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Old April 2nd 09, 10:53 PM posted to rec.radio.amateur.antenna
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First recorded activity by RadioBanter: Mar 2009
Posts: 14
Default vertical antenna loading coil vs toroid

On Apr 2, 8:33*am, Cecil Moore wrote:
wrote:
I was wondering if the self shielding properties of the toroid would
have contributed to this conclusion, and because of these properties,
the toroid not have any electrical degrees, so to speak, so when it
come to the radiating element it would need to be slightly longer to
see the electrical degrees for the wavelength or resonance frequency
injected into it. thanks again for the info.


I suspect that the VF of the toroidal loading coil is much
higher than the VF of an air-core loading coil, i.e. the
toroidal loading coil occupies fewer electrical degrees of
the antenna. It makes sense that if the toroidal loading
coil occupies fewer electrical degrees of the antenna that
those degrees must be furnished somewhere else. The toroidal
loading coil seems to be closer to the lumped circuit model
than is the large air-core loading coil which generally
requires analysis using distributed network techniques.

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

There are two things happening with a base loading coil.
The loading coil occupies a certain number of degrees,
e.g. ~36 degrees for a 75m bugcatcher coil. The stinger
occupies maybe ~11 degrees for a total of ~47 degrees.
The other ~43 degrees comes from the phase shift at the
impedance discontinuity between the coil and the stinger.

With a center loading coil, a few degrees are lost at
the impedance discontinuity between the base section and
the coil. That's why a larger coil is needed for a
center-loaded mobile antenna.
--
73, Cecil, IEEE, OOTC, *http://www.w5dxp.com


I am a little confused, you say about the coil and the stinger
occupying a portion of the total 90 degrees, (I can follow this not a
problem), however I thought the purpose of the coil was to add
inductive reactance, due to the shortened length of the radiator, less
than 1/4 wave, therefore having a capacitive reactance overhaul. Let
the shortened vertical be 34-j234 ohms. My understanding is that
depending on on what the reactance is at some freq, I need to offset
this negative reactance with an equal positive reactance. I wasn't
looking at from a degrees point for view. Or is it just 6 of one, half
dozen of the other, both be equal just expressed differently, I like
the degrees point of view for a couple of other arrays I am
experimenting with. (long wires) I think it will simplify things a
whole lot. thanks again for the info and the links, very valuable
info. 73 brett
 
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