THE MAGIC SPARK.

Auckland Star, Volume LV, Issue 283, 28 November 1924, Page 15

THE MAGIC SPARK.

HOME COIL CONSTRUCTION. SOME FURTHER PARTICULARS. SHORT WAVE TRANSMISSION. (By "PHOXOS.") The prominence given to wireless progress and particularly to the success of jf eW Zealand amateurs' efforts, is a point worth noting in the recent speech of the Postmaster-General at St. Helier'B. It indicates that usually cold officialdom is alive to the developments "and achievements of the wireless world, and recognises the future of radio activities in the Dominion. Radions have long felt that they possessed the BVmpathy of the Minister in their desire for expansion of radio facilities, and his recent utterances have but confirmed those impressions. It was bound to come. Americans cannot resist the temptation for abbreviation, and in U.S.A. to-day a microphone is generally referred to as a " mike." An innovation in this week's local broadcasting is the provision of lecturettes on topics of interest. These lecturettes have become very popular features of broadcasting programme in other parts of the world, and if properly managed, should be equally popular here. There are three essential features for the radio address —conciseness, public appeal of the topics chosen, and clear diction of the suitable radio voice. SHORT WAVES. Such congestion exists in the Uuited States at present owing to the great volume of hut partially controlled broadcasting, that authorities there are extending the wave band facilities for ■wireless telephony. The Bureau of Navigation has authorised the issue of restricted licenses to amateurs to use the lands between 75 and 80 metres, 40 and 43 metres, and 4 to 5 metres, for C.W. transmission. Previously the amateur band had been from 150 to 200 metres. Though the present permission is in the nature of an experiment, the facilities provided on these short wave lengths will give much greater freedom of operation than at present exists, for on the jhort waves stations can operate with a variation *of only half a metre without interference. In America, too, as in New Zealand, the amateur is being drawn to investigating the full possibilities of very short wave transmission. HOME-MADE INDUCTANCE COILS. Following the particulars which were X supplied last week, the amateur constructor is here supplied with further details on a subject which is of very general interest to that large body of wireless enthusiasts who find particular joy in constructing for their own use "apparatus which they can later point to with pride both from the point of view cf.workmanship,, and from the degree of efficient results obtainable. A reference to one of last week's diagrams is required to follow out this ■week's instructions. WINDING COILS. In winding coils of the honeycomb type it first must be figured out how jnany turns are going- to be necessary. As & comparison standard honeycomb coils may be used for the approximate wave-length band with various size condensers. If only a few turns are to be need then only a few turns per layer should he used. The more turns to be used the more turns per layer. The number of turns per layer is by the number of pegs (dowel pins) on one tow. Thus if ten pegs are used there will be ten pegs in each row or twenty in all, and a ten turn per layer coil will be obtained. !A ten peg row is suitable for coils up to fifty turns; above this sixteen pegs for coib up to one hundred, and the full twenty per row for coils larger. It is preferable to have a separate form for each number of pegs, but this is not necessary. Start winding the coils by tying the end of a coil of wire to the nut, then bring the wire around nail No. 1 as ibown in Fig, IA. (See last week's diagram). Then carry the wire over to nail No. 7 on opposite row and back to nail No. 2 on starting row; from there to nail 8 and so on. There is a formula that all fans should use in conjunction with these winders to find-out how many pegs to skip when carrying the wire from one side to the other; in other words, to figure out what peg on the opposite row the wire should be taken to after leaving peg No. 1. In this case it is seven, as can be seen by the following formula. N-2 plus 1 equals pegs to be skipped. N equals the number of peg? in one row, therefore, in the example it is easily seen that with ten pegs in a row, ten divided by two gives five and five plus one givee six; hence, the wire ia carried to nail No. 7, which is six pegs from No. 1. WINDING FORMULAS. In winding the duo-lateral coils the binder with the odd number of pegs is used. To figure out how many peirs are necessary the number of turns per layer anat be known. The name ruling for "is holds good as for honeycombs. When this is found then use the follower row--* t0 find tbe number of P e -? s 2N plus 1 equals pegs per side. a equals the turns per layer. When Pegs tp skip in the carry-over from side 10 side use N plug 2 equals pegs to skip. J2™ c ° ils of this type have been Jinißhed the easiest method of tying d&V° tf™ them a ooatinTof Mraight collodion diluted to about half Ms consistency with alcohol. J v, oatinK t,le coils let them dry Jor a while and then remove them from we form bylossening the lock nut on 11 \ Then carefully remove the t.T Cn f y ° ne ' and when aU have been removed carefully remove the side pieces * and C and then most carefully slip ™c f fr <"» Piece B. Give the Inside eoUodio 868 a li£ht ° Oat ° f the dilute This finishes the honeycomb and duo. lateral coils. The finer winding touches, «_» as making- untuned primary and recqnoary coils on one form, are for the »n to wind himself, though the prol«r c ,s ., the came ac ™th a singleSons W ° Und aS Per ab ° Ve tentiL epi i er T eb COils nest M 1 f °r attention Each coil of this type has to whirl, •? 7 n I*™"*-* f°nn. upon Wuch it stays when wound; therefore, wS Mc - can be made fro,n etiff card - ltaYp A r ? or ?P oeition . » standard template should be.made to cut them from. Mil 'J* , ? t ™ BtiM, ' of tn ie standard form T". be dealt with and illustrated in ■X* week's notes.