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Old June 7th 06, 06:25 PM posted to rec.radio.amateur.antenna
Steven R. Jones
 
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Default How to model linear loading in shortened dipole of vertical using EZNEC?

I want to work out a design for a linear loaded off center fed vertical
dipole for 75M (perhaps will work multiband as well?) using linear loading
in an "S" configuration, i.e:
feedpoint
I-----------------------------------()-------------I
I I
I----------------------------------I I------------I
I I
-----------------------------------I I-------------

Which per my reading should let me design a 75M vertical that is only 60%
of the length of a conventional radiator. A recent article in QST showed
the successful use of 450 ohm ladder line with interwoven 3rd wire as a
conveient way to build this sort od linearly loaded design. In attempting
to model this design in EZNEC, I do not seem to get the loading effect and
shorter length of the radiators to achieve resonance, nor do I get the
feedpoint impedance lowering that is described for this sort of loading.
I was hoping that the OCFD design would allow direct feed through a choke
balun without having to deal with impedance transformations. with either
an excessively low center feed impedance (with loading) or the typical
~200 feedpoint impedance and 4:1 balun required with the OCFD design at about 1/3 distance from
one end.

Any thoughts or prior experience to share?

Steve
KQ4WB
 
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