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Page:Popular Science Monthly Volume 89.djvu/464

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Popular Science Monllih/



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

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��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,

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