Radio mirror (Jan-Oct 1923)

May 19. 1923 RADIO DIGEST 11 First Steps for Beginners in Radio Chapter III — Part I; Pointers About Aerials and Grounds By Thomas W. Benson, A. M. I. R. E. STRICTLY speakinp. the aerial is that part of a receiving set which collects or rather has currents induced in it by the passage of Radio waves. Therefore it often happens that the wirina: in the Radio set proper acts as an aerial to receive over fairly long distances. However, we usually connect the term with some partioular device arranged for the purpose of receiving the wave impulses. Aerials can be classified Into two general classes, namely, capacitive and inductive, although the action of most aerials combines both properties in their operation. Outdoor Aerial The usual outdoor aerial structure comprising one or more insulated wires suspended between elevated supports is of the capacitive type, that is. the elevated conductors form one plate of a condenser, the ground being the other. As regards types they are either of the inverted L or T type as shown in Figure 6. We shall first consider how these aerials function and then decide which method of construction is preferable. For an example let us take an inverted L. as shown in Figure 7, with the free end pointing in the direction from which the waves are coming. 'When the wave strikes BEGINNERS will find the accompanying series by Mr. Benson very helpful in learning the rudiments of the popular science of Radiophony. The first chapter of his series appeared in the May 5 issue. The articles yet to appear are: Chapter IV— About Condensers and Inductances. Chapter V — Tuners and How to Tune Your Set. Chapter VI— About Crystal Detectors. Chapter VII— Tube Detector Theory and Operation. Chapter VIII— The Regenerative Detector. Chapter IX — Radio Frequency Amplification. Chapter X — Audio Frequency Amplification. Chapter XI — How Super Regeneration Is AccompUshed. Chapter XII— Reflex Circuit Operation. Chapter XIII— About Headsets and Loud Speakers. Chapter XIV— Batteries Used in Radiophony. its free end. In the T aerial, where the lead-in is brought down from the center, the directional effect is not so noticeable. Resistance of the Aerial Since the induced currents are at best very weak, it is advisable to keep the resistance of the aerial circuit as low as INVERTED L Figure 6— Two Types of Capacitive Aerials the aerial the electrostatic component or the wave place an electric field between the two plates of the condenser formed by the aerial and the ground. We know that when an electric charge is put on two plates separated by a dielectric, an electric stress is present between the plates. Conversely, when we put an electric stress between two plates as in this case an electric charge will be induced on the plates, hence a difference of potential exists between the elevated wire and the ground which causes a current to flow between the two plates. In addition, when the wave passes the vertical wire or lead in the magnetic component induces a current in the vertical wire that either as WAVE FRONT ELECTROSTATIC FIELD FROP-I WAVE Figure 7 — Wave Striking Aerial, Showing How Stress Between Aerial and Ground Results in Current Being Induced in Aerial Circuit Cists or opposes that induced by the electrostatic field. We see then that this so-called capacitive aerial has currents induced in it by virtue of its capacity and also by electromagnetic induction. The relative values of these currents from the two sources will vary as the length of the plate portion and the height of the aerial are altered. The most noticeable effect of these two currents is in the fact that an inverted L aerial is directive in its effect. An aerial of this type will receive best away from possible. We cannot always do this by using simply a heavier wire because another phenomena comes into effect; namely, skin resistance. When the current in a wire is of very high frequency, say 750,000 cycles at 400 meters wave length, as we learned previously, the alternations in direction of flow take place so rapidly that the current does not penetrate to the center of the wire. Figure 8 — Showing Resulting Fields When Wires Are Spaced Close and Far Apart At such frequencies it flows only on the surface of the wire. Therefore we reduce the resistance by using a stranded wire, usually 7 strands of Xo. 22. For the same reason it is advisable to use a wire that is noncorrosive or is protected in some way from the action of the elements. The tinned wire is then to be preferred, while a wire made up from enameled wires stranded together makes an excellent aerial. PHANTOM-CIRCUIT Build Your Own. This marvel of mystery, using no loop, no aerial and no ground, brings In music instead of interference. We bave beard stations 950 miles distant on one tube. By using WD-11 tube set can be entirely self