Page:Popular Science Monthly Volume 88.djvu/651

 Popular Science Monthly

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��curately to the inductance value which gives the loudest signal when the coup- ling is made fairly loose. This primary adjustment is then left fixed, and the condenser Ci cut into circuit to tune the secondary. By selecting the best set- ting of Ci in connection with several values of L3, one particular value which gives the best signals is found. This is left fixed, and the coupling is gradually opened. For each looser position of coupling, the primary inductance and the secondary tuning condenser are varied slightly, to the point which gives loudest signals; thus a final adjustment is found which gives either (i) the loud- est possible signals from the desired station, or (2) readable signals with a minimum of interference.

��How to Build the Mast for a Wireless

THE person who wishes to install a wireless station can easily find ample directions. When it comes to a support for his aerial, however, it usually says to erect a mast sixty to ninety feet high, without gi\'ing the details of its construction. Following are the materials needed for a mast sixty feet high : 10 pieces, 12' by 2" by 4", straight- grained hemlock. 2 pieces, 4' by 2" by 4 ", chestnut.

1 J/^-inch bolt, 10" long. 29 ^-inch bolts, 8" long.

116 blank nuts to fit on ^<?-inch bolts. 120 ft. of rope.

2 pulleys; also guy wires and in- sulators.

The first thing to consider is the foun- dation. This is made of two 4' chestnut pieces, shown at a Fig. 2. The durabil- ity of the wood may be increased by ap- plying a coat of tar paint. Bore a 3^- inch hole in each timber 3' from the

end. Nail a block b, 4" thick, between the other ends; this holds the pieces the proper distance a part. Dig a hole

���Construction details

��where the mast is to be erected and place the wooden pieces in it, with the block at the bottom. Allow the ends to project 8" above the ground, which should be stamped down very firmly to insure stability.

For the mast proper, saw one of the 12-foot pieces in half. Lay one of the halves on top of a 12-foot piece so that their butts are even at one end ; and 3" from their butts bore a 3^-inch hole through both. Bore another 3^-inch hole 3' from the butts; then one every 2' along the whole length of the mast.

Bolt the one 6-foot piece and the three 12-foot pieces together. The bolt is slipped through the holes, four blank nuts put on the bolt and then a threaded nut screwed on. The blank nuts are designated by a and the threaded one by b in Fig. i. This 24-foot section is laid so that its butt can be bolted to the foundation with a 3^-inch bolt 10" long, as in Fig. 2. Before raising this section, drive a 6-inch spike bent as shown in Fig. 4. Thread a pulley with rope and hook it upon this spike. The tackle will then be in place when the section is raised. After raising the 24-foot section to a vertical position and guying it temporarily, drive a 6-inch spike into the end of a 12-foot timber, after bending the spike as shown in Fig. 4. Then hook the second pulley c on the spike, Fig. 5. The end of the rope from pulley b is tied to the piece a few inches from the center. The reason for this operation will be made clear by examining Fig. 5. Each time a 12-foot piece is raised, the tackle is alwa^^s rais- ed for the next tim- ber. When in posi- tion, each piece is bolted to the one raised before, and so on to the top. Two sets of per- manent guys are at- tached to the finish- ed mast, as indicat- ed in Fig. 3, one set being 30' and the other 60' from the ground. The guys should be insulated every 30'. — E. R. Thomas.

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of the wireless mast

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