512 



BELL SYSTEM TECHNICAL JOURNAL 



The series and bridged phantom 21 -type circuits co-act in the 

 phantom circuit to ampHfy without echoes, the waves traversing the 

 phantom in the same way as the corresponding parts of the side circuits. 



S|S 



^mr^iTM^ 



-SiHy 



^smJ^^^\(m^ 



SiB 



PB 



I — oro^r^t^ow^ 



i-^iJMrRQMr- 



S2B 



SaHy 



S2S 



pw s 



Si w 



S2W 



-/IJM^ 



-.mu — ' 



-vMb- 



L^JM^ 



— OHJF- 



— ^sm^ 



SiE 



S2E 



>PE 



PS 



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PHy 



Fig. 16 — Twin 21 -type phantom group of repeaters. 



Field Trials 



In order to demonstrate the operativeness of the twin 21 -type of 

 repeater and to gain some experience with it, a complete phantom 

 group of repeaters was built, installed at Princeton, N. J., and connected 

 into a phantom group of cable conductors extending from New York 

 to Philadelphia. 



This apparatus functioned in a satisfactory manner despite the fact 

 that certain transformers and other parts specially designed for this 

 work were not available, and it was necessary to make use of some 

 equipment designed for other purposes. 



