HE OUTLINE OI RADIO JOHN V L. HOGAN U^^RTlfc^ W^ iAJ^Uc^ cfnU< 4PiH4.lUi^, THE OUTLINE OF RADIO i TOWERS AND AEKIALS OF THE BROADCASTING STATION AT AEOLIAN HALL, NEW YORK CITY Two transmitters (wjy and wjz) have been installed, so that two independ- ent programs may be simultaneously transmitted on different wavelengths. THE USEFUL KNOWLEDGE BOOKS Edited bt GEORGE S. BRYAN THE OUTLINE OF RADIO BY JOHN V. L. HOGAN CONSULTING RADIO ENGINEER; FELLOW AND PAST PRESIDENT, INSTITUTE OF RADIO ENGINEERS; MEMBER, AMERICAN INSTITUTE OF ELECTRICAL ENGINEERS With Many Full-page Illustrations and Numerous Diagrams in the Text BOSTON LITTLE, BROWN, AND COMPANY 1923 Copyright, 1923, By John V. L. Hooak. All rights reserved Published October, 1923 Printed in thi United States of Ambbioa Co E. M. H. ; EDITORIAL INTRODUCTION The Useful Knowledge Books make a com- prehensive appeal. They have been designed for persons with favorite hobbies ; for laymen (and women, as well) w^ho wish to be more in- telligent and effective in some phase or phases of their daily living; for all those general readers who seek to keep in touch with the progress of human achievement and the increase of informa- tion. This wide audience is not looking for pro- fessional texts or elaborate and difficult treatises. Neither is it content with the inadequate volumes of a so-called "popular" character. It is seeking compact, simplified books that may be read with confidence and kept at hand for reference; for, says an anonymous author, "To know where you can find anything, that in short is the largest part of learning." To meet this need, the present series has been planned. The individual books are to be by authoritative writers. They will be of handy size, but not superficial. They will aim to pre- sent the main features of their respective sub- jects in a thorough, clear, and distinctive manner to be not only reliable but readable. They will viii EDITORIAL INTRODUCTION be generously supplied with illustrations that really illustrate. Acknowledgment should here be made of the cooperation of the Publishers, who have striven to render these books truly helpful and have spared no pains to give them an attractive dress. "The Outline of Radio" is by John V. L. Hogan, who, as engineer, inventor, lecturer, and writer for the technical press, has long been prominently identified with the development of radio in this country. Mr. Hogan has brushed aside the more or less ephemeral details that have collected so thickly about the radio art, and has explained the basic principles on which the whole science rests and must largely continue to rest. His is a fundamental book — original in plan and individ- ual in method. It is that much-sought thing, a satisfactory radio volume for progressive amateurs and general readers. G. S. B. FOREWORD Perhaps you are tired of hearing about radio. For a year or two the newspapers have been full of it ; magazines have run story after story about it; new books and new periodicals have been spreading the superstitions (and occasionally the gospel) of radio. Possessing not only inherent merit but also a lively appeal to the imagination, radio has grown riotously. The tremendous fas- cination of stretching out one's personal contacts far enough to intercept wireless messages arriving, over continents and high seas, from points hun- dreds or even thousands of miles distant, has at- tracted millions of people all about the world to the study of radio. By far the greater part of this huge increase of popular interest has come as a consequence of radio-telephone broadcasting. There is now no village in the United States where it is impossible to intercept wireless music or speech. So rapid an expansion has necessarily given radio some- thing of the appearance of a fad ; and undoubtedly many who took up radio receiving did so because X FOREWORD it was a craze. Fortunately, underlying the more transient attraction of hearing radio concerts is the valuable and permanent essence of a vital public service. The modern wireless is not merely an amusement or a toy, though on occasion it may be both of these. Radio is daily performing its man's-size tasks, including transoceanic com- munication ; the guidance of ships along fog-bound coasts; the tracing of criminals who, without the wireless, would have made good an escape by sea; the transmission of time signals and meteor- ological data of immeasurable importance to mariners and the pilots of aircraft; and the dis- tribution of entertainment and instruction to thousands who are home-bound or otherwise iso- lated. If you are weary of radio publications, take heart. Beneath the froth of writing that has been stirred up to meet (but hardly to satisfy) the wants of radio