OUR WIRELESS CORNER.

Star (Christchurch), Volume XLIV, Issue 471, 4 June 1932, Page 18 (Supplement)

OUR WIRELESS CORNER.

COILS FOR CRYSTAL SETS. (By “ AERIAL”) This is the several! article of this . series,: the first has’ißg appeared on April; 16. v Class 2, Coils, sub-class (a) (continued),—The “flat” coil is probably the easiest to construct and, as it. is . also easy to operate, enjoyed a wide popularity when first made known to radio: V fans.” V;. L; j : Obtain a piece of dry wood about 6 or 7 inches long, 2 to 3 inches wide and from I to 1 inch thick. Select a very dry piece .of wood, i plane or smooth it on 'all sides, ' then gently round off the four sharp edges qn the long sides. This is to enable you to wind on the wire tightly, as sharp edges would nesplt in Jhe_ f wire turns “ bulging ” at" tm? edges arrd probably becoming loose—hn undesifable thing to happen. If you have a bottle of shellac handy, give the wood (after it has been heated in an oven to drive out all the moisture) two or three coats of shellac, waiting for a coat to dry before putting on the other. If shellac is not available, take a candle and, after you take the wood out of the oven and while it is still hot, rub the whole of it with the candle (don’t forget the , ends—moisture seeps in there more easily than elsewhere) until it has been well coated. Place it on a piece of paper or wood and replace the coil former in the oven in order that the wood may absorb the grease, thus increasing its insulating qualities. Drive a tack almost wholly in at one end (about one inch from the end) of the wooden former on what is to be the top side of the coil. Using No. 18 or 20 enamelled wire, take a ttvrn or two round the tack, 'then drive it down *so a's to hold the wire fast. Next, wind on. the wire as tightly and as closely as you .can, finishing off . the coil about One inch from the other end with a tack as before. Bore or drill a hole i an inch from each end of the coil and nail or screw the coil down on a baseboard that will be large enough f

to allow you to mount on it as well a crystal detector, two terminals for ’phones (one will also serve as the earthing terminal) and a terminal for the lead-in. At a point opposite the centre of one long side of the coil mark off a position fpr the aerial lead-in terminal, to which also is connected the tuning slider. Using this point as a centre, extend a pair of compasses so that their arc will sweep over the coil in a path that will cover all the turns of wire, from the first to the last turn. The compasses will then show you how long your slider will require to be. Make it of springy brass as described in the article of May 21. Now mount the slider in the way also described that week. Here again (as before) you have the choice of two wiring systems—it is a simple matter to find, out which will give you the better results. By the way, I have found, sometimes, that an improvement results from using a .001 mfd. (microfarad) capacity fixed condenser (I’ll tell you, one day, how to make fixed condensers of various capacities) across the output. You merely connect one end of the condenser to one ’phone terminal and the other end to the second ’phone terminal. By this time you have probably made up one or other of the crystal sets described, so here is a little “ stunt ” whereby half a dozen or more can “ listen-in ” on one pair of ’phones. Obtain two large (ordinary shape) breakfast cups, place them a couple of inches or so apart, then, after you have tuned in 3YA or 3ZC at loudest, take your ’phones and place each earpiece upright in a cup. A little juggling about will give you the best position, the result being loud-speaker reception.

“Arthur” is a Celtic name meaning “ high ” or “noble.” It has always been a popular English' name, and many famous men have borne it, as iur example, the Duke of Wellington and the late Loqd Balfour. The great British national hero was King Arthur, of Round Table fame.