CROSSTALK AND NOISE FEATURES 



159 



It is necessary to filter only the longitudinal circuit at an open-wire 

 tap, because: (1) the voltage to ground on the open wire is larger 

 than the metallic circuit voltage, and (2) the coupling between the 

 longitudinal circuit and the disturbed carrier pair is greater than the 

 coupling between metallic circuits. 



Figure 17 is a schematic diagram of the longitudinal filter developed 

 for a phantom group. It consists of two longitudinal retardation 

 coils and a set of condensers connected between the line wires and the 

 cable sheath. This filter has relatively high carrier frequency longi- 

 tudinal impedance to minimize effects of impedance in the ground con- 



r' 



1 



PAIR 

 IN 



PAIR 2 

 IN 



■njij^ 



^uw^ 



■nm^ 



^im^ 



I ^" 



I I (GROUND 



^im^ 



^im^ 



L2 



^wr^ 



L 



I 



PAIR I 

 OUT 



PAIR 2 

 OUT 



Fig. 17 — Schematic of longitudinal filter. 



nection. The major portion of the carrier frequency impedance of the 

 coils is obtained by designing them to have high core loss at these 

 frequencies. The filter has little effect on voice frequency transmission, 

 precaution having been taken to hold the transmission loss, crosstalk 

 and unbalance to ground to low values. 



Noise Arising in Existing Repeater Offices 



The noise caused by carrier frequency voltages generated in existing 

 repeater offices is due to d-c. telegraph, telephone speech and signaling 

 voltages, power supply, etc. Figure 1 shows the path by which they 

 reach the carrier plant and the means used to suppress them. In this 



