Radio Digest (Oct 1923-July 1924)

June 7, 1924 RADIO D I G E S T— Illustrated 30 Minute A-B-C Lessons for Radio Beginners Chapter XII — Catching Radio Waves By P. E. Edelman TN THIS series of articles the story of 1 Radio is told in so simple a manner that the uninitiated can follow theory and practice whether he knows anything1 about electricity or its application to broadcasting and reception or not. The series consists of twenty-five chapters, of which the five next will be: Chapter XXII — The Radio Detective. Chapter XIV — Tuning1 In. Chapter XV — Working Through Interference. Chapter XVI — The Power Voice of Radio. Chapter XVII — Reproducers, The Finishing Touch of Radio. TO OPERATE a receiving set it is necessary to intercept sufficient of the available Radio energy coming from a broadcast station, so that the detector will operate. There are several methods of doing this. Aerial The most generally used means for catching Radio waves is the aerial. It enables more energy to be put into a re ^SUPPORT WIRE insulator. INSULATOR. ■75 TO 100 FT. LEAD 7" Figure 111 Figure 112 ceiving set than can be had from substitutes such as the loop. Probably the best form for an aerial for broadcast reception is a straight wire about 100 feet long suspended to clear nearby objects, as indicated by Figure 111. This can be done as in Figures 112 or 113 The aerial wire should preferably be stranded, and the wire should be put up in a substantial manner. The lead-in wire must not touch the roof and should be insulated from the building. It can be brought into a room by means of an insulated bushing in a board, as shown in Figure 115. The underwriters require lightning arrester installation and permit an indoor ground connection. There is usually very little danger from lightning caused by an aerial, and more acci Figure 114 dents occur from careless stringing of wires which can short circuit by touching power lines. There is no advantage in using more than one wire in receiving, but it is important to have this well insulated and clear from metal roofing, etc. Indoor Aerial Where an outdoor aerial is not feasible good results can be had with a well con mm w WIRING IN BUILDING. POVJER. ^UNE WINDOW BRASS OR COPPER, N RUBBER TAPE^*" DETAIL OF LEAD-IN INSULATOR. RECEIVING SET LEAD-IN INSULATOR, LIGHTNING ARRESTER. TT SERIES (CONDENSER. ANTENNA PLUG RECEIVING SET .©Q®o GROUND CONNECTION Figure 115 IMOOa AERIAL STRUNG BACK OF PICTUR.E MOULDING ALL AROUND ROOM Figure 117 i END TO SET PICTURE MOULDING IN DOOR AERIAL Figure 116 structed indoor aerial. Insulated wire is preferred for use in an indoor aerial, and may comprise from 25 to 100 feet concealed behind picture molding, as illustrated in Figure 116. For novelties, there are several other types of indoor aerial. Sometimes connection is made to a buzzer or telephone line. In many localities a so-called antenna plug gives good results. It consists of two small mica condensers to insulate the line from the receiving set, but allow Radio frequency to pass. When an antenna plug or socket attachment is used as an aerial, the wiring in the building acts as the aerial wire. Sometimes this operation is not feasible because of the kind of wiring or excessive interference from interruptions in the lighting circuit, making noise in the reproducer of the receiving set. Phantom Aerial A so-called phantom aerial is a capacity effect permitting reception by use of a ground connection only. A circuit is shown in Figure 118 which gives good results on local broadcasting reception without an aerial, and sometimes over long distances. Usually the receiving set and its connections form a small condenser 2 with the ground. Loop A loop will usually not pick up more energy than a phantom arrangement as in Figure 118, but has a directional effect. A loop is shown in Figure 119 and con sists of a coil or inductance of larger diameter than is usually employed in a receiving set. It really gets little energy compared to what an aerial can pick up. but also gets less interference and permits selection between stations of the same wave length provided they are located nearly at right angles with respect to the receiving station. Usually a loop requires one or more stages of Radio frequency amplification to boost the incoming energy so that it will operate a detector. A suitable circuit is indicated in Figure 120. Figure 118 A loop acts like a coil. In Figure 121 there are diagrammed three broadcasting stations and two differing loops. Loop Number 1 is pointed in line with station Number 1 and is at right angles to station Number 2. Waxes from station Number 1 will set up current in loop Number 1, but waves from station Number 2 will THE PORTABLE AUTOMOBILE RADIO SET Requires 2 Special Radio Frequency Transformers and Condensers The Transformer Units Used by the Author of the Article on Page 17 are "LINCOLN BUILT" These variable transformers were designed especially for (his circuit. It mi necessary to build them special because ordinary transformers would ool give the proper results. Each Unit consists of primary and secondary windings, with variable coupling and a .00025 variable condenser. FEB PAIR $19.85 See your dealer first. If he cannot supply you order direct. When ordering direct send money order to avoid delay. Send for catalog of other Lincoln Products LINCOLN RADIO CORPORATION, 224 North Wells St, CHICAGO, ILL not. The lines of force In the field sent from station Number 2 thread through ljut do not cut the win In loop Numb Another way of regarding this d tional effect Is that the fi'-ld of force from station Number 1 strikes the front of Figure 119 loop Number 1 first and the back side later, thus setting up a current in the loop, whereas station Number 2 sends out a wave front which strikes both sides of loop 1, together so that the opposed effects do not send current through the wire in the loop. A loop Number 2, however, will get no energy from station Number 1, but will get some from either station Number 2 or Number 3. For instance in the example shown, loop Number 2 can TUNING C0NDEMSER, „.„,. TUNING am^,.p1cdampljfier 0ETECTC* AMPLIFIER \ ,,0002 LOOP Figure 120 get energy from station Number 3, but less than if it was pointed towards station Number 3. The effect is as if the size of this loop Number 2 was the dimension B instead of (Continued on page 10) It's Capacity that Counts! 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