How a boy constructed a wireless instrument
By the aid of the accompanying diagrams I think any boy should be able to construct a simple, easily adjusted wireless receiving set, whose cost is trifling. I will first give a brief explanation of the use of the various instruments. First comes the tuning coil. When a station is in the act of sending great waves of oscillations, unseen, unheard, unfelt, are being radiated in all directions. If a station sends with a very long aerial, or antenna, the wave radiated is long, and if sending with a smaller aerial, the wave set up in the ether is correspondingly short. For this reason, we have the tuning coil at the receiving end so constructed that it will add more wavelength to the receiving station to correspond to any station to which it is desired to tune.
The detector is the center of the whole outfit, for here, the incoming wave, surging between the brass point and the silicon crystal, sets up a current which may be heard in the receivers which are connected across it.
To construct the tuning coil, first obtain a perfectly smooth cylinder of some soft wood 3 inches in diameter and 10 inches long, and on it place two ends 4-1/2 inches square. Upon the spool thus formed, wind enough wire to cover it with one layer, and bring one end of the coil to a binding post. The wire should be No. 24 enameled copper, and it will require about one-quarter pound.
The sliding contact consists of a brass rod 10 inches long, 1/4 inch square, to be drilled at both ends and screwed to coil ends when the slider is finished. The slider consists of a piece of square tubing which just fits the rod. Solder a piece of brass spring to it, as shown at 8. When the slider is placed on a coil connect it to a binding post, bend the spring so that it makes light contact with the coil and scrape the coil where the spring connects. Give the coil several coats of shellac.
To make the detector, take a strip of brass three inches long, one-eighth inch thick and a half inch wide. Bend as shown at B. Drill and thread it for a brass screw 1-1/2 inches long and with the top of the spool bolted to the head. File screw as shown at E. Drill the other arm of the bent brass strip and screw it to a base about four inches square.
Solder a piece of brass tubing to a piece of the spring brass a half inch wide and 2 1/2 inches long, brass tubing to be a fourth of an inch deep and one half inch wide, in which is to be set a piece of polished silicon. Screw spring and cup thus formed to base, after bending spring as shown at P. Silicon must come direct under brass screw. Mount two binding posts on the base and connect one to the “bridge band” and the other to the spring.
To make the condenser, cut two bases 7×15 inches. Cut two strips of common wrapping paper six inches wide by one yard long, two cardboards 6×3 inches, and obtain two strips of tinfoil five inches wide and one yard long. To build up the condenser, lay a strip of paper on a table. Above it lay a strip of tinfoil, being sure to get all perfectly even. Then lay another strip of paper and another of tinfoil. Place the two cards at one end of the strips and then bring wire connectors from each strip of foil out on opposite sides and roll condenser on cards. Press between the two bases and screw down at four corners, if desired, mounting two binding posts on one of the bases, to which connect the two wires from the strips of tinfoil. The instrument is then complete.
For the aerial, as long as we are only to have a receiving station, iron wire well galvanized to prevent rust is as good as any other. The aerial can be as big or as small as you desire, but try to get it up in the air a little if you wish to get good results. Get it good and long if possible. For a ground instrument the gas pipes or water pipes are excellent. For the hookup of the instruments, I would refer you to the diagram. The telephone receivers, the one part of the apparatus that we can not make ourselves, may be bought at any good electrical store.
With a set such as I have described, very good work can be done. I myself have read Cape Cod very clearly with it.