Owen Duffy wrote in
:

....
Simply, I doubt that Tom's experiment, as far as described, was likely
to reveal the value of Beta, except were resonance was observed (which
implies 90° one way phase change along the equivalent line). The test
setup was unlikely to reveal the true undisturbed resonance of the
helix alone, there would be better configurations.

In thinking a little more about this, and thinking aloud, there is no
reason to think that the blip on Tom's delay measurement at around 16MHz
was for a mode of resonance where the one way phase change would be 90°, it
may well have been the next higher mode.

Owen