Jim Kelley wrote:
VF = 0.04 is incredible.

Ignorance makes a lot of things seem incredible.
Not at all incredible according to the Fig. 1
graph that you referenced a few days ago at:

http://www.ttr.com/TELSIKS2001-MASTER-1.pdf

Here's how to do it. Draw a horizontal line at
0.04. Where it intersects the lines on the graph
are the real-world coils exhibiting a VF of 0.04.
If you need help drawing that line, send me an
email.

Hint: Those large loading coils are slow-wave
devices described in my Ramo and Whinnery
college textbook from the 1950's. It's on page
410 of the 2nd edition of "Fields and Waves
in Modern Radio", (c)1944, 1953 (the year you
were born). Isn't it about time you read it?

The approximation they use for vp (phase velocity)
is c*sin(pitch-angle)

I thought you were going to send me the coil
so I could measure it.

The coil has been chopped up and used in numerous
projects including my Bugstick article. Don't you
or your students know how to wind a coil? Do you
need step by step winding instructions?
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com