Current across the antenna loading coil - from scratch
 

Cecil Moore wrote:


I have been very careful to talk about the standing wave
current *at* the bottom and *at* the top of the coil, not
about the current *flowing* into the bottom of the coil
and out the top of the coil as you and W8JI have.

Cecil,

The wave is stationary. The current is not. It is as simple as that.

Distinctions between *at* and *flowing* are meaningless. Current is what
it is, and mere words don't change anything.

You seem to be reduced to arguments about semantics, which is both good
news and bad news. The good news is that there does not appear to be any
disagreement about the physics. The bad news is that the argument will
never end.

73,
Gene
W4SZ

Current across the antenna loading coil - from scratch
 

Roy Lewallen wrote:
John Popelish wrote:

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.


I see that Cecil is still having trouble with RMS, as well as with
current. Otherwise he couldn't have come up with the nonsense question

He seems to confuse energy in the wave traveling along a conductor
with the current it induces along that conductor, as it travels. I
have had a few such mental blocks and made a fool of myself a couple
times because I was sure I was right. But when the light finally came
on, lots of related things suddenly crystallized in my mind and I
jumped to a better understanding. One of my regrets is that I didn't
go back and apologize to my 7th grade science teacher for arguing with
him with so little tact, when I found out a year later that he had
been right and it was I who had been laboring under a misconception.
Same thing happened, on a different topic, in 8th grade science. So I
think I understand his attitude. I just hope that he sees that my
intentions are honorable, in this discussion. I am not attacking him,
but working for his understanding. I may be mistaken and end up
having another seventh grade moment here, but I'm not trying to
embarrass him.

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

The RMS value of current doesn't flow. Charge flows, and current is the
rate at which it flows. RMS is one way of expressing the magnitude of a
time-varying current. In a steady state environment of pure sinusoidal
waveforms, any current can be expressed as Ipk * cos(wt + phi) where Ipk
is the peak value of the current, w (omega) is the rotational frequency,
and phi is the phase angle. This gives you precisely the value of
current at any instant in time, t. You can equally well express it as
Irms * cos(wt + phi) where Irms is the RMS value of the current. Nothing
is lost or gained by choosing one convention or the other, and using RMS
doesn't require abandoning the time varying or phase information. (In
EZNEC I chose to use RMS; NEC uses peak. They differ only by a constant
factor of the square root of 2. Both report phase angle along with
amplitude.) In either case, if you know or assume w, the current at any
instant is known if you know phi and either Ipk or Irms.

A point of clarification to John's posting:

When a standing wave exists on a transmission line, the phase of the
voltage or current is fixed (other than periodic phase reversals) with
position only if the end of the line is open or short circuited.
Otherwise, the phase of voltage and current will change with position.

Is that because the result is not a pure standing wave (superposition
of two equal and oppositely traveling waves), but a superposition of a
pair of traveling oppositely traveling waves of different amplitudes?

Current across the antenna loading coil - from scratch
 

On Sun, 09 Apr 2006 13:12:29 GMT, Cecil Moore
wrote:
Yes, that way I am the owner of the thought, unlike other
people who like to engage in mind fornication using
someone else's mind.

Glad to hear you only use your own mind for that.

So your religion practices Onanism?

Current across the antenna loading coil - from scratch
 

Cecil Moore wrote:
John Popelish wrote:

From an earlier posting: For example, if we took a snapshot of the
current, all along the line at the moment it peaked it might look like
this:(length of arrow represents current magnitude, and head shows
direction)(view in fixed width font)


....--- --- -- - - -- --- --- -- - - --......
hole-------------------50 ohm coax-------------------hole

x y
There is a standing wave current node at 'x' and a standing
wave current antinode (loop maximum) at 'y'. Let's say we
installed coils at those two points

....--- --- -- - - -- --- --- -- - - --......
hole--------------/////----50 ohm coax----/////------hole
x y
Now we have current flowing into both ends of the coil
located at 'x' and current flowing out of both ends of
the coil at 'y'. How does the lumped circuit model handle
that situation?

If we assume the coil is an idealized lumped inductance with no stray
capacitance at all (not a real inductor) then it would have the same
instantaneous current at each end and that current would be zero,
since it has zero size. In other words it would fit entirely in the
point that holds the node.

