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"Dave VanHorn" wrote in message ...
"Mark Keith" wrote in message om... George Cronk wrote in message . 154.205... Does anyone know where I can get plans for this antenna? Materials needed to build one? Thanks You would be better off with a 1/4 wave ground plane on 2m. Seriously. And one of those can be as simple as five 19 inch pieces of wire and a So-239 connector. MK Why would he be better off with a 1/4 wave, with it's large vertical lobe? Cuz it's easier decoupled with it's 1/4 wave radials, and is less likely to have feedline radiation than the funky 5/8 antenna with 1/4 wave radials. In direct comparisons here, the 1/4 GP was a good bit better than the 5/8 with 1/4 radials. The maximum gain of an elevated 1/4 wave GP on 2m, mounted at 35 ft at the base, is appx 6.2 dbi at 3 degrees. The maximum gain of a 5/8 GP with horizontal 1/4 wave radials, at the same height, is about 4.7 dbi at the same angle. And this does not yet take into account any decoupling problems! If the feedline radiates, any gain on the horizon is likely lost as the pattern is skewed up off the horizon. The average 5/8 antenna is ruined by using 1/4 wave radials. A 5/8 should be paired with a mirror image 5/8 to function properly. IE: dual 5/8 collinear such as the isopole, etc... And decoupling must still be used even on those. I agree with one thing Richard said about height and a 1/4 wave..If you get the tip of the 1/4 GP at the same height as the tip of a tall dual 5/8 collinear, there is little real difference between the two. And the dual 5/8's collinear is better than a 5/8 GP. 2m is real critical as far as the low angles used, and also to the effects of feedline radiation lowering the gain at those low angles. Now on 10m, many times I do prefer a 5/8 GP over a 1/4 GP, but there the angles used are less critical. If your 5/8's works, I wouldn't worry much, but in comparing them in A/B tests, "at appx 35 ft" I've never seen a 5/8 GP with 1/4 radials beat a 1/4 wave GP with 1/4 radials. I once built a fancy 5/8 GP with a nice larson coil, lots of 1/4 wave radials, etc...Was a super dud...I tore it up the 1st day and went back to a 1/4 wave. The 1/4 wave was an average 3-4 S units better on local rptrs, and simplex. About the same difference as comparing a undecoupled ringo ranger, to a decoupled ringo ranger 2... MK |
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