INSTALLATION OF FIXED EQUIPMENT 



103 



telephone set, and three single-pole, double-throw, ba'by knife-switches. With all the 

 three lines connected just the telephone remains across the line, the three extension 

 bells being disconnected. 



When it is desired to receive buzzer signals at a switching station, each line must 

 be separately .equipped with howler and condenser. Since it is impracticable to vary 

 the tones of buzzers sufficiently to enable them to be distinguished readily one from 

 another, it may be necessary to locate the various howlers in different parts of the 

 room or building in order to be able to tell which line is calling. 



Mote 



Fig. 



co//, remove 

 Wiring and connections on 47-A repeating coil 



oc/or new co//s. 



3 STANDARD REPEATING COIL 



The 47-A repeating coil is the most reliable and serviceable coil, both from a 

 talking and signalling standpoint, and should be used wherever possible. This coil 

 is also used for phantom work. By " phantom " i,s meant the utilizing of both sides 

 of a metallic line as one wire. As illustrated in Figs. 57 and 87, an additional tele- 

 phone circuit is thereby obtained. The repeating coil is also used whenever it 

 becomes necessary to jom a grounded to a metallic line. An 8-A repeating coil is 

 cheaper than the above and may sometimes be used for the latter purpose. 



The details of construction, and the arrangement and designation of terminals 

 of the 47-A coil, are shown diagrammatically in Fig. 56. 



4 PHANTOM CIRCUIT 



It is possible under certaiji conditions to carry on two or more conversations 

 simultaneously over the same telephone wire without interference. This is done by 

 installing a phantom circuit, the most common type used in forest lines being ;= 

 grounded phantom out of a metallic rural line. 



The following equipment is necessary: Two 47-A repeating coils, one extension 

 bell, and one double-pole, double-throw, baby knife-switch. By the method shown in 

 Fig. 57, the Forestry Branch utilizes both wires for their line, the connection with th 



