Page:Popular Science Monthly Volume 92.djvu/493

 Wireless Work in Wartime

VIII: The Power Circuits of the Transmitter By John L. Hogan, Jr.

���IN last month's article a general review of the technical fundamentals of radio communication systems was given. The two basic methods of producing alternating current were described in brief, and two types of radio transmitter were shown. All this was preliminary to this second group of articles, which will include six monthly instalments devoted to telegraphing.

Since large numbers of skilled operators are and will be needed by the Naval and War Department radio services, and since the more familiar these men are with the practical and technical basis of radio apparatus and design, the more useful they will be, this new group of articles \vdll continue to point out various successful ar- rangements of ra- dio apparatus and the best ways of handling them.

Classification of Transmitters

Detailed attention must first be given to the transmitter. Each sending ap- paratus for radio telegraphy may be classified into one of two main groups, according to the type of wave emitted from the aerial system. If power is ap- plied intermittently to a condenser, which is first charged to a high potential and then allowed to discharge with oscilla- tions through an inductive circuit (as shown in Fig. 30, reproduced from last month's article), there are produced cur- rents which more or less rapidly die away in maximum amplitude. The application of these currents to a radiating aerial system, when the circuit constants are ad- justed to produce alternations at ex- tremely high (or radio) frequencies, results in the emission of groups of waves. The amplitude or intensity of the alternations in these groups of waves dies away in ac-

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��Fig. 30. — Radio transmitters which produce wave- groups in this way are of the damped wave type

��cordance with the current-groups which produce them. Radio transmitters which produce wave-groups in this way, one for each charge-and-discharge of the con- denser, are of the damped wave type, which we may call Class I. This class includes practically all of the numerous variations of spark and buzzer sending arrangements; and the class may be subdivided by reason of the particular characteristics of each form of spark transmitter.

When waves are generated by means of an apparatus which supplies power to the aerial system as fast as it is radia- ted, so that the waves never die away, there are no wave-groups produced. Energy is sent off into the ether continu- ously, and the amplitude re- mains practically

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��constant as long as the transmitter is in operation. Such senders, which include the radio-frequency alternators and arc transmitters, are of the undamped or sustained wave type, which may be called Class II. As with Class I, there are many different sorts of instruments which give this same general result and which may be made the basis of sub-groups under the main classification of undamped or con- tinuous wave senders.

The damped wave transmitters are used far more than the undamped wave type at the present time. They are par- ticularly suitable for short wave trans- mission. Speaking broadly, the un- damped wave is superior to the damped wave for any type of service, but suitable sending mstruments for generating the short undamped waves preferred for short distances have only recently been de- veloped. Consequently, by far the greater number of ship stations, as well as of shore stations used for small or moderate

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