Ian White GM3SEK wrote:
I flatly do not accept your notion of a special kind of "standing wave
current" that has its own special kind of phase properties.

We already know that, Ian. Please drag out your dusty math book
and try to understand the difference between the standing wave
current function, func(kx)*func(wt), and the traveling wave
current function, func(kx +/- wt). They are obviously different.
Calling the standing wave current a "current" is something of
a misnomer since it doesn't exhibit the characteristics of a
normal current at all. What are the implications of a "fixed
phase" for a current, i.e. its phasor doesn't rotate?

Do you disagree with Gene's technically accurate posting on the
subject?
************************************************** ***************************
Gene Fuller, W4SZ wrote:
In a standing wave antenna problem, such as the one you describe, there is no
remaining phase information. Any specific phase characteristics of the traveling
waves died out when the startup transients died out.

Phase is gone. Kaput. Vanished. Cannot be recovered. Never to be seen again.

The only "phase" remaining is the cos (kz) term, which is really an amplitude
description, not a phase. The so-called "phase reversal" in longer antennas is
not really about phase either. It is merely a representation of the periodic
sign reversal seen in a cosine function.
************************************************** ****************************

The current that the loading coil experiences is plain old ordinary
alternating current flowing in the wire ...

False! Standing wave current is different from DC, AC, or RF
traveling waves. Please take time out to understand the
implications of a non-rotating phasor for a current. All other
AC currents have rotating phasors but the standing wave current
phasor doesn't rotate all up and down a 1/2WL thin-wire dipole.
That makes it extremely different from any other AC current.

Any special kind of current that requires electronic components to
behave in some different way from normal is simply not real.

The forward current and the reflected current are not special. The
superposed standing wave current doesn't behave as normal current at
all. It's phase doesn't change along the entire length of a 1/2WL thin-
wire dipole. I have said this a dozen times and it hasn't yet soaked
in yet so I will continue to repeat it. What does unchanging phase imply
about a standing wave current? All other AC currents change phase.

You have a fundamental misconception of what a standing wave of current
really is. You repeat all the words about "standing waves", "cos kz",
"scientific logic", "laws of physics" etc; but you don't actually let
any of it into your mind.

I am open-minded, Ian, and use the scientific method to correct my
mistakes and thus zero in on the technical facts. One of a guru's
presuppositions is that he already knows everything. I have no
such misconceptions about myself.

All the questions you ask other people are rooted in your own
misconceptions. In other words, the questions are rigged so that they
cannot be answered except by agreeing with you.

No, Ian, my questions are rigged so they cannot be answered except
by agreeing with the laws of physics and gurus cannot afford to show
their ignorance of the laws of physics. That leaves them between a
rock and a hard place as far as answering my questions are concerned.
That's the only reason for the "Silence of the Gurus".
--
73, Cecil http://www.qsl.net/w5dxp

Cecil Moore wrote:
We already know that, Ian. Please drag out your dusty math book
and try to understand the difference between the standing wave
current function, func(kx)*func(wt), and the traveling wave
current function, func(kx +/- wt). They are obviously different.
Calling the standing wave current a "current" is something of
a misnomer since it doesn't exhibit the characteristics of a
normal current at all. What are the implications of a "fixed
phase" for a current, i.e. its phasor doesn't rotate?

This can be improved.

Current is charge movement. DC, traveling waves and standing waves
all are *exactly* charge moving