. Annual report of the Board of Regents of the Smithsonian Institution . Pig. 5.—Circuit; modulationaccomplished by changinginductance of one of oscil-lating circuits. Electrical World and Engineer, October 31, 1905. 186 ANNUAL KEPORT S_MITIiSONIAN INSTITUTION, 1908. several methods have therefore been devised for talking and listeningsimultaneously, which methods can, of course, also be applied to du-plex wireless telegraphy. Among these methods may be mentionedthe commutator method °- and the balance method.^ The former method is fairly well known and consists in rapidlyconnecting alternatel
. Annual report of the Board of Regents of the Smithsonian Institution . Pig. 5.—Circuit; modulationaccomplished by changinginductance of one of oscil-lating circuits. Electrical World and Engineer, October 31, 1905. 186 ANNUAL KEPORT S_MITIiSONIAN INSTITUTION, 1908. several methods have therefore been devised for talking and listeningsimultaneously, which methods can, of course, also be applied to du-plex wireless telegraphy. Among these methods may be mentionedthe commutator method °- and the balance method.^ The former method is fairly well known and consists in rapidlyconnecting alternately the transmitter and receiver. The balancemethod 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. Theapparatus is shown in plate 18, figure Fig. G.—Balance method with phantom aerial P. In order entirely to cut out disturbances in the receiver whilesending, an interference preventer, I P, the elements of which areshown 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 betterwith wireless telephony and telegraphy than with line telephony andtelegraphy, for the reason that the radiation resistance of an antennais absolutely definite and is not affected by the weather, as are linecircuits. 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. Smithsonian Report, 1908.—Fessenden. Plate 16.
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