Art Unwin wrote:
You never did supply the information needed to
justify the values of E,I and R when
the current value crosses the zero line on a graph.

In simple terms, when the standing-wave current has
a zero amplitude at a current node, none of the energy
is in the magnetic field and all of the energy is in
the electric field. That's why a voltage maximum appears
at a current minimum. When the current equals zero, the
virtual impedance, E/I, is infinite.

This is essentially what happens at the end of a dipole
or monopole or open-circuit stub. The characteristic
impedance of a #14 wire 30 feet above ground is very
close to 600 ohms. Given that Z0, we can treat a dipole
element as a lossy transmission line and calculate the
voltage at the end of the dipole element.

If we model a 1/4WL 600 ohm open-circuit stub with
EZNEC and adjust the resistivity to 0.0000021 ohm-m
to simulate the radiation resistance of a dipole
wire, the feedpoint impedance of the stub is 35 ohms
and conditions on the lossy stub are very close to
the conditions on a dipole element.
--
73, Cecil http://www.w5dxp.com

On Dec 29, 9:11*am, Cecil Moore wrote:
Art Unwin wrote:
You never did supply the information needed to
justify the values of E,I and R when
*the current value crosses the zero line on a graph.

In simple terms, when the standing-wave current has
a zero amplitude at a current node, none of the energy
is in the magnetic field and all of the energy is in
the electric field. That's why a voltage maximum appears
at a current minimum. When the current equals zero, the
virtual impedance, E/I, is infinite.

This is essentially what happens at the end of a dipole
or monopole or open-circuit stub. The characteristic
impedance of a #14 wire 30 feet above ground is very
close to 600 ohms. Given that Z0, we can treat a dipole
element as a lossy transmission line and calculate the
voltage at the end of the dipole element.

If we model a 1/4WL 600 ohm open-circuit stub with
EZNEC and adjust the resistivity to 0.0000021 ohm-m
to simulate the radiation resistance of a dipole
wire, the feedpoint impedance of the stub is 35 ohms
and conditions on the lossy stub are very close to
the conditions on a dipole element.
--
73, Cecil *http://www.w5dxp.com

At the end of the radiator you state the energy is transfered to the
field
so I would imagine there is zero skin effect at that point and the
chain of
skin effect is still present on the outside of the radiator, this
because a full period has not yet elapsed
This equates to a displacement current across the capacitance gap
(plates) between
the outside and the inside of the radiator which is the only current
route available
when the capacitor field expires. Note that this energy is released
prior to the end of the current flow period
because of the absence of the skin effect at that time.
Cecil I am examining all the holy cows that pervade the science of
radiation
as it is universally accepted that radiation is not fully understood,
thus the many hats!
At the moment I see no mechanism that supports the capacitor field to
expire in the direction of incoming current
prior to the completion of the forward period.
Regards
Art

Art Unwin wrote:
At the moment I see no mechanism that supports the capacitor field to
expire in the direction of incoming current
prior to the completion of the forward period.

The "capacitive" field is the *electric* field which is
at a *maximum* amplitude at the tip of a dipole. It is
the magnetic (inductive) field that is close to zero
at the tip of a dipole.
--
73, Cecil http://www.w5dxp.com

On Dec 29, 10:26*am, Cecil Moore wrote:
Art Unwin wrote:
At the moment I see no mechanism that supports the capacitor field to
expire in the direction of incoming current
prior to the completion of the forward period.

The "capacitive" field is the *electric* field which is
at a *maximum* amplitude at the tip of a dipole. It is
the magnetic (inductive) field that is close to zero
at the tip of a dipole.
--
73, Cecil *http://www.w5dxp.com
Cecil
I still am looking for an explanation that prevents current flow thru
the center.
I recognise that the common thinking is to accept reflection but I
fail to see
how that can happen so I can follow up with the numbers.
The capacitor is limited with respect to the energy that it can retain
so what happens when that
limit is reached and the forward period has not come to an end? Yes,
the common thinking
is that the current changes direction to oppose the forward moving
current as with a reflection
where the eddy current in the reverse direction cancels the eddy
current moving in the other direction.
It is here that I am looking for a mechanism that justifies this
reasoning of reflection so I can begin to dispel the
closed circuit aproach as seen with a full wave radiator in
equilibrium
Best regards
Art
Art
but I am looking for actual proof

Art wrote:
"The capacitor is limited with respect to energy it can retain so what
happens when that limit is reached and the forward period has not come
to an end?"

