EVOLUTION OF INDUCTIVE LOADING 1241 



that the most important apparatus-cost reduction developments were com- 

 pleted in time for exploitation during periods of peak demand for new coils. 



With respect to the effects of other developments in reducing the demand 

 for exchange area loading, the introduction of improved subscriber sets 

 during the 1930's warrants special mention. By permitting higher losses in 

 the trunks, somewhat longer non-loaded trunks could be used. 



Looking towards the future, the prospective use of a new low-cost re- 

 peater of an entirely new type (El telephone repeater) is expected to reduce 

 the demand for the heavier weights of loading. Also, the new Type N 

 short-haul cable carrier system, referred to on page 1240, may have some 

 considerable use on relatively long non-loaded exchange trunks along heavy 

 traffic routes. It is also of interest that a greatly improved telephone set 

 (500-type) now in the final stages of development will probably reduce the 

 need for loading on long subscriber loops. 



Although it is not possible at present to make accurate quantitative 

 estimates of the ultimate effects of the just mentioned new developments 

 upon the future demand for new exchange area loading, there is no reason 

 to believe they will be so drastic as the effects of carrier system develop- 

 ments upon the ultimate future demand for toll cable loading. It seems 

 especially probable that the low-cost H-spaced loading will continue in- 

 definitely to be an important factor in the economy of design of new exchange 

 area cable plant to provide telephone service for a continually increasing 

 number of subscribers. 



Loading for Incidental Cables in Open-Wire Lines 



The impedance-matching loading systems used on entrance and inter- 

 mediate cables have made vital contributions to the excellence of the 

 over-all performance of the open-wire transmission systems. These are of 

 great importance relative to the amount and the cost of the loading actually 

 used. 



In consequence of the increasing utilization of open-wire carrier systems, 

 the voice-frequency loading is much less important than it was two to three 

 decades ago. However, an indefinitely continuing, though small, demand 

 seems certain, because of the valuable transmission improvements which 

 the loading makes available at low cost. 



The demand for additional carrier loading is expected to continue in a 

 somewhat rough proportion to the number of additional open-wire carrier 

 systems that are installed. However, in consequence of the high cost of the 

 loading for multi-channel systems (which is much higher than formerly in 

 consequence of greatly increased labor and material costs), it seems probable 

 that more and more consideration will be given (especially on **long" 



