142 



BELL SYSTEM TECHNICAL JOURNAL 



Since the altitude of the transmitting antenna was small compared 

 with that of the airplane, we would expect, on the basis of the optical 

 picture, that the field received would depend on the distance and the 

 angle of elevation of the plane as seen at the transmitter. In the 

 figure, the distance has been eliminated by recourse to the inverse 

 distance law, which applies to the separate component waves. The 

 result has been plotted for two elevations with varying distance. 

 The peaks and troughs of the Lloyd's fringes are fairly well indi- 

 cated. '^ 



While little weight can be given to the absolute values as measured 

 in the airplane,^^ it is of interest to estimate the conductivity of the 



</)40 



^30 



p20 

 ^10 



10 20 



DISTANCE— KILOMETERS 



Fig. 12 — Theoretical characteristics for transmission over salt water (o- = 1.5 

 X 10"^!^ e.m.u., € = 80 e.s.u.) on the basis of simple optical reflection. Upper 

 curve: 36.4 mc. Lower curve: 80 mc. 



water from the relative values. Fig. 11-B shows the theoretical 

 location of maxima, minima and their ratio as functions of the con- 

 ductivity of sea water. Four experimental values have been plotted. 

 Their average indicates a conductivity of 1.7 X 10"^^ This, at least, 

 has the correct order of magnitude, but the experimental data are too 

 inaccurate to justify much faith in the numerical value otherwise. 

 The important point is that the field pattern is qualitatively what 

 would be expected. The theoretical characteristic for this value is 

 also plotted in Fig. 11-^4. 



Turning now to the more accurate data taken on the ground (already 

 presented in connection with Fig. 3), theoretical curves have been 

 fitted to the data in Fig. 12. In the experiment, the antennas w^ere 



1^ Similar fringes were obtained over land by Englund, Crawford and Mumford. 



18 Because of the irregular shape of the airplane, the orientation with respect to 

 the line of sight affects the gain of the receiving antenna. Each oithe two curves 

 has been plotted from data taken with approximately constant orientation of the 

 airplane. 



