How to Become a Wireless Operator 



IV. — Simple Adjustments and Connections 

 By T. M. Lewis 



{Continued from November Issue) 



IN THE article published last month 

 there were giv^en descriptions of a 

 crystal-detector and stopping-condenser 

 to be made and used in connection with the 

 transmitting set of the October article, for 

 sending wireless messages over a distance 

 of a mile or thereabout. Both the detector 

 and the condenser are of types which can 

 later be used in receiving stations which 

 will pick up the messages from large 

 commercial or government plants not only 

 nearby, but hundreds of miles away. With 

 the small sender using a spark-coil, however, 

 the range will be limited to a mile or so, 

 unless the aerials at both stations are large. 



The Test-Buzzer 



In using a crystal-detector it is necessary 

 to be able to find out instantly whether or 

 not the adjustment is sensitive. When the 

 needle-point bears lightl)' upon some parts 

 of the crystal, the receiver is sensitive and 

 able to translate messages coming from a 

 distance; with the contact at other points, 

 however, the instruments seem absolutely 

 dead. 



Obviously, to be certain that messages 

 can be received effectively, one must be 

 sure that his detector is properly adjusted. 

 The best way to do this, and the way 

 which is used bj' the professional operators 

 in most large stations, is to take advantage 

 of the feeble signal-waves induced by a 

 buzzer. By setting up a small sending- 

 outfit, such as described in the September 

 issue of the Popular Science Monthly 

 in the first article of this series, the sensitive- 

 ness of the detector may be tested by 

 listening in the recei\'ing telephones and 

 at the same time pressing the testing-key. 



Figure i shows how to wire up the buzzer, 

 strap-key and dry cell described in the 

 first article. The only difference from the 

 little sender used to signal from one room 

 to another is that the vibrator-contact post 

 of the buzzer is connected to a miniature 

 aerial wire only a foot or two long, instead 

 of to a genuine, full-sized antenna. The 

 miniature aerial is run along the table 



about 2 or 3 in. from one of the wires 

 leading to the detector, as indicated in 

 the illustration. Fig. 2. 



The Change-Over Switch 



In order to shift connections from sending 

 to receiving, there must be provided a 

 good-sized double-pole double-throw knife- 

 switch. The lever -arms of the switch 

 should be at least six inches long, and the 



8UZZER ^ 



TE5T AERIAL 



It is necessary to use a test buzzer to 

 find out if the adjustment is sensitive 



jaws should be mounted upon a slate, 

 marble, or fiber base a corresponding 

 distance apart. If the switch used is too 

 small it will not have enough insulation to 

 prevent the sparks from the secondary of 

 the induction-coil from jumping to ground 

 by way of the receiving contacts. 



A second-hand knife-switch of this size 

 and type can be bought for about one 

 dollar or less; if none can be obtained, it 

 is not difficult to improv-ise from },^ by 

 J-2-in. strip copper, an instrument which 

 will work perfectly. It is only necessary 

 to obser\-e closely the construction of the 

 big knife-switches of the double-throw 

 type, in some central station, and to 

 imitate them as accurately as possible. A 

 number of brief articles have been published 

 in the technical magazines, gixing details 

 of construction and dimensions for such 

 switches. The connections for the change- 

 over switch are shown in Fig. 2. 



The Detector-Protecting Switch 



When the wireless station is completely 

 equipped with detector and spark-coil, it 

 is essential to make some provision which 

 will protect the delicateh' adjusted cn,-stal 

 from the \Iolent impulses set up by the 



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