CARRIER IN CABLE 263 



versations were transmitted over this broad band circuit without 

 difficulty due to cross-modulation. 



Each carrier telephone circuit was designed to yield a frequency 

 band at least 2500 cycles wide, extending from about 250 cycles to 

 somewhat above 2750 cycles when five such carrier links are connected 

 in tandem. This liberal frequency band and the very satisfactory 

 linearity of transmission over the entire system, gave a very excellent 

 quality of transmission. In order to exaggerate any quality impair- 

 ment which might have been present the nine carrier circuits were, 

 as noted previously, connected for test in tandem giving a total length 

 of about 7650 miles of two-way telephone circuit. The quality of 

 transmission over this circuit was also found very satisfactory. In 

 fact, the quality was not greatly impaired even when twice this length 

 of one-way circuit was established by connecting all the lengths in 

 tandem, giving a 15,300-mile circuit whose overall loss without 

 amplifiers was about 24,000 db. 



As noted previously, the fact that the cable pairs are left non- 

 loaded gives the cable carrier circuits the advantage of very high 

 transmission velocity. Including the efifect of the apparatus this 

 velocity is approximately 100,000 miles per second — five or six times 

 as great as the highest velocity loaded voice-frequency toll cable 

 circuits now employed in the U.S.A. This velocity is ample for 

 telephoning satisfactorily over any distances possible on this earth. 



Conclusion 



Under the present economic conditions there is no immediate de- 

 mand for the installation of systems of this type. Consequently 

 development work is being pursued further before preparing a system 

 for commercial use. The final embodiment or embodiments of the 

 cable carrier system will probably differ widely, therefore, from the 

 system described in this paper. Since the transmission performance 

 of the experimental system was so completely satisfactory, emphasis 

 is now being directed toward producing more economical systems 

 which will be applicable to shorter circuits. Preliminary indications 

 from this work are that some form of cable carrier system will ulti- 

 mately find important application on circuits measured in tens rather 

 than hundreds of miles. 



