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## Re: [TowerTalk] YOed older 4 el 20 meter CC Skywalkers

 To: Trentkd5ia@aol.com, towertalk@contesting.com Re: [TowerTalk] YOed older 4 el 20 meter CC Skywalkers Bill Tippett Tue, 11 May 2004 07:28:08 -0400
 At 06:46 PM 5/10/04, Trentkd5ia@aol.com wrote: I'm confused. When I model my future tower using YT, the best performance (pattern and gain) occurs with a spacing of 0.5 wavelength. This spacing outperforms 0.6, 0.9 and 1.0 wave spacings on my flat ground (Texas panhandle). So, why would 50 feet spacing on 20 meters be better than 35 feet? Plans are to have 4 elements for 20 meters at 70' and 105', and hopefully someday another one at 140'. ``` Trent I am not familiar with YT, but I have used HFTA to for modeling my terrain. If YT works as HFTA does, it simply assumes fixed point source antenna gain and shows the effects of ground reflections, etc. HFTA does not actually compute your gain, it just assumes what you tell it. A modeling program like Eznec or YO will actually compute the interactions of multiple antennas in a stack and allow you to determine the optimum stacking distance to maximize system gain (in free space).``` ``` Optimum stacking distance is a function of your antenna pattern. Antennas with narrow beamwidths need wider stack spacing to optimize gain. An old rule of thumb I recall from somewhere is to take the square root of the boom length in wavelengths. If we follow this guideline, the 20-4CD with a boom length of 31.5' should be stacked at about 47' for optimum gain. SQRT (31.5 / 70) = .67 wavelengths = 47'. Of course you should really use a program like YO to first determine the best stacking distance and then optimize antenna dimensions in the stacked configuration, which may be quite different than if they were optimized as a single Yagi. The interactions between antennas in a stack will be greater the closer you space them, so it becomes even more important to optimize them if you use close stack spacings.``` ``` As N4ZR said previously, I am not aware of a program which will automatically optimize over actual terrain, although I believe AO may be capable of it (manually) in combination with YT. I don't have either AO or YT but perhaps someone who does will comment since I am interested to know also.``` 73, Bill W4ZV _______________________________________________ See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions and ask for Sherman, W2FLA. ```_______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk```
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