TRENDS IN PRACTISE AS AFFECTING COORDINATION 169 



small amount of noise current greatly impaired transmission because 

 of the weak incoming voice currents. Although the repeaters naturally 

 amplify the noise currents as well as the voice currents, the fact that 

 the voice level is kept high throughout results in great benefit which in 

 this case, assuming similar exposure conditions in the various repeater 

 sections, gives an improvement in the ratio of voice currents to noise 

 currents of slightly over five. 



1000 



DISTANCE IN MILES 



Fig. 6 — New York^Denver circuit level diagrams. 



Repeaters probably also have some effect in reducing certain of the 

 eft'ects of low frequency induction by the fact that they sectionalize 

 cable lines at about 50 mile intervals and open-wire lines at intervals of 

 200 miles or less, and limit the power which can be transmitted from 

 section to section. There is some evidence that this tends to limit 

 acoustic shocks. 



Carrier Telephone Systems. — A third important trend in telephone 

 practise is the extension in the use of carrier telephone systems for 

 long circuits and the associated changes in aerial wire construction 

 practises. The growth in use of this type of circuit is indicated in 



