INDUCTIVE LOADING FOR TELEPHONE FACILITIES 455 



portions as regards transmission and cost features in the expected wide use 

 on 22 ga. cables. For optimum economies in potting and installation, en- 

 tirely new types of loading coil cases would be required for this design. 



In conformity with this plan, the temporary standard 88 mh loading 

 coil. Code 601, became commercially available late in 1924, and its suc- 

 cessor design. Code 602, approximately nine months later. 



The 601 coil used a 2-ring core of compressed, unannealed, powdered 

 iron. The over-all coil dimensions were such that 200 coils could be potted 

 in the largest size of exchange area loading coil case then standard, which 

 had originally been developed for potting 98 coils of the 574 and 575 coil- 

 size. A larger size of case which potted toll cable loading coils was modified 

 to pot 300 No. 601 coils. During 1924 and 1925, while the production of the 

 602 coil was being built up to meet the large demand for H88 loading, over 

 80,000 No. 601 coils were manufactured. 



The 602 coil also used compressed, unannealed, powdered-iron cores, and 

 it had much better proportions of axial length to diameter. Similar sizes 

 of potting complements were standardized in the new cases. Coil F in the 

 headpiece is a 602 coil. (Coil F in relation to Coil B shows the size difference 

 for the contemporary standard coils designed for 22 ga. and 19 ga. cables, 

 respectively.) 



Because of their smaller size, the 601 and 602 coils had a higher ratio of 

 resistance to inductance than the older coils which had been developed for 

 use on lower resistance cables. 



Making more efficient use of core material and copper, and using smaller- 

 size, higher-speed winding machines, the 602 coil was substantially cheaper 

 than the 601 coil, which in turn was considerably cheaper than the prior 

 standard cable loading coils. In both instances, substantial economies in 

 potting and installation costs also resulted. 



18.2 Coils for HI 35 Loading 



Further consideration of the transmission economics of the new H135 

 loading led, about the middle of 1925, to a decision to develop a new 135 

 mh loading coil using the same core and the same types of loading coil 

 cases as for the 602 coil. Under the code No. 603, this coil became available 

 for commercial service during 1926. 



The 603 coil was intended for use on 22 ga. and 19 ga. cables, and yielded 

 large economies during 1926-27 in these fields. The larger-size 575 coil was 

 temporarily continued as a standard design, for use on long 19 and 16 ga. 

 trunks where a better coil than the 603 coil could be justified. With this 

 coil, the attentuation was about 0.03 db/mi better than that obtainable 

 with the 603 coil. 



