734 THE BELL SYSTEM TECHNICAL JOXJRNAL, JULY 1951 



operations, suitable inspection tests were made to assure satisfactory con- 

 formation to specification requirements. After the final inspection tests, the 

 outer end of the stub cable sheath was sealed to prevent entry of moisture. 



When phantom loading started, the phantom coils were much larger than 

 the side circuit coils. To conserve potting space in cases containing both 

 types of coils, the individual spindle-assemblies consisted of only one type 

 of coil. The phantom unit cross-connections between the phantom coils and 

 their associated pairs of side circuit coils were made at the top of the case 

 between quadded spindle unit-cables containing the OUT terminal leads 

 of the phantom coils and the IN terminal leads of the side circuit coils. 

 The quadded IN terminal leads of the phantom coils and the OUT 

 terminal leads of the side circuit coils constituted the main line terminals 

 of the complete loading units. 



In general, all of the stub cable leads to the IN and OUT terminals of 

 non-phantom type coils, and to the main line terminals of phantom unit 

 combinations of side circuit and phantom circuit loading coils, were con- 

 tained in a single stub cable sheath. Necessary exceptions to this practice 

 occurred, however, in the submarine cable loading coil cases (which had two 

 stub cables extending from opposite ends) and in the underground and aerial 

 cable cases containing very large complements of P-B type loading units. 



The first important change from the original potting practices followed 

 soon after the introduction of phantom group loading. The original wax- 

 dipped textile-insulated stub cables were found to be seriously objectionable 

 sources of phantom- to-side and side- to-side crosstalk. To reduce crosstalk, 

 and also to improve transmission, the practice started of using strip-paper 

 insulated quadded conductors in a machine-stranded stub cable. This re- 

 quired a splice to be made inside the case, at the top, between the paper- 

 insulated stub and the textile-insulated spindle unit-cables. 



Apparatus Group-SegregaHon,Four-Wire Circuits: Several years later, when 

 the development work on long-distance four-wire repeatered circuits got 

 well under way, the assembly arrangements in the loading coil pots and the 

 stub cable designs were changed to provide crosstalk segregation between 

 the groups of coils used on the opposite-direction branches of the four-wire 

 circuits. The segregation arrangements in the stub cables included shielding 

 between the gioups of terminal quads associated with the opposite-direction 

 circuit groups. These loading coil case and stub segregation -arrangements 

 were details of a fundamental plan for complete group-segregation between 

 the opposite-direction branches of four-wire transmission systems (including 

 the main cables themselves and the repeater office circuits) in order to con- 

 trol the intergroup near-end crosstalk coupling and prevent it from being 

 a serious factor in the over-all crosstalk. (The relatively high amplification 



