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Show i CARDBOARD TORMX5!r WIRES HELD TOGETHER, f l WITH ORDINARY STRING. t 3 ' Method of Winding to Produce the Doughnut Coil, One of th Latest and Most Satisfactory Improvements In Radio Construction. together with string proved to be too flimsy for practical use, bo a form waa designed to hold the winding, made of a material that did not add to the 'apaclty of the coll. Now that the Indentations In the winding for allowing string to be threaded through to hold the wires tog'ether were no longer necessary. It waa found that they were responsible for the low distributed capacity losses snd the high performance of the coil Without indenting the windings. It waa necessary to separate sepa-rate the wires further apart, resulting result-ing In a larger and more Impractical coll, with magnetic field losses. The final coll developed, the low-toss low-toss doughnut colt, has the wires Indented In-dented all around. Special complicated com-plicated machines had to be developed and perfected to accomplish this. The coll Is rigidly held In an attractive holder. Comparative tests were run with every other type of coll obtainable on the market, for measuring losses. It waa found that the doughnut coll had lower losses In every measurement measure-ment than any other coll, and when built Into a receiver had mow volume ' and signal strength, tube for tube, nod coll for coll, than had ever been known before. By FRANK REICHMANN, B. 8., E. M. Improvement In apparatus, rather thon new and revolutionary circuits, Is responsible for the rapid Increase In efficiency of our radio receiver This Is accomplished by the elimination elimina-tion of tosses, balancing up of circuit, cir-cuit, and the confining of straying capacltlea, Improvements that are the result of months of experimentation and practical test work on the part of far-seeing radio engineers, and very rarely stumbled upon or accidentally discovered. The latest radio improvement, the Relchman doughnut coll, may at first glance aeem to be the result of a few minutes' playing with a coll of wire ang broomstick. The real facts of the case are that the coll la the product of six months' Intensive Inten-sive work on the part of three radio engineers seeking a new type of Inductance In-ductance that would be free from the drawbacks commonly associated with coll Pioneering In a new field, without with-out the successes or failures of previous pre-vious experimenters to guide them. the pitfalls and blind alleys along the way . were thoroughly investigated while alow progress was being made toward the ultimate roll. Corrects Loss of Energy. In ordinary layer-wound colla a eon-vlderable eon-vlderable loss of energy takes place, due t the fact that, through a con-ilenaer con-ilenaer action, the current tends to ravel between adjacent wires as well is through the conductor Itself. This ondenser action Is due to the "self" vr "distributed" capacity of the coll, a used by the paralleling of the con-luctors. con-luctors. In the low-loss and honey- omh-coll type of windings, this is -emedied to a certain extent by ni riling ri-ling the wires at right angles to each ther and crossing nt Intervals. The first experimental roil form was nade by cutting out a circle of cardboard card-board with little protruding tabs on he Inside and outside edges. A nar-n nar-n atrip of pasteboard was bent iround In the form of a circle and tasted on each side of the fiat circle. The original Idea was to wind the lre around the form, hooking It over he tabs at intervals. When this coll vas constructed and tested. It was 'ound to be no better thun present Kills, due to the fact that the wires ii n parullel to quite an extent, mak-ng mak-ng the distributed capacity of the oil high. The next attempt was made by wlnd-ng wlnd-ng the wire' around the form, dlsre-ardlng dlsre-ardlng the protruding tabs, so as to nake a closed coll. supported by the our edges of the eanlhoard strips. I'hls coll was an Improvement, so 'irger forms were tried and It was eclded to continue to experiment vlth this type of coll. Winding the wire over and over the Irculur form by hand became rather iborlous. so one of the engineers rled winding the coll on a straight i ortn, then removing and bending the oil in a circle to form a toroid coll. t was difficult to keep, the wires In ilnce with this method, so he tried pushing the wire In at every other ace of the winding form with his humh nail, so that a string could he hreaded through the Indentations and so hold the coll together when he form was removed Measurements of this coil showed a decided Improvement Improve-ment over other types, as the greoter share of the losses, due to the distributed dis-tributed capacity and coll support logges. had been eliminated The Final Coll Developed. Over two hundred colla were built up In this manner In search of the proper diameter, size of wire, and general over-all dimensions of the coll. consistent with low losses and efficient Inductance, The colla held |