But I'm kind of dense. Can one of the many other readers of this group
kindly explain how Cecil's equations and explanations are used to
actually figure out what the current will be at the top and bottom of a
loading coil? Yuri, you seem to understand it -- can you explain it to
me? Richard? Surely the necessary equations are in one of your books?

Roy Lewallen, W7EL


I will leave Cecil's equation to Cecil, but I will point out that you can use
your own creation EZNEC 4+ and HELIX feature to model the quarter wave vertical
with loading coil. I did it after your pointed out HELIX feature and posted it
at the beginning of my thread, here it is again, actually using "worst" case of
10m loaded whip (not too much loading) and demonstrating significantly
different (not equal) currents at coil's ends. Did I do anything wrong?

Here it is again:

I took the time to check out the Helix feature in EZNEC 4.08 and modeled the
"worst" case - CB whip or 10 m whip with loading coil - helix half way up and
then the same helix moved up to 3/4 way up. Things will get more pronounced
when more turn, more inductance coil is used and frequencies are lower. Yes,
Virginia there is a CURRENT DROP across the loading coil, unless you have more
"appropriate" or "scientwific" term for it.

Rough dimensions: 1m mast (5 mm copper wire/tubing), 20 cm long coil/helix with
5 cm diameter turns, 5mm wire diameter, 10 turns, spacing 2 cm followed by 1 m
whip
Resonated at 27.05 MHz
With base current 1 A, at the end of mast/start of coil the current is 0.87457
A
at the end of coil/start of whip the current is 0.66884 A - a decent drop of
0.20573 A or 20.5 % - not an "EQUAL" (you DC coil believer types!!!)

Then I moved the same coil up 50 cm, so the mast was 1.5 m, same coil, followed
by .5 m of whip.
Again with base current of 1 A, the bottom of the coil had current this time
was 0.65479 A, while top of the coil 0.37127 with larger drop of 0.28352 A or
28.3 % - even bigger not "EQUAL" with resonant frequency moving up to 28.7 MHz,
which corresponds to REALITY measured, experienced and finally properly (close
enough) modeled. Even M0RON (with apologies if there is call like that issued
:-) can see the nice current drop across the coil displayed in the VIEW.

Thank you Roy (now you believe it?), Cecil, Richard. Now the unbelievers can
even model this case themselves and SEE it properly. So ON4UN, K3BU, W9UCW,
W5DXP, KB5WZI were and are right. W8JI, G3SEK et al are sooooo wrong :-) Some
still persist, some are converted and many will be enlightened.

Now if Roy can incorporate elegant way of modeling real life coil/inductance by
inputing Inductance L and its physical size and have it calculate things
without modeling turns, that would be a winner and a segment saver.


Not sure if you saw it, but it looks to me that even EZNEC 4+ is on "our" side.

73 Yuri, K3BU.us