VOLUME EFFICIENCY OF REPEATERED CIRCUITS 527 



unbalance in the office wiring and to repeating coils, repeaters, and 

 other office apparatus. 



The crosstalk in the cable outside the ofhce is due to loading coil 

 unbalance, series resistance unbalance, and cai)acitance unbalance. 

 Crosstalk between different quads is normally due almost entirely to 

 capacitance unbalance. 



When the complete repeater sections have been installed, cross- 

 connection of the circuits at certain repeater points is generally used 

 to reduce the overall crosstalk between circuits. In the case of two- 

 wire circuits, this cross-connection consists of breaking up all phantom- 

 to-side and side-to-side combinations in a given quad at each repeater 

 station, and the system is designed to make it improbable that any 

 two of these circuits will ever be in the same quad again. In the case 

 of four-wire circuits, this cross-connection is resorted to only at the 

 ends of each pilot wire regulator section. 



The method of computing the crosstalk limitations of a given cable 

 circuit is as follows: Determine the r.m.s. (root mean square) within- 

 quad crosstalk coupling per loading section by adding together the 

 r.m.s. crosstalk coupling due to capacitance unbalance, resistance 

 unbalance and loading coil unbalance as the r.s.s. (root sum square) 

 of the parts expressed in crosstalk units. From this, get the r.m.s. 

 unamplified crosstalk coupling per repeater section by properly attenu- 

 ating the crosstalk coupling from each loading section. The attenua- 

 tion in each case equals the loss from the output of the repeater 

 transmitting into the disturbing circuit (in that repeater section) to 

 the point of crosstalk coupling plus the loss from this point to the 

 input of the repeater receiving from the disturbed circuit. The total 

 r.m.s. vvithin-quad crosstalk coupling per repeater section is the r.s.s. 

 of the crosstalk coupling from each of the loading sections and from 

 the office. The between-quad crosstalk coupling per repeater section 

 is obtained in a similar manner. 



In the case of near-end crosstalk on two-wire circuits, the unampli- 

 fied crosstalk coupling so determined is then amplified or attenuated 

 by the gains or losses from the transmitting terminal of the disturbing 

 circuit to the repeater section in question and then to the receiving 

 terminal of the disturbed circuit. Next, the r.s.s. of this crosstalk 

 coupling and the between-quad crosstalk coupling from the same 

 disturbing circuit in other repeater sections is obtained. The proba- 

 bility of this total crosstalk coupling exceeding 1,000 units is then 

 determined, making due allowance for the variations of net loss. For 

 near-end crosstalk, in a circuit without variations, the probability that 

 1,000 units of crosstalk will be exceeded when the total r.m.s. crosstalk 



