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Page:Popular Science Monthly Volume 89.djvu/965

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Popular Science Monthly

��951

��best both for sending and receiving mes- sages. The wire in the loading coil has the effect of lengthening the aerial; it is there- fore perfectly clear that, since it is desired to have both antenna systems of the same total length, less of the loading coil must be included in circuit v.-ith . the longer antenna wire. The coiled wire is more cfTecti\e in increasing the station's wa\e- length tiian the straight wire in the aerial, however; so less of it needs to be added than one would imagine if he merely considered the difference in the lengths of the two aerial wires themselves.

Adjusting and Operating

When the apparatus is set up as shown in Fig. 2, the first thing to do is to put the transmitter into operation. Throw the change-over switch to the left-hand or sending side, and set the spark-gap at about 1/16 in. separation. Making dots and dashes with the key, adjust the induc- tion-coil vibrator to the position which gives a clear, sharp spark between the electrodes of the gap. The spark should be white and snappy, and should sing with the tone of the vibrator. If >-ou cannot get this kind of spark, the set is not working properly and you must go over the antenna insulation to be sure that it is good. If the coil gives a good spark without the aerial connected with it, but won't spark when the antenna and ground are put in the circuit, it is proof that the insulation is not good enough, or that the spark-gap is too wide for the power of the coil. The gap should not be opened more than }/$ in. at any time.

Having adjusted the transmitter, swing the change-over switch to the right-hand or receiving side. Put on the telephones, see that the detector-protecting switch is open, and hold down the strap-key connec- ted with the test-buzzer. Mo\-e the needle- point of the detector around over the surface of the crystal, witli light pressure, until the loudest signals are heard in the telephones. The detector is then adjusted and the receiver is ready for use.

The next step is to arrange a sending schedule with your friend who operates the other station. At some fixed time, say four o'clock, let him close his detector- protecting switch, throw his change-o\-er switch to the sending side, and send some predetermined test signal such as "B" in Morse, over and over again, for five minutes. During these same five minutes

��have your telephones on, your detector- • protecting switch open, your detector adjusted to its best sensitiveness, and your change-over switch in the receiving po- sition. If you have built your apparatus correctly and have set it up in accordance with the instructions of these articles, you should have no difficulty in recognizing the "dash-dot-dot-dot" signals being sent from the other station. Promptly at 4:05 your correspondent should stop sending, throw his change-over switch to the receiving side, open his detector-protecting switch, put on his telephones and adjust his detector. At the same time you should go through the opposite change-over, and begin to send him test signals for five minutes. If all is well he will "pick them up" at once, and when you stop at 4:10 he will be read}- to reply to you b\' wireless that he has iieard you; you can then give him the corresponding information and proceed to exchange messages.

You must always bear in mind, however, that whatever your station or his sends out will be heard by other stations which happen to be within range and tuned to the same wavelength. Your signals may even cause interference, and prevent the other stations from reading important messages addressed to them. For these reasons, only such transmitting as is necessarv should be attempted; and the Government

���TE5T BUZZER ANTENNA

��J"

��LOADING COIL

��CONDENSER -^-

��-CRV5TAL DETECTOR

���"^^ GROUND

��FIG. 3

��Wiring diagram for a receiver where it is only- desired to transmit messages in one direction

regulations as to the use of a pure wave shorter than 200 meters should be strictly observed. As pointed out in the October article, if over half the loading coil is used at each station and if neiliicr antenna is more than 75 ft. in length, the federal requirements will, as a rule, be met.

Station for Receiving Only If it is desired to transmit messages in only one direction, the change-over and

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