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Old August 17th 03, 09:12 PM
Roy Lewallen
 
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There are a couple of problems with the analogy. First, of course, is
that there is no secondary winding to convert the primary's magnetic
field to the current I you reference. The "aether" has no N and no I,
and doesn't do this. The second problem is that a simple transformer
model, or any other lumped-element circuit model, is valid only if its
dimensions are very small compared to a wavelength(*). A mobile whip
loading coil is often long enough that a current gradient can occur from
one end to another, so a single lumped element model might be inadequate.

Roy Lewallen, W7EL

(*) A particular problem with the mobile loading coil in an electrically
small whip is that the current changes a great deal over even a very
short distance, as it goes from zero at the end of the whip (assuming no
top loading) to a large value at the base. It sounds like sort of a
circular argument, but a lumped element model loses accuracy any time
there can be a current gradient across the component. Interestingly, the
problem becomes less and less severe as top loading is increased,
because it reduces the current gradient along the whip. You *could*
quite accurately model a loading coil as a single lumped element if you
had enough top loading.


Art Unwin KB9MZ wrote:
Yuri,
I think you would better understand what is happening
if you view the inductance in question as half of
a transformer, where the other half is the aether.
This allows you to bring in the formular NxI one side =
NxI the otherside. This way you can see that I is constant.
If it wasn't a constant then the lines of flux would have a
very distorted shape at one end of the inductance.
The fact that transformers have impedances that are not
totally resistive is because of other factors than Inductance.
If I am incorrect with this analogy I would apreciate any
corrections as I am sure Yuri would to
Art


 
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