314 



Popular Science Monthly 



to the point from which the signals were 

 heard most clearly. Then they knew that 

 the amateur must be located at the point 

 where these two lines of direction inter- 

 sected ! 



After repeating their maneuvers many 



Fbsition of loudest 

 receiving 



Diagram illustrating the principle em- 

 ployed to locate the sending station 



times, continually getting nearer and nearer 

 to the unsuspecting amateur, the inspectors 

 found themselves within a block of his 

 station. The rest* was easy. There was 

 only one antenna on that block from which 

 the signals could come. The arrest of the 

 youngster followed. Needless to say he 

 has been taught a lesson and is not likely 

 to cause any further trouble. 



How to Make a Kick- Back Preventer 

 for Wireless Apparatus 



IN many instances where a wireless set is 

 employed for sending purposes the fire 

 underwriters require a kick-back preventer. 



The several instruments are con- 

 nected as shown to make the 

 kick-back preventer effective 



This piece of apparatus is, in some cases, 

 expensive to purchase; but it can be 

 easily made, at little expense. 



The essentials are a 16-C.P. carbon 

 filament electric-light bulb, with a socket to 

 fit it — a Mazda bulb will not do — two fuse- 



blocks and fuses, three binding-posts with 

 holes in the center to admit pieces of copper 

 wire, and a baseboard on which to fasten 

 the apparatus. The binding-posts are 

 used for a three-point safety-gap. The 

 several instruments must be carefully con- 

 nected as in the diagram, or the coil will 

 not work. 



This device is intended for no volts 

 with grounded power line. To find the 

 grounded side of the line take a 1 10-v. bulb, 

 with wires attached, and connect one wire 

 with the ground and the other with one of 

 the mains. The bulb lights only when it \i 

 connected with the other main — not with 

 the grounded side. 



In using this kick-back preventer, when 

 the key is pressed the bulb will light up and 

 the coil or transformer will operate. In 

 case of a kick-back this device will send the 

 excess current into the ground, and will 

 save the coil and fuses from burning out. 



Variable Primary Coil Using a 

 Switch Instead of a Slider 



IN winding tuning coils for long wave- 

 lengths, if the slider runs the 

 whole length of the tube it 

 causes extra labor and expense. 

 The following plan may be 



1 ■■ ■■ Switch points used instead of slider 



contacts on a vertical primary coil 



used to prevent it from doing so. Scrape a 

 few inches of the wire and use a rod of the 

 length designated. At intervals equal to 

 the length of the scraped wire take off taps 

 and run leads to switch-points. The 

 finished coil is manipulated in the same way 

 as the primary of a Navy type inductive 

 coupler. — Glenn Dunfee. 



A Use for Discarded Cylindrical 

 Food Boxes 



CYLINDRICAL cardboard boxes, such 

 as certain food products are packed 

 in, make excellent forms upon which to 

 wind tuning coils. By using two, one of 

 which is slightly smaller than the other, 

 a very satisfactory inductive coupler may 

 be made. — Edward McClure. 



