142 



ANNUAL. EEPOET SMITHSONIAN INSTITUTION, 1911. 



purpose the twisted-pair telephone line was equipped with a com- 

 plete standard local battery telephone set, as installed for commercial 

 practice, and in addition one of the wires of the pair was equipped as 

 in figure 1, the circuit being shown diagrammatically in figure 2. 

 This particular arrangement was employed in this experiment for the 

 reason that it was desired to have the battery telephone operate 

 on its usual circuit with the introduction of ground connections 



at the ends of the 



r-®- 



LABORATORY 



OF 

 SIGNAL CORPS 



j^ Unu 



Fig. 1. 



line for the super- 

 position of the high- 

 frequency circuit. 

 When such ground 

 connections were 

 introduced directly 

 without tuning ele- 

 ments therein the 

 metallic circuit ex- 

 perienced the usual 

 disturbances found 

 under city conditions, but the metallic circuit could be reduced to 

 silence again by introducing in the ground connections the necessary 

 tuning elements of magnitudes suited to wireless telegraphy. 



Next, the twisted-pair telephone line was equipped with a com- 

 plete standard local battery telephone set, as installed for commercial 

 practice, with the exception that the local battery circuit of the 

 transmitter t e 1 e - 



~ " " " CT> 



"7«l 



phone set was 

 opened and a few 

 turns of coarse wire 

 inserted in series 

 with the two dry 

 cells which are nor- 

 mally used, as shown 

 in figure 3. Induc- 

 tively connected 

 with this coil was 

 the armature circuit 

 of the generator. A hot wire milliainmeter was placed in the line 

 circuit to indicate the magnitude of the high-frequency current which 

 was flowing on the line. With this arrangement tests were made to 

 determine whether or not there were any effects upon the transmission 

 of speech, due to superimposing high-frequency currents upon the 

 battery telephone sets. With an operator at each end of the line, 

 using the equipment in the regular commercial way, the direct-current 

 voltage and the alternating-current voltage in series with it in the 



Fig. 2. 



