Page:Popular Science Monthly Volume 89.djvu/642

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across the secondary winding will break down whenever the vibrator is starte<l buzzing, and a singing, clear spark will jump across as long as the key is held down.

��Popular Scirncr Monthly

at C. Four yi-'m. holes are then bored in each, at points a little less than 2 in. from the corners, along diagonals as shown in Fig. 4. Twelve porcelain

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��The Spark-Gap spark-gap for the

��wireless shown in Fig. 2.

��A good sender can be made as Two battery zincs, Z, Z', which can be bought from any electrician, are cut off to about 3 in. in length, leaving the' connection screws at the head of each.

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A spark gap made from two battery zincs and a hardwood base boiled in paraffin

Holes to fit these a trifle loosely are bored through two stubby brass stand- ards or pillars, P, P'. A smaller hole is bored lengthwise through each pillar and tapped to take a 10-24 machine screw, such as 5 and 5', to clamp the zinc electrodes in any position desired. Sim- ilar screws, S^ and S^, pass upward through counter-bored holes in a hard rubl)cr base, B, and serve to fasten the ]jillars in place. Hardwood boiled in paraffin may be used for the base, but rubber is better because it is a bettor insulator. The ends of the zinc rods, where they come close together, should be filerl i)erfectly smooth and parallel.

The Loading Coil

It is essential to use a "loading coil" with this outfit in order to get the best results, and to make the transmitter meet the rciiuircnicnls of the l<"ederal laws governing the ojjeration of wireless telegraph senders. This coil can easily be made l)y following the suggestions given in Figs. 3 and 4. Two square boards, about 12 by 12 in. with rounded corners, are first cut out of hardwood about I in. thick. A hole |.f in. in (li.iiiicler is drilled at the center of each, and I oniiter-bored to about I in. in diameter in the bottom of the baseboard

��Twelve insulators of the sort shown in Fig. are slipped over each of four yi-'m. hardwood dowels, whose ends pass through the yi-'m. holes just referred to and are cut off (lush with the upper and lower surfaces of the top and base. A long ]/i-\n. brass bolt is passed upward through the central holes, so that its head drops into the counter-bored space in the base and its threads project a short distance above the top. A washer and nut put on the upper end will then hold the entire framework together.

Some No. 10 bare copper wire, or some stranded bronze tiller-rope or aerial wire, is to be wound spirally on the insulators. Referring to Fig. 3, the end is first wrapped around the upper front right-hand insulator A and spliced on itself. The wire is then led straight back to the toji insulator of the back right upright, then across to the top back left insulator, as shown by the dotted line, then forward to the top front left insulator, and then to the ne.\t lower front right porcelain. The winding is continued as shown until the last insulator, B, is reached; there the wire is made fast by splicing, as before.

Two connected clips must be made or purchased. The spring testing cli])s sold by electrical su|iply houses are admirable for tliis, though anything of the sort will

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��A loading coil to make the transmitter meet Uic requirements of the federal laws

do. I'^lexible wires are soldered to each of them, so that connection to any part ol I lie bare wire-spiral may be maile merely by clipping on the ilesin-jl point.

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