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| - Welcome to the first of our construction projects END FED 1/2 HALF WAVE DIPOLE for 2M All you need are the materials as follows- * 1.5m long, 10mm dia. fibreglass electric fence pole - available from any farm material supplier (For local builders - Sargents rural supplies, Wellington st, South Burnie Tasmania). Cost (was) $5 * A short (1-3m long) RG58 coax with PL259 connector attached one end. A second piece of RG58, 100mm long (no connectors) for capacitive tuning stub. * Braid (maybe from old RG8, RG213 coax, etc) to fit over and cover the fibre glass rod for a distance of at least 1metre. * A supply 0.85mm enameled wire. * 16mm dia. heat shrink tubing 1.2m long. Jaycar have in catalogueat less than $4 and so should be available at Leading Edge, Burnie, etc. http://www.jaycar.com.au/heatshrink Will need a heat gun (or hairdryer) for the heatshrink. At less than $15 total cost, this works out to be a cheap, sturdy, lightweight 2m ground independent vertical, ideal for home or portable use. To get best SWR the coaxial capacitor is made about 100mm long and cut a few mm off at a time. This is the tuning capacitor and brings circuit to resonance. My stub ended up about 25mm long. If you cut off too much then you will need a new peice of coax and have to start trimming again. Also adjust the spacing of the coil turns below the feed point tapping or move tapping point around to bet the best match at the same time. Another technique is to use a trimmer capacitor to see if you get a 1:1 match. If not then then adust the lower turns spacing or tap point until a 1:1 can be achieved by adjusting the capacitor. Once this is achieved the the trimmer can be removed and coax tuning stub can then be trimmed to the same value as the trimmer. The coax is used as it is more structurally unobtrusive under the heatshring which is applied and less likely to be damaged. Heatshrink is applied over the whole antenna and coil for the waterproofing. The heatshrinking process may have an adverse effect on the final SWR I have already built the prototype and found it performing well, and has VSWR of less than 1.2/1 across 2 metre band.. |