MULTIPLEX TELEPHONY AND TELEGRAPHY SQUIER. 



143 



daK 



primary circuit of the transmitter were varied individually and rela- 

 tively in a variety of ways, with the striking result that just at the 

 point where the direct-current voltage was decreased, so that no 

 sounds were received, the line became absolutely silent, although the 

 alternating voltage in the circuit was at its largest value, or, again, 

 speech would reappear at the receiving station at the moment when 

 sufficient direct-current voltage was introduced to produce it, and the 

 simultaneous presence of both the maximum direct voltage and 

 maximum high-frequency voltage in a circuit produced exactty the 

 same result as the 

 maximum direct-cur- ^ H_j^ 

 rent voltage did alone. 

 When, however, the 

 high-frequency cur- 

 rent in the local circuit 

 was forced to a point 

 which caused "burn- 

 ing" in the transmit- 

 ter itself, then, and 

 then only, did the 

 high-frequency cur- 

 rent in any way inter- 

 fere with the trans- 

 mission. 



By transferring this 

 coil from the local 

 circuit of the tele- 

 phone set directly into 

 the line itself, so that 

 the high-frequency 

 oscillations would be superimposed upon the line beyond the iron- 

 cored induction coil of the telephone transmitter, it was not possible 

 to detect the presence or absence of high-frequency currents. 



As a test under severest conditions the effect was noted upon 

 speech received at the same station at which the high-frequency 

 current is being impressed, for here are the attenuated telephonic 

 currents at the receiving end of the telephone line, on which is super- 

 imposed a high-frequency current of vastly greater magnitude at 

 the same point. No effects of any kind could be detected under 

 these conditions. From the above experiments it appears that in 

 any attempt at multiplex telephony by means of electric waves of 

 ultra sound frequencies superimposed upon the minute telephonic 

 currents employed in battery transmission there is nothing to fear 

 from disturbances of such currents upon the operation of the ordinary 

 battery equipment. 



Fig. 3. 



