Art Unwin KB9MZ wrote:

Cecil
I would like to ask you a question regarding inductance coils even tho you
know I believe the current is constant

Current *is* constant in EZNEC's lumped inductive reactances, Art, but
that doesn't represent reality. This weekend, or maybe even tonight, I
will be posting coils modeled out of wire, like Wes has done, to make
my point.

An inductor develops a field that travels thru the core
and then slays out thru 360 degrees to return to the other end of the coil.
Thes lines are directly correllated to the current flow within the
inductance and are in equilibrium
in terms of mechanical forces.
If the current is not constant thru-out the inductance
then there are more lines of force at one end than there is at the other,
such that the ends would not repel each other,one end will domimate
something I have not seen happen.
How do you account for the inbalance of the end fields
because of so called current gradient that you refer to.If there is no
imbalance what happens to dissapate the energy created by the increase of
current flow ?
I would appreciate your input on the above problem.
even tho it appears so simplistic.

Capacitance is the answer, Art. If a transmission line didn't possess capacitance,
it wouldn't be able to exchange energy between the capacitive reactance and the
inductive reactance to allow the currents at 1/2WL intervals to be traveling in
opposite directions. A coil completely devoid of any capacitance would indeed have
a constant current. But there are no real-world coils that are completely devoid of
capacitance as illustrated by Roy's and Tom's real-world measurements.
--
73, Cecil http://www.qsl.net/w5dxp



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On Thu, 05 Feb 2004 19:40:52 -0600, Cecil Moore
wrote:
Instantaneous standing wave current moves
UhHuh

Richard Clark wrote:

wrote:
Instantaneous standing wave current moves

UhHuh

Richard, can you give an example of a situation where RF current
ever stands still? If charges are not moving, how can there be any
current? If a tree falls in the forest, ...
--
73, Cecil http://www.qsl.net/w5dxp



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Tdonaly wrote:
Actually, net current doesn't flow at all in a standing wave.

Instantaneous standing wave current moves in one direction during
1/2 cycle, and in the opposite direction during the next 1/2 cycle.
If you think otherwise, you are simply wrong. Have you never observed
standing waves on an o'scope? It looks like a kid's jump rope.


You didn't read the rest of my posting. Current is dQ/dt, the rate of
flow of charge with time.



And Tom, one of the strictest laws of physics is that current cannot
stand still. Saying that "current doesn't flow at all" is ridiculous.


Wrong. It's the charge that moves. In general, if you're talking about
instantaneous current, it changes constantly at a point. But you never
talk about instantaneous current, Cecil, the current you always refer to
is RMS current. However, if you want to refer to instantaneous current,
that's fine with me. In that case, you have a traveling, standing wave
oscillating in and out of your coil. That's interesting, but it isn't what is
happening.


When the current is flowing into both ends of the coil at the same time,
charge is being stored in the coil. 1/2 cycle later, the charge flows
out of the coil at both ends.

In one of my examples, the current at the bottom of the coil is 0.18
at - 54 degrees. The current at the top of the coil is 0.2 at 126 degrees.
Last time I checked, 54+126 = 180 degrees indicating that the current
at the bottom of the coil is 180 degrees out of phase with the current
at the top of the coil. That means the two currents are flowing in
opposite directions at the two ends of the coil.
--
73, Cecil http://www.qsl.net/w5dxp


Actually, the two charge collections are oscillating in opposite directions at
the same time, and, I'll tell you that each individual infinitesimal volume of
charge doesn't go very far before it's whacked back the other way.
The problem here is that you don't remember your basic definition of
current. Go dig out your old physics book and read the definition.
73,
Tom Donaly

Cecil wrote,

Tdonaly wrote:
I wrote "charge," not "energy." There's a difference. Cecil writes that
current, by which I think he means charge, can flow into both ends of
a coil at the same time. He's right, if he indeed is talking about charge
and not current, in which case, the charge density will increase in some
part of the coil, energy will be stored in an electric field, and the coil
will
be acting just like a capacitor (with the capacitance to free space
understood).

