A CARRIER TELEPHONE SYSTEM FOR TOLL CABLES 81 



merit objective the maximum length was taken as 4000 miles, with as 

 many as five separate systems linked together. On the basis of results 

 thus far obtained it is expected that for these exacting conditions the 

 performance with respect to crosstalk, noise, transmission stability, 

 width of voice band and other characteristics will equal or exceed that 

 of previous facilities for much shorter distances. 



Superior performance has been achieved without material effect 

 on the cost of the system. For distances of a few hundred miles, on 

 moderately heavy traffic routes, it will provide telephone circuits at a 

 much lower cost than previous facilities. The minimum distance for 

 which the system will be useful may be less than 100 miles. 



Interesting features of the new system are: 



(1) A line of very high attenuation, requiring high-gain repeaters 



spaced at approximately 17-mile intervals. This would mean, 

 for the maximum distance for which the system is designed, 

 more than 200 repeaters in tandem. 



(2) The use in the repeaters of the negative feedback principle of 



amplification to obtain the requisite stability and freedom from 

 modulation. 



(3) Small auxiliary repeater stations, established between existing 



voice-frequency repeater stations, housing equipment which can 

 be left for considerable periods of time without attention. 



(4) A system of transmission regulation whereby huge variations of 



attenuation, differing at each frequency, are automatically 

 . equalized to a high degree of accuracy. 



(5) New methods qf crosstalk and noise reduction. Small adjustable 



mutual inductance coils are connected between carrier pairs to 

 balance out the crosstalk. The noise is kept at an extremely 

 low level to permit the high gains. 



(6) Channel terminal equipment designed so that it may be used in 



other types of carrier systems, thus simplifying development 

 and manufacture, and facilitating the interconnection of dif- 

 ferent types of systems. 



(7) Speech bands considerably wider than those of existing facilities. 



The increase is obtained by spacing the channels at uniform 

 4000-cycle intervals, and employing channel band filters con- 

 taining quartz crystal elements. 



(8) High-speed transmission, which is of considerable value from the 



standpoint of minimizing delays and echoes. 



A general description of the system is presented herein, and the 

 different parts are taken up in greater detail in other papers. 



