Current across the antenna loading coil - from scratch
 

John Popelish wrote:
At any point along the wire, and at any particular instant, whether as a
result of a standing or traveling wave, the current flows in the
direction of the wire, one way or the other. Such current does not have
a phase. It has a direction.

In what direction is the RMS value of standing wave current flowing?

Those wave currents could not travel at nearly the speed of light
without the displacement currents.

You and I are talking about different displacement currents.
I'm talking about displacement current between a transmission
line and the ground. We had previously been talking about
displacement current between a loading coil and ground.

Then you are silly. You cannot describe the reason for wave velocity of
a conductor, transmission line or EM wave without displacement current.

How does the displacement current get to ground when it's
inside a shielded piece of coax with no common mode current
on the outside braid?

Displacement current into the space around the node.

How does the displacement current get past the coax shield
to the outside world?

So please stop saying that displacement current is negligible in some
cases of traveling or standing waves.

I'll even say it again. Inside a piece of shielded coax, the
displacement current to ground is negligible yet the standing
wave still exists.
--
73, Cecil http://www.qsl.net/w5dxp

Current across the antenna loading coil - from scratch
 

Richard Clark wrote:

Cecil Moore wrote:
movement requires current - true but completely irrelevant.

the myth of zero (0) current is busted.

Please tell us about the position and velocity of each
charge carrier, Richard.
--
73, Cecil http://www.qsl.net/w5dxp

Current across the antenna loading coil - from scratch
 

Cecil Moore wrote:
wrote:

Current is by definition is the flow of charge.


And two equal EM waves flowing in opposite directions
in the same wire use the same charge carriers.

At points where those waves cause equal and opposite instantaneous
current, the standing wave current hits zero (is at a node). At all
other points, there is some net instantaneous current that is the
superposition of the current caused by the two waves at that point and
moment in time.

By definition and by physics, we cannot have charges flowing two
directions at once at one point.


A charge carrier cannot be moving in two directions at
the same time. Two currents can certainly exist in opposite
directions at the same time.

No. Current is the rate of charge movement. The charge cannot be
moving two directions at a point.

That's what forward current
and reflected current is.

Those are forward and reverse waves, not forward and reverse currents.
you are confusing the wave with the water.

If you want to deny the existence
of forward and reflected current, be my guest.

I deny it. There is only current at a point, just as there is only
water jiggling around under a wave on the ocean.

This is precisely the current we would measure with a current meter
sampling the magnetic field, it is the current we would measure
sampling radiation, and it is the current that would determine phase of
the radiation or induction field.


Yes, but if it's phase is unchanging, which direction is
it flowing?

Phase doesn't indicate the direction charge is flowing (current is
going). For both traveling waves and standing waves, charge sloshes
back and forth with no average movement over a cycle. The phase of
that movement just tells you how that sloshing is timed with respect
to the phase reference. The only case where charge moves in one
direction (unidirectional current) is DC.

When the forward current and reflected current
are of equal magnitudes, which direction is the phasor sum
of those two currents flowing?

As long as you refer to waves as current, you are never going to get
it. Waves travel on current reversals, but he wave is not current.

(snip repetition)

Current across the antenna loading coil - from scratch
 

wrote:
But what I really want to know is how Cecil can have current flowing
both directions at the same instant of time in a single point of single
conductor,

Forward and reflected EM waves, of course. Would you like to deny
the existence of the two waves in the following equation?

I(x,t) = I1*cos(kx+wt) + I2*cos(kx-wt) = Io*cos(kx)*cos(wt)

Your lack of math skills is really getting to be embarassing.

... can dismiss displacement currents as trivial things that can
be ignored when they are required to define the most important aspects
of transmission or antenna behavior,

The only displacement currents that I said were secondary were
the displacement currents to ground. In fact, in a shielded coax
with no common mode current, displacement currents to ground
are literally non-existent, yet the standing wave is still there
inside the coax, with its nodes and loops.

... and say the very thing that is
used to measure current suddenly doesn't measure his imaginary two-way
reflected and forward current's vector sum.

