94 BELL SYSTEM TECHNICAL JOURNAL 



occur in an aerial cable are very rapid, it is practically essential to 

 make these means automatic. In the case of X.L.L. 19-gauge cir- 

 cuits whose variation is greatest, it is necessary to locate the automatic 

 regulators, in general, at every third or fourth repeater station in 

 order to keep the transmission levels within proper limits. In Figure 

 1-a, a typical method of locating the regulating devices along a cable 

 is indicated. In this sketch each square indicates a master automatic 

 transmission controlling device while the loops extending in either 

 direction from the squares indicate the cable circuits which control 

 the functioning of these devices. 



An automatic transmission regulator is shown schematically in 

 Figure 15. The device comprises a Wheatstone bridge arrangement. 

 In one arm of the bridge, pilot wire pairs, extending in either direc- 

 tion in the cable, are included as indicated in the figure. The Wheat- 

 stone bridge has associated with it certain apparatus which will not 

 be described here in detail, which functions in such a manner as to 

 automatically keep the bridge balanced at all times. In the process 

 of maintaining balance of the bridge, angular motion is conveyed to 

 a shaft which is proportional to the resistance variations which the 

 cable circuits undergo. The movement of the shaft causes different 

 contacts to be made and thus controls relays which in turn control 

 the gains of the telephone repeaters, one way of doing this being 

 indicated in the figure. The repeater gains are thus caused to be 

 raised and lowered automatically, and thereby overcome the dif- 

 ferences in attenuation caused by the temperature changes in the 

 cable conductors. 



