DB, when I noticed the pattern with no radials and the mast connected...I knew something was different. I checked the ground type right then and started to do my models with 0.001 and 5, but I changed my mind on that and left it at 0.005 and 13 using Eznec Average Earth feature for Ground Description.There is a difference, but that is not the difference I see between our patterns.
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If you used the capacitor in the Imax antenna, then it is obviously having and effect of making all your antenna configurations look similar with a couple of exceptions as you've noted.
If the capacitor has that much effect on the current distribution in the real antenna...then my ideas about the currents on the mast is out the window, but I will be checking that out on a more conventional model to be sure.
I also added your wires and I still get the same pattern, I just didn't have the 12" tube for the mount in the model. So, I can only figure the cap makes the difference.
Here is the difference my setting the segment length to 3" inches.
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I also had my radiator set at 271.4" inches and you at 277.1564" inches. That change did not change the shape of the pattern...just the gain changed. So the segments, the length, and adding the mount to the radiator did not make the difference. It must be the load you added...what are the values you used?
BTW, somebody mentioned recently that the Super Penetrator 500's mount design may create a capacitor type of function (tube inside a tube) similar to the Maco V58, and a few other antennas. IMO this is to allow some adjustment at the base of the antenna for the real antenna, but it could be more than that if your idea of adding capacitance to the Imax produces performance gains that would not be there without such an object added to the antenna. I think I recall you or somebody else talking about this as a possible modeling problem if the feature has consequences like the Imax or maybe it was Bob.
Did that cap mod' to your Imax model help with performance?
Do you have a model of the SP500 and if so did you model the mounting bracket that raises the radials up about 12" to 14" inches above the bottom of the mount? I see that feature in my model making a notable difference in performance.
Yesterday I was working on my Big Mack and checking everything I could find on the Internet. I found someone that described part of the base coil area, saying there was an insulator inside of a tube that held the base of the radiator. IMO that can add capacitance and maybe a model would have to have this object included in order to work as intended like you may be suggesting on the Imax. If so, then a 5/8 wave might not always be a 5/8 wave...so-to-speak.
What is the value of the capacitor you used on the Imax and how did you add it to the radiator?
Sorry to launch off into the weeds, but I figured I might have your ear a little with this new work you produced going on.
Good luck.
