Mark Keith wrote:
The current through the coil is not the issue as far as my "camp" is
concerned.

Apparently it isn't now, but it was quite an issue for a while there.
Initially it seemed the only correct point of view was the one which
held that loading coils behave strictly as lumped inductances. Remember
that?

The issue as far as I'm concerned is: does this taper drastically
cause error in modeling compared to lumped elements?

I think the answer is essentially, no.

For me the issue was always whether current can be unequal at opposite
ends of an inductor. I find the fact that it can to be very
interesting, and I wanted to understand just how it could be so. I
guess I'm just not willing to accept the notion that just because
fundamentals such as these may be inconsequential to how well an antenna
is modeled, that they are also inconsequential to a thorough
understanding of how it works.

73, Jim AC6XG

On Thu, 04 Dec 2003 15:11:29 -0800, Jim Kelley
wrote:
I find the fact that it can to be very
interesting, and I wanted to understand just how it could be so.

Hi Jim,

It is simply that Kirchhoff's laws have been corrupted in discussion.
The Kirchhoff law of current relates to the flow into and out of "a
closed surface" or a point (where any number of components' common
leads come together) and not to the components themselves (as they
have been incorrectly injected as argument). The corruption is found
in that the current law has been expressed in the language of
Kirchhoff's voltage law by nearly EVERY correspondent.

EZNEC treats loads as lumps, lumps are the metaphor for the "closed
surface" or a point. EZNEC conforms to Kirchhoff's current law, but
not the physical reality simply because in nature a load cannot
exhibit its characteristic within a point (there are no infinitesimal
capacitors or inductors). Hence a protocol was offered to decimate
the inductor and spread its characteristic across the apparent
physical space to achieve the same, virtual response of a true
inductor immersed in reality.

The result of the protocol exhibits roughly the same characteristics
offered by ON4UN's drawings (which are also approximations
themselves).

73's
Richard Clark, KB7QHC

Jim Kelley wrote:

Mark Keith wrote:
The issue as far as I'm concerned is: does this taper drastically
cause error in modeling compared to lumped elements?

I think the answer is essentially, no.

So you haven't tried to model an antenna with a 180 degree phase-
reversing coil, have you? :-)
--
73, Cecil http://www.qsl.net/w5dxp



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Cecil, W5DXP wrote:
"So you haven`t tried to model an antenna with a 180 degree
phase-reversing coil, have you?"

Kraus` Figure 23-21(b) has phase-reversing coils used as traps. "Here
the elements present a high impedance to the coil which may be resonated
without an external capacitance due to its distributed capacitance."

Kraus` trap is a self parallel resonant circuit, not just another
inductance.

However, a center-tapped coil can make an excellent phase inverter as in
the vacuum tube type Detroit Electric Company (Delco) Buick car radios
of the late 1930`s and early 1940`s. This radio had great sound despite
limited frequency response inevitable with choke and transformer
coupling.

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:
Kraus` trap is a self parallel resonant circuit, not just another
inductance.

Point is that all real-world coils possess distributed capacitance
and distributed resistance as well as inductance. There is capacitance
but no capacitor in Kraus' trap. If one replaces the "phase-reversing
coil" with a phase-reversing stub, EZNEC gives the correct current
distribution.
--
73, Cecil http://www.qsl.net/w5dxp



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