NEW SINGLE CHANNEL CARRIER TELEPHONE SYSTEM 175 



compensate for these variations. Variations due to the equipment are 

 small in comparison with the line variations. The transmitting gain 

 at a terminal may vary ± 0.5 db and the receiving gain ± 0.3 db for 

 variations of ± 10 volts in the a-c. supply. With a more stable a-c. 

 supply or when operated from regulated plate and filament batteries 

 such as are employed in the larger telephone offices, these variations 

 will be less than half the figures given above. With suitable main- 

 tenance it should be possible to maintain the overall circuit net loss 

 within ± 2 db of its normal value. 



A representative load characteristic, as measured with 1000-cycle 

 current for a system without a repeater, is shown in Fig. 12. On a 



Zo 



-12 -10 -8 -6 -4 -2 +2 +4 +6 +8 



1000-CYCLE INPUT IN DECIBELS REFERRED TO 1 MILLIWATT 



Fig. 12 — Representative system load characteristic. 



repeatered system some additional limiting of high inputs may occur. 

 However, even on repeatered systems, there should be no noticeable 

 distortion for input volumes such as are obtained directly from a 

 switchboard. 



5 



4 ■ — ^= 



3 



Reactions on Voice Frequency Circuit 



In superimposing a carrier system on a voice-frequency circuit, line 

 filters are added to provide separate paths for the voice and carrier 

 circuits. The introduction of a filter in one side of a phantom group 

 requires the addition of a network on the other side to maintain the 

 balance of the phantom circuit from a noise and crosstalk standpoint. 

 It is also necessary for return loss reasons to balance these units in the 

 network circuits of voice-frequency repeaters that may be located at 

 the same point as a carrier terminal or repeater. The networks re- 

 quired to take care of these conditions are included with the carrier 

 system. 



In some cases it is desired to apply the Type H system to circuits 

 equipped with bridged telephone stations at intermediate points. 

 Such arrangements are common on railroad communication systems, 

 and occur to a small extent in the Bell System. In such cases, ex- 