Real inductors with stray capacitance and imperfect magnetic coupling
for all parts of its internal current path, would have a phase shift
in the current at opposite ends, so they would have current at their
ends that was 180 degrees out of phase, if they were centered on the
node points. For half of each cycle, current would be entering each
end, and for the other half of each cycle, current would be leaving
each end. Both those currents would detour out the sides f the
inductor into displacement current through the stray capacitance of
the surface of the inductor to its surroundings.

I think (with very little actual knowledge of the software) this
conceptual model is how EZNEC handles current through a modeled
inductor and how it can have different currents at the inductor ends,
without being aware of whether those currents are driven by traveling
or standing waves. It is all based on current through inductor
segments and voltage across capacitive segments. If the segments are
small enough, it is a good approximation of a distributed solution.

Continuing with this posting:

Please don't be silly. Distributed networks have points. An infinite
number of them. Calculus is used to smoothly move through this
infinity of points. But at any particular point, current is defined
as the rate of movement of charge past that point.


No argument, but that is instantaneous current and that is NOT
the subject of this discussion. We are discussing the RMS phasor
value of current used by W8JI and W7EL for their measurements
and reported by EZNEC as in the graphic at:

I am not arguing this point. RMS values capture the amplitude of a
cycle of variation. I am inside the cycle. But the two views are
consistent.

http://www.qsl.net/w5dxp/travstnd.GIF

Please look at the standing wave current phase and tell us how
that flat phase curve can be used to measure the phase shift
in a wire or coil.

The current reported by EZNEC and measured by W8JI and W7EL is
*NOT* instantaneous current. It is RMS current. Instantaneous
current is completely irrelevant to this discussion.

I am not arguing for the validity of that measurement. Argue about it
with someone who is.

I've been waiting for that to happen. There's no point
continuing an argument with someone who denies one of
the cornerstones of EM wave theory.


So you deny that there are any points (where voltage can be defined or
that charge passes) in all distributed networks?
How strange.


:-) You have your points confused. I was talking about a logical
point. Here, let me translate for you. There's no *reason* to
continue an argument with someone who denies one of the
cornerstones of EM wave theory. John, is English your native
language? For the record, I did NOT deny the existence any
physical points!!!

The fact remains that standing wave current phase cannot
be used to measure phase delay through a wire or through
a coil. There is no phase information in standing wave
current phase.


Yes. That fact remains.
It is a non sequitur in the above discussion, however.


Whoa there, John, it is the entire reason for this discussion.

According to you, you are finished talking about coils, and want to
delve strictly into wave concepts. To honor your request, I have
tried to keep the discussion general, and avoid bringing up the effect
on and measurements of coils. But, in this post, you talk about
almost nothing else but coils. I get the distinct feeling that you
want to win a debate far more than you want to reach an understanding
with no internal contradictions. And you are willing to use dishonest
debate tactics (like telling me not to discuss a topic with you, and
then telling me that that exact topic is "the entire reason for this
discussion". Do you get beat up a lot in face-to-face arguments?

W7EL used that standing wave current phase to try to measure
phase shift through a coil. If there is no phase information
in standing wave current phase, then his entire argument
falls apart and he is back to square one with his flawed
lumped circuit model.

Yes. But I cannot concede that point of discussion for someone else.
Are you going to hit me over the head with this till every person in
the World agrees with you? I am trying to think the general case
through with you.

In case you don't realize, there is more than one person out here,
responding to you.

You remind me of a type of insanity where the sufferer thinks that
everything he is experiencing an organized illusion by a single
offending intelligence (you against the Matrix) bent on forcing him to
think that a lie is the truth, regardless of who or what he deals
with. Everyone he meets, every apparently random happenstance, the
actions of his dog and the weather, generally, are all a conspiracy to
force him to think that black is white, and he isn't going to fall for it.

If you cannot carry on a conversation with more than one person at a
time, and treat each of them as a separate mind, then this is the
wrong venue for you.

Current across the antenna loading coil - from scratch
 

Cecil Moore wrote:
John Popelish wrote:

To the center conductor, carrying the standing wave, the shield is the
outside world. If there is no shield, the outside world is the
outside world, as far as displacement current goes. Do you imagine
this current changes in some way other than magnitude and wave
velocity when you wrap a shield around a wire carrying a standing wave?


No, that is your point, not mine. My point is that displacement
current to real ground is non-existent outside of a coax shield
(unless common mode current exists)

With you, so far..

and that it is usually a
secondary effect if the coax shield doesn't exist.

