Reg, G4FGQ wrote:
"For present purposes the length and impedance of the antenna below the
coil is not relevant. It can be part of the generator."

I infer that Reg is saying that at a particular frequency, a loading
coil has a unique voltage across and a unique current through it.

Probably sometimes so, but the simple argument was that the current at
the coil ends can be different. This is caused by superposition of
forward and reflected waves. The same power may have any number of
voltage to current ratios (impedances). The purpose of a loading coil is
to transform an antenna impedance to an impedance more compatible with a
radio. There is a difference in impedance between the ends of a loading
coil so that the current at its ends are different.

The length and impedance of the antenna below the coil participate in
the imbalance seen at opposite ends of the loading coil. The height of
the loading coil on an antenna is thus significant.

The length and impedance of the antenna below the coil participates in
radiation. The function of a transmission line is to convey energy. The
function of an antenna is to radiate energy.

Radiation is a function of unbalanced current and the length through
which it travels (page 864, Terman`s 1955 edition). The current per unit
length below a loading coil is higher than above the coil. More
radiation per unit length results from more current. This affects
impedance at the coil ends.

"For present purposes" we may declare anything so long as we don`t
define our purposes, but Fig 9-22 on page 9-15 of ON4UN`s "Low-Band
DXing" is significant and no one has said his pictures are wrong and
given reasons.

Best regards, Richard Harrison, KB5WZI