INDUCTIVE LOADING FOR TELEPHONE FACILITIES 



195 



It should not be inferred from the foregoing that the MF (and SM) 

 loading units have unimportant significance in the economy of Bell System 

 toll cable plant-design. For example, during the period 1942-1949, a total 

 of about two million side and phantom coils were manufactured for assembly 

 in these smallest, standard, phantom loading units. A large majority was 

 installed subsequent to VJ-day, as part of the Bell System program of plant 

 expansion to meet the greatly increased demand for long-distance telephone 

 service, and to restore the speed of service to the pre-war standards. 



Table VI 

 Electrical Data — Most Important Voice- Frequency Phantom Loading Units 



Notes: (1) The listed inductance values are the mean specification inductance values 

 (at 1800 cycles). 

 (2) The coil resistance values allow for 19-gauge stub cables of 7.5-ft. external 

 length. 



(12) Comparative Electrical Data, Voice-Frequency 

 Phantom-Group Loading Units 



Comparative electrical data regarding the commercially most important, 

 former standard and present standard, voice-frequency phantom-group 

 loading units are given in Table VI, above. Those coded in the "F" and 

 "PB" series used compressed permalloy-powder cores; the M, SM, and MF- 

 type units used compressed, molybdenum-permalloy powder cores. Prior to 

 the standardization of the P and PB-type units, the side circuit and phantom 

 circuit coils had their own individual code numbers. They were intercon- 

 nected in loading unit formation during the case assembly and cabling pro- 

 cedures. 



