NEUTRAIJZATION OF TELEGRAPH CROSSFIRE 431 



Phantom Group Network^ 

 Gauge Loading Non-Phantomed Pair Diagonals Sides 



1 . 7 mf. 1 . 7 mf. 1 . 2 mf. 



1.1 " 1.1 " 0.55" 



1.1 " 1.1 " 0.8 " 



0.8 " 0.8 " 0.4 " 



The superposition of carrier-current channels by means of filters 

 connected on the drop side of the d-c. composite set of course has no 

 appreciable effect on crossfire. However, the use of "transfer fil- 

 ters" at intermediate points to transfer the carrier from one pair to 

 another increases the coupling between wires of a pair and this may 

 be taken care of by increasing the capacity of the diagonals of the 

 condenser network. 



The arrangement shown in Fig. 10 has been found to be suitable 

 for use with 90 to 120 mile (145 to 190 km.) sections of No. 13 B.&S. 

 gauge (0.072 in., 1.8 mm.) loaded cable circuits. 



In the case of open-wire circuits, receiving-end crossfire is com- 

 monly not serious excepting in special cases where high-frequency 

 carrier telephone or telegraph transfer filters are employed. In 

 such cases, effective neutralization may be secured by coupling the 

 wires of each pair by means of a transformer, no such coupling being 

 provided between the wires of separate pairs of a phantom group. 



In some cases the neutralizing arrangements and the telegraph 

 repeaters have been wired to jacks in such a manner that it is pos- 

 sible to patch the neutralizers from set to set by means of cords 

 when the line assignment is changed temporarily. In some cases 

 it is not desirable to provide such elaborate arrangements and, 

 therefore, switches are provided for disconnecting the neutralizing 

 apparatus from each set independently. In the case of the con- 

 densers, the duplex balance of the other telegraph sets associated 

 with the particular group of condensers is preserved by switching 

 directly to ground the connection from the artificial line of the set 

 to be disconnected, as shown in conjunction with the lowermost 

 duplex set in Fig. 10. Switches for disconnecting the neutralizing 

 transformers are illustrated also for the same duplex set in this figure. 



Practical Results Obtained with Neutralization 



The following table gives data which show roughly the amount 

 of crossfire between wires of a phantom group without neutralizing 

 * See Figure 9. 



