How to Become a Wireless Operator 



II. — Construction of a One- Mile Wireless Transmitter 



By T. M. Lewis 



(Continued from September issue) 



IN AN article published last month, 

 directions were given for putting 

 together a little buzzer wireless 

 telegraph set which would operate over 

 a distance of a few hundred feet or even 

 more. This small outfit was sufficient 

 to demonstrate such of the principles of 

 wireless telegraphy as should be known 

 by ever>' student and to send messages- 

 from one house to another nearby. The 

 receiver was sensitive enough to pick up 

 messages from commercial stations for 

 some distance around, provided that a 

 fairly long antenna wire was connected 

 to it and properly tuned. 



The amateur who has built and tested 

 the buzzer set will want next to own and 

 operate an outfit with which he can 

 signal over greater distances. It is the 

 purpose of this article to describe the 

 construction of a wireless telegraph 

 sender which can be made cheaply and 

 easily, and which will give good strong 

 signals at a suitable receiving station 

 located as much as a mile or more away. 

 The apparatus for the receiver will be 

 taken up in later articles; the experimen- 

 ter may well spend the intervening time 

 in building his sender. 



Transmitting Coil 

 One of tiie first requisites in increasing 

 the distance over which messages can be 

 sent is to increase the effective power of 

 the sender. The buzzer run from a 

 couple of dry cells is not strong enough 

 to make waves which will carry ver>- far, 

 so it becomes necessary to get an instru- 

 ment which will do better. Such an 

 apparatus is the ordinary induction or 

 spark-coil. The amateur may build his 

 own spark-coil by following the descrip- 

 tions which are given in a great man\- 

 books on experimental electricity, but 

 in the long run he will find it cheaper 

 and more satisfactory to buy one. An 

 automobile jump-spark coil is about as 

 good a small induction coil as can be 

 obtained. Often it is pos.sible to get one 



at a nominal price from a garage or an 

 electrician in the neighborhood. Even if 

 purchased new from an electrical supply 

 house, a good coil capable of giving a i-in. 

 spark between needle points in air will 

 not cost more than three or four dollars. 



There is also needed a Morse key, for 

 sending the dots and dashes which make 

 up the signal letters. This may be an 

 ordinary' telegraph key, which costs 

 about seventy-five cents, or e\'en a 

 "strap" or signal key of the kind that 

 sells for only twenty-five or thirty cents. 

 If he desires, the experimenter may build 

 his own key as shown in last month's 

 article. For the heavier currents used 

 in the spark-coil (as compared to the 

 buzzer) it is a good plan to use larger 

 key-contacts than those illustrated. 

 They may be made by soldering copper 

 washers on each of the contact screws. 



To furnish power for the coil, the best 

 thing is a 6 or 8-volt storage-battery. 



Twelve dry cells arranged so as to 

 distribute the load between the two sets 



This is quite expensive, however, and 

 also requires occasional recharging. 

 Satisfactory results may be secured by 

 using 12 dr>' cells connected as shown in 

 Fig. I. With the battery arranged in 

 this way the voltage is no greater than 

 can be had from 6 cells, but the load is 

 distributed between two sets of cells 

 working side by side in parallel. As a 

 result, the battery will last much longer 

 than if onh- 6 cells were used. The vibra- 

 tor on the spark-coil should be adjusted 

 so that it buzzes freely, with a high- 

 pitched sound, whenever the sending 

 key is pressed. A spark-gap connected 



