That may be the theory 24, but my Eznec model of the project that Captain Kilowatt showed us, a 1/4 wave tower over good conductive ground as he describes it…showed us the results he indicated happened at the work site, and it was not over Perfect Earth. My model shows that, but I don’t think anybody has noticed the distinction yet.
So, I’m just not convinced that the theory tells us…that we’ll see ~35 ohms only when the 1/4 wave antenna is ground mounted and over an infinite and perfect ground plane.
I received that Bronco model from Henry and changed the frequency and scaled the model to 27.205 mhz. I’ll try to find that model, and post it 24.
I believe you may be the only one around here that will appreciate what I was trying to show, right or wrong, when I posted those two mobile models in this thread, because nobody has made a comment about the models until you posted above.
Yes, and that is exactly the point I was trying to make to Robb with his arrow head mobile he posted. I see this model this way, because all of the vertical elements close to the feed point are flush with currents, and IMO the vertical elements are in phase and the horizontal elements are out of phase. I think the slanting window posts are what raises the impedance we tend to see with a mobile 1/4 wave radiator. We also see very low gains and higher angles as a result too, just like the very low frequency broadcast radio antennas do.
I see the same, there is no change in impedance weather in free space or over real Earth, but I don't believe that is the way it works either. I can't explain this, but I don't see it in my models. This is why I don't believe the 35 ohm theory tells up the antenna has to be over an infinite and perfect ground plane.
I haven’t really studied these mobile models yet, but again that is because nobody seemed interested, and I don't use mobiles any more.
That may be 24, but it does not compute for me. Capacitance is just too important in antennas for modeling to ignore the effects. In fact I originally thought that Eznec did show us some signs of capacitance when I checked out the currents log. However, I did not do an extensive study.
That will be great 24.
I suspect that you will see the resistive part of the match increase at resonance even more, and the pattern will become far less directional.
I try and tune all of my 1/4 wave models to resonance, unless I’m comparing antennas.
When you make the change you suggest above, you’ll also have to shorten the radiator significantly, and that tells me that capacitance is affecting this response in a big way. So, again I think capacitance is working in Eznec.
Yes, my model mounted on the bed rail shows ~63 ohms impedances. With
your increase in segments…your feed point actually gets closer to the base, and up to some point in the segment count…the model improves in accuracy, but the performance results may get a bit worse.
Yes you did see a higher impedance with the antenna mounted on the bed rail at about 54” above the Earth. I think that is because the antenna is higher up, compared to my model with the antenna sitting on the bumper at about 12” on my P/U model.
I don’t know the answer to this. I think we are both seeing something happening that needs more discussion however, but I was never able to get anybody to discuss these models, right or wrong, until you popped up with some questions.
For now, I’m probably the only one that even has a clue to what you’re talking about, but hopefully this conversation will bring others out of the wood work.
I have the version that allows only 500 segments and I’m just below that limit. I try to get my segment distribution as close to the same as possible, and I strive for about 6” per segment with my mobile models and a large number of wires. On my 1/4 waves I shoot for about 2.5” per segment.
On the mobiles I use about 50 wires. I haven’t yet tried more or less wires to see how that affected the models.
Thanks for your comments on my mobile models. I will send you this Bronco model if you want it.
