152 METHODS OF COMMUNICATION FOR FOREST PROTECTION 



before each test. The distance between the clapper ball and the gong after rebound 

 of the clapper ball should be approximately KG in. If in proper adjustment, each gong 

 when struck by the clapper should emit a clear, ringing sound. 



5 PORTABLE TELEPHONES 



The two standard portable instruments, the 1375-A and the 1004- A, are so con- 

 structed that they are very unlikely to give trouble unless tampered with. Owing 

 to the small size of the battery employed in both these telephones it is necessary to 

 make more frequent renewals than in the permanent sets. No adjustments are 

 required in the 1375-A set, but in order to get the best results from the buzzer of the 

 1004-A set it is sometimes necessary to alter the .spark gap. This should not be 

 attempted in the field, and any instruments not working satisfactorily should be 

 returned to the district inspector for repairs. 



The 1004- A hand set and the hand set of the 1375- A 'instrument being of rather 

 thin sheet aluminium are very liable to serious injury through denting. Such dents 

 may cause short circuits which interfere with the successful use of the instruments. 

 When these occur they may often be removed by pressing out from the inside, using 

 a smooth piece of hardwood with a rounded surface. 



Section 93 " Trouble " 

 1 BROKEN CONNECTIONS AND OPEN COILS 



In the instruments that the Forestry Branch has adopted as standard the chances 

 for trouble have been reduced to a minimum. Lightning is the greatest source of 

 trouble. 



The riniger coils, which are constructed of fine insulated wire wrapped around 

 an iron core, occasionally burn out. When this happens it is necessary to substitute 

 a new coil. The armature in the generator may also burn out, necessitating replace- 

 ment. (The armature is the part in the generator that revolves between the per- 

 manent magnets. This is composed of two windings around an iron base on opposite 

 sides' of the centre. The generators used on some sets are protected to a certain 

 extent by means of a " shunt.") 



In the receiver the small coil of insulated wire wrapped around the end of the 

 permanent magnet is sometimes burned out by lightning or heavy outside currents. 

 The induction coil is sometimes similarly damaged. 



The following methods of testing may be used to locate trouble as just described : 

 Connect one side of a receiver to one pole of the battery. If when the other side of 

 the receiver is touched to the other pole of the battery no click is heard, the receiver 

 is open. 



By the use of a receiver, if in serviceable condition and the batteries as shown 

 in Fig. 95, any of the wire coils may be tested. 



A test of the generator may be made by disconnecting the instrument and placing 

 the moistened tips of two fingers over the two screw binding-posts on the end of the 

 generator. If the latter is in adjustment, current will be felt when the crank is 

 turned. If no current is felt probably the armature of the generator is open, and a 

 new armature must be obtained. The hard-rubber bushings sometimes carbonize, 

 due to oil or grease getting on them, and cause generator trouble. 



It is impossible to talk through the transmitter when the induction coil is open, 

 when the batteries are weak, or when there is a loose connection somewhere in the 

 instrument, as at one of the connections on the batteries or at the switch-hook. 



2 DETECTION AND KEMEDY 



Trouble in any place is likely to affect the entire system. Inexperienced persons 

 should not be allowed to tamper with telephone instruments. It is usually well to 



