12 AUSTIN! RESISTANCE OF ANTENNAS 



Curve A is the Bureau of Standards, B the U. S. S. Dolphin 

 and C the Washington Navy Yard. In curves B and C the resist- 

 ance rises gradually as observed by Fischer but the rise is much 

 slower than in his curves. The height of the flat-top antenna of 

 the Dolphin is approximately 90 feet above the water, while that 

 of the Washington Navy Yard is 150 feet. The Navy Yard has 

 practically a water ground the station being but a few feet from 

 the river which is moderately salt at this point. The fundamen- 

 tal of the Dolphin's antenna is 315 meters and its capacity is 

 0.0073 microfarad. The fundamental of the Navy Yard antenna 

 is aboiit 1000 meters and the capacity is 0.0036. The radiation 

 resistance for these two antennas calculated according to the 

 equation. 2 



R r = 1600 ft 2 /X 2 



is shown in the dotted curves B' , C. It is seen that the observed 

 curves for the shorter wave lengths follow with a considerable 

 degree of approximation the curvature of the calculated radiation 

 resistances although the observed curves lie somewhat higher, 

 while beyond the minimum the two curves lie far apart. We 

 have here an indication of two factors in the resistance; one 

 decreasing as the square of the wave length, while the other 

 increases nearly directly as the wave length. It seems to me 

 probable that the portion of the resistance which increases as the 

 wave length is ground resistance, or more properly earth current 

 resistance. * 



The resistance of the Bureau of Standards antenna is shown in 

 curve A. This antenna is an 8-wire harp, 180 feet high at top 

 and 60 feet high at bottom. This makes the center of capacity 

 120 feet from the earth. The natural period is 425 meters and 

 the capacity 0.0012 microfarad. The ground wires are con- 

 nected to the water pipes of the laboratory. It is seen that the 

 minimum ground resistance is much higher than in the case of the 

 Dolphin and Navy Yard and that the straight portion of the curve 

 slopes more steeply upward than was the case in the other two 

 antennas measured. It has been observed that the steepness of 



* R. Ruedenberg, Ann. d. Phys., 25: 446. 1908. 



