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Quad loop supported by single tower  NEC2 modeling question
Hi,
I am modeling a vertically oriented, vertically polarized loop for 160 meters. The loop will be supported at the top of a 130 foot tall tower with a 6 foot standoff arm. The Bottom of the loop will be 10 feet from the ground. I was modeling the exact physical layout of the loop with NEC2 without considering the tower structure in the model at all. The tower is Rohn 45G with nonconductive guy wires. Not wanting to duplicate the exact tower model in NEC2 (by hand), I substituted in essentially a wire with a diameter of 1 foot, using steel for the conductor. I am modeling the antenna over 'real ground'. Putting in this wire next to the antenna had a pretty big impact on the resonance frequency that NEC2 reported. The pattern is slightly altered as well. My question is, 1) Am I taking too much of a shortcut to use a single wire to represent the tower? I just wanted a *rough* idea if this tower length (1/4 wavelength on 160) was going to have some impact on the pattern in the real world. Resonance frequency shifted down in frequency 35Khz in my model. I've modeled and built loops that I've installed between trees and the results have matched NEC2 very well, but I don't know what to make of the support steel tower in this case  am I overstating its effect the way I modeled it? Scott, WU2X 
#3




Quad loop supported by single tower  NEC2 modeling question
Thanks Roy!
I guess I was confused about the obvious connection the tower base has to the ground. Will this have any addition affect? Scott, WU2X On Dec 7, 3:34 pm, Roy Lewallen wrote: You've done the right thing. The tower features are a tiny fraction of a wavelength, so the single wire substitution is fine. To improve the accuracy of the model, use the equivalent radius of 0.421 foot for a triangular tower with one foot sides. This will likely make a noticeable difference only if the tower is somewhere in the vicinity of self resonance. Roy Lewallen, W7EL wrote: Hi, I am modeling a vertically oriented, vertically polarized loop for 160 meters. The loop will be supported at the top of a 130 foot tall tower with a 6 foot standoff arm. The Bottom of the loop will be 10 feet from the ground. I was modeling the exact physical layout of the loop with NEC2 without considering the tower structure in the model at all. The tower is Rohn 45G with nonconductive guy wires. Not wanting to duplicate the exact tower model in NEC2 (by hand), I substituted in essentially a wire with a diameter of 1 foot, using steel for the conductor. I am modeling the antenna over 'real ground'. Putting in this wire next to the antenna had a pretty big impact on the resonance frequency that NEC2 reported. The pattern is slightly altered as well. My question is, 1) Am I taking too much of a shortcut to use a single wire to represent the tower? I just wanted a *rough* idea if this tower length (1/4 wavelength on 160) was going to have some impact on the pattern in the real world. Resonance frequency shifted down in frequency 35Khz in my model. I've modeled and built loops that I've installed between trees and the results have matched NEC2 very well, but I don't know what to make of the support steel tower in this case  am I overstating its effect the way I modeled it? Scott, WU2X 
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Quad loop supported by single tower  NEC2 modeling question

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