 



Kilometers 



Frequency lOOMc 

 Horizontal Polarization 

 Antenno Height 9.14 meters 

 l< = 4/3 



Figure 9. Contours of constant radio gain factor for horizontal polarization on 100 mc over sea water. 



Kilometers 



Frequency 3000 Mc 

 Horizontal Polarization 

 Antenno Height Smeters 

 K=4/3 



Figure 10. Contours of constant radio gain factor for horizontal polarization on 3000 mc over sea water. 



