INDUCTIVE LOADING FOR TELEPHONE FACILITIES 737 



near the outer periphery of circular mounting plates, and the inner end of 

 the stub cable extends through a circular opening at the center of these 

 plates, (Fig. 13). In the very small complements, the MF units are stacked 

 one above the other as shown in Fig. 14. 



The concentric layer-type stub cables, used with new cases potting P-B 

 type loading units and subsequently with the M-type, SM-type, and MF- 

 type loading units, had an improved color-code for the conductors of the 

 terminal quads which provided a counting-scheme type of identification 

 for each of the individual loading units potted in a given case. To facilitate 

 this full-scale identification of the individual units, it was necessary to have 

 a precise wiring coordination between the positions of the individual units 

 on the case assembly frames and the positions of their terminal quads in 

 the stub cable (which were identifiable in terms of the quad-count color- 

 code). This permitted the necessary coordination of the coil-grouping 

 arrangements which were desirable for crosstalk reasons in complements of 

 four-wire circuit loading (as previously discussed) with the group segregation 

 and shielding arrangements of the associated stub cable terminal quads. 

 A simplifying factor was the use of adjacent quads for the IN and OUT 

 terminals of same loading unit. 



The improved stub designs greatly simplified the manufacturing problems 

 involved in providing, (a) full flexibility as regards loading complement 

 sizes, and (b) full flexibility for desirable combinations of different types of 

 loading units. 



(a) Using a relatively small number of case sizes, provision was made for 

 obtaining any total-complement size, ranging from one up to the maximum- 

 complement size, in steps of one loading unit. A different size of stub cable 

 was used for each different size of case. When less than a full complement 

 was desired in a particular size of case, the unused terminal quads were left 

 open at the inner end of the stub cable and were tagged at the outer end. In 

 terms of "quad counts" these non-used quads had contiguous numbers at 

 the ''high" end of the quad counting-scheme, and were readily identified by 

 means of the quad-count color-code and the tags previously mentioned. 

 (A name-plate on each case recorded the number and the code types of 

 loading units potted in the case.) In the prior art, different stub cables had 

 been provided for fitting the different partial and full potting-complements 

 in particular sizes of cases. 



(b) For several years prior to the standardization of the improved as- 

 sembly and stub design it had been a common practice to use mixed potting 

 complements of different types of loading units, in order to realize the 

 maximum potting and installation economies inherent in the use of larger- 

 size loading complements made practicable by size-reduction of the loading 



