Yuri Blanarovich wrote:
Now I also understand the small "bump" increase in the current at the bottom
of the coil due to some loses that reflected wave encounter on the way
"there and back" to the tip of the radiator from the bottom of the coil (?)

I suspect that current bump is caused by magnetic linkage
between the central windings while the end windings would
not experience it to such a degree. It is the thing that
increases the velocity factor over the purely helical
path.
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73, Cecil http://www.w5dxp.com