Reg Edwards wrote:
(snip)
What was the formula used to calculate
propagation time?

Glad you asked. I calculated (1/f)*(angle/360) or period of one cycle
times fraction of a period. I assumed that all the phase shifts
given were less than one period, total. I was hoping someone else
would calculate the delays and correct any mistakes in my method or
results.

If the correct formula was used does this point to
somthing peculiar with EZNEC's own calculations?

Can't think any more.

Or it points to the coil in question not acting purely like a
transmission line over this range of frequencies. How would a short
length of transmission line act if you parallel it, end to end with
capacitance? This coil certainly has end to end capacitance.

At some high frequency, that capacitance will, first resonate with the
inductance, forming a trap (with a rapid phase change with respect to
frequency), and above that, bypass the antenna current around the
inductance. At very low frequencies, with a low impedance on each
side, almost pure inductance probably dominates. In between these,
(with appropriate impedance connections), there is probably a
frequency range where it acts mostly like a short piece of
transmission line, with approximately (a lot less approximate than +-
60%) constant delay.

In such a large beast, at the intended frequency of operation,
unintended parasitic effects may be as big as the intended inductive
effect. These are the problems that make designing good (as in, "act
as lumps of inductance") coils interesting.