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BELL SYSTEM TECHNICAL JOURNAL 



wire circuits are restricted to shorter lengths, the curve being given 

 simply for comparative purposes.) 



In addition to this matter of frequency band width, there has been 

 improvement in the 1,000-cycle efficiency of long distance circuits and 

 also improvement with respect to noise and crosstalk. The original 

 loaded transcontinental circuit, for example, gave, during good weather. 



NEW YORK TO 

 SAN FRANCISCO 



165- MIL I OPEN-WIRE 

 NON-LOADED CARRIER 



1000 2000 



CYCLES PER SECOND 



3000 



1000 2000 3000 



CYCLES PER SECOND 



Fig. 1 — Transmission-frequency characteiistics of representative types of 



telephone circuits. 



a 1,000-cycle transmission loss of about 20 db with a variation from 

 this of at least 10 db during bad weather. The non-loaded circuit gave 

 about 12 db during good weather with smaller variations. With both 

 of these circuits the noise was somewhat in excess of 1,000 noise units. 

 The carrier and cable systems compare very favorably with non-loaded 

 voice- frequency circuits in the matter of transmission loss and are 

 much quieter. 



With the two-wire cable circuits shown, the H-245 circuit gave about 

 12 db loss at 1,000 cycles, the H-174 circuit 10 db loss and it is ex- 

 pected that the B-88 circuit will give about 9 db loss at 1,000 cycles. 

 All of the cable circuits are strikingly quiet as compared with older 

 type voice-frequency open-wire circuits. The cable circuits are also 

 considerably better from the standpoint of crosstalk. 



It is of interest to consider the effect on service of the change in 

 standards of toll circuits as illustrated by the characteristics of the 



