Radio Digest (Oct 1923-July 1924)

RADIO DIGEST — Illustrated October 27, 19i RADIO FOR EVERYBODY (.Continued from page 15) is no serious harm done if this ratio approaches 1 to 1. Bank Winding In their efforts to reduce distributed icity and effective resistance, manufacturers and engineers have developed some remarkable methods of Winding, a few of which are shown in our illustrations. Figure 10 shows a "bank-wound" coil and Figure 17 gives a cross-sectional view to make clear how the turns are laid on. Let us say there are to be -1 turns. If our coil is wound in two layers shown in Figure is. it not only is longrer, but the potential or pressure difference between adjacent turns is high and there is tremendous loss through distributed capacity. Between turns 1 and 2i there is the potential difference developed by 24 turns. If, however, we wind our coil as shown in Figure 17, it is shorter, and between any two adjacent turns there is only the potential difference developed by four turns, as between 5 and 9 or 20 and 24. Bank-winding is not at all difficult, is far more efficient than a long single layer or the double layer of Figure IS. As stated before, tapping is bad because of the energy absorption by unused turns Figure 22 — Spider-web coils are wound on a slotted disk; the wire is laid in the slots, crossing itself from one side to another which is known as "dead end effect." To reduce this, it has been found good practice to wind bank-wound inductances as snown in Figure 19, and throw the sections entirely in or out of the circuit by switches. Thus, when the right-hand section is in use it is not connected in any way to the remaining sections and, as they are some distance away, they absorb little energy. Honeycomb "Duo-Laterals" Honeycomb coils are an excellent means of obtaining inductance with low loss. A close-up of a section of a "honeycomb duo-lateral" coil is shown in Figure 20. The word "honeycomb" refers, of course, to the little cells formed by the crisscrossing wires; the word "duo-lateral," however, needs some explanation. In our drawing, three layers are shown with A as the lower layer, B the middle and C the outermost layer. The turns of layers LOUD SPEAKER Large. Scientifically correct, (h Q (\(\ Non-metal prevents tinny N X Mil sounds. Complete T v# v v Single Control Distant Receiving Tube Set. Easily assembled, mahogany cabinet, drilled panel, vernier condenser and vernier rheostat, tube, batteries and phones with directions. 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This coil is excellent because the turns of the adjacent layers A and B cross at a considerable angle, resulting in small distributed capacity: turns in the same layer as well as turns in parallel layers are well separated by the duolateral winding. The Giblm-Remler Figure 21 shows the Giblin-Tlemler method of winding. It was developed after the honeycomb appeared in the belief that greater inductance could be obtained without materially increasing the distributed capacity. Between the honeycomb and the Giblin-Remler coils there is practically no difference in efficiency and the average of ten samples of one would probably be the same as the average of t#h samples of the other. In Figure 21, the diagonal lines represent yarn, while the horizontal lines show turns of wire. Five turns are wound as shown by A; then the parallel groups of yarn numbered 1, then the five turns B; then the groups of yarn numbered 2; then wire we call C. On top of C would be another layer of yarn, the turns running parallel to the two turns, and this alternate laying on of diagonally wound yarn and horizontal turns of wire can be continued to make a compact coil of considerable inductance with low losses. The inductance is increased by winding the wire in groups of five turns and keeping all groups parallel, and the yarn separates wire groups, keeping down the distributed capacity losses. Spider Webs A fourth method of winding is the "spider web," as shown by Figure 22\ Here, the paralleling and close proximity of turns has been kept down, but solid material is introduced. Solid matter, which separates two metal surfaces or wires between which there is condenser effect, is known as the "dielectric" and there is more or less dielectric loss depending upon the material of which it is composed. 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But to get back to our "spider web"; a circular form of thin material is utilized and radial slots are cut from the circumference inward to provide fan-shaped sectors. An uneven number of sectors are provided so that after the first layer of wire is wound on I and it, in turn, introduces distributed pacity, but probably not as much as woul solid dielectric. An edge view of a Sickle coil is shown in Figure 23. At points B, C, etc., there were wooden spokes: tt lowest layer, number 4, comes in from the left above spoke A, passes below both A and B, then across and above C and D, then across and below E and F. Turns 3, 2 and 1, when laid on. follow this same practice (above two spokes, across, below two spokes), but do not all cross at tfc c'S^p'^^E^g^ Figure 23— Sickler winding looking at the edge. Air is the only dielectric and the distributed capacity is low the form, the wire of the second layer will cross the wire of the first in the slots, and the straight portions of this second layer will be on the opposite sides of sectors to the nearest portions of the first layer. When the third layer is placed on the form, its straight portions will be on the same sides of sectors as are the straight portions of the first, but they will be separated by a distance which is the diameter of the wire used. Such a coil has an excellent ratio between inductance and loss but seems limited to use on shorter wave lengths, as a coil of many turns would have an impractical diameter and be unwieldy. "Sickles" Coils Another form of winding these flat or "pancake" coils is the Sickles method. This coil is wound on a form consisting of a hub with radiating spokes which are later removed leaving only the wire. 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