158 



BELL SYSTEM TECHNICAL JOURNAL 



to heavy atmospheric static induced directly into a carrier pair in the 

 outside cable is below thermal plus tube noise at the top frequency. 



There are additional types of noise, not shown, whose sources lie 

 within the carrier system: e.g., modulation in amplifiers, inter-system 

 cross-induction, battery noise. While control of such noise is an 

 integral part of the fundamental carrier system design, it is not the 

 purpose of this paper to cover this class of noise. 



Conductors Tapping the Carrier Cable 



Carrier noise may come from open-wire pairs which connect to 

 conductors in the cable. Its sources may be static; corona on power 

 lines; power line carrier or other carrier frequency voltages on power 

 lines paralleling the open wire; induction from radio telegraph stations; 

 or carrier frequency voltages arising in the office to which the open 



CARRIER PAIR 



^ 



COUPLING 

 WITHIN CABLE 



CARRIER 

 REPEATER 



'-f=^ 



NON-CARRIER PAIR 



u 



OPEN-WIRE 

 PAIR 



CARRIER- ^^.^^ 



FREQUENCY I xSLJ' ' 



NOISE VOLTAGE j 

 TO GROUND ~=- 



Fig. 16 — Schematic of path followed by induction from open-wire taps. 



wire is connected, such as voltages generated by d-c. telegraph or 

 telephone signaling systems. The limited experience to date indicates 

 that, in a long cable carrier system, the effect of heavy static will be 

 larger than that of the other sources if telephone and power supply 

 plants are coordinated so as to be satisfactory from voice frequency and 

 low frequency standpoints. Branch cables connected to the carrier 

 cable have a similar but generally smaller effect than that of open-wire 

 taps. 



Figure 16 illustrates the path followed by this induction. A voltage 

 to ground impressed on the open-wire pairs passes by secondary in- 

 duction over to the carrier pairs in the cable, and, on account of the 

 unbalance to ground of these pairs, produces a metallic voltage on 

 these pairs at the repeater input. The effect may be greatly reduced 

 by interposing a filter at the junction of the open wire and the cable. 



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