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Photo C. The compotlent parts ofrile loading coil form are made of a slice of PVC pipe with plexiglas end pieces. about 4 " long . Fro m 1/4 " Plexiglas" cut 3-1/4" x 4" lengths 10 usc as spacers. With PVC cement, glue these, eq ua lly spaced, around the PVC form. This wi ll pro vid e room for an alligator cl ip to be used later. Wrap 14 to 15 turns of 14 or 16 gauge so lid bare copper wire around thi s form. The width of the total tu rns sho uld be 3". With a d iameter of about 1- 1/2", thi s coil sho uld p rovide approximately 3. 2 IlH of matching induct ance. So lde r two e lectrical connectors to the leads of the coil. Cons truct a mounting platform, as shown in Figu re 2, using thin sheet steel and Plexig las. Use a 3/8" bolt to attach the coil to the Plexiglas portion and a 1/4 " to gro und the co il to the steel portion. This platform can be mounted almost an ywhere inside your trunk provided it's with in reach of the RG-58 feedl ine . Drill a 1/4" hol e and mount th is platform w ith a Photo D. The matching coil assembtv mOl/nrs inside ofthe vehicle. Grounding and feedtine alligator dips allow for fine tuning of the resonance and impedance ofthe alllellna. hex-head bolt. Again allow about I " extra on the bolt length for the coil and j umper connectors. Solder the two electrica l connect ors to the RG-58 antenna feed inside the trunk AFTER IT HAS BEEN FED THROUGH THE G RO MM ET. (7/16" for the shielding and 3/8" for the center lead.) To make the jumper, remove the shielding from a piece o f RG·58 about 6" to 7" long and solder an alligator cl ip to one end. C UI a length of heat sh rink that will insulate all but 1/4" of this shie lding and shrink it on. Slide the alligator clip's rubber cove r over the heat shrink to the cl ip. Finally, so l der a 1/4" connector to the other end of the j umper where the bare shield ing extends. A ttach both the jumper and one end of the matching co il over the platform's 1/4" bolt. Attach the ot her end o f the coil to the Plexiglas support using a 318" bolt (see Figure 2). If you use 16 or 14 gauge wire for the inductor it will be ab le to support itself by its leads. To finish the matching unit, cut a 6" to 7" length of RG-58 co ax and connect a PI. 259 connector to one end. Solde r an all igator clip to the other end's center lead. Insulate the shie lding with heat-shrink tubing, as before , w ith the jumper and attach a 7/16" electrical connector to the end. (Allow these two leads to be long enough for the center lead to extend to both sides of the mat ch ing coi l when the shie ld ing is connected to the 7/ 16" bracket mounting bolt.) A t this po int you c an add a variable capacitor. Remember to wire it in parallel and you're all set. Loading Coil Cut a piece of 4" PVC tubing into Slices, referri ng to Table I . Make these cuts as sq uare a s possible . This will determine the straightness of the antenna. Because bolts and washers ex tend toward the inside of the coil, the PVC slice shou ld not b e cut le ss than I " wide. On a sheet of 1/4" Plexig las , outline two disks for e ac h loading coil by using one of the slices as a g uide. I ' ve had excellent re sults using a s abe r sa w with a moderate tooth blade ( 12/inch) under moderate pressure . This sho u ld avoid chipping but may create meltin g . Pliers can be used to pull off the melted excess. Drill a 3/1 6" ho le through both disks at the same time to help ce nter the antenna studs. Then drill one of these to 5/ 16". Drill carefully to avoid chipping or cracking. For added strength, drill three holes in a triangular pattern thro ugh both disks. The holes should be about 518" in from the edge to provide clearance for the PVC tubing thickness (114"). The size of these hol es depends on the size of the plastic bolts you'll be using. I strongly suggest that you tap these holes to allow the bolts to thread. P lastic bolt s aren't very strong and the added benefit will be need 'd. Tap the center 3/16" an d 5/16" holes to 1/4"-20 and 3/8"wI6 thread, respectively. Using fender washers to help disperse the pressure, thread each bolt through to ensure a clean tap.. Back the bolts out about 1/4 " and apply a generous amount of in stant glue to the threads. Re-tighten to a snug fit. Placing the threads outward, glue the two disk s to a PVC s lice wi th five-minute epoxy (clear type) and let the m dry. An important point when gluing is to have all the pieces under moderate press ure to ensure a tight bond. To do thi s, th read the plastic bolts through and tighten them before the glue dries. DO NOT USE METAL BOLTS FOR T H IS-they wi ll interact with the load ing coi l and could distort the radiation pattern. Once dry, solder a 1/4" electrical connecto r to one end of the 18 gauge enamel w ire that will be used fo r the co il. Bolt th is to the top part o f the coil form using spacing washers and the 1/4 " coupler. With a flat iron tip melt a groove into the edge of the top P le xiglas disk. Press the enamel wire into the groove while it's still so ft. T his w ill stop the coil from unraveling. Wra p with an appropriate number o f tu rns for the band you've chosen. Try and keep th e turns as tig ht as poss ible and pressed together. Use plenty of electrical tape to temporarily hold the coil wire in p lace. Mount the 3/8" connector to the lower side as you did w ith the top stdc. but don't so lde r the enamel wire-you' ll need it loose for tuning later on. Fine-luning A nach an SWR met er to the matching co il's PL-259 connector. H ook up your radio as it would normally be and attach the feedline to the other side of the SWR meter. T he feedline a lligator cl ip should be attached to the ung round ed side o f the matching coil where the antenna feedline is c onnected . T he coil 's g round ing jumper should be unconnected. (You can cl ip it to the end of the PVC fonn.) Assemble the antenna and attach it to the coupler on the mounting bracket. (I added a second support higher up to allow the lower antenna to stay permanentl y on the car.) (See Figure 3.) File the enamel off the tip of the lower load ing coil wire that isn't attached. Use an alligator clip to temporarily hold the con- 22 73 Amateur Radio Today· November, 1992
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Page 3 and 4: NEW TECHNOLOGY • Follows & Locks
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Page 32 and 33: - - - - - ----------------- 1 reel
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Page 38 and 39: PholO B. A gearmolor and bell drive
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Page 73 and 74: with chec k, 00 phone reservanons.)
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Spread Spectrum Primer Continuedfro
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VIC-20 USER I/O PORT A B c D E F G
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