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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fl&.4 



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 



477 



