So, was that a yes or a no? I have trouble with your accent.

Roy Lewallen, W7EL

Cecil Moore wrote:
Roy Lewallen wrote:

Tell us, Cecil, at steady state at one frequency, can a lumped
inductor (presumably like the experimenter's toroid) tell whether it's
at the base of an antenna or simply in series between a generator and
load impedance?


This question proves you don't understand the problem. The inductor
cannot tell if it is installed in an antenna or transmission line.

So I will turn the question around: Does a standing wave antenna
have standing waves? Reference _Antenna_Theory- by Balanis, page 17,
section 1.4 Current Distrubution on a Thin Wire Antenna. Is Balanis
correct when he says: "If the diameter of each wire is very small,
the ideal standing wave pattern of the current along the arms of
the (1/2WL) dipole is sinusoidal with a null at the end."

This is after he takes an unterminated transmission line, discusses
standing waves, and then slowly opens up the ends of the transmission
line to create a 1/2WL dipole.

I took Balanis' antenna course at ASU in 1995. I asked a lot of
questions about inductively loaded antennas. The current and
standing wave pattern on each side of a loading coil is NOT the same.

No, that's not what I asked. Let me try again.

I have an antenna whose feedpoint impedance I measure as R + jX. I put a
lumped (physically very small and short) coil in series with it and
drive it with a generator. You and Yuri say that the current going into
the coil is different from the current going out.

Now, I replace the antenna with a series resistor and capacitor or
inductor which also has a terminal impedance of R + jX ohms. My question
is, does the inductor now have equal currents at its two terminals, and
why or why not?

Roy Lewallen, W7EL

Cecil Moore wrote:
Roy Lewallen wrote:

If you answered "yes", please explain how and why, and how we'd
calculate the current through and voltage across the inductor. If we
moved it an inch up the transmission line from the antenna base, can
it still tell?


Forget about an inductor becoming conscious. The impedance looking
into a six foot whip is the same whether the coil is there or not.
The impedance looking into the bottom of the coil is certainly not
the same as looking into the six foot whip. I suspect this can be
proven by modeling a mobile antenna and then moving the source point
from just under the coil to just above the coil.

If you answered "no", please write us the equations showing just how
much the current should be expected to be different from one end of
the inductor to the other.


The current will be approximately the same as at the two points
of wire it replaces in the antenna without the inductor. I earlier
asked you a question that you seem to have missed. Do you agree
or disagree with Fig 9-22 of ON4UN`s "Low-Band DXing", included
on Yuri`s web pages.?

And where those coulombs are going, that go into one end and don't
come out the other.


You can answer your own question. Where do the coulombs go that enter
one end of a 1/4WL stub and don't exit the other end? Please stop
using lumped circuit analysis on distributed network problems. You
know and I know that it doesn't work.

Because you're seeing different currents at the two stub terminals, you
must be modeling it with wires, which should reflect reality quite well.
Look carefully at the currents along the stub and you'll find they're
not equal and opposite on the two conductors. Such a radiating stub *is*
very different from a coil. That shouldn't be surprising. I have a high
level of confidence that if you built the antenna just like you modeled
it, you would find the results to closely agree with the model.

Roy Lewallen, W7EL

Cecil Moore wrote:
Wes Stewart wrote:

On Mon, 03 Nov 2003 09:26:05 -0600, Cecil Moore
wrote:

|Roy Lewallen wrote:
| If you could build an antenna from | straight conductors and
lumped inductors, the result would be very close | to EZNEC's
predictions.
|
|Hard to prove since lumped inductors are impossible in reality. Why
|does EZNEC show so much difference between lumped inductors and stub
|inductors?
I see no such difference in my model.


There shouldn't be a lot of difference. I have modeled two short dipoles,
one loaded with a lumped inductive reactance and one modeled with the
same reactance using an inductive stub. EZNEC reports the following:

Inductance lumped j335 10'stub

current in segment just before the coil .8374 amp .8384 amp

current in segment just after the coil .7971 amp .5642 amp

The relative difference just before the coil is quite small, 0.12%.

The relative difference just after the coil is quite large, 41.28%.

There just cannot be that amount of difference between a coil and a
stub.

Yes. If any real component has signficant length, it's best to model it
as wires if possible. If it's not possible or practical to model it as
wires, about the best you can do is as I've suggested befo model it
as a wire of the length and diameter of the component, and insert one or
more loads to represent the low frequency impedance of the component.
That's about as good as you can do with the limited set of modeling
objects you have.

Roy Lewallen, W7EL

Jim Kelley wrote:

Roy Lewallen wrote:

I use lumped circuit analysis when dealing with lumped circuits, and
distributed circuit analysis when dealing with distributed circuits.
EZNEC's loads are lumped elements, so when you're talking about EZNEC
loads, you're talking about lumped elements.

Roy Lewallen, W7EL


Hi Roy,

Wouldn't it be better not to lump any portions of an antenna that are a
part of its electrical length?

