Hi Dan

If you can measure the resistance at more than one point on the surface
of the rod, does this imply that the rod surface is conductive
everywhere along its length?

I am not sure having fully understood your remark. I presume that, the materal being homogeneous, the rod surface is conductive everywhere the same way. The various elements of the rod touch each other, so there is electrical continuity along the whole rod. Clearly, toward the rod top, resistance will be higher due to the thinner diameter

If you could attach the wire to the rod so that it touches everywhere
along the length, then the current would divide between the rod and the
wire according to their respective resistance per length (most of the
current would flow in the wire) and the currents induced in the pole
would be in phase with the currents induced in the wire.

I agree that currents would divide between the rod and the wire according to their respective resistance, but this is not my main worry as the very low-resistance copper wire would nearly fully bypass the rod resistance. What I am instead worried about is that, the rod being thick, the RF current may not be the same along the rod circumference. In other words, at the point of contact between the rod and the copper wire, the rod current could be lower than that at its opposite side. Such extra current could develop due to the rod electromagnetic coupling with the radiating wire. However, I am not sure whether my reasoning makes real sense


I think it would help to have the wire attached at least at the bottom
of the pole and the top of the pole.
If you attach the wire only at the top and ground the bottom of the
pole, you make a rather lossy folded monopole. If you attach the wire
at both the top and bottom of the pole and insulate the whole structure
from ground, it's more like a cage monopople with one lossy wire and
one good wire.

My idea is to have the wire attached at both the bottom and the top of the rod as you suggest. The bottom copper lead would also be connected to the center conductor of the coaxial feed cable (the cable braid would instead be connected to the radial system).

Now an interesting case. Suppose that the copper wire is instead kept fully insulated from the rod (though very close to it). Would you expect power loss to occur in the conductive rod due to RF currents flowing through the rod due to its electromagnetic coupling with the radiating wire?

73

Tony I0JX