Current across the antenna loading coil - from scratch
 

Cecil Moore wrote:
John Popelish wrote:

Cecil Moore wrote:

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.


There is only water juggling under two or more waves in the
ocean. Anyone who has stood on the beach has observed ocean
waves moving in opposite directions.

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

Your assertion is easy to disprove. In the following example,
the two sources have identical outputs and are phase locked.
They are each equipped with circulators and 50 ohm loads.

Source1---------------50 ohm coax------------------Source2

Got it.

There is current flowing from Source1 heating up Source2's
load resistor to the tune of I1^2*R.

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 charge that makes up the current passing
back and forth through the load to produce the heat does not come from
the source. It comes from the load itself and and the nearby part of
the line (within less than a 1/2 wavelength). That charge is caused
to move by the energy in the wave.

There is current
flowing from Source2 heating up Source1's load resistor
to the tune of I2^2*R.

No, for the same reason. The current is local to the end of the line
near the load. It is not current that travels the length of the line
from source to load, but the energy in the wave, just as the water
from the underwater landslide is not what washes up on the beach a
hundred miles away. Local water is pushed up on the beach by the
energy in the traveling wave that connects the landslide with the beach.

Your denial seems to be a denial
of reality and more of a religious gut feeling than anything
else.

My denial is a recognition that current does not connect the source to
the load, traveling energy waves do, however. Local current carries
that wave along the line.

If you disconnect Source2 completely in the example above
the conditions will be the same except Source1 will be
dissipating its own power after a round trip to the open
end and back by the energy waves.

Yes, its wave energy will return to the source and cause current local
to the source to pass through that load.

Incidentally, in the double source example above, which
direction is the standing wave current flowing?

At any point that is not a node, back and forth, every cycle. At
nodes, back and forth across the dielectric of the line.

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.

Current across the antenna loading coil - from scratch
 

On Sun, 09 Apr 2006 04:10:15 GMT, Cecil Moore
wrote:
That seems like a religious act to me, not a technical choice.

seeming again?

Current across the antenna loading coil - from scratch
 

John Popelish wrote:
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.

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

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.

Roy Lewallen, W7EL

Current across the antenna loading coil - from scratch
 

John Popelish wrote:
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.

I hope you guys realize that the stated equation is correct only when I1
= I2. Otherwise the solution is a sine or cosine function with a phase term.

Roy Lewallen, W7EL

Current across the antenna loading coil - from scratch
 

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?

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:

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'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.
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.
--
73, Cecil http://www.qsl.net/w5dxp

Current across the antenna loading coil - from scratch
 

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

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.
--
73, Cecil http://www.qsl.net/w5dxp

Current across the antenna loading coil - from scratch
 

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.

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

They don't say current is "created" at the load. They say
current is a *continuous single-valued function* between
source and load. Do you have a reference for your "creation"
of current?

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.

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.

In a DC circuit, is the current also "created" at 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.
Anything is possible in your mind. Just don't expect that to
work in reality.

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.
--
73, Cecil http://www.qsl.net/w5dxp

Current across the antenna loading coil - from scratch
 

Richard Clark wrote:

Cecil Moore wrote:
That seems like a religious act to me, not a technical choice.

seeming again?

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.
--
73, Cecil http://www.qsl.net/w5dxp

Current across the antenna loading coil - from scratch
 

Roy Lewallen wrote:
The RMS value of current doesn't flow.

I'm glad you agree. That is what I have been telling
you for about a year now. Obviously, my question was
rhetorical.

Your assertion sure shoots down your and W8JI's argument
that current flows into the bottom of the coil and out of
the top of the coil, doesn't it? You guys reported measuring
RMS current flowing into the bottom of the coil and out
the top. Now you deny that the current you measured was
flowing at all. I would say we are making progress.

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.
--
73, Cecil http://www.qsl.net/w5dxp

Current across the antenna loading coil - from scratch
 

Roy Lewallen wrote:
I hope you guys realize that the stated equation is correct only when I1
= I2. Otherwise the solution is a sine or cosine function with a phase
term.

Of course, I1=I2 is the definition of a standing wave
which is the topic of this discussion. Any current left
over is traveling wave current, by definition.

The concept is akin to the separation of differential
current from common-mode current. Differential currents
are equal by definition.

Standing wave component currents are equal by definition.
--
73, Cecil http://www.qsl.net/w5dxp