Popular Science Monthly 



623 



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. 



/y J 



of the wireless mast 



