Cecil, W5DXP wrote:
"Please explain why a centuries old method of determining phase shift
through a coil by measuring its self-resonant frequency is not good
enough for you?"

A coil is an RLC circuit. At resonance, L offsets C and all that is left
is R. In a resistance, the current is in-phase with the applied voltage.

But, in a physical length of a tuned circuit or in a straight conductor
in its place, in a circuit with reflections, you have energy coming from
both directions creating an interference pattern, which is repeated
every 1/2-wave (180-degrees) in the line Peaks are 1/2-wave apart,
considering the velocity factor of the line. To determine the phase
shift, count the maxima.

The wavelength of a line is the distance a wave must travel for one
complete cycle (360-degrees). If you want the phase shift for a line,
take the length of line required for one degree of phase retardation and
multiply it by the length of line you have.

Best regards, Richard Harrison, KB5WZI