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i dont know why you cant seem to find what your looking for other than your not wording the search right Finding them is not the problem. Finding two that come even close to giving the same dimensions is the problem (apart from ones that are obvioulsy direct copies of a design on another site.) Why should this be a problem? Yagi-Uda antennas are complex beasts, due to the interactions between the various elements. There is no single "best" design for all uses... different designs are optimized for different parameters. If you try to push the optimization quite hard in favor of one design factor (e.g. maximum forward gain, or maximum front/back ratio) you're likely to pay a price in terms of sub-optimal behavior in other parameters (e.g. very narrow SWR bandwidth). Many older Yagi-Uda designs were done by cut/try/measure methods. More recent designs often take advantage of modern computer modelling and optimization techniques, and can vary significantly from the older designs. I would imagine that most (almost all?) of the published designs meet their design goals pretty well, despite the differences in the details of their construction. Want a simple, direct-coaxial-attachment Yagi with a 50-ohm feedpoint impedance? You can have one. Want a Yagi with a narrower element spacing and lower feedpoint impedance which is conveniently matched using a double-parallel-quarter-wave section of RG59? You can have that, too. Want a ultra-short-beam Yagi to fit on a small roof and not stick out into the neighbor's trees? You can have that, too. These three different Yagi antennas will look rather different from one another, since they're optimized for different goals. So, you ought to first decide what you want, in an antenna... what the importance of the various design parameters are. Then, choose a decent design tool and go at it! Even better, try two or three different design tools, and see how the resulting antennas model out. Finally, build the darned thing, get on the air, and don't sweat that last dB or so of gain or F/B ratio. "The best, is often the enemy of the good" - if you focus too hard on having the Ultimate (Yagi, or car, or whatever) you're likely to miss the pleasure of having a good one to use, much sooner. -- Dave Platt AE6EO Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
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