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BELL SYSTEM TECHNICAL JOURNAL 



culated from the height and distance data and the constants '' of the 

 sea water, assuming ordinary optical reflection from an earth of 5260 

 miles radius. These theoretical curves are adjusted best to fit with 

 the observations, the ordinates for all the curves being the decibels 

 left in the receiver attenuator.^ These results can be summarized 

 briefly as follows: 



At 8000 feet the fit with theory is excellent at both wave-lengths. 

 The grazing distance for this altitude is 137 miles and the entire 



25 30 35 40 45 50 55 

 MILES FROM TRANSMITTER 



60 65 70 75 



Fig. 4— Wave-length — 1.58 meters; Altitude— 8000 feet. 



reception is, as it should be, optical. The " out " curves for the 1.58 

 meter reception show a middle distance roughness which characterizes 

 all the " out " curves for this wave-length. This roughness is due to 

 a minimum in the polar characteristic of the plane which was, unfor- 

 tunately, directed at the transmitter for the first part of the outward 

 flights. 



At 2500 feet the fit with theory is good for the greater part of the 

 optical range for the 4.6 meter wave transmission. Both curves (5 

 and 6) show a definite diffraction effect. 



^ Dielectric constant = 80. 

 Ohms per cm. cube = 20. 



" The set gain was determined together with the average transmitter ammeter 

 readings for each run. With these and the exi)erinienlally deterniined polar char- 

 acteristics of the plane antennas, the curves are corrected to set gains of 100 and 110 

 db respectively for the 4.6 and 1.58 meter receivers and for specified transmitter 

 currents. 



