JOURNAL 



OF THE 



WASHINGTON ACADEMY OF SCIENCES 



Vol. V SEPTEMBER 19, 1915 No. 15 



RADIOTELEGRAPHY. — Resistance of radiotelegraphic antennas. 

 L. W. Austin, Naval Radiotelegraphic Laboratory. 



The resistance of a radiotelegraphic antenna may be divided 

 into three parts: first, the ohmic resistance of the wires; second, 

 the so-called radiation resistance; and third, the so-called earth 

 resistances. The first is generally negligible where a sufficient 

 number of wires in parallel is used. The second is derived 

 from the expression for the radiated energy of an antenna, which is 



E = 1607r'^7' 



2^« 



where h represents the height to the center of capacity of the 

 antenna, X the wave length, and /« the current measured at the 



base of the antenna. The expression IGOtt"'— is called the 



A 



radiation resistance, as it takes the same position in the energy 

 equation as that occupied by R in the case of ohmic losses. 

 The expression shows that the radiation resistance falls rapidly 

 as the wave length is increased. 



Up to the present no satisfactory theory of ground resistance 

 has been developed. The experimental curves of antenna 

 resistance, on account of the decreasing radiation resistance, 

 fall rapidly at first, as the wave length is increased, and then, 

 as the wave length is further increased, remain nearly con- 

 stant if the ground conditions are good as in the case of a ship's 



525 



