638 THE BELL SYSTEM TECHNICAL JOURNAL, MAY 1957 



Thus if 400 nics and 4,000 mcs wen; propagat(>(l <)\er the same path, the 

 antenna gains being identical for the two systems, then, on the average, 

 one would expect the received power relative to the free space value at 

 400 mcs to be 10 db higher than that at 4,000 mcs because of the charac- 

 teristics of the troposphere. 



Case 11. Equal antenna apertures for the two wavelengths. 

 For this case, ai/ao = X1/X2 and (14) reduces to 



Rl 



P 



(18) 



Experimental data for this case was obtained on the 150 nautical mile 

 test circuit between St. Anthony and Gander in Newfoundland.^ The 

 antennas for both wavelengths were paraboloids 8.5 meters in diameter. 

 Simultaneous transmission tests at Xi = 0.074 m and X2 = 0.6 m were 

 conducted for a full year. For this circuit, 



= 0.94° (4/3 earth radius) 



a, = 66 ^^ = 0.575° 



8.0 



0.6 



aa = t)D — — 



8.5 



66 ^ = 4.65° 



Using these values in (18), we get for the ratio of received powers, 



Pri/Pr2 = 1.01 

 For antennas of equal aperture in free space, 



Pri/Pr2 = (X2/X1)' = 65.5 



Therefore, 



Pr\/Pr2 (Beyond Horizon) ^ J_ ^ - 18 1 db 



Pri^Pr2 (Free Space) 65 



The Summarj'^ of Results, Sections 1 and 2 on page 1316 of Reference 8, 

 gives — 17 db for this ratio. The agreement between calculated and meas- 

 ured values is very good. 



