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## Re: [Antennaware] antenna project and software...

 To: antennaware@contesting.com Re: [Antennaware] antenna project and software... Terry Conboy Tue, 13 Feb 2007 05:22:33 -0800
 ```At 08:53 PM 2007-02-12, Ed K4SB wrote: >Terry Conboy wrote: >> Not only will the \$80 version of EZNEC model this array, but even the >> free version of EZNEC (limited to 20 segments) will work well unless >> the elements exceed 1/2 wl long. >You absolutely CANNOT model an antenna of this sort with the free >version. Consider that at a minimum, you will have about 140' of >elements. With only 20 segments, you would be looking at the currents >every 7' along the element. > >W4RNL's site has a good article on proper segmentation. The absolute length of a segment really isn't the issue, it's the fraction of a wavelength. With NEC-2 based models, you can get reasonable accuracy for simple antennas (dipoles, verticals, inverted Ls, 2-el yagis, etc.) with only 10 segments per half-wavelength. However, it's also true that very closely spaced wires can require more segments. Accurately modeling structures such as transmission lines are an extreme case of this. W4RNL at http://www.cebik.com/amod/amod1.html states: "Because we are impatient, a bad habit has set in among many program users: to divide the antenna elements into as few segments as possible, again within certain generalizations in the instruction manuals. For MININEC, the recommended minimum number of segments per half-wavelength is 10, while for NEC-2 it is 9 or 11. (When center feeding an antenna element, use an even number of segments for MININEC and an odd number of segments for NEC.)" On that page, L.B. gives an example of a 20m half-wavelength dipole above ground. The apparent gain rises from 7.97 to 7.99 dBi as the number of segments is increased from 11 to 45. The impedance changes from 67.51 - j0.22 to 67.56 + j0.56 ohms. These differences are certainly far less than the variations due to a real world environment (conductor sag, ground conductivity variations, wire insulation, end insulators, bird droppings, etc.) and exceed most hams' measurement capabilities. Here's what W7EL says in the EZNEC Help file under 'Segmentation': "A useful rule of thumb is 10 segments per half wavelength for pattern/gain analysis, and perhaps twice that number if really accurate impedance values are required. Wires joining at very acute angles may require more segments (see Acute Angles). If in doubt, a straightforward way of telling whether you've specified enough is to increase the number and see how much the results change." And on http://www.eznec.com/demoinfo.htm, Roy says: "Even with the 20 segment limit, the demo program does a very respectable job analyzing a two-element quad, two- and four-element phased vertical arrays, simple Yagi, W8JK, and many other antennas" I often recommend the free demo version of EZNEC for new modelers to get them "hooked". W7EL's customer support is impeccable and his program's user interface is the result of years of user feedback, so the full versions of EZNEC are a bargain, in my opinion. (I've been using Roy's programs since ELNEC 1.0). My only complaint is that they keep me up late at night building models (and some do use all 1500 segments in EZNEC 4.0+)! 73, Terry N6RY _______________________________________________ Antennaware mailing list Antennaware@contesting.com http://lists.contesting.com/mailman/listinfo/antennaware ```
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