I didn't say that. I said the standing wave phase cannot be used
to measure the phase through a wire or a coil. That is readily
apparent at: http://www.qsl.net/w5dxp/travstnd.GIF which you
have been avoiding like the plague.

The phase information is there in the standing wave current, but
it is in the magnitude, not the phase. And you have to understand
arc-cosine functions to be able to extract that phase information.

That's what is really important, especially in light of the fact Cecil
is quick to play superior.

"Play superior"??? I'm not the arrogant one claiming to be so
omniscient that he is never wrong.

Anyone who is really superior should be able to walk us through the
physics of two-way current ...

Already done - please reference the above web page. All the data
is exactly what EZNEC reported. I can lead you to water but I
can't make you drink. If you will tell me what you don't understand
about that web page, I will walk you through it, step by step.
--
73, Cecil http://www.qsl.net/w5dxp

Current across the antenna loading coil - from scratch
 

Tom Ring wrote:

wrote:
Answer the question Cecil, how can we have charge movement over a small
length of conductor (in terms of the wavelength) in two directions at
the same time, or a drift velocity in two directions at once?

Cecil and Co. are not interested in real physics, math, or engineering.
They have made up their own. As I said to Roy, you may as well give up.

Tom, I learned this stuff at Texas A&M in the 50's and it was
decades old already, having been developed before I was born.
Are you also willing to deny the existence of simultaneous
forward and reflected EM waves?
--
73, Cecil http://www.qsl.net/w5dxp

Current across the antenna loading coil - from scratch
 

On Sat, 08 Apr 2006 22:20:10 -0400, Roger D Johnson
wrote:
I don't understand your statement. Explanation he

http://www.tpub.com/neets/book3/7k.htm

Hi Roger,

Yes, I understood. And from your reference:
"The electrostatic meter movement is actually a large variable
capacitor in which one set of plates is allowed to move. The
movement of the plates is opposed by a spring attached to the
plates. A pointer that indicates the value of the voltage is
attached to these movable plates. As the voltage increases, the
plates develop more torque."

When a current is applied to a capacitor (aka voltage applied, but as
we all know, a current moves charge to those plates), there is a force
developed between the plates (actually in the dielectric) which is
tangential to the plates. This force has the tendency to eject the
dielectric. Our usual experience with capacitors is we rarely have
enough charge AND enough capacitance to measure this effect.

By making one plate movable, the force of the current flow is
expressed in the movement of that plate against a spring (the exact
analogue of opposing magnetic fields, one fixed and the other imparted
by a continuous current flow).

"To develop sufficient torque, the plates must be large and
closely spaced."

That necessary condition of high capacitance; and

" A very high voltage is necessary to provide movement, therefore,
electrostatic voltmeters are used only for HIGH VOLTAGE
measurement."

enough charge to reveal the force.

Your reference is actually

********** W R O N G !! or at least incomplete *************

because what it is describing with two plates in repulsion is NOT a
capacitor (at least not in the conventional sense). This is because
the two plates share the same charge (because they are the same
conductor), hence the repulsion. Further, as this is a variant on the
Leyden Jar, there is another true capacitive plate either in the
nearby structure, or the earth. Otherwise there is no reason for the
charge to flow there in the first place.

73's
Dr. Science (actually, he only has a B.A. in English)

Current across the antenna loading coil - from scratch
 

Tom Donaly wrote:
Cecil can't prove that charge can move in two opposite directions
at once. No one can. It's impossible.

I agree with you. That topic is just another straw man from
W8JI who is afraid to discuss EM waves moving in opposite
directions at the same time. It's the EM waves that are
moving in opposite directions at the same time, not the
individual charge carriers.

I have seen waves flowing in and flowing out at the same
time in the Pacific Ocean. That doesn't mean that individual
water molecules are moving in two opposite directions at once.

