Cecil Moore wrote:
(snip)
Here's what EZNEC reports as the phase shift through the coil
in the traveling wave antenna previously tested at 5.89 MHz.

5.5 MHz: 14.1 deg, 5.89 MHz: 15.7 deg, 6 MHz: 16.2 deg,
7 MHz: 21.4 deg, 8 MHz: 29.5 deg, 9 MHz: 45.9 deg,
10 MHz: 89 deg, 11 MHz: 141.4 deg, 12 MHz: 163.0 deg,
13 MHz: 172.3 deg, 13.7 MHz: 183.82 deg.

Here is that list repeated in units of time, instead of degrees:

MHz ns delay
5.5 7.1
5.89 7.4
6 7.5
7 8.5
8 10.2
9 14.2
10 24.7
11 35.7
12 37.7
13 36.8
13.7 37.3

I would have to graph this on a log frequency plot to see the
frequency breakpoints, but I think this looks a lot like a short piece
of transmission line below about 6 MHz and like a resonator above
that. I expect the delay to start to fall at higher frequencies as
the turn-to-turn capacitance takes over.

What do you see?