Radio Digest (Oct 1923-July 1924)

April 5, 192 Jk RADIO DIGEST — Illustrated Id 30 Minute A-B-C Lessons for Radio Beginners Chapter III — How Radio Is Broadcast By P. E. Edelman IN this series of articles the story of Radio will be told in so simple a manner that the uninitiated can follow theory and practice whether he knows anything about electricity or its application to broadcasting and reception or not. The series will consist of twentyfive chapters, of which the five next will be: Chapter IV— What Radio Inductances Dp. Chapter V — What Condensers Are Good For. Chapter VI — Uses of Resistance in Radio. Chapter VII — Essentials of Radio Electricity. Chapter VIII— The Key to Radio Circuits. THE broadcast listener may regard the term "ether" as meaning' space. In such sense, ether exists everywhere, surrounding the earth, in it, and in everything' in it. Material things which appear solid in reality contain ether or space voids. Consider two bushel baskets, both said to be full, one containing carrots and the other sand. Obviously there are air spaces in the basket containing carrots. Though apparently full there are certainly voids or spaces and pockets of air in the basket containing sand. Going further, one can regard any material thing, as a piece of wire for example, as containing more or less ether or space. Dense materials have less ether voids in such a sense. It suffices here to regard ether or space as extending everywhere. What Is Meant by Electrons Explanations of Radio are based on the theory of electrons. The term electrons can be understood as meaning electricity in its smallest unit. Electrons are intimately related to material things and can be moved if proper force is applied. In Radio circuits they are moved rapidly back and forth and comprise Radio currents. The enormous number of elec Electrons in a Wire Take a look at Figure 13. The mo of electrons through the wire < an electric current, [f too much current is sent through the wire, the molecules are made to push out and the wire expands. The number of molecules and electrons present in any material varies acoording to the kind of material. It is difficult to comprehend how tiny an electron really is, by itself. Although the molecule just mentioned is the smallest physical particle unit, it is comprised of chemical units still smaller, called atoms. Some electrons attach themselves to atoms and govern the nature of the molecules formed, others are free to fly about in and near the molecule. The view is sometimes taken that all matter is made up of electric particles, of which electrons are the atoms of negative electricity. But the picture of Figure 13 is intended merely to fix the term "electrons" in mind. The important point here is that it requires force to move electrons as desired in Radio apparatus and that the motion is an electric current. Another thing is that the action of vacuum tubes depends on a certain type of electron flow. The reason a listener is concerned with the broadcasting is because it controls what is heard. If the modulation is poor a strong carrier may be recognized as a whistle but the voice may be scarcely recognizable. In Figure 14, Radio waves are pictured in the diagram. Explaining Modulation Modulation is important in broadcasting. A well modulated small station is preferabTe to an incompletely or poorly modulated station of larger power. A Radio or carrier wave is represented by chart A, and has a certain frequency, as i on within a range of wave tha amounting substantially to 81 550 meters, with a few lower. Some relucted on at.otit. 100 meters. Seldom do the broadcasting This aerial consists of a span of wires insulated from the earth. When the aerial arged and discharged rapid!} alternating currents, i i ompre iloiu are set up between it and Cross Section of Copper Wipe o» o •••°*o: o • • o • o Vo^-0* • • o • • °« • • ,0 • • . • o*°. «n • o°-o.:o-0.:o°-.°?-.0-:o-';.°:^-c ■<v • • o .'a°-j *°o :°-.p.' -o.-o\3r vro Outside" Cir. of Wire Molecules' Elections Cl?05S CUT L.ENGTHWI5E CUT Figure 13. trons in even a thick piece of copper wire can be moved almost instantly at tremendous speed when such a driving force is applied. If you have looked at a razor blade under a microscope, the supposed sharp edge would be seen as a series of rough flaked teeth. If there was an instrument so that one could look into a piece of copper wire and recognize what was there, a crowd of material particles or -molecules would be seen intermingled with electrons. If more electrons were poured into this wire the molecules would be moved about violently, and this motion is the same thing as heat. That is what happens when you use an electric toaster. the the for example, 600,000 cycles. At B same carrier wave is shown with same frequency, but with intensity varied or modulated. At C a voice wave envelope is shown modulating a series of waves. At D poor modulation is illustrated. At the point in the voice envelope 3-4, the radiation is too much, as shown by 1-2. Many broadcasting stations now operating have good radiation, as their carrier waves can be picked up clearly at great distances, but the modulation is imperfect. The effect is that poor modulation is the same as a much weaker station with better modulation, and the quality is imperfect. The main broadcasting at the present Your prompt action gives you one bound volume with each annual subscription. New or renewal. Greatest Collection of Radio Information A. B. C. Lessons for Radio Beginners. Two, Three, and Four Tube Reflex Circuits. The Famous Miloplex with Various Hook-ups. 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Name Address • City state _■ \ illi. — — ^ Chicago j Serving as a Carrier Padio Waves -TiME Waves Modulate? 1 vl VVoice E C. — -Time Envelope Radio Waves P. Figure 14. ►Time tions adhere strictly to the assigned or supposed wave lengths and in some cases a station staterl to operate at 380 meters will vary some ten meters either way. Some stations give much attention to careful maintenance of radiated frequency. Transmission in Brief Radio, it will be recalled, is in a sense, another form of light. It would be possible to set up an oscillating circuit in back of a parabolic reflector, much like a searchlight. But for broadcasting, an aerial is vised. Transmission in all directions is here desirable. earth. This compression sends waves traveling outward in all directions, much like the waves from a stone thrown into water. The alternating current used to charge the aerial must be of high frequency, and is termed "Radio frequency." For comparison, two common frequencies are here tabulated, with the corresponding wave length: Wave Length Frequency 300 meters 856.628 cycles 200 meters 1,J99,100 cycles (Continued on page 24) Build and Test / Step by Step and Possessions, and Canada. This offer not good through dealers or subscription agencies, but must be sent us direct with the full subscription price. Remittance must be by check, /////// k money order or draft. M//'/ w «/*» attt um> ottn i, BREMER-TULLY again leads with this new Three-Circuit Transformer and Radio Frequency Circuit. For range, selectivity, clearness of signal, tone quality, ease of control and simplicity, we know of no other hook-up that will approach it, This circuit permits of a new Form of Construction of immense benefit. Each part of the circuit may be developed STEP by STEP, and tested ON THE AIR before adding the next step, showing the characteristics of each unit and removing the difficulty of locating any weakness that might develop. 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