[TowerTalk] worlds biggest yagi
w1ksz at q.com
Fri Mar 28 17:42:50 EDT 2008
Clearly, these guys need a hobby. Just too much time and money on
their hands. Something simple, like F1 racing !!
73, Dick, W1KSZ
> From: donovanf at starpower.net> To: TowerTalk at contesting.com> Date: Fri, 28 Mar 2008 17:37:00 -0400> Subject: Re: [TowerTalk] worlds biggest yagi> > This description of the 13 element 20 meter Yagi on a 100 meter boom is copied from:> http://jplarc.ampr.org/calling/1996/feb/feb96.html#yagi> > A photo of Yagi is located at:> http://jplarc.ampr.org/calling/1996/feb/bigyagi2.jpg> > Modern Giant Yagi> Excerpted from "Antennas and Propagation," June 1991> > What may look like six separate HF yagi antennas pointing the same direction is actually one large 13 element 20-meter beam! This giant antenna was designed, constructed, and demonstrated, by Jack Hachten, W6TSW, JPLer Bud Ansley, W6VPH, and JPL Amateur Radio Club member Dan Bathker, K6BLG. (That is W6VPH on the top of the far tower).> > Thirteen widely-spaced elements had been disposed on six towers in a fixed-azimuth application. Overall antenna dimensions were 10 by 100 meters, by 25 meters above the ground: a structure roughly 0.5 x 5.0 x 1.0 wavelengths in the WARC-allocated 20-meter amateur band. The elements were arranged for a considered balance among forward gain, sidelobe level, impedance level, and bandwidth, and structural wind survival and construction economies, with an EM emphasis on forward gain.> > Recently-available MININEC-based multiple optimization software has very conveniently and efficiently automated several of the EM-related design steps, requiring brute-force iterations. In fact, without such (PC-implemented) method-of-moments analysis and weighted, multi-parameter optimization such a project would not likely be initiated. The wire and optimization codes have clearly enabled such a large undertaking to be approached with high confidence, with assurance that multiple objectives will be sensibly realized, and with trivial (or none at all) final adjustment. Still, indispensable human judgment, experience, and strategy remain necessary ingredients, despite over 15,000 machine-aided EM design iterations, in this instance.> > The 100 meter, divided-boom, antenna operated at a center frequency of 14.150 MHz . The design provided a feed-point resistance (30 ohms), with a bandwidth somewhat more than 2 percent. In free space, the predicted directivity was 15.8 dBi. The predicted directivity was fully 21.5 dBi, at a favorably-low elevation angle, when arrayed over low conductivity (in fact, good dielectric) ground. Each element was built with heavy-wall aluminum tubing, starting in the center with 32mm diameter, stepped twice, and ending with 19mm diameter at the tips. Each of the six 75mm-diameter boom segments measured 9 meters in length.> > To assure EM field purity in the six-tower environment, the topmost tower guys were dielectric. A conductor-free zone of a half-wavelength (minimum) radius was thus provided for the intended horizontal polarization.> > The antenna operated from Southern California, at a boresight of 15 degrees East of true North, on a great-circle heading to cover selected portions of Europe and Asia. The azimuth beamwidth is slightly less than 30 degrees to the minus 3dB points. Following first turn on in February, 1991, it was evident that the performance in both transmission and reception equaled or exceeded all expectations> > > _______________________________________________> > > > _______________________________________________> TowerTalk mailing list> TowerTalk at contesting.com> http://lists.contesting.com/mailman/listinfo/towertalk
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