LONG DISTANCE CABLE CIRCUIT 569 



back and forth in the cables between New York and Pittsburgh so 

 as to produce a circuit 2,200 miles in length. Tests were made on 

 this circuit over a period of several months and very satisfactory 

 results were obtained. It is, therefore, planned to make extensive 

 application of this system and eventually program circuits may be 

 provided in cable over practically all of the long toll cable routes. 



So as to appreciate what is involved in the design of this system 

 there will first be presented a discussion of the transmission require- 

 ments. Following this, the new system will be described and its more 

 important transmission characteristics set forth. 



Transmission Requirements 



For program transmission the ideal, of course, is to provide a trans- 

 mission line such that no distortion whatsoever will be caused to 

 program material transmitted over the line whatever be its length. 

 Ideally also, program pickup apparatus, radio transmitters, radio 

 receivers and loudspeakers should be such that the program delivered 

 from the loudspeaker should sound exactly like the original program 

 delivered to a direct listener in the best location. To meet this ideal, 

 however, would require that the whole audible range of frequencies, 

 extending from about 20 to 20,000 cycles, and a tremendously wide 

 range of volumes representing power differences of more than a 

 million-fold be handled without any distortion whatsoever. 



Actually the radio art is far from attaining this ideal. It does not 

 seem reasonable, therefore, to provide lines very much superior in 

 transmission performance to the rest of the system since this would 

 unnecessarily increase the cost for providing the service. However, 

 telephone lines represent a fixed investment which must remain in 

 service for many years in order to keep costs within reason and, 

 furthermore, it is, in general, not practical to change the transmission 

 characteristics of the lines once they have been installed. It is, 

 therefore, necessary to take into account the fact that the broadcasting 

 art has considerably improved in the past and is likely to improve in 

 the future and provide telephone lines of sufficiently good charac- 

 teristics to anticipate the improvements which are likely to come 

 within a reasonable period of time. 



These general considerations have led to the adoption of the follow- 

 ing as practical standards of performance for the new cable system: 



Frequency range to be transmitted without material distortion — 



about 50 to 8,000 cycles. 

 \^olume range to be transmitted without material interference from 



extraneous line noise — ^about 40 db, which corresponds to an 



energy range of 10,000 to 1. 



