Page:Popular Science Monthly Volume 91.djvu/330

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��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.

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