University of Santa Clara - Redwood Yearbook (Santa Clara, CA)

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Radio Telephony Francis B. Tinney RESUMABLY the foremost achieve- ment of modern science in the last twenty-five years, with the excep- tion of the air- plane, is Wire- less Communication; and in the past ten years, the development of the Radio Telephone. The desire of man to communicate with another at a dist- ance is probably as old as man himself, but the first human to accomplish any noteworthy success was Samuel F. Morse. His invention, the line tele- graph, is also the basis of the present day trans-oceanic cables. The next person to make a noteable adva nce in the field of electrical communication was the famous Alexander Graham Bell, who found a means of modulation by which the voice could be transmit- ted electrically over great distances and reproduced into sound again. Mod- ulation causes electric currents to fluc- tuate in amounts proportional to the sound vibrations. The first discovery of the underlying principle of Wireless Telegraphy was made in 1888 by Heinrich Hertz, a Ger- man Physicist, who found and determ- ined the velocity of electrical oscilla- tions, from which fact they received the name Hertzian Waves. It remain- ed, however, for Marconi, in 1896, to realize the importance of Hertz ' s dis- coveries and put them to use in a very crude wireless telegraph system. This first set, although very cumbersome and bulky, was capable of covering a distance of only about three miles. About 1905, after many improve- ments in radio equipment, Lee de For- est, an American Scientist, invented the three element Audion Tube, which will be explained later, and made Radio Telephony practical. Before leaving the Audion Valve for the present, it might be well to state that it has a three fold role: that of detection, of amplification, and of setting up pure, constant amplitude oscillations. Before proceeding deeper into the subject a few principles of Physics will be appropriate in order that the reader may obtain a better conception of the topic. Radio Communication of any form is conducted by Ether waves. These will be understood by an analogy. Should we drop a pebble in a pool of still water, waves will be propagated and extend radially from the point of the disturbance. Each wave consists of a peak and a hollow, the distance be- tween two adjacent peaks or hollows is the wave length. The number of these waves per second is called the frequen- cy. If the distance covered by a cer- tain number of waves in a second is kept constant, as in the case of Wire- less Communication, and the frequency increased, it is obvious that the wave length must be decreased in an inverse proportion. Similarly, if the frequency

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St. John Berchmans . . in juventutis flore, maturus coelo . . EEP Kast delved, unstarred Astronomer, Far beyond tKe stars. Droopest wingless— wings, all Keaven KearetK, Wearily beating upon empyreal bars. Stillness, as of pool ' s profundity, SilencetK tKy tongue; Yet listetK Keaven to tKe lay tKat lulletK Caroling SerapKim— songless for tKy song! MARTIN M. MURPHY

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THE REDWOOD is decreased, the wave length will be increased. Sound is a kindred phenomenon, ex- cept that it uses a gas, a liquid, or a solid as a conducting medium, and has a frequency range from 16 to 32000 vi- brations a second, which are audible to the human ear. Since the elements of wave motion are now understood, we will take up ether vibrations. In general, these con- sist of six distinct forms, known as the electromagnetic phenomena or waves, whose essential differences are their frequencies, viz: 1— Radio, 16x10 ' to 3x10° vibrations per second. 2 — Laboratory, 3x10 ' to 10 vibra- tions per second. 3— Unknown, 10 to 6x10 ' = vibra- tions per second. 4 — Heat, 6x10 to 4x10 vibrations per second. 5 — Light, 4x10 to 8x10 vibrations per second. 6 — Actinic, 8x10 to 3x10 vibra- tions per second. Since these waves are all an electro- magnetic phenomena they necessarily travel at the same velocity, which Hertz proved to be 186,000 miles per second. Expressed in the Metric Sys- tem this is 300,000,000 meters per sec- ond. From this we derive the funda- mental formula of radio: 300,000,000 Wave length= frequency in cycles per second It is a known fact that in order to produce these waves, there must be a vibrating medium, which sets them up. In the case of sound the vibrating me- dium is a solid, a liquid, or a gas ; but in the case of ether, it is a conductor which vibrates electrically; that is. one which contains a vibrating elec- trical current, which we term oscilla- tory. There are four main ways of setting up these oscillations: (1) By the charge and discharge of a Leyden Jar; (2) By the Poulsen, Duddell, or Janke Arc Converter; (3) By the Al- exanderson or Goldschmidt Radio Fre- quency Alternator; (4) By the Audion Tube Oscillator. The first mentioned method is suita- ble for wireless telegraphy only, be- cause each succeeding wave of a train of oscillations is of less amplitude than the preceeding wave. This form is called discontinuous or damped os- cillations, a familiar example of this type being the spark transmitter. It is impossible to modulate damped oscilla- tions for telephony because of their al- ready varying amplitude. The Wireless Telephone is possible by means of the last three Avays men- tioned, but due to inherent characteris- tics of the Alternator and the Arc it is difficult to properly modulate their output with speech, so the Audion re- mains almost alone in this wide but new field. However, it might be well to say, before passing, that radio tele- phony was first transmitted by an Arc Converter, and even the Janke Arc has accomplished very good results along this line. In order to obtain the proper con- ception of the functioning of the Radio Telephone, it is essential that the ac- tion of the Audion Valve must be un- derstood. First we will take its de- velopment. In 1884 Thomas A. Edison found that by placing two filaments in a high vacuum, and lighting one to brilliancy a very small current was induced in the other filament, in one direction only.