SINGING ON TWO-WIRE CABLE CIRCUITS 629 



ki = anti logio I ^ ) == current corresponding to 



Sn in same way as 7i corresponds to Si. 



ki = anti logio I ~. j = current corresponding to 



5i2 in same way as 1 2 corresponds to Si. 

 L = loss of a cable section. 



Lk = the loss in db from the West side of the critical 



repeater to the output of the k th repeater to the 

 West, plus the loss from the input of the k th 

 repeater W-E to the input of the critical repeater 

 W-E. 

 Me = the end path singing margin, i.e., the singing margin 



with no currents returned from intermediate 

 paths (e.g., with a four-wire circuit). 

 Mi = the internal singing margin on an active line, i.e., 



the singing margin without any currents returned 

 from the end paths (e.g., with the terminal 

 repeaters turned down). 

 Ms = the singing margin of the circuit; i.e., the singing 



margin with currents returned both from inter- 

 mediate paths and from end paths. 

 nik = total number of loading sections in the k th repeater 



section. 

 m = value of mk when all repeater sections have the same 



number of loading sections. 

 N = number of repeater sections in the part of the circuit 



for which the active return loss is to be computed. 

 n = number of cases considered as a group. 



px = relative probability of obtaining a returned current 



ix from one active or passive return loss. 

 P{x > y) = probability that the value of x selected at random 



from a distribution curve is greater than a pre- 

 selected value y. 

 P = probability that a singing point will have a lower 



value than a pre-selected value y. 

 Pm{n, y) = Pm = probability that the minimum of n values will be 

 as high or higher than a pre-selected value y db 

 below the true average. 

 Q = probability that a lower value of singing margin 



will be obtained. 