There is a sudden flash as energy jumps the gap between the plates.

The energy a capacitor can store expressed in joules is equal to its
capacitance in microfarads times the voltage (squared) across its plates
divided by two million.

For a fixed capacitor, the only vatiable is the voltage. So, the greater
the voltage across the capacitor the greater the energy it stores. The
only limit is the breakdown voltage.

Best regards, Richard Harrison, KB5WZI

On Dec 29, 12:25*pm, (Richard Harrison)
wrote:
Art wrote:

"The capacitor is limited with respect to energy it can retain so what
happens when that limit is reached and the forward period has not come
to an end?"

There is a sudden flash as energy jumps the gap between the plates.

The energy a capacitor can store expressed in joules is equal to its
capacitance in microfarads times the voltage (squared) across its plates
divided by two million.

For a fixed capacitor, the only vatiable is the voltage. So, the greater
the voltage across the capacitor the greater the energy it stores. The
only limit is the breakdown voltage.

Best regards, Richard Harrison, KB5WZI

So one acknowledges the presence of a capacitor at the end of a
radiator
So now we determine the capacitance and the voltage withstand
together
with what comprises as a capacitor at the end of a radiator to relate
to
which way the current flows.
The question with respect to current flow is still present and
unanswered
despite all of the manouvaring the face the question head on.
If the past means anything this subject could go to a 1000 posts with
neither
a modicom of science to bolster the talk
Art

I still am looking for an explanation that prevents current flow thru
the center.

Well, being a logical person, I would ask what mechanism
of physics keeps the forward current from flowing through
the center to start with? Why doesn't the forward current
flow through the center and the reflected current flow
back on the surface?

Whatever that mechanism is, it seems logical to conclude
that it might also prevent reflected current from flowing
back through the center.

If we put a signal generator at each end of a wire,
which current flows on the outside and which flows on
the inside?
--
73, Cecil http://www.w5dxp.com

Art wrote:
"Yes, the common thinking is that current changes direction to oppose
the forward moving current as with a reflection where the eddy current
moving in the reverse direction cancels the eddy current moving in the
other direction."

Transformers are laminated to reduce eddy current core losses.

Reverse currents on a transmission line or on an antenna are usually
called the reflected current.

Reflections are caused by discontinuities in the path of the EM wave.

In the case of an open circuit, the reflection coefficient is infinite
and the incident and reflected waves have the same magnitude and phase.
The voltage at the discontinuity is thus doubled. See Terman`s 1955 opus
page 89. But, the current goes to zero as conduction ends at the open
circuit. No energy is lost in the open circuit. It is just concentrated
in the electric field as the magnetic field loses its energy.

Best regards, Richard Harrison, KB5WZI

Art Unwin wrote:
So one acknowledges the presence of a capacitor at the end of a
radiator

Let's use IEEE definitions to avoid confusion. A "capacitor"
is a physical component that exhibits capacitance. Capacitance
can be exhibited without the existence of a physical lumped
component. At the end of a radiator, we would have a
distributed capacitance, not *a* lumped capacitor. And
actually, it is not only at the end since it is "distributed".
In fact, an antenna element can be modeled as a distributed
RLC network where the R includes all "losses" including radiation.
--
73, Cecil http://www.w5dxp.com

Richard Harrison wrote:
In the case of an open circuit, the reflection coefficient is infinite

Richard, I'll bet you know that the reflection coefficient
is 1.0 for an open circuit and -1.0 for a short circuit.:-)
--
73, Cecil http://www.w5dxp.com