EVOLUTION OF INDUCTIVE LOADING 



1231 



in the extent of use, reaching its all-time peak in growth during 1930. The 

 four-year period of most rapid expansion of toll cable loading coincided 

 with : (a) the full scale introduction of four-wire repeatered loaded (H44-25) 

 circuits for long haul long-distance facilities, (b) the introduction of 

 permalloy-core loading coils which resulted in large loading economies, and 

 (c) the planned use of relatively large circuit-groups in order to speed up 

 the long-distance service. 



The business depression of the early 1930's terminated the rapid expansion 

 period in all types of loading. Several years later, when business conditions 



1920 1922 1924 1926 1928 1930 1932 1934 1936 1938 1940 1942 1944 1946 1948 1950 



YEAR (estimated) 



Fig. 35 — Annual production totals of voice-frequency cable loading coils for Bell Tele- 

 phone facilities. 



improved sufficiently to require another large expansion in the toll cable 

 facilities, the demand for new long-haul circuits was taken care of generally 

 by the use of Type K carrier systems on non-loaded cable pairs and pairs 

 from which loading was removed; and the use of new toll cable loading was 

 largely restricted to short-haul repeatered and non-repeatered circuits. 

 Thus it happened that, during the 1939-1942 period of rapid plant expansion, 

 the production of exchange area loading coils substantially exceeded that 

 for toll cable loading in the struggle to meet the demands for additional 

 facilities required by the war effort. 



The post-war drive to meet the greatly mcreased demands for long- 