And then we part ways.

The primary
reason for the variation in standing wave current along the line
is the phasor sum of the forward and reflected wave phasors that
are rotating in opposite directions. Do you understand phasor
addition? 1 at zero + 1 at 180 deg = zero at a standing wave
node? Displacement current to real ground doesn't cause that.

I am making the point that if the displacement currents were
insignificant, outside a coax, then the speed of light for waves out
there would be infinite. And they are not, therefore those
displacement currents cannot be assumed to be insignificant.

I am explaining distributed network theory to you.


:-) How? By denying the existence of the individual H-fields
in forward and reflected EM waves? Now, that's really funny.

Exactly the opposite. I am explaining the distributed effect of the E
field along the wave.

http://www.qsl.net/w5dxp/travstnd.GIF


And I have agreed with that. Why do you keep bringing it up?


Because that's the whole point of this discussion. If you
agree with that, there is no reason to continue. I just
don't care about instantaneous current, Brownian motion, or
the exact location and velocity of every electron carrier.
There's too much uncertainty involved.

You are avoiding the very facts that would allow you to make an air
tight argument for your beliefs about "the whole point of the
discussion". You somehow picture current as a continuous thing from
one end of a conductor to the other, when it carries a traveling
energy wave. This is a misconception.

You appear to accept that current is a localized kind of thing (parts
of the conductor carry current, but those parts are separated by
nodes) when two traveling waves going in opposite directions
superpose, but have no concept that explains how this happens, only a
mathematical function that quantifies it.

What you don't get is, that the currents that each of those traveling
waves would have generated were localized, to begin with. Local
current cycles and voltage cycles are the water the energy waves ride
on over arbitrarily long distances along conductors and transmission
lines.

I know you don't care about this factoid, but understanding it would
allow you to think about "the entire reason for this discussion" much
more clearly.

Current across the antenna loading coil - from scratch
 

Cecil Moore wrote:
John Popelish wrote:

So waves can move in one or more directions while any bit of water
moves only locally. Same with charge.


My point exactly. I'm glad you agree.

We shall see.

There is energy heating the load resistor. The current does not come
through the source. It is created at the end of the line by the
traveling energy wave.


The H-field energy in the load originated in the source.

Yes.

Current is directly proportional to the H-field in the EM wave.

Yes.

Let me quote Ramo and Whinnery:

I = e^jwt/Z0[(V+)(e^-jwz/v) - (V-)(e^jwz/v)]

This is the *continuous* equation for source current at
z = 0 and load current at z = (distance). Essentially the
same equation is found in every reference on transmission
lines.

Yes. That equation describes the instantaneous current you would find
at any point as the wave pases through it.
It does not imply that the current at one point is the same current at
another point. It implies a continuity of the energy wave. At some
points along that wave, the current has some positive value (charge
going in the same direction as the wave. At other points, the current
has some negative value, indicating that charge is moving the opposite
way from the wave direction. The current is continuous only in that
there is a smooth, sinusoidal variation in its magnitude and direction
as you look along the wave path. but the current at one point is not
the current at some other point.

They don't say current is "created" at the load. They say
current is a *continuous single-valued function* between
source and load.

A current described by a continuous single valued function is not a
continuous current. The water that drowns people in a tidal wave in
California is a current dragged over the beach by an energy wave that
caused a continuous pattern on of local currents from the landslide in
Hawaii. But the actual water current (movement of water molecules
carrying the wave energy) did not flow continuously from Hawaii to
California. There are no Hawaiian fish carried to California by a
current of water that connected those two locations.

Do you have a reference for your "creation"
of current?

Only Maxwell's equations.

That the H-field experiences a delay and transformation on its
way to the load doesn't mean that current is magically created
out of thin air at the load.

Current is created and reversed (charge is sloshed back and forth) all
along the line, from source to load. Just as water is moved up and
down all along the path of a wave over the surface of the water. But
if you pick any bit of water, it does not follow the wave.

Hang some modulation on the current at the source. You will
measure that modulation arriving at the load in the form of
current exactly in accordance with the laws of physics
embodied in the distributed network model.

Yes, delayed by the speed of light in that medium.

In a DC circuit, is the current also "created" at the load?

No. DC has an infinite wavelength, so there is no significant
distance (in wavelength units) no matter how far apart the source and
load appear to be. If a battery near earth is connected to a load
near Alpha Centauri by a perfectly conducting loop, and you consider
the DC case (DC has an infinite duration), then there is no
significant distance between that source and load, so local current
connects them. Electrons that are pushed out of the battery will
reach the load and return to the battery. The definition of "local"
is wavelength dependent.

Back to the RF case: Do you imagine that electrons from the source
reach the load?

My denial is a recognition that current does not connect the source to
the load, ...


Then by all means, disconnect the source and keep the current.

Be happy to. For the amount of time it takes for a wave to pass the
full length of the line, energy will continue to be delivered to the
load (current will pass through it), even though the source has been
disconnected and causes no further current in the line.

Anything is possible in your mind. Just don't expect that to
work in reality.

I am doing my best to limit my mind to strictly what reality allows,
in this discussion.

How could
its unchanging phase be used to measure the electrical
length of the coax?


You measure the difference of the node positions, with and without the
coil. The shift in distance (in wavelengths) between the two nodes
that straddle the coil is the phase shift of the coil for each of the
traveling waves that make up the standing wave.


Someone needs to tell that to W7EL. I've tried to tell him but
instead of thanking me, he 'ploinked' me.

Perhaps he has lost interest in this thread.
Perhaps he is taking this topic personally.
Perhaps he enjoys yanking your chain.
Perhaps ...

What does any of that have to do with our conversation?

Your thoughts are in a rut.

Current across the antenna loading coil - from scratch
 

Gene Fuller wrote:
The good news is that there does not appear to be any
disagreement about the physics.

On the contrary, Gene. The disagreement is whether W7EL's
use of standing wave current phase to try to determine
phase shift through a coil was valid or not. That is the
present point of disagreement.

I have posted what you said many times but W7EL doesn't
read my postings. So would you kindly point out to W7EL
that there is no phase information in standing wave
current phase?
--
73, Cecil http://www.qsl.net/w5dxp

Current across the antenna loading coil - from scratch
 

John Popelish wrote:
He seems to confuse energy in the wave traveling along a conductor with
the current it induces along that conductor, as it travels.

It's not confusion, John. It is engineering convention. Every
engineering reference book I have refers to current flow at
one point or another. Most of them also refer to power flow.
"Transmission Lines and Networks", by Walter C. Johnson even
refers to "The Conservation of Power Principle". Since there
is no such thing as an RF battery, we know exactly what Mr.
Johnson meant.

You are discussing the conventions used by physicists. Since
this is basically an RF engineering convention newsgroup, you
need to adjust your concepts accordingly or tell everyone that
you are nit-picking based on the conventions from the field of
pure physics.

In the engineering world: Power companies generate power and
transfer the power to the consumers over transmission lines.
RF transmitters generate power which is transferred over the
transmission line and radiated by the antenna.

There is always a convention for placing an arrow on a wire
to indicate direction of current flow, whether RMS AC or DC
or RMS RF. The AC conventions are left over from the DC
conventions. If you are trying to change those conventions,
please say so.

Food for thought: If an electron can pass through two different
holes at the same time, can it also travel in two directions
at the same time? Quantum physics says that is a possibility.

Is that because the result is not a pure standing wave (superposition of
two equal and oppositely traveling waves), but a superposition of a pair
of traveling oppositely traveling waves of different amplitudes?

Yes, but the definition of a standing wave is that the two waves
are of equal amplitudes. The wave you are describing is a hybrid
wave containing both a traveling wave and a standing wave. Any
real-world system contains hybrid waves in various ratios of
traveling waves to standing waves.
--
73, Cecil http://www.qsl.net/w5dxp

Current across the antenna loading coil - from scratch
 

Richard Clark wrote:
Glad to hear you only use your own mind for that.

So your religion practices Onanism?

It means that if I decide to mentally masturbate, I'll use my
own mind, thank you, not someone else's mind, as do a lot of
the posters on this newsgroup.
--
73, Cecil http://www.qsl.net/w5dxp

Current across the antenna loading coil - from scratch
 

On Sun, 09 Apr 2006 17:53:07 GMT, Cecil Moore
wrote:
So your religion practices Onanism?

It means that if I decide to mentally masturbate, I'll use my
own mind, thank you, not someone else's mind, as do a lot of
the posters on this newsgroup.

Lot of bafflegab in that. I will take it to mean yes.