186 



THE BELL SYSTEM TECHNICAL JOUBNAL, JANUARY 1951 



The compressed powdered-permalloy core toll cable loading coils remained 

 standard until 1938, when much cheaper and slightly better compressed, 

 powdered molybdenum-permalloy core coils became available, as discussed 

 in subdivision 11. 



S 



INDUCTANCB COILS USiD 

 FOR CROSSTALK ADJUSTMENTS 



SIDE CtRCUlT 

 COILS 



PHANTOM COIL 



Fig. 10 — P-B type loading unit potting assembly prior to placement in unit shielding 

 container. Phantom coil is below the two side circuit coils. Midget inductance coils are 

 used in phantom-to-side crosstalk adjustments. 



(10) Improved Loading Standards for Two- Way Repeatered Toll 



Cables 



During the late 1920's considerable attention was given to the improve- 

 ment of transmission standards made possible by the use of the improved 

 repeaters and the improved loading. This included reductions in the allow- 

 able net losses between terminals and improvements in crosstalk perform- 

 ance. Also, steps were taken to obtain better control of attenuation- 

 frequency distortion, the important objective being to provide fairly uniform 

 transmission in the frequency-band between 250 and 2750 cycles per second.^^ 



The transmission requirements over the frequency-band just mentioned 