73, Jim AC6XG

Roy Lewallen wrote:
I don't have Balanis. Can you provide a short quote where he states that
the current at the terminals of a two-terminal lumped component are
unequal?

He doesn't use lumped components and probably for good reason. But here's
the quote that allows my analysis. "Standing wave antennas, such as the
dipole, can be analyzed as traveling wave antennas with waves propagating
in opposite directions (forward and backward) and represented by traveling
wave currents 'If' and 'Ib' in Figure 10.1(a)." This means that net total
current equals If+Ib.

The fact that the feedpoint current occurs at a current maximum point ties
both ends down. 'If' must traverse 90 degrees and 'Ib' must traverse 90
degrees in addition to the 180 degree phase shift due to reflection from
the open end. Besides the coil, an 8' whip gives about 22 degrees phase
shift in a round trip. Adding the 180 degree phase shift due to the open
end reflection gives 202 degrees. But we know the phase shift is actually
360 degrees. Where can the additional 158 degrees of phase shift
come from except from the coil?

Center-loaded mobile antennas are still an electrical 1/4 wavelength. If
there's no phase shift through the coil, where's the missing 158 degrees
of phase shift taking place?
--
73, Cecil http://www.qsl.net/w5dxp



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Roy Lewallen wrote:

A radiating stub does act differently than a lumped inductor, in both
modeling and reality. EZNEC should reflect this difference accurately.
If you're aware of a situation where you think it doesn't, please email
me the models illustrating the difficulty.

I have already done that but I just sent them to you again.

If you model a stub using a transmission line model, it should behave
exactly the same as a lossless lumped inductor at a given frequency.
However, it's an accurate model of reality only if the real stub has
exactly equal and opposite currents on the two conductors. That is, it's
an entirely non-radiating stub.

The difference in current between the two configurations that I sent to
you means the vertical stubs are radiating better than the horizontal
antenna which is unlikely since EZNEC doesn't show any vertical radiation.
--
73, Cecil http://www.qsl.net/w5dxp



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Roy Lewallen wrote:

So, was that a yes or a no? I have trouble with your accent.

It's a no. Lumped inductors are not conscious of anything
including their locations.
--
73, Cecil http://www.qsl.net/w5dxp



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Roy Lewallen wrote:

No, that's not what I asked. Let me try again.

I have an antenna whose feedpoint impedance I measure as R + jX. I put a
lumped (physically very small and short) coil in series with it and
drive it with a generator. You and Yuri say that the current going into
the coil is different from the current going out.

Yes, just as the current going into a 1/4WL stub is different from the
current going out. If you use an inductive stub, is the current the
same going in as going out? If so, you have invented faster than
light transfer of current.

Now, I replace the antenna with a series resistor and capacitor or
inductor which also has a terminal impedance of R + jX ohms. My question
is, does the inductor now have equal currents at its two terminals, and
why or why not?

You have replaced a distributed network with a lumped circuit. If the
lumped circuit model worked on distributed networks, you would be right
and there would be no need for a distributed network model (but there is).
--
73, Cecil http://www.qsl.net/w5dxp



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Roy Lewallen wrote:

Because you're seeing different currents at the two stub terminals, you
must be modeling it with wires, which should reflect reality quite well.
Look carefully at the currents along the stub and you'll find they're
not equal and opposite on the two conductors. Such a radiating stub *is*
very different from a coil.

Instead of a knee-jerk defense of your ideas, why don't you actually take
a look at the problem? Those stubs are vertical. EZNEC shows virtually zero
vertically polarized radiation. According to EZNEC, those stubs are radiating
a negligible amount, just like the lumped inductance. Why the 40% difference
in current between the two configurations? Is this a characteristic of NEC?
--
73, Cecil http://www.qsl.net/w5dxp



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On Mon, 03 Nov 2003 15:19:44 -0600, Cecil Moore
wrote:

Roy Lewallen wrote:

Because you're seeing different currents at the two stub terminals, you
must be modeling it with wires, which should reflect reality quite well.
Look carefully at the currents along the stub and you'll find they're
not equal and opposite on the two conductors. Such a radiating stub *is*
very different from a coil.

Instead of a knee-jerk defense of your ideas, why don't you actually take
a look at the problem?
Ah the quality of sneer review.

Those stubs are vertical. EZNEC shows virtually zero
vertically polarized radiation. According to EZNEC, those stubs are radiating
a negligible amount, just like the lumped inductance. Why the 40% difference
in current between the two configurations? Is this a characteristic of NEC?

Cecil, you have two stubs and they are driven antiphase (typical of a
doublet) and through symmetry would have equal antiphase currents when
compared to their opposites, but not necessarily equal currents within
their twin-pair of lines. The sum of ALL currents (and not just the
myopic view of one of two stubs) would suggest exactly what Roy has
offered.

This, of course, returns us to the question of what part of the
radiator radiates. Sadly, the convention of the current pulse (or
maxima, or other equivalent term) trips up discussion just in these
matters. ALL elements radiate, it is only in the far field where
their contributions negate, not literally within the structure.

73's
Richard Clark, KB7QHC