INDUCTIVE LOADING FOR TELEPHONE FACILITIES 763 



(V-C) Voice Frequency Phantom Loading for Combination with Side 

 Circuit Carrier Loading 



Voice-frequency, impedance-matching, phantom circuit loading is avail- 

 able for use in coordinated combinations with C4.1, C4.8, and B15 carrier 

 loading in situations where the need for improving the phantom circuit 

 transmission in an incidental cable warrants the use of loading. This brings 

 up a factor not previously mentioned, namely, that the early applications of 

 carrier telephone systems made use of the side circuits of open-wire phantom 

 groups. This is still the general situation, especially with the short-haul, 

 single-channel systems. On the other hand, a substantial fraction of the 

 Type C systems installed since the late 1920's, including those that now 

 work in the frequency-band below a Type J system, uses open-wire pairs 

 that are not arranged for phantom working. 



The phantom loading under consideration is limited to voice-frequency 

 operation because of the serious technical difficulties and high costs that 

 would be involved in the satisfactory operation of carrier systems simul- 

 taneously on open-wire side circuits and their associated phantoms, and 

 through the incidental cables. 



The phantom group full- weight loading units and terminal loading units, 

 which provide the phantom circuit loading, also include carrier loading 

 apparatus for the associated side circuits; i.e., the phantom loading appara- 

 tus is not separately available. Thus, when phantom loading is required, it is 

 necessary to engineer and install the loading on a carefully coordinated 

 phantom-group basis. 



The "full-coil" inductance of the phantom loading used in association 

 with 30- kc. side circuit loading is 12.8 mh. and the full loading-section 

 capacitance corresponds to that of "E" spacing. Thus its loading designation 

 is El 2.8, and the complete phantom-group loading designations become 

 CE4.1-12.8 and CE4.8-12.8. The corresponding phantom circuit loading for 

 use in association with B15 side circuit loading is designated H15, and the 

 phantom group loading is designated BH15-15. 



There must be an integral number of side circuit carrier loading sections 

 in each voice-frequency phantom loading section. This ratio is 2 to 1 with 

 BH loading. With CE loading, it may be 7 or 8 or 9, to 1, depending upon 

 the average amount of building-out in the side circuits. This numerical 

 variability with CE loading results from the fact that the condensers which 

 are used primarily for building out the (carrier) side circuits add negligible 

 capacitance to the phantom. An adjustable four-wire type of condenser is 

 available for capacitance building-out adjustments of the phantom circuit. 

 Depending upon the amount of capacitance building-out used in the carrier 



