Arc Light Interference 



IN the November and December issues 

 of Popular Science Monthly there 

 were published several queries and 

 answers on the matter of arc light inter- 

 ference with received signals. Our read- 

 ers were asked to contribute suggestions 

 which they found helpful in overcoming 

 or reducing this 

 sort of disturbance. 

 A large number of 

 replies have been 

 received, and the 

 proposed methods 

 are here described. 

 It appears that at 

 least two kinds of 



no y Power line 



6 round -^^ 

 Grounding line 

 through the lamp 



Balanced 



inductive disturbances are encountered. 

 The first of these is the ordinary "induc- 

 tion hum," heard in nearly all wireless 

 stations that have alternating current 

 power lines run- 

 ning into or very 

 near them. The 

 second type is that 

 which is caused by 

 the flickering and 

 fluttering of carbon 

 arc lights in opera- 

 tion, and which is 

 usually transferred 

 to the receiving 

 wireless aerial by 

 induction from ad- 

 jacent power lines. 

 The induction 

 hum is the most 



common and the easiest to eliminate. It 

 is troublesome when direct-coupled re- 

 ceiving tuners are used, but may often be 

 cut out by changing over to an induc- 

 tively-coupled receiver. One experi- 

 menter states that by running his aerial 

 lead through a fixed condenser i)cfore 

 connecting to his tuning coil, he reduced 

 the interference greatly. Another writes 

 that he secured good results by placing a 

 7-volt tungsten lamp in series with the 

 antenna lead, keeping the lamp lighted 

 to a certain brilliance (determined by ex- 

 periment) by means of a battery and 

 rheostat. The real reason for any im- 

 provement gained from either of these 

 last two methods is not apparent; the 

 use of inductively-coupled apparatus, 



J ma// oer/o/ near 

 power /lauie 



however, has not only been found effec- 

 tive by practical test, but also is theo- 

 retically correct. 



Another way of cutting out the hum is 

 efi^ected by merely opening the main 

 switch which brings power into the 

 house containing the receiving instru- 

 ments. This method prevents internal 

 induction from the leads, but, of course, 

 cannot be used when it is desired to 

 utilize the electric power for transmitting 

 signals or for lights. In some stations 

 the trouble has been stopped by connect- 

 ing one side of the incoming i lo-volt line 

 to ground, through a fuse which will 

 blow on 2 amperes or so, or by grounding 

 through a condenser or small iio-volt 

 lamp. Which of the two power wires is 

 to be grounded through the lamp, con- 

 denser or fuse in this way must be de- 

 termined by trial. 

 In grounding 

 through a condens- 

 er the fuse should 

 also be used, for 

 protection in case 

 the condenser 

 punctures. 



Some of the 

 above methods are 

 effective not only 

 for the alternating 

 current induction, 

 but also for the 

 ragged, harsh 

 noises from arc 

 lights. Especially helpful is the plan of 

 grounding the power lines, for in many 

 cases the arc induction is picked-up by 

 the regular lighting lines and brought to 

 the wireless station over them. Both 

 kinds of disturb- 



^ ~- Ground 

 primary method of reducing arc 

 light interference 



ance have also been 

 reduced in wireless 

 stations by con- 

 necting the dia- 

 phragms of the re- 

 ceiving telephones 

 to ground, either 

 directly or through 

 a condenser. Often 



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2 m f con (fencer 

 fuse 



Oraand^ 

 Grounding line 

 through the conden- 

 ser and the fuse 



it helps merely to 

 touch the aerial or ground lead with the 

 finger, or to rest the hand upon a metal 

 plate connected to the blocking condens- 



617 



