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## [TowerTalk] Ant Modeling (long)

 To: [TowerTalk] Ant Modeling (long) w7why@harborside.com (Tom Osborne) Thu, 17 Jan 2002 23:05:12 +0000
 ``` Hi All In looking over previous posts, there seems to be an awful lot of credence to computer modeling of antennas. I've seen things like "A three element beam with lengths of (n) and spacing of (n) will give 7.13 dbd and 18.34 db FB. How do we know this? Has someone built and tested every conceivable spacing, length, height and checked them with a field strength meter. How about 4 elements on a 32 foot boom. There are hundreds of different configurations available. Then after that is figured out, What if the boom diameter is changed? Do all the readings change again. Then how about raising it up 5 feet. Do all the readings change again? It seems to me that there are thousands of different configurations when you figure boom size, element size, taper, element spacing, element length, ground below the antenna, terrain, etc. Surely each configuration hasn't been verified manually. But if I put in "2 elements on 20 on a 12 foot boom", I'd probably get a gain of 5.34 dbd and FB of 12 db or something like that. It seems to me that in order to say that such and such an antenna with a certain length of elements and height has a certain amount of gain, you'd have to measure 360 degrees around the antenna for side lobes, rear lobes, etc, the do the same thing from 0 degrees to 90 degrees 360 degrees around the antenna to check the take-off angle. Where does the data that we take so religiously come from? I know we can model a 3 or 4 element antenna and move each element a couple of inches or so and see different amounts of gain and FB. If these antennas are modeled at VHF frequencies, it would be hard to make the same assumptions at HF. It seems as there are just too many variables to take the data as absolute. If I wanted to model my 20 meter beam, how would I take into effect the fact that half of it overhangs my shack roof and the other half is directly over one of my 40 meter verticals, and about 20 feet away in a tree is my 80 meter inverted "V." Plus the ground slopes to the N.E. at about a 25 degree angle for a half mile or so. The hill in back goes up another couple of hundred feet. How in the world would I ever be able to take into effect everything that effects the antenna. It just seems to me it's hard to put in certain dimensions and get an absolute answer. 73 Tom W7WHY ________________________________________________________________________ Where do you get ICE bandpass filters & beverage matching boxes? The same place that pays for the hosting of this list: The eHam Store. Order online at http://store.eham.net. ----------------------------------------------------------------------- ----- FAQ on WWW: http://www.contesting.com/FAQ/towertalk Submissions: towertalk@contesting.com Administrative requests: towertalk-REQUEST@contesting.com Problems: owner-towertalk@contesting.com ```
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