users, exists a substantial litera- ture of the art and science. Not all of this may interest you, for much is highly technical and therefore unpalatable to many readers. A good deal of what is both dependable and clearly phrased is also somewhat out of date; for the progress of the past few years has taken radio forward in great strides. A large part of the material recently published has already been for- gotten, for it was neither accurate nor readable. However, the fact remains that radio is accom- FOREWORD xi plishing great things. Its principles and uses are well worth a little attention by any of us. You, for instance, will not have to read far to experience something of the fascination that comes with a knowledge of how radio works. The radio faddist who gains an understanding of how the apparatus operates becomes a devotee of the art. The radio reader who finally arrives at a knowledge of the physical principles embodied in the instruments becomes an adept, even though he may have had to wade through reams of "popularized" and pseudo-scientific writings. The listener who realizes just what happens inside his radio receiver becomes a true lover of this newly applied science, a veritable amateur, striv- ing for improvement and development. If you are using a radio instrument, but are not quite sure how it works, study the science of radio. If you would like to put a receiver into your home, first find out what to expect of it. If you are merely curious about this new topic of conversa- tion, read a little concerning it. But now for a word of warning : Don't expect any one book, or any five books, to tell you all there is to know about radio. Begin with an outline of what radio has done; and next, find out how to-day's radio accomplishes its surprising results. Then you will be ready to think about special applications and subdivisions of the science and the art; you may go into details of construction or operation, xii FOREWORD concentrating upon problems of generation, modu- lation, application, or what-not. But, primarily, get in mind the groundwork that forms the solid foundation of the whole of radio. From these fundamentals you can carry forward your in- vestigation and, with astonishing ease, gain a vivid picture of the philosophy of nature upon which our daily lives are built. No other practical scientific accomplishment embodies so wide a variety of natural phenomena as does radio, which extends into the provinces of heat, light, sound, magnetism, electricity, and the properties of matter both at rest and in motion. Because it thus embraces the whole field of physics, radio is forever interesting. In its possibilities it seems limitless ; and even to-day its applications are so multiplied that they offer endless attraction. Imagine that you are spending a week-end at my home ; that we have drawn our chairs before the fire; and that you have asked me, **Just what is this radio, anyway ? How did it happen ? What makes it work.?" — and that, after a long pull at my pipe, I've said, "Well . .it's like this ..." If you wish answers to those ques- tions, read on. I am going to give you a some- what informal (but, I hope, none the less helpful) introduction to radio. John V. L. Hogan Forest Hills, Long Island. ACKNOWLEDGMENT For courtesies in supplying the special photo- graphs reproduced in the half-tone illustrations of this volume, the author's appreciative acknowl- edgment is made to the American Telegraph and Telephone Company ; the Connecticut Telephone and Electric Company; Mr. C. L. Farrand; Prof. R. A. Fessenden; the General Electric Company ; the Radio Corporation of America ; the Western Electric Company; the Westinghouse Electric and Manufacturing Company; and the Wireless Specialty Apparatus Company. An ex- pression of thanks is also due to Mr. Anthony E. Zipprich for his careful execution of the line- drawings for the diagrams accompanying the text. CONTENTS PAGig Editorial Introduction vii Foreword . ix CHAPTER I A Brief Historical Review The inception and development of radio II Thoughts Pass Between Us The basis of all communication systems III An Intangible Carrier ... 48 Electro-magnetic waves as a medium of transmission. rV Radio Waves Are Created ... 65 The generation of high-frequency cur- rents and carrier waves. V Messages Are Sent Forth ... 87 How code, speech, and music are im- pressed upon the radio waves. VI The Signals Flash Through Space . 106 The passage of electro-magnetic waves from sender to receiver. xvi CONTENTS CHAPTER PAOB VII A Million Listening Ears . .127 Intercepting and selecting the signal waves. VIII The Inaudible Is Heard . 147 Separating the signals from the silent radio-frequency currents. IX The Whisper Becomes a Shout .