On Apr 2, 7:17*pm, Cecil Moore wrote:

It depends upon which math model is being used and
whether the math model is valid under the existing
conditions. We can neutralize capacitive reactance
with a lumped inductance or with a stub or with a
helical coil. The results are approximately the
same but there are differences.

If the current amplitude changes significantly
between the bottom and top of the loading coil,
the lumped circuit model is not valid because
the coil is an appreciable percentage of a
wavelength more akin to a transmission line
than a lumped circuit.
--
73, Cecil, IEEE, OOTC, *http://www.w5dxp.com

Now it is clearer to me. I understand why there is a difference using
lumped circuit analysis as opposed to the the actual coil or stub
analysis. You have provided much valuable info on this subject. Thanks
again. I will load some math program on my pc any do some of the
analzsis of my design and compare it to what I have measured now with
the ones I have built

The reason this came about to me was to use some very short but
extremely strong 1.5" insulators that I have.In order to get the
required inductance with the length of insulators that I have the
losses in the coil would be large, that is why I chose the toroid.

Did you ever try to model a resonator where the coil required is
actually longer than the insulator, so that the vertical part of the
resonator is actually inside the coil , would it somewhat have a
larger inductance then the expected air wound value, similar to a coil
with a ferite inside it (tuning slug) or would the radiator not even
see the amount of the coil that it covered therefore have a lower
inductance. I was thinking, instead of spreading the turns on the
coil to adjust amount of inductance simply move the vertical element
in and out of the coil to adjust it. There discussions before were for
a center loading coil which will be constant, but this last part of
discussion I would like to try for base loaded coil and make it
variable but not tap it conventionally . Hope I described well enough
for you see what I have in mind, Again thanks for the info.73 brett