336 AUSTIN: COIL ANTENNAS 



L 



height by NH2 tt t^ cos 6 where NH is the height of the coil times 



the number of turns, and we find for a 



Coil Sending and Antenna Receiving 



IsN,H, Ls h, 



Ir = 120T 73 — ^^ ^ ^^^ ^^ P" 



IsN,H,LA 



In the same way for an 



Antenna Sending and Coil Receiving 



(2) 



Ir = 2369 j^2J^ cos 0, (3) 



and for 



Coil Sending and Coil Receiving^ 



IsNsHsLJV,H,L, 

 I^ = 14880 3JT-, cos 9^ cos 0y. (4) 



The effective height h of an ordinary antenna equivalent to 

 any coil NH may be expressed if ^ = 0, by 



NHL area X turns 

 h = 2Tr — ^ = 2 TT ^^^ • (5) 



The equations show that, other things being equal, if an antenna 

 be used, both for sending and receiving, the received current falls 

 off as the wave length, while if one coil be used, it falls off as the 

 square of the wave length, and with two coils as the cube of the 

 wave length. 



The value of the constant in the equation for a sending coil 

 requires some consideration. The value given assumes that as 

 the radiated field grounds itself, it takes the form of a field 

 formed by the coil and its image as in the case of an antenna. 

 This is probably true, at least for a coil whose dimensions are 

 large compared with its distance from the ground. In the case 

 of reception, this question does not enter. 



^ Dr. Dellinger, of the Bureau of Standards, has published coil formulas in 

 practical units with slightly different constants in a confidential report for the 

 Signal Corps, Radio Transmission Formulas, July 191 7. 



