INDUCTIVE LOADING FOR TELEPHONE FACILITIES 



187 



could be met without undue difficulty on the H44-25 four-wire and two-wire 

 facilities, but were not feasible on the HI 74-63 facilities then being used 

 mainly on a two-wire basis. 



The work on the improved standards problem resulted in the development 

 of the B 88-50 and H88-50 toll cable loading systems, data for which are 

 given in Table V. 



In effect, this development established a new minimum cut-off standard of 

 about 4,000 cycles per second for loading used on repeatered circuits. Also, 

 as noted in the table, the transmission velocity was increased in H88-50 

 loading. B88-50 loading, using a coil spacing of 3,000 ft. (i.e., one-half of 

 H-spacing), was originally intended for use in "long" repeater sections. The 

 cheaper H88-50 loading was used on "short" repeater sections, and in con- 

 sequence some facilities had tandem combinations of the two new types of 

 loading. In the early applications H88-50 loading was used in repeater sec- 

 tions ranging up to about 45 miles in length and the more expensive B 88-50 



Table V 

 H88-50 AND B88-50 Loading 



loading was used on longer sections. Later, improvements in the control of 

 crosstalk and special procedures for reducing loading section capacitance- 

 deviations made 1188-50 loading suitable for longer repeater sections. Dur- 

 ing recent years, the voice frequency repeater points have usually been laid 

 out to permit the use of H88-50 loading, and at present there is little use for 

 new B88-50 loading. 



New loading coils were developed for the new loading systems, and were 

 coded in the "PB" loading unit series, pw-eviously mentioned. This apparatus 

 development included substantial improvements in crosstalk performance 

 obtained by new assembly-methods, and refinements in the crosstalk adjust- 

 ments and test circuits. These new assembly-methods were applied to all 

 standard toll cable and toll entrance cable loading units and provided 

 flexibility for potting different types of loading units in the same case, and 

 for identification of their terminal leads in the stub cables. 



The new H88-50 and B88-50 loading became available for general use 

 during 1932, 



