TWIMC:

I have been using the following formula to find the self-inductance of a
whip in free space:

4l
L = 5.08*l(ln---- -1)
d

Anyone have a more accurate equation?

Also, I need to compute the self-capacitance of a whip. Anyone have a
reasonably accurate equation for such?

Regards,
JS

On Sun, 17 Jun 2007 09:25:43 -0700, John Smith I
wrote:

Anyone have a reasonably accurate equation for such?

This does not work for structures with any significant size in
relation to wavelength.

A simple example reveals this with your inductance formula for a 1mm
thick 10 meter whip in the 20M band which suggests it "should be" 50.8
(whatever units your formula reveals). Experience informs us it is
not. This formula similarly fails throughout HF (and in fact would
lead us to the conclusion it was capacitive, not inductive at all).

Such formulas are generally useful at 1Khz (or where otherwise
specified).

73's
Richard Clark, KB7QHC

Richard Clark wrote:

...
Such formulas are generally useful at 1Khz (or where otherwise
specified).

73's
Richard Clark, KB7QHC

Yes Richard, those are the exact problems I am running into when
attempting to put together a small utility to get me in the ballpark on
some antenna computations/designs ...

I tossed that question out fishing for responses which might provide
methods, ideas, clues, hints on accomplishing the task ...

But, you reaffirm the difficulties in obtaining suitable accuracy ...

Regards,
JS

On 17 jun, 18:25, John Smith I wrote:
TWIMC:

I have been using the following formula to find the self-inductance of a
whip in free space:

4l
L = 5.08*l(ln---- -1)
d

Anyone have a more accurate equation?

Also, I need to compute the self-capacitance of a whip. Anyone have a
reasonably accurate equation for such?

Regards,
JS

On 17 jun, 18:25, John Smith I wrote:
TWIMC:

I have been using the following formula to find the self-inductance of a
whip in free space:

4l
L = 5.08*l(ln---- -1)
d

Anyone have a more accurate equation?

Also, I need to compute the self-capacitance of a whip. Anyone have a
reasonably accurate equation for such?

Regards,
JS

Hi John,

Your formula requires: no ground or other conductors present, uniform
current distribution along length of conductor, no other currents
present. The formula is only valid when all magnetic field is
generated by that wire segment only. This is practically
impossible.

Are you looking for an LC or transmission line model that is valid
(for example) around a halve wave or quarter wave length?

Best regards,

Wim
PA3DJS
www.tetech.nl