LOADIXG FOR TELEPHONE CIRCUITS 



25: 



etricienc-\- ctTccls. The stanclardi/.ition of the \\-\7\-iV-\ ])hciii((>in 

 group loading system, therefore, marked the abandonment of use in 

 new facilities of the old standard H-245-15r) phantom-group loading 

 system. 



Attenuation — Frequency Distortion. In addition to their impro\ed 

 velocity and cut-off frequency characteristics, the H-44-2o and H-174- 

 63 loading systems ha\e an important ad\antage from the standpoint 

 of attenuation-frequency distortion effects, as is illustrated in Figs. 

 10 and 11. The frequency distortion effects illustrated in Fig. 10 



0.001 



0.01 



500 



1000 1500 2000 2500 

 FREQUENCY-CYCLES 



Fig. 11 — ^Attenuation-frequency characteristics of short and long loaded toll cable 

 circuits having a net attenuation loss of 10 TU at 1000 cycles 



may become very serious in ^ ery long lines. An indication of this is 

 given in Fig. 11. The heavy line curves in this diagram illustrate 

 the attenuation-frequency characteristics of a 500-mile 19 A.w.g. 

 cable circuit involving the various types of loading noted, assuming 

 that "perfect repeaters" are used in each case to reduce the totaMine 

 loss to 10 TU at 1,000 cycles. The foregoing "perfect repeater" is 

 assumed to have the same amplification at all frequencies. Of course, 

 in order to have the same over-all efficiency in the different t\-pes of 

 circuits at 1,000 cycles, it is necessary to assume diff'erent total amounts 

 of repeater gain. The dotted lines in Fig. 11 illustrate corresponding 

 frequency characteristics of short non-repeatered cables having the 

 same types of loading as before; in each case the length of 19 A.w.g. 

 cable circuit being chosen so that the non-repeatered circuits have the 

 same loss (10 TU) at 1,000 cycles. A visual inspection of the dotted 

 and heavy line curves indicates how the line losses pile up in long 

 connections. In the old standard low cut-off loading, the accumulated 

 losses in very long lines amoimt to a suj:)pression effect for frequencies 

 above 1,600 cycles. 



