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

How to model linear loading in shortened dipole of vertical using EZNEC?
 

sorry, the diagram came out mangled on the post. the idea is a derivative
of the construction used in "The K4VX linear loaded dipole for 7 MHz"
QST, July 2002, pages 40-42.

Thanks

Steve

On Wed, 07 Jun 2006 13:25:44 -0400, Steven R. Jones wrote:

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

How to model linear loading in shortened dipole of vertical using EZNEC?
 

On Wed, 07 Jun 2006 13:25:44 -0400, "Steven R. Jones"
wrote:

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.

Hi Steve,

This may well be due to its inability to resonate as advertised. This
is not an infrequent complaint.

One compelling contradiction is seen in the description of the antenna
as being 60% of the conventional length; and the illustration of the
antenna built in thirds which would suggest it is 33% of conventional
length. Simple errors such as this lead to massive failures in
expectation.

This leads us to the observation that if you can erect a 1/6th
wavelength vertical, what do you stand to gain with this spaghetti
design that would put it ahead so much further?

73's
Richard Clark, KB7QHC