contained. Very easy to build from our instructions, use your own spare parts, nothing complicated like radio frequency or super regenerative. Only one tuning control. Complete instructions, with hookup and photo of circuit mailed to you for 60 cents. Stamps accepted. VESCO RADIO SHOP, Box D-704. Vacaville. Calif. BETTER LOUD SPEAKERS $0.85 ^^■JCT.T.T'^ TRUE CABINET TYPE, like the finest ^^^|^k modern phonographs, with all their beauty ^T\ ^^B and perfect tone. Makes your two-step set a real EXTER■vF^H TAIXER for family and friends. SPIROLA DUPLEX uses any ^B ^m headset. SPIROLA SIMPLEX uses Baldwin or other unit. ^^^B^^ Either type, black with nickeled fittings, $3.85; mahogany finish with bronzed throat, $4.85. At dealers or postpaid (C. O. D. if preferred). Absolutely guaranteed. T,u H. PONTTEIX MFC. COMPANY. Dent. P. Box 70. AVX ABBOB, MICH. 1000 Miles Guaranteed on One Tube A real radio set at a low price Consisting of the following parts: 180= Variocoupler, Variable Condenser, 7x15 Panel already drilled, 2 Dials, Switch Lever Points Stops, Rheostat Socket, Binding Posts, Bus Bar, Sphagetti, Lugs and complete blue print to assemble in one-half hour. At the special low price -. .$15.00 Two Stage Amplifier for above $15.00 S3.00 Audio Transformer $2.95 $5.00 Variocoupler, 180° 2.25 $1.25 7x10 Panels 80 $1.00 Phonograph attach single 50 $6.50 1^ Volt Tnbes Guar 3.95 .50 W.D.ll Bakelite Socket _35 $8.00 Long range receivers $4.50 $1.00 Freshman Var. Leak & Cond 75 .75 Freshman Var. Leak only 60 S5.00 Elect, soldering Iron 3.75 $5.00 Detector Tube Guaran 3.50 $6.50 Amplifier tube, Guaran 3.95 Write for complete list of other bargains FrnNHMY PAnin m i32 Nassau street ^p* r d EA-» Wl^WlYl I X\-f\LJl\J \^\J., NEW YORK CITY, NEW YORK Number of Wires Used Another point often in question is how many wires to use in the flat top. The usual practice is four, separated at>out it as shown the added field is but slightly larger, whereas, when Ihe wires are spaced 10, 12 or 15 feet apart, then an appreciable advantage is obtained. The effect of placing the wires close together is then only that of one wire, but with a lower resistance due to the increase of conducting surface. Length of the Aerial Another factor that is important is the length. For efficient operation the length of an aerial should be considered from the point of view of the wave lengths to be received. The length should be such that the fundamental or natural wave length of the aerial is less than the wave length to be received. A simple method of calculating the wave length of an aerial is as follows: Add the length in feet of the flat top, lead-in and ground wire, and multiply their sum by 1.5. "When more than one wire is used in the flat top the result is increased by one third, due to the inductance of the additional wires. Where a T aerial is used only one half of the length of the flat top is used in the formula. INSULATOR HOOP CONDUIT MAST ■* Figure 9— Preferred Type of Outdoor Aerial 3 feet apart. As a matter of fact it is the writer's belief that there is no advantage in using more than one wire unless they are separated 10 or 12 feet. The reason for this will be apparent from Figure 8. Consider one wire used as an aerial and its effective field will take the form shown by the lines. If this wire is 30 feet high and we put another wire within 3 feet of Natural Wave leng-th The natural wave length of the aerial should be enough shorter than the wave length to be received that sufficient inductance can be used in the tuner that a high voltage drop will be obtained across same if of the straight tuned type, or enough turns can be employed to transfer (Continued on page 14) § ^niHMUMiiiiniiiHiiiUHuimiiiiiiHHiritiinmiiiiMniiiiniiMiiimiinn^ SENIOR" SET WONDERFUL! That one word appears in nearly every one of the hundreds of letters written to us by happy owners of MICHIGAN "SENIOR" and "JUNIOR" Regenerative Receivers They tell us how stations two or three thousand miles away come in so clear that they can scarcely believe their ears when the announcer tells his location. How our patented Split Hair Vernier Dial Control enables them to tune in to almost any station, on which they had made previous record of dial-positions. How the tone-quality and volume they get through their Loudspeaker (with the Michigan Senior Receiver) approaches that of headphone reception on ordinary sets. Regeneration — or feeding the output of the detector tube back into the same tube instead of into a second tube; gives an enormous increase in the sensitiveness of the detector. This invention by Armstrong made modern radio telephony what it is. "Michigan" Receivers are licensed under Armstrong's U. S. Patent No. 1.113,149 and pending letters patent "JUNIOR" SET No. 807,388. ^lilJiniUllliliiniiiiiiiiiimiiiiiiiiiitiiiiniiiiiiiiiiiiiiniiiiiiiiiiiiiiiiig _