INDUCTIVE LOADING FOR TELEPHONE FACILITIES 461 



19.6 Coil Data 



Some detailed data regarding the new coils above described are given in 

 Table XI. The resistance data include 0.5 ohm for 22 ga. stub cables. The 

 615 coil was made available primarily for emergency replacement use in 

 old plant using 250 mh loading. 



(20) Second Increase in Minimum Cut-Off Frequency For Loaded 



Exchange Cables 



20.1 General 



During 1932 there became effective a second increase in the minimum 

 cut-off frequency standards for loaded exchange trunks, which in terms of 

 frequency ratio was about as large as the first change that was decided upon 

 in 1924, the successive (minimum) standards being 2300, 2800, and 3500 

 cycles. 



The new cut-off frequency standard was implemented by the standardiza- 

 tion of a graded series of higher-impedance, lower-attenuation loading 

 systems described below. These made it possible to secure a substantial 

 reduction in the over-all costs of the exchange area trunks by permitting 

 a more extensive use of the cheaper types of cables, even though the cost 

 of the loading per mile became greater in consequence of the closer coil 

 spacing. The improved transmission characteristics, i.e., lower attenuation 

 and reduced frequency-distortion, resulted from the use of standard coils 

 at substantially closer spacings. 



The above mentioned change in the relations between cable costs and 

 loading costs recognized a considerable departure from plant cost equilib- 

 rium that came about during the late 1920's and early 1930's in consequence 

 of the substantial reduction in loading costs that was realized by extensive 

 use of the permalloy-core coils previously described. Moreover, the prospect 

 of further savings was an encouraging factor in the adoption of the new 

 standards. 



20.2 The New Loading Systems 



The general characteristics of the new standard loading systems are 

 given in Table XII. The letters H and B in the loading designations signify 

 6000 and 3000-ft. spacings. In the cable designations, ''high" and ''low" 

 capacitance have the same significance as in Table VIII. 



Some typical attenuation data are given in Table XIII, for comparison 

 with attenuation data given in Table IX. The attenuation comparison by 

 itself, however, is not a completely adequate comparison since it ignores the 

 distortion-reduction advantage of the wider frequency-band transmitted by 



