Reg Edwards wrote:
. . .
For years, my approach to loading coils at HF has been to calculate
the inductance and capacitance per unit length of coil from DC
principles. And then calculate the velocity factor and Zo from
transmission line principles. Which gives results in the right ball
park according to what few experiments I have made with actual anennas
and helices on the 160 and 80 meter bands.

How do you calculate the coil C to use in the transmission line formulas?

Roy Lewallen, W7EL