I think you’re right Bob, but you are ignoring the broader context in the text.
IMO this is what Roy is saying. Isn't that the way the theory of coax is supposed to work, based on the conditions he stated in his quote below.
Roy explains this in the first paragraph of that section on “Using Transmission Lines.” See the manual below. Here Roy explains how using Eznec works to solve the 3rd conductor issue, and he explains why. IMO Roy is not ignoring the facts about a third conductor. He goes on to tell us how Eznec handles this when the load is not purely resistive for some reason.
I don’t understand all the ramifications of Transmission Line theory like you do Bob, but these words describing NEC rules and how Eznec handles a TL…seems pretty clear to me.
IMO, if we tapered a coaxial cable like this cone, we would have to insure that the ratio of the differences in the radius for the center conductor to the radius for the shield was maintained the full ¼ wavelength of the cone. IMO, if we don't maintain the correct coaxial ratio, then we sure can't call the cone coaxial.
A 4” coaxial pig tail will radiate antenna currents just because the correct coaxial ratio as been skewed. This is why we do our best to keep pig tails short, to help minimize radiation.
You can also extend the wire lengths of a pig tail out to near a 1/4 wavelength each, and you’ll have a working dipole radiating antenna mode currents into the far field.
For a while back in the good old days I believed Freecell…when he too used to try and convince me that the cone on the S4 worked just like a coaxial feed line. He said the cone feeds the bottom end of the S4 ½ wave radiator, and thus made a smooth transition to a match for the end of the ½ wave element above. I didn’t see it and I didn’t believe it, because in order to feed the end of a ½ wave element requires a very high impedance connection. Coax presents a need for a very low impedance.
Are you referring to the ARRL Open Sleeve article? This idea is new to me.
I was thinking that transmission-line mode currents follow the rules of feed lines…and do not radiate into the far field, because of the equal, opposite, and cancellation rule that applies to coax construction?
Am I wrong?
Bob, to be clear here, I also think this theory or rule regarding coax also includes that the load is perfectly matched, and maybe this is why Roy talks about the subject this way. Apparently this issue is a NEC thing.
Consider this
Again, are you getting this conclusion from the same article above?
Bob, my S4/NV4K models do show very little imbalance in currents between the monopole and the sum of the radial currents. These currents are also out of phase and cancellation occurs.
I think it was Freecell that first referred to the cone area as a coaxial feed line. Later I think Donald was suggesting the same thing. I’m not sure if you ever mention this however.
W8JI wrote that a cone or sleeve basically helps decouple antenna CMC’s, similar to what radials do with any other vertical radiator, but he says nothing about the cone being coaxial. He shows Eznec model results with the cone attached to a J-Pole.
Bob, there are more of your comments below, but for now I’m going to stop here. I’ll try and get to the rest later, OK?
