Page:Popular Science Monthly Volume 92.djvu/333

 Wireless Work in Wartime

VII. — Fundamental Principles of Radio Apparatus By John L. Hogan, Jr.

��THE six preceding articles of this series comprise a fairly complete set of instructions in learning wireless operating, from the simple viewpoint of telegraphing. Memorizing the code, read- ing Morse signals by sound, and practice in overcoming the difficulties of "station" and atmospheric interference have been taken up in some detail. All of these matters are essentials in the study of radio telegraphy, and they must be completely mastered if one is to become a first-rate operator. To be of the greatest value in radio work, however, and to advance in the naval, military or civilian radio services, it is important to be more than a skilled telegrapher. In addition to the ability to transmit and receive messages s\viftly and accurately under even the most adverse conditions, one should know how and why his instruments work. Such technical

knowledge is of the greatest use to the radio man in war work, for without it he is likely to be unable to make urgently needed re- pairs and adjustments. This, and the suc- ceeding articles will go into the simple technology of radio telegraphy, and should prove helpful in studying to qualify as one of the expert radio workers who are and will be so much needed in the Signal Corps and the Naval Communication Service.

The main purpose of these articles, then, is to guide the student to a thorough under- standing of the radio station, and to point out the precautions which must be taken if the best possible working is to be obtained. This wdll involve both the discussion of apparatus design, and the elementary theory of radio telegraphy. These two branches of the general art are so closely interwoven, however, that it is scarcely possible to tell where one stops and the other begins. One cannot design and build good radio apparatus, or operate it most effectively, without having a genuine appre- ciation of what it is to do and how it can be made to do it. Neither can one under- stand the theory in such a way that it will prove really useful to him, unless he has also a knowledge of the practical apparatus to

��which the theory applies. In these articles the concrete elements of design and opera- tion and the reasons for them will be carried along side by side. The only theory used will be working theory, and the only con- structional points explained will be those which have been found satisfactory in the experience of radio engineers in the military and commercial fields.

The Elements of Signaling Systems

To understand the radio transmitter itself we should fully understand its object. In the first place, then, let us consider the essentials of any communica- tion system. Just as the natural act of

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Fig. 27: General form of radio waves as they pass from the sender in direction of arrows

speaking to another person in the same room calls into play the three main ele- ments of any system for the transmission of intelligence, so does the sending of a wire- less message involve these same three things. We cannot convey ideas from one point to another without having something which can act as a transmitting medium connecting the two points. In the wireless telegraph, the connecting medium is the so-called "ether" of space, which lies between the two stations. In talking, the medium of transmission is the air which lies between the speaker's vocal cords and the listener's ear. In both cases, the medium is vibrated according to some pre-arranged code, and the vibrations pass from the sender to the receiver.

Evidently, the two remaining elements are the transmitter and the receiver. The first of these is merely an apparatus which

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