Austin M. Curtis
The following is a description of a wireless telegraph receiver which is very sensitive, yet simple, and which needs very little adjusting.
Make a base of | in. mahogany, or other hard wood, 3 1/2x3 1/2 in. Plane it off smoothly and round off the top edges. In the center of this base drill a 1/2 in. hole, 1/2 in. deep. Shellac and polish the base. Next get a piece of glass tubing with 1-16 walls and an outside diameter of 1/2 in. Cut off a piece 1/2 in. long and smooth the edges by holding in the flame of a bunsen burner until the edges begin to fuse.
Get a piece of platinum wire one inch long, about
24 gauge, and solder it to a piece of No. 22 copper wire about six in. long. From a point on top of the base near one corner, drill a 1-16 in. hole at an angle, so that it comes out near the bottom of the 1/2 in. hole and ends there. See Fig. 1. Push the piece of No. 22 wire through this so that the part which has the platinum pointing upwards. Break up some good sealing wax into small pieces and pack these tightly around the point of platinum wire. Next heat one end of the glass tube until it is hot enough to melt the wax and force the tube into the hole. The wax will melt and adhere to the glass, making a perfect joint and leaving the piatinum wire projecting above the wax.
Screw two double contact binding posts into oppo-ite corners of the base. Fasten to one of these the wire which comes from the bottom of the tube, and to the other piece of No. 24 copper wire which is coiled into a spiral for about 1/2 in, and the end left straight for 1 1/4 in.
Get a cork to fit the top end of the glass tube and drill in it a hole about 1/8 in. in diameter with a hot wire or twist drill. Boil the cork in paraffine until it is thoroughly saturated.
Some glass tubing 1/8 in. in diameter and platinum wire .002 in diameter is needed. This will cost about
25 cents per foot and 6 in. is needed. Take a piece of the tubing 4 in. long. Heat the middle of it in a gas flame and draw it out until it is the shape shown in Fig. 2. Break the two pieces apart, leaving a minute opening. Put a piece of the platinum wire 1/2 in. long in each piece of tubing, leaving a short piece of the wire projecting outside of the small end of each tube. Heat the tube until the wire is sealed into the glass and the glass hardens. Next grind down the glass on a dry whetstone until the wire flush with the glass. Fill the tube one half full of mercury, shaking it down until it touches the platinum wire inside the tube. Make about six of these points.
Put about one-half inch of mercury into the larger tube which is mounted upon the base. To the mercury add five or six small slivers of zinc. Put about 1/2 in. of dilute sulphuric acid (10 per cent) in the tube on top of the mercury. Now push one of the points in through the hole in the cork and put the cork in the tube. Put the end of the coiled wire into the point so that it touches the mercury. Connect a pair of head telephones of the highest procurable resistance across the two binding posts. A faint click should be heard when the wire is pulled away from the mercury in the point or touched to it. If no click is heard, grind the point down a little.
This receiver maybe used untuned by connecting-one binding post to the aerial wire and the other to the ground, with the telephones bridged across as above directed. It is particularly adapted, however, for working with a tuning coil.
Do not leave the cork in the tube all the time for the first three days or until all the zinc is dissolved in the mercury, otherwise the accumulated hydrogen gas may blow the cork and point out of the tube. If the point does not work satisfactorily, grind it down until it does.
With this receiver tuned the writer has received readable messages from a commercial station on a steamship over 500 miles away.