Popular Science Monllih/ 



COPPER WASHERS 

 'SCREW 

 EYE 



450 



and valuable of these are the following, 

 which are named in the approximate 

 order of their complexity: 



"The Elementary Principles of Wire- 

 less Telegraphy," by R. D. Bangay. 



"Experimental Wireless Stations," by 

 P. E. Edelman. 



"Wireless Telegraphy," by A. B. 

 Rolfe-Marlin. 



"Textbook on 

 Wireless Telegra- 

 phy," by Rupert 

 Stanley. 



"Wireless Telcg- 

 rapliy," by W. H. 

 Marchant. 



"Elementary 

 Manual of Radio 

 Telegraphy," by J. 

 A. l'"leming. 



"A Handbook of 

 Wireless Telegra- 

 phy," by J. Ers- 

 kine-Murray. 



"Wireless Teleg- 

 raphy," by J. Zen- 

 neck, translated by 

 A. E. Seelig. 



The above list should be useful as a 

 guide in hunting for technical informa- 

 tion about radio telegraphy. There arc 

 many other books on the subject, a 

 large number of which are excellent. 

 Those named, however, include one or 

 more of each type from the most 

 elementary to the most advanced. 



A Simple Transmitter 



In beginning experiments on wireless 

 telegraphy it is best to take up first the 

 least complicated arrangements, which 

 are suitable for very short distances, 

 and then to work along gradually from 

 these to the more important instruments. 

 This first article, therefore, will descril)e 

 the use of a complete wireless set which 

 is capable of demonstrating the prin- 

 ciples involved. By its use you should 

 be able to send messages a distance of a 

 lew hundred feel, from one part of the 

 house (o another; by using long aerial 

 or antenna wires, upward of a (|Iku lor of 

 a mile may be cfjvered. 



The sending station involves nothing 

 more than a simple buzzer, a telegraph 

 key, a tuning coil and a few cells of dry 

 battery. These are to be connected 



together as shown in Fig. I ; a good 

 kind of wire to use is No. i8 annunciator, 

 since this has a strong waxed double 

 cotton covering which is easily removed. 

 The buzzer can best be purchased from 

 any electrical supply store for about 

 forty cents; the key may be bought, or 

 simply impro\ised by cutting and bend- 

 ing some thin strips of brass as shown in 

 Fig. 2; the dry 

 cells will cost from 

 twenty to thirty 

 cents each. 



The tuning coil 

 may easily be built 

 by winding about 

 fifty turns of an- 

 nunciator wire on 

 a cardboard tube 

 a 15 proximately 

 three inches in di- 

 ameter. The ends 

 may be fastened 

 and at the same 

 time made avail- 

 able for convenient 

 connection by at- 

 taching them to 

 into the tube at the 

 There is no need of 



The Construction of the Buzzer 

 for Sending Apparatus 



Key Made by Cutting and Beading 

 Some Thin Strips of Brass 



binding posts let 

 top and bottom, 

 building this tuning coil of any specific 

 size. The diameter may be anything 

 from two to four inches, and the number 

 of turns from thirty to seventy. It is 

 only necessary that two identical coils 

 be built, one for the sender of Fig. I, 

 and the other for the receiver of Fig. 4. 

 In setting up the sender it will be 

 found that one end of the tuning coil 

 must be attached to the contact post of 

 the buzzer, which is marked 3 in Fig. I ; 

 this can be done b\' removing the cover 

 of the buzzer and wrapping a bare 

 cojiper wire firmly about the post. Care 

 must be used to ]irc\ent the contact 

 wire from touching the metal base, 

 however, or the operation of the buzzer 

 will be stopped. Binding post 2 is to be 

 connected with "earth" as indicated at 

 K in the diagram. The earth connection 

 is easih' made b\- rinming a wire to a 

 water pipe or ste.un radiator and wrap- 

 |)iiig tlu' iiare end tightly about a scrajjed 

 or plated portion of the pil>e. The 

 uppt'r end of the tuning coil is to be led 

 to the aerial or antenna wire, at .1. This 

 antenna may be of any convenient size, 



