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 



