Mike, W4EF wrote:
"Is there any indication in the text as to where the actual current data
came from?"

Not exactly, on page 464 of the 3rd edition of Kraus` "Antennas", that I
saw. Below the diagrams of current versus distance from the center of
the dipole, the text says:

"It is generally assumed that current distribution on an infinitesimally
thin antenna---is sinusoidal, and that the phase is constant over
1/,2-WL interval, changing abruptly by 180-degrees between intervals."

On page 295, Kraus says:
"If the dimensions (of a helix) are small (nLlambda), the maximum
radiation is in the xy plane for a helix oriented as in Fig 8-69a, with
zero radiation in the z direction."

In other words, radiation is perpendicular (normal) to the axis of small
diameter coils.

On page 295, Kraus says:
In the preceding discussion on the normal mode of radiation, the
assumption is made that the current is uniform in magnitude and in phase
over the entire length of the helix. This condition could be
approximated if the helix is very small (nLlambda) and is end loaded.
However, the bandwidth of such a small helix is very narrow, and the
radiation efficiency is low."

It is obvious that the inductance and delay of a coil depend upon on the
coil`s diameter and pitch, in addition to the length of the coil.

Best regards, Richard Harrison, KB5WZI