Richard Clark wrote:

EZNEC has the capacity to model wires with insulation. I presume that
is a legacy of NEC, but I will await tutoring on that point from other
posters.

Although it's a feature of NEC-4, it's not part of NEC-2. The insulated
wire capability of EZNEC was developed independently from other sources.

Carry that a bit further, it has at least "some" capacity to
model wires with material nested between them. After all, the
difference is in degree, not in concept, and the degree is hardly
remarkable.

No, they're different things. The insulated wire feature slightly
modifies the field from a wire, and is valid only for thin insulating
layers. Insulation between conductors has a considerably larger effect
on the field and consequent coupling between them. Adding insulation to
a parallel wire line gives you a model of something like an
air-insulated ladder line made with insulated wire.

When I observe common window line, it is not all that
different from two insulated wires.

It's enough to drop the differential mode velocity factor down to
somewhere around 0.91 - 0.95 (from various sources - I haven't measured
any), which indeed isn't very different from the common mode velocity
factor of insulated wire. Whether or not the difference is significant
depends on the application.

Further, there is nothing
remarkably different to the degree that the Lattin analysis is so
entirely thrown off as to be wholly useless. For that matter, I
haven't observed any postings here on any Lattin analysis other than
my own. If this all hinges on TV type twin lead, then too much credit
is being given to too little plastic.

You could probably make a model with EZNEC which would be fairly close,
then manually adjust it to optimize performance. A real antenna would
have similar performance if optimized for the type of line it's
constructed from, although the final dimensions would be a bit different.

Roy Lewallen, W7EL

On Tue, 03 Oct 2006 17:33:14 -0700, Roy Lewallen
wrote:


No, they're different things. The insulated wire feature slightly
modifies the field from a wire, and is valid only for thin insulating
layers.

Hi Roy,

And insulated wire is different from wire insulated by window line
insulation?

Insulation between conductors has a considerably larger effect
on the field and consequent coupling between them.

? Insulated wire HAS insulation between conductors. Air certainly
qualifies to some degree, the insulation on the wire another.

Adding insulation to
a parallel wire line gives you a model of something like an
air-insulated ladder line made with insulated wire.

That makes sense only in that it repeats the obvious. How is
insulated parallel wires (air-insulated ladder line made with
insulated wire) different from window line? Or twin lead? Except by
degree?

When I observe common window line, it is not all that
different from two insulated wires.

It's enough to drop the differential mode velocity factor down to
somewhere around 0.91 - 0.95 (from various sources - I haven't measured
any), which indeed isn't very different from the common mode velocity
factor of insulated wire. Whether or not the difference is significant
depends on the application.

This is not a very compelling argument for how Lattins WORK (seeing as
most reports suggest they do not). It is not a very compelling
argument for very remarkable differences in where they do work
(however, few seem to be offered in that regard either).

Quite simply, velocity factors do not explain away the lack of
resonance ANYWHERE near the intended frequency. What you suggest is
percentages where actual performance misses the target, not just the
mark and as a multiband structure is so wildly useless as to be a
product of chaotic, random doodling.

Further, there is nothing
remarkably different to the degree that the Lattin analysis is so
entirely thrown off as to be wholly useless. For that matter, I
haven't observed any postings here on any Lattin analysis other than
my own. If this all hinges on TV type twin lead, then too much credit
is being given to too little plastic.

You could probably make a model with EZNEC which would be fairly close,
then manually adjust it to optimize performance. A real antenna would
have similar performance if optimized for the type of line it's
constructed from, although the final dimensions would be a bit different.

Having modeled more than a few Lattins (and there are so many as to
beg the definition), any claim to resonance associated with a stub
dimension FOR ANY "ELECTRICAL LENGTH" is a fantasy of the first order.

The inability to model a working Lattin has no basis in these
arguments about the shortfall of EZNEC/NEC insulation issues. The
antenna design fails quite abysmally for bare wire when designed to
the purported rationale of trapping by stub construction. To think
the design can be resurrected by unmodelable insulation tricks is
based on hope and charity.

73's
Richard Clark, KB7QHC