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Show Dun Tells You Materials Needed and What to Do By R. L. DUNCAN, Director, Itadlo Institute of America. All set to bejfln building your radio receiving Instrument? The first part Is the construction of the looso coupler. Oct a cardboard tube six and one-half one-half Inches long and four and one-quarter one-quarter inches In diameter This Is for tho primary or stationary coil. Take another cardboard tube five ' and throo-quarter Inches by throe and one-quartor inches. This Is the secondary second-ary or sliding coil. Give tho tubes two coats of shellac boforo utartln gto cover them with wire and place in warm oven to take up all possible shrinkage. Then get these supplies Three-quarters of a pound of No. 22 cotton covered copper wire. A square brass rod seven und one-half one-half inches long and three-slxttenths , JWITCI1 I CONSTRICTION OF IOOSE COUPLER. COUP-LER. A AND BCD. BINDING POSTS. S. SLIDE. inch squaro for the support of the primary slider. Two round brass rods 13 1-2 Inches long and 3-16 Inch In diameter for tho support of the secondary coll. Those ; should bo so arranged that It will bo easy to move the coll In and out of i tho primary. Four binding posts Switch knob and blade. Switch contact points. Nuts, screws, nails MAIN BASE. The main base can be made of well seasoned wOod about 18 inches long and 10 Inches wide. For the prlmorv supports use pieces about nlnu inches square One of these should be cut I Through to permit the passing In and out of the secondary coll. The other should be partly hollowed for the rear end of the primary. Now for the winding: Start a half Inch from the end of the prlmury tube. Tighten tho wlro securely and then wind tbjhtly around tube In a single layer. Stop about half an Inch from the end of the tube and lead wire to binding post A which connects with aerial. Run wlro from point on slider to binding post 13 which connects with ground. Brace tube on wooden supports. Then tako secondary coll and fir with its two small discs. rrlll holes for tho slider rods WINDING SECONDARY. Start winding the secondary or .smaller coll the sam0 as the primary, but on tho tenth or twelfth turn punch two holes through the tubo one-quarter of an Inch apurt. After twolve turns cut tho wire fle or six Inches from (ho tube and punch through tho flmt hole Then take the wlro you had beon winding and force through tho second hole, twisting the two ends Inside the tube On the outward end of tho secondary second-ary roll mount the coWct points on tho disc with small terminals on the nsldo. nun wire from your firt contact con-tact point to the two twisted ends Inside In-side tho tube. Then wind from 18 to 22 more turns and repeat as abovo ,morc taP9, on your secondary! coll, tho more elective the tuning of your loose coupltr a rfaTfC?ne!lerUtb,0 1WOUnd within a naif inch of the edge, null tho wtr. flexible cord to on, of the .econdary binding po.ta. The switch lever is connected to the other Make sure that both nrimarn and secondary coll. are wound In S! -h.il.. to hofth. Xta" f Use a sharr pen knife or hot soldering solder-ing iron to scrape off th. ligation run! aThr.m CO,U Wher the 38S runs. This slider Is made of a piece ,, J?at 11 cn mov easlln with small flexible, metal strip contacTnJ |