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ANNUAL KEPORT S_MITIiSONIAN INSTITUTION, 1908. 



several methods have therefore been devised for talking and listening 

 simultaneously, which methods can, of course, also be applied to du- 

 plex wireless telegraphy. Among these methods may be mentioned 

 the commutator method °- and the balance method.^ 



The former method is fairly well known and consists in rapidly 

 connecting alternately the transmitter and receiver. The balance 

 method consists in using a phantom aerial as shown in figure 6, 

 where P is a phantom aerial, the circuit having such capacity in- 

 ductance and resistance as to balance the radiating antenna. The 

 apparatus is shown in plate 18, figure 1. 



Fig. G. — Balance method with phantom aerial P. 



In order entirely to cut out disturbances in the receiver while 

 sending, an interference preventer, I P, the elements of which are 

 shown in plate 18, figure 2 and plate 19, figure 1, is used in the receiv- 

 ing circuit. 



It may be here mentioned that balance methods work much better 

 with wireless telephony and telegraphy than with line telephony and 

 telegraphy, for the reason that the radiation resistance of an antenna 

 is absolutely definite and is not affected by the weather, as are line 

 circuits. Consequently, the balance can be made very sharp and 



a United States application, No. 350199, December 31, 1906. 

 » United States application, No. 366528, April 5, 1907. 



