CARRIER-CURRENT COMMUNICA TION 



(A7 



balance, every part of the line circuit was matched by a similar part 

 in the network circuit. All filters and transformers on the line side 

 of the Inbrid coil were duplicated in the network, and on the San 

 Pedro side a 13-gauge carrier-loaded cable pair was included in the 

 network circuit between the ofifice and the cable hut, and the in- 

 equality ratio transformer and basic network simulating the cable 

 were located at the latter point. In addition to providing a balance 

 within the carrier range, it was necessary at the San Pedro end for 

 the network circuit to balance the cable within the voice-frequency 

 range as a through-line repeater is employed on the voice-frequency 

 circuit. Not only was it necessary to duplicate all parts in the line 



15 XO «5^ 



HUNDREDS OF CYCLES 



Fig. lU 



and network circuits but in addition they were carefully selected 

 and paired so that the two parts associated would have, as nearly as 

 possible, the same electrical characteristics. All wire pairs within 

 the ofifice which appeared in the carrier frequency circuits were indi- 

 vidually shielded by means of a grounded metallic covering. The 

 13-gauge carrier-loaded pairs in the cable joining the hut and the ofifice 

 were also individually shielded by means of a lead foil wrapping. 

 This was done in order to preserve the balance and prevent cross- 

 talk with another system which may be placed on the second cable 

 at some future time. 



Although extreme care was exercised in making the refinements 

 described, the balance was still lower than was desired so that small 



