INDUCTIVE LOADING FOR TELEPHONE FACILITIES 167 



before the loaded, repeatered transcontinental open-wire circuits were ready 

 for service. To permit more satisfactory repeater operation in the remaining 

 loading complements of these cables, and in many more coarse-gauge toll 

 cables which were installed during the next few years, a series of high- 

 stability type of loading coils was standardized during 1916/'^ The coils 

 in this series used air-gaps in their 65-permeability, iron-wire cores. Since 

 the availability of satisfactory types of telephone repeaters had reduced 

 the need for 10-gauge conductors, the new coils were "compromise" designs, 

 suitable for either 10 ga. or 13 ga. conductors. Accordingly they were inter- 

 mediate in size between the two different series of coarse-gauge cable coils 

 that were developed in the 1911-1913 period. 



These new loading coils remained standard for toll cable uses for only a 

 few years. The practice of installing 10 ga. and 13 ga. toll cables substantially 

 stopped before 1920, because theoretical studies of the possibilities of 

 improving repeaters and loading systems were indicating that it should 

 ultimately be possible to usp repeatered, loaded 19-gauge or 16-gauge 

 conductors for spanning the longest distances likely to be involved in the 

 long-distance cable plant. The use of 4-wire repeatered facilities became a 

 very important objective in the new development plans, making necessary 

 an intensive development of transmission equalizing and regulating net- 

 works and practices. 



(6) Compressed Powdered-Iron Core Loading Coils for Repeatered 

 AND Non-Repeatered 19 AND 16-Gauge Toll Cables 



6.1 Compressed Powdered-Iron Core-Material 

 General 



This was the first new loading coil core-material to be developed since 

 the establishment of the first loading standards. Many other possibilities 

 had been considered on a number of occasions, notably silicon steel in fine- 

 wu-e form, but no core-material had been discovered that was superior to 

 the 65-permeability iron-wke in its major performance characteristics. 



The compressed powdered-iron development was the pioneering begin- 

 ning of an entirely new and very important art in the design of high-stability, 

 low-loss, magnetic core-materials. It was started by the Engineering Dept. 

 of the Western Electric Co. as an independent project, alongside the basic 

 research work on various phases of transcontinental telephony, and reached 

 the first stage of commercial fruition during 1916. An important objective 

 was to obtain much better magnetic stability than that of iron-wire cores, 

 and at a lower cost than that of wire cores having series air-gaps. Also, from 



<0 Additional information regarding this development is given in References (8) and (9). 



