Tuning Coil.
Next you need a “tuning coil.” This has a wooden base twelve inches by six and an inch thick. To make the coil itself a stick twelve inches long and one and a half inches in diameter—a piece of an old curtain pole will do—and wind carefully on it a half pound of the No. 22 single-covered copper wire. The end of this wire is fastened to the stick with a small tack, and it should be wound very evenly and closely. The last end is left free for a connection. After it is wound give the wire three coats of shellac, making sure that each coat is dry before another one is put on. When it is thoroughly dry mark two straight lines from end to end, a quarter of an inch apart. With a sharp knife scrape off the insulation so that the wires are bare on the outside, but be careful not to disturb the insulation between the wires. To mount the coil, nail at each end a wooden strip three inches wide, three and a half high and one inch thick. This has also to be nailed to the base, and it should be placed so that the coil will clear the base by a half inch. The strip of bare wire on the coil should be uppermost. Now get a brass rod one quarter of an inch square and thirteen inches long; a thin brass strip one quarter inch wide and two inches long; another strip one inch wide and one and one-quarter inches long; and two round headed brass screws. Bend the wider brass strip around the brass rod to form a slider. Bend the narrow brass strip in the center to form a V spring. Solder one end of this to the slider so that it is in the position shown in the drawing. Slip the slider on the brass rod, place the rod in position directly over the pathway of bared wire on the coil so that the lower end of the V spring will press on this pathway, and fasten the rod securely with the brass screws to the wooden end pieces.
Aerial.
Switch.
For the “aërial” get three or four hundred feet of wire—No. 16 galvanized wire will do, though aluminum or copper wire is better—some insulator knobs, and two cross spreaders three feet long. The parallel wires in the aërial should be at least two feet apart, and the aërial should be placed as high as possible so that surrounding buildings, etc., will not interfere with the wireless wave. The bare wires, wherever they are fastened to poles or trees must, of course, be wound around insulators. For a ground connection, fasten an ordinary insulated wire to a water pipe or to a piece of iron pipe sunk five feet in damp ground. A safety switch may be made, like the drawing, from a piece of wood six inches square and an inch thick, a piece of stiff brass three inches long and a half inch wide, and three round-headed brass screws.
Diagram of Circuit.