Doesn't it mean you are losing the argument when you have to
make up false stories about what I have said?
--
73, Cecil http://www.qsl.net/w5dxp

Current across the antenna loading coil - from scratch
 

Cecil Moore wrote:
John Popelish wrote:

At any point along the wire, and at any particular instant, whether as
a result of a standing or traveling wave, the current flows in the
direction of the wire, one way or the other. Such current does not
have a phase. It has a direction.


In what direction is the RMS value of standing wave current flowing?

That's easy. RMS current is an AC measurement of current along the
conductor. Over any integer number of cycles, the total movement of
charge is zero. The current spends half the time going one way, and
half the time going the other way. This applies to both standing and
traveling wave induced currents. The only current that describes a
net movement of charge in a single direction is DC.

Those wave currents could not travel at nearly the speed of light
without the displacement currents.


You and I are talking about different displacement currents.
I'm talking about displacement current between a transmission
line and the ground.

If the transmission line is a center conductor in a grounded shield,
then that is what I am talking about. If the transmission line is
balanced, then the displacement current is mostly the current between
the two lines.

We had previously been talking about
displacement current between a loading coil and ground.

That's also included in what I am talking about. Ant current caused
by a voltage swing in a conductive surface along the wave path is
included.

Then you are silly. You cannot describe the reason for wave velocity
of a conductor, transmission line or EM wave without displacement
current.

How does the displacement current get to ground when it's
inside a shielded piece of coax with no common mode current
on the outside braid?

The shield is the ground potential for the center conductor. If you
could mount a tiny current pickup loop between the center conductor
and shield, surrounding nothing but the coax dielectric (so you could
look through the hole, if you were an observer on the center
conductor), that pickup loop would measure a current if there is any
voltage wave on the center conductor. That is a displacement current.

Displacement current into the space around the node.


How does the displacement current get past the coax shield
to the outside world?

As far as the center conductor is concerned, the shield is the entire
universe.

So please stop saying that displacement current is negligible in some
cases of traveling or standing waves.


I'll even say it again. Inside a piece of shielded coax, the
displacement current to ground is negligible yet the standing
wave still exists.

You have a blind spot as to where there is current in a coax. Do you
deny current through any other capacitor that has voltage swing across
it? Then why deny that the capacitance between the center conductor
and a carefully surrounding grounded surface separated by a dielectric
conducts current when there is voltage swing on the center conductor?

If the coax carries a standing wave, then at the points on the center
conductor that are current nodes (for current along the conductor) the
capacitive current to the shield is at its peak, because that is where
the voltage peaks of the standing wave occur.

Current across the antenna loading coil - from scratch
 

Cecil Moore wrote:
wrote:

But what I really want to know is how Cecil can have current flowing
both directions at the same instant of time in a single point of single
conductor,


Forward and reflected EM waves, of course. Would you like to deny
the existence of the two waves in the following equation?

I(x,t) = I1*cos(kx+wt) + I2*cos(kx-wt) = Io*cos(kx)*cos(wt)

Those two expressions describe patterns of current over time and
location that produce current in each direction half the time (except
at nodes, where the current is zero).

The amplitude of a current cycle is constant for the first one
(traveling wave), but the phase differs at different locations (by the
amount of kx).

The amplitude of current cycle described by the second one (traveling
wave) varies with location, and the phase has only two possibilities
(one when cos(kx) is positive and 180 degrees different when cos(kx)
is negative). But in both cases, current at any point reverses twice
a cycle (cos(wt)) and charge goes nowhere over a cycle.

Current across the antenna loading coil - from scratch
 

Yuri wrote:
You agree that impedance along the radiator changes, being low at the
bottom, around tens of ohms, to being high at the top, around thousands of
ohms.

)Tom replied:
)I never said that. What do you mean by reactance? The X can be very
)high but radiation resistance very low even near the open end.

I really give up. What's the point. This is a typical example of Tom's
response to technical argument or trying to go step by step. I am talking
impedance, he "knows" I mean reactance. As I said, I get better response
from a brick wall.
No wonder he duntgetit! Oh well!

73, Yuri, K3BU