136 



METHODS OF COMMUNICATION FOR FOREST PROTECTION 



coil in the circuit, direct metallic connection between the two lines is avoided, as each 

 is joined to a separate winding of the coil. Transmission, therefore, through the coil 

 is accomplished by induction and if desired it may be accompanied by a stepping-up 

 or a stepping-down of the voltage in passing from one line to another. A great many 

 repeating coils, however, do not alter the voltage, but have both windings of the coil 

 alike. 



Protector 



Protector 



tc C/rct/if f s~\ \ / 



Von [\Q) { 



Sec ft on 



Repecrfing Co// 



Fig. 8'6 Method of inserting a metallic circuit section in a grounded line to overcome 



induction disturbances 



Fig. 87 Diagram of a phantom circuit 



To connect a grounded and a metallic circuit through a repeating coil, both wires 

 of the metallic line are joined to the ends of the same winding of the coil. The single 

 wire of the grounded line is then joined to one end of the other windings, the second 

 end being grounded. By using two such coils, a grounded line may be transformed 

 into a metallic line through a noisy portion of the length, and all foreign noises 

 perfectly eliminated. This method of connection is shown diagrammatically in 

 Fig. 86. 



