Stránka:roll 1917.djvu/158

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26 Woodcraft Manual for Boys ‘

brass balls and insulated handles which slide through a pair of brass standards fixed to a marble or other insulating base. The spark-gap is connected to the terminals, that is the ends of the wires of the secondary coil. TEE TUNING COIL. The tuning coil of the sending apparatus is simply a coil of heavy brass or copper wire one eighth or one fourth inch in diameter, wound in a helix around a wooden frame, and it is used to enable the operator to give the electric waves sent out by the aErial a certain length in order to conform to the Government Regulations. The tuning coil is connected in circuit with the spark-gap and the condenser, and the aerial and ground wires are connected to it as we shall presently see. Tm: HIGH TENSION CONDENSER. This can be either a bat- tery of Leyden jars or it can be made of a number of sheets of glass covered with tin-foil. The sending condenser must be pro- portioned to the size of the tuning coil and the larger it is, within certain limits, the shorter and thicker the spark at the gap will be and the more efiective the electric waves that are sent out by the aérial. Connecting Up the Transmitter When you have made or bought all of these pieces of apparatus connect them up as shown in Fig. 3 with No. 14 copper wire, ' which should be insulated, that is the primary of the induction coil, or transformer; the battery, or other source of current, and the key are connected in series as it is called. Next the spark-gap, the condeneer, and the tuning coil are connected in series and then the end of the aérial wire is con- nected with the top binding post of the tuning coil, while one of the clips of the tuning coil and the ground wire are connected together, all of which is clearly shown in Fig. 3. Before sending wireless telegraph messages with this or any other set you must have a Government license and the way to obtain a license is fully explained in a pamphlet entitled Radio Communication Laws of the United States and which you can get by sending fifteen cents to the Superintendent of Documents, Government Printing Ofiice, Washington, D. C. THE INTERNATIONAL MORSE Cons: The following code is used throughout the world on land and sea for sending wireless telegraph messages and for this reason it is called the International Morse Code. It is a little difierent from the ordinary Morse Code, but it is easier to learn than the latter. You must be able to send at