INDUCTIVE LOADING FOR TELEPHONE FACILITIES 735 



in the four-wire repeaters made very desirable the rigorous control of this 

 type of crosstalk coupling.) Initially, the loading apparatus and associated 

 stub cable quads intended for use on two-wire repeatered circuits were seg- 

 regated in the coil cases from the two opposite-direction groups of four-wire 

 circuit apparatus. Later on, this apparatus segregation between two-wire 

 circuit coils and four-wire circuit coils was discontinued. 



In mixtures of the two types of coils, the two-wire circuit apparatus was 

 divided into approximately equal groups, each of which was combined with 

 one of the four-wire opposite-direction groups. In order to simplify potting 

 practices, the two-group segregation plan became the standard plan for all 

 toll cable loading cases and was used in loading complements containing 

 mixtures of two-wire circuit and four-wire c'rcuit loading apparatus, and 

 for complements consisting wholly of two-wire circuit coils, or of four-wire 

 circuit coils. 



In the most recent (1948-1949) general redesign of toll cable cases and 

 stub cables, the segregation arrangements just described have been simpli- 

 fied, largely because of the present very small demand for additional H44-25 

 four-wire circuits. Group segregation of the apparatus within the cases is 

 used only when four-wire H44-25 loading is involved. The use of shielding 

 and of group-segregdtion arrangements in the stub cables has been discon- 

 tinued. In complements of units for H44-25 loading, one of the opposite- 

 direction groups is connected to a group of terminal quads having contigu- 

 ous "quad counts" at the low end of the quad counting scheme described 

 on page 737, and the other group is connected to the quads having "quad 

 counts" at the high end of the quad counting scheme. When two-wire circuit 

 coils are included in a loading complement containing four-wire circuit coils, 

 the terminal quads of the two-wire coils use terminal quads having "quad 

 counts" intermediate between those of the two opposite-direction groups of 

 four- wire coils. 



Phantom Coil Size-Reduction: The next important potting-practice change 

 resulted from the size-reduction of the phantom coils to side circuit coil- 

 size. From then on, the phantom coils were mounted on the same spindles 

 as the side circuit coils, with each phantom coil immediately adjacent to its 

 associated pair of side circuit coils. This permitted a more efficient use of 

 potting space and made unnecessary the use of spindle-unit cabling for the 

 cross connections between the coil components of the phantom loading units. 

 The miniature inductance coils used in the loading-unit crosstalk adjust- 

 ments were mounted on a frame located at the top of the coil spindle-assem- 

 blies and were connected in the circuit at the splices made between the stub 

 cable and the spindle unit-cables leading to the coil line terminals. 



Assembly Redesign, Exchange Area Coils: The first major change in the 



