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## [TowerTalk] How accurate is EZNEC?

 To: [TowerTalk] How accurate is EZNEC? W8JI@contesting.com (Tom Rauch) Thu, 6 Sep 2001 07:19:59 -0400
 ```Hi Richard, > question the accuracy of such programs. Such as: can EZNEC or similar > modeling programs accurately determine which quad array: 1/4 waves, > 1/2 waves, or 5/8 waves... will outperform the other in real life? EZNEC, like any other modeling program, is a tool. The results we get with any tool depend on how well we understand how to use the tool. This especially includes modeling phased systems, where the user has a choice of both current or voltage ratios and phase. The user is the biggest limitation, and persons with deep understanding of how systems actually work can model "new" or "unconventional" ideas faster. For example, people often try to model elements that are not fed at current maximas in phased arrays the same way they do current fed elements, using current sources not placed at the current maxima in the element operating with well known current and phase ratios. Doing so results in incorrect current and phase distribution in arrays, and the conclusion often is the array "won't work" when the modeller is actually at fault. This common modeling error appears mostly with shunt-fed elements, or non-1/4wl verticals in phased arrays, and leads to the old wive's tales that "shunt fed towers can't be phased" or that "1/2wl verticals won't phase correctly". Even though nothing is further from the truth. I phased a shunt-fed 1/4wl tower against a dissimilar height series-fed T antenna and got well over 20dB F/B. I can also model that system and it works. Models by nature, are shortcuts but virtually none of the short- cutting is in the antenna calculations of NEC based programs. There are shortcuts in ground calculations because EZNEC and other NEC based programs treat the ground as a homogeneous medium. In truth, soil characteristics vary widely with depth and direction. Whenever there is a shortcut, there is potential for notable error. I do not have great confidence in the ability to accurately calculate loss of conductors very near earth. Some real world data seems to bear that out, although data is sparse. > Again, I am not against using EZNEC for a general idea of how an > antenna array might work. But I have a serious problem believing > EZNEC has all the answers and much prefer to hear or read about actual > side-by-side antenna comparisons. I believe it's the difference > between "projected performance" and "actual real life performance". There are far more errors in using S meters, and making actual FS measurements, than most people realize or are willing to admit. Too many errors to talk about even. No wonder some think they have supergain antennas that break the rules of physics. It is often difficult to accurately know if one antenna is actually better than another, let alone determine what the dB difference is! My favorite example is a test I did on 75 meters between a G5RV and a dipole. The dipole won easily in dozens of on the air reports when I announced which antenna was which during the test. Problem was, I wasn't changing anything at all except what I told the other guy. When a few people couldn't see the change on an S meter, they told me the dipole audio was better! 73, Tom W8JI W8JI@contesting.com List Sponsored by AN Wireless: AN Wireless handles Rohn tower systems, Trylon Titan towers, coax, hardline and more. Also check out our self supporting towers up to 96 feet for under \$1500!! http://www.anwireless.com ----- FAQ on WWW: http://www.contesting.com/FAQ/towertalk Submissions: towertalk@contesting.com Administrative requests: towertalk-REQUEST@contesting.com Problems: owner-towertalk@contesting.com ```
 Current Thread [TowerTalk] How accurate is EZNEC?, RLVZ@aol.com [TowerTalk] How accurate is EZNEC?, Tom Rauch <= [TowerTalk] How accurate is EZNEC?, David Jordan [TowerTalk] How accurate is EZNEC?, David L. Thompson [TowerTalk] How accurate is EZNEC?, EUGENE SMAR [TowerTalk] How accurate is EZNEC?, David O Hachadorian