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Re: [TowerTalk] worlds biggest yagi

To: <>
Subject: Re: [TowerTalk] worlds biggest yagi
Date: Fri, 28 Mar 2008 21:42:50 +0000
List-post: <">>
Clearly, these guys need a hobby. Just too much time and money on
their hands. Something simple, like F1 racing !!
73, Dick, W1KSZ

> From:> To:> 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:>> > A photo of 
> Yagi is located at:>> > 
> 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 
> roug
 hly 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 
 e-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 Nort
 h, 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> > > 
_______________________________________________> > > > 
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