Richard Harrison wrote:
Cecil, W5DXP wrote:
"The following web page is representative of the side that asserts there
is virtually zero delay through a 75m loading coil. But the backers of
that argument have grown strangely silent of late."

Current does not jump off the rails in a coil.

Not disagreeing in general but just fine tuning a bit.
In an HF mobile loading coil, the EM waves are photonic
in nature so a few photons are capable of migrating to
adjacent turns - certainly not enough to cause the 3
nS delay through a 10 inch long 100 turn coil reported
by w8ji, but the effect is enough to roughly cut in half
the time taken for the current to negotiate the coil wire.

I have modeled a 75m Texas Bugcatcher coil at:

http://www.w5dxp.com/coil505u.EZ

The length of the wire used in that coil is ~48 feet.
A wavelength at 3.8 MHz is ~259 feet. So that 48 feet
equals about (360)(48/259) = ~67 degrees. Yet EZNEC
reports a phase shift of only ~38 degrees. The effect
of the interaction between adjacent coils increases the
velocity factor of the coil to roughly 1.8 times what it
would be if all the current were confined to the coil
wire. That's a VF increase from ~0.009 to ~0.016 but
certainly still magnitudes short of w8ji's reported
value of 0.988

The measured velocity factor as a function of the ratio
of coil-circumference/wavelength is presented by Kraus,
Figure 8-34 in the 3rd edition. Note that the phase
velocity is not a straight line function of circumference.

The velocity factor as a function of the ratio of
coil-diameter/wavelength has been plotted in Fig. 1
of: http://www.ttr.com/TELSIKS2001-MASTER-1.pdf
and is also not a straight-line function.
--
73, Cecil http://www.w5dxp.com