356 IDEAL HOME LIFE
The Receiving Apparatus
A wireless receiver is easily made, that is, all except the head telephone receiver, or you can buy the whole receiving apparatus ready made. Many boys have only receiving stations, for a license is not required to listen in and wherever you live you are almost sure to be within signaling range of some other station. A receiver consists of (1) a crystal detector, (2) a tuning coil, (3) a variable condenser, and (4) a pair of head telephone receivers.
A crystal detector in its simplest form is merely phosphor-bronze, or a German silver point, pressing gently on a crystal of silicon or of iron pyrites. A metal framework screwed to a hard rubber base is used to hold the crystal in place and to provide the means for obtaining the right pressure of the point on the crystal.
The tuning coil is made by winding a single layer of No. 20 or 22 insulated copper wire on a cylinder of wood, glass, or other material; the insulation of the wire is scraped off in two parallel lines the length of the coil and two springs sliding on brass rods make contact with the turns of wire.
The tuner, as it is sometimes called, is used to tune in any station, that is, to adjust the aerial wire and circuits of your receiver to the wave length sent out by the station which you want to listen to. It is also useful to tune out interfering signals and to make the received signals ring clear and loud in the receiver.
The best kind of a receiving condenser is of the variable type. It is made of a number of thin sheet brass semi-circles, called leaves, half of which are fixed in position and the other half, which alternate with the fixed leaves, are made movable. The movable leaves can be turned by means of a knob and very sharp tuning can be obtained when it is used in connection with the tuning coil.
To receive over long distances a good pair of head telephone receivers must be used. A receiver wound to 500 ohms resistance is good enough to receive over distances of 100 miles or so, but for longer distances each receiver should be