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On Thu, 17 Mar 2005 10:54:50 -0800, Roy Lewallen
wrote: Actually, it is possible to lower the takeoff angle (the elevation angle at which the pattern is maximum) without changing the antenna height. The method is to narrow the free-space elevation radiation pattern. For example, modify the EZNEC example file W8JK.ez by changing the height (Z coordinates) to 0.5 wavelength. The takeoff angle is 25 degrees. Delete one of the elements to make a dipole and note that the dipole's takeoff angle is 28 degrees. The lowering is due to the substantially greater elevation directivity of the W8JK. There aren't too many modestly sized horizontal arrays that have enough elevation directivity to make much of a difference in takeoff angle, however, so the difference is generally small at best. It's also interesting to note that the takeoff angle of this dipole over real ground is 2 degrees lower than the takeoff angle of the dipole over perfect ground. All true. I see my response was too encompassing. What I was trying to refer to was Art's "magic" design. To wit: "Would hams have an interest in a two element 20 M antenna that have (sic) lower TOA than the norm, say 9 degrees instead of the normal 14 degrees?" I can't imagine anything that will make a 2 (or any other number) element horizontal antenna of any configuration have a TOA of 9 degrees other than placing the array center at a height of ~105' above real ground at 14 MHz. |
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