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BELL SYSTEM TECHNICAL JOURNAL 



Representative return loss versus frequency curves are shown in 

 Figs. 1 and 2 for B-88-50 and H-88-50 circuits, respectively, the 

 points plotted being corresponding measurements on actual field 

 facilities. 



In the case of four-wire circuits, impedance irregularities are not so 

 serious. However, for practical reasons, the same tolerances are 

 usually followed for the several parts. 



Control of Crosstalk 



For two-wire circuits, the important crosstalk is near-end while 

 for four-wire circuits it is far-end. For both of these, crosstalk between 

 circuits within a single quad is greatest but crosstalk between circuits 

 in different quads is also important. For two-wire circuits, in order 

 to avoid long crosstalk exposures between any two circuits, it is the 

 practice to carry three circuits together in a single quad only in a 

 single repeater section, the circuits being systematically mixed at each 

 repeater station. In the case of four-wire circuits this mixing is done 

 only at the ends of regulator sections. In both outside cables and 

 in the ofifice cable, care is exercised to segregate the oppositely bound 

 pairs of four-wire circuits because of the relatively large level differ- 

 ences. 



In the outside cables control of crosstalk involves adjustments of the 

 fortuitous unbalances in the loading units and unbalances between 

 circuits in the loading sections. The following table shows the 

 standards for phantom-to-side crosstalk expressed in decibels ordinarily 

 worked to for the component parts of cable circuits: 



* For two-wire circuits on the average these values must be decreased about 8 db 

 to compare with overall value; for four-wire circuits about 9 db should be added 

 to these values to compare with the overall. 



Note: All values in table are for a frequency of 1250 cycles. 



