528 BELL SYSTEM TECHNICAL JOURNAL 



coupling ^^ is "x" crosstalk units is approximately 



p _,3 , , 1,000 

 Fn = e where k = • 



X 



An approximate method of allowing for circuit variations is to con- 

 sider a circuit with variations equivalent to a circuit without variations 

 with a net loss smaller than the average net loss of the former circuit 

 by one-quarter of the variations; i.e., if the variations are ± Fdb, the 

 value of k to be used in the above formula is 



k = \m 10-....., . 



X 



Fig. 3 shows the value of P„ plotted against k. 



When these probabilities have been determined for all circuits having 

 a similar within-quad exposure to the circuit under consideration, 

 the total probability of the crosstalk coupling exceeding 1,000 units 

 from any circuit may be determined and is approximately the sum of 

 the probabilities of excessive crosstalk coupling from each of the dis- 

 turbing circuits. (The probability of excessive crosstalk from circuits 

 not having within-quad exposures is considered negligible.) When 

 this probability is .01, the circuit is considered just satisfactory from 

 a crosstalk standpoint. 



Far-end crosstalk coupling is computed in a similar manner, using 

 the probability relations applying to far-end crosstalk and four-wire 

 circuits, which are somewhat different from those applying to near-end 

 crosstalk and two-wire circuits. In this case, the probability of ex- 

 ceeding 1,000 units of crosstalk when the r.m.s. total crosstalk is "x" 

 units is approximately 



A p'^'.-r2j. ...u_„_ L 1.000 



V' TT Jo 



or with variations of ± F db, 



2 A-. ._ 

 Pf = \ - ~= e-'-dt, where k = 



V TT Jo 



k = hm io-<«., . 



X 



Fig. 3 shows Pf plotted against k. 



Variations 



When the minimum net loss at which a circuit will be satisfactory 

 has been determined, or when the minimum working net loss is com- 



1^ The ratio of the average near-end crosstalk to the r.ni.s. near-end crosstalk is 

 about Vt/2. The similar ratio for far-end crosstalk is V2/Vt. 



