AUSTIN: coil, ANTENNAS 335 



RADIOTELEGRAPHY.- — Quantitative experiments with coil an- 

 tennas in radiotelegraphy. L. W. Austin, U. S. Naval 

 Radio Laboratory. 



The use of large inductance coils for sending, receiving, and 

 direction determination was first proposed by the late Professor 

 Braun,' who carried out experiments at Strassburg on signals 

 from the Eiffel Tower and gave the general theory of a coil used 

 as an antenna.^ 



Received current measurements, such as the laboratory made 



some years ago for the verification of the theory of transmission 



between ordinary antennas, have now been made for closed 



coils. According to the theory, a rectangular vertical coil of 



A^ turns, height H and length L, is equivalent to two vertical 



antennas of effective height NH at a distance apart L, with their 



respective currents in opposite phase. Taking into account 



the phase difference due to the difference in path, either in sending 



to a point p, or in receiving from p, the effect will be the same 



as that of one antenna of height NH multiplied by the phase 



L 

 difference 2 tt t^ cos d where 6 is the angle between the plane of 



A 



the coil and the direction of ^.^ 



Now, the expression for the received current in a receiving 

 antenna, with an antenna sending sustained waves, is, disre- 

 garding absorption:"^ 



S S Y / \ 



where I^ is the sending antenna current, h^ the effective height 

 of the sending antenna, h,^ that of the receiving antenna, X the 

 wave length, d the distance, and i? the receiving antenna resis- 

 tance, expressed in amperes, ohms, and meters. If either or 

 both of the antennas is replaced by a coil, we must replace its 



* Braun, F. Jahrb. Draht. Telegr. 8: 1-132. 1914. 



^ Mr. KoivSTER, of the Bureau of Standards, has developed an excellent direction 

 finder on this principle. 



' Zenneck. Wireless Telegraphy. 1915. p. 234 and note 307, p. 425. 



* ZennEck. Wireless Telegraphy. 1915. p. 248; Bur. Stand. Bull. 11: 70. 

 1914- 



