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Old April 2nd 09, 12:33 PM posted to rec.radio.amateur.antenna
Cecil Moore[_2_] Cecil Moore[_2_] is offline
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First recorded activity by RadioBanter: Mar 2007
Posts: 3,521
Default vertical antenna loading coil vs toroid

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