Roy Lewallen wrote:
When the ground was removed and replaced by a wire, the
transmission line properties of the coil changed dramatically, while the
C across the coil didn't change significantly.

Moral: The self-resonant frequency of a loading-coil needs to
be measured in the mobile antenna system, no on the bench.

Yes again, with one slight modification. You'll note from the EZNEC
models that the current actually increases some as you go up from the
bottom of the inductor. This is the effect noted by King which is due to
imperfect coupling between turns. It results in currents at both ends
being less than at the center.

It results in a deviation away from the perfect cosine envelope
exhibited by a 1/2WL thin-wire dipole. In any case, the delay
through a 75m bugcatcher coil is tens of degrees, not 3 nS.

If the
reasons for this aren't obvious, many texts cover it quite well. No
special "traveling wave" analysis is required.

The self-resonant frequency of that modeled coil is around 9 MHz.
Since the coil is 90 degrees at 9 MHz, it would be ~59 degrees
at 5.9 MHz. Dr. Corum suggests a 15 degree limit at which the
lumped-circuit model needs to be abandoned in favor of the
distributed-network model or Maxwell's equations.
--
73, Cecil http://www.qsl.net/w5dxp