Nice crawfishing job, Tom. The direction of charge flow is the same as
the direction of current flow, assuming electron current flow (as opposed
to hole current flow). If charge is flowing into each end of the coil at
the same time, then instantaneous current is, by definition, flowing into
each end of the coil at the same time for 1/2 of the RF cycle. Good to
see you coming to your senses like I knew you would.
--
73, Cecil http://www.qsl.net/w5dxp



Instantaneous current changes with time in a standing wave but it doesn't
go anywhere. The only way current can go anywhere is to be part of a
travelling wave, in which case it stays the same in time, but travels in
space. You want it to do both, Cecil, and that doesn't happen very often.
73,
Tom Donaly
(PS Check your definition of current, again.)

On Thu, 05 Feb 2004 22:06:11 -0600, Cecil Moore
wrote:
Instantaneous standing wave current moves

UhHuh

Richard, can you give an example of
Obviously you've been seduced by the fictions of your own invention.

Art Unwin KB9MZ wrote:
... surely Bart's posting gives you something to ponder upon as
your present stance has not won over any converts and which could possibly
be presented in a different manner to make your case more digestable.

Bart, an intelligent, educated, and knowledgeable engineer, and I have
been in email contact for years, so I have pondered much of what he
has said. His virtual "center tap to ground" is certainly a valid concept.

But I can demonstrate a 180 degree phase reversal in a helical coil
in free space so the capacitance to ground is not the complete answer
to what is happening. A real-world helical coil is made out of real-world
wire and possesses some of the characteristics of real-world wire including
the ability to change the phase of the current every 1/2 wavelength
whether over ground or in free space. Light exhibits the same
characteristic. Technically, RF is light, just not visible light.
--
73, Cecil http://www.qsl.net/w5dxp



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Tdonaly wrote:
You didn't read the rest of my posting. Current is dQ/dt, the rate of
flow of charge with time.

Yes, and at a current loop in a standing wave, dQ is positive
for 1/2 cycle and negative for 1/2 cycle. If the forward and
reflected current are in phase at zero degrees, dQ is moving
toward the load. If the forward and reflected current are in
phase at 180 degrees, dQ is moving toward the source. That's
the convention.

You seem to have lost contact with reality when it comes to AC.
Remember the e^jwt term? The standing wave current at a loop
changes sign, and therefore direction, every 1/2 cycle. Current
cannot stand still because dQ would be zero.
--
73, Cecil, W5DXP

Someone wrote:
"Instantaneous standing wave current moves."

Current is movement. Standing waves stand still.

Forward (incident) waves move forward. Reverse (reflected) waves move
rearward. Interference between incident and reflected waves makes a
stationary current pattern. It also makes a stationary voltage pattern
(VSWR). Voltage and current standing wave patterns are displaced by
90-degrees.

In dealing with a-c (r-f) it is usually convenient to use effective
(rms) values because instantaneous values change from instant to
instant. The peak instantaneous value is simply: (sq.rt.2)(vrms).

Instantaneous currents move in the same directions and have peak
amplitudes in all locations which are related by 1.414 (sq.rt.2) to the
rms values.

Best regardfs, Richard Harrison, KB5WZI

Cecil, W5DXP wrote:
"But I can demonstrate a 180 degree phase reversal in a helical coil in
free space so the capacitance to ground is not the complete answer to
what is happening."

Cecil has used the Kraus example of a coil installed as a phase inverter
between 1/2-wave segments of a collinear radiator. Kraus` example uses
self-resonant coils. Self-capacitance resonates with self-inductance in
the Kraus coils.

Inversion is caused by current exchanged between L and C. When the
magnetic field collapses, current flows in a loop through capacitance
and coil whether the resonating capacitance is external or internal to
the coil. The apparent instantaneous current direction is into one end
of the coil and out of the other end of the coil. In the next part of
the cycle, the instantaneous current direction is reversed when the
capacitance is discharging the energy back into the inductance.

Point is, opposite ends of the reactances are 180-degrees out-of-phase
at resonance.

Best regards, Richard Harrison, KB5WZI