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Show pTHEFIOME RADIol How to Make and Use Ii SJv? By a. hyatt verrii i I LOOSE-COUPLED COILS Poll? or, as tbey nre more often ,,leJ "luning coils, are very essential ns'of radio telegraphy and tele-P'i'oiiv tele-P'i'oiiv The old style tuning coil, as eii'ln .wireless telegraphy, has been I'V.elv superseded by the type known s "loose-coupled coils or adjustable-lls adjustable-lls which may be altered or adjusted une much finer or more closely than bv the old type coil. Although It is Dot difficult to make a loose-coupled coil yet, as is the case with many of tbc parts of radio sets. It is as cheap and fur more satisfactory to purchase them ready made. The conventional ,vpe of loose-coupled coil consists of wo distinct coils, one within the other, s shown in Fig. 46. One of these ,s ,i,e primary coil, the other the secondary or induction coll. The two ore so arranged that the inner or secondary coil slips back and forth within the larger or primary coil, thus varying the coupling or induction induc-tion for the electricity or oscilla- tions-ln the secomnuy coil is merely induced l,v the primary circuit lj the outer coil, so tlint if a portion of the secondary coil is withdrawn with-drawn from the primary coil, as shown in the figure, there will be less Induced current and In His way tuning is accomplished. ac-complished. To allow of still finer adjustment, adjust-ment, the primary coil Is provided with an adjustable ad-justable slider A, and the secondary coil has a multi-pointed switch B. Another type of loose-coupled loose-coupled coll is arranged so that one coil revolves re-volves within the other ; while another type, which Is the simplest of all for the amateur to construct and gives the best results, is composed com-posed of three discs or experimenting after the coil i3 lu five "h -"S St"rter' about twenty fe or thirty turns on one, about on and one-half times as many, or sa thirty e.glu to forty-five on the second and twice as many on the third as on the first, or from fifty to sixtv. will bt somewhere near right. Then, by removing re-moving or adding a few turns, as vou-adjust vou-adjust your receivers you can finally secure the very best results To mount this coll so it may be used, the coll or disc with the least turns or, in other words, the primary coil should be mounted rigidly and immovably im-movably and should be connected by means of binding posts to the aerial and ground wires. The secondary coil and the tickler coil should then be fastened to brass or metal strips about two 6r two and one-half inches long, one-sixteenth inch thick and half an inch wide. One end of each strip should be attached by small bolts or screws to the coils and the other end 0n( Cy ;- C -Hi-en ittsieYCi. Flj.47 V- ffn.sai.rrtrt-o-iMrMr. C'VcZStvo- colls "stagger-wound" which may he adjusted back and forth. To make one of these inductors you will require re-quire some stiff, smooth cardboard, heavy Bristol board, thin fibreboard or similar composition and about half a pound of No. 24 D. C. C. wire. Also, in setting up and arranging the coils, you will require binding, posts, knobs, a little sheet brass and a. few other odds and ends. With a pair of dividers di-viders or compasses draw three circles on the cardboard or fibre, each about four to five Inches in diameter, having nil exactly the same size. Then, using us-ing the dividers, scribe off an unequal number (five, seven, or nine) marks nround the circumference of each circle. Fig. 47, A. Next, still using the dividers, draw a smaller circle, say one and one-half inches to two and one-half Inches In diameter within rach circle (B). If the circles are four Inches in diameter use the smaller circle inside, if five inches the larger one, end with a rule draw radiating lines one-fourth of an inch apart from each of the marks on the outer circumference cir-cumference to the center of the circle (C). With a pair of scissors or a starp knife (if cardboard is used) or a fine saw (if fibre), cut out the discs and cut slots in each disc accord-ln5 accord-ln5 to the marks, as shown at (D). Next, if you have used cardboard, five ench slotted disc a thorough covering with shellac, using at least tliree coats, and when thoroughly dry Proceed to wind the discs or coils. ,n (Icing this, start the wire being sure to leave enough for connections -at a. point at the inner end of one dot nnd wind over one segment and ndor the next, and as the number Is uneven you will find that the' wires '"l thus cross, as shown at (E). The number of times the wire should he Passed can only be decided upon by attached to a movable peg or bolt with a fibre or bakelite knob at the opposite end. Fig. 4S shows clearly how this Is done. In this way, the secondary and tickler may be swung back and forth to cover more or less of the primary; but gntit care should be used that the tick or does not touch the primary coil. When the coil is thus mounted on a proper panel or stand, it should be wired as shown in Fig. 49, and when the whole set is in good working order and final adjustments made, it should all be enclosed in a neat wooden case with a hinged top or cover, Fig. 50, although, of course, this is merely a protective measure and does not affect the working efficiency of the set. It must be clearly understood, under-stood, however, that this type of coil can only be used in connection with a vacuum-tube outfit as shown. When all wiring is complete and adjustments are ready to be made, connect the storage battery, as shown ; place the lamp or tube in its socket and gradually gradual-ly turn on the rheostat to see if the tube glows properly. Never turn on . the current to the bulb quickly or to full power, or the filament will he needlessly burnt out and wasted long before its time. Next, connect the B, (or dry) battery, the ground and aerial and, finally, the phones. In" using this outfit, turn on the bulb slowly, adjust the knobs carrying the coils so that all tliree are in line and then adjust or tune the variable condenser until the signals you wish to hear are clear. Then, by gradually adjusting the movable coils, you can cut out interference and also make the signals, music or other sounds louder. When the two movable coils are entirely entire-ly away from the primary-coil you will liave your shortest wave length, while when 'all three are together, you will have the longest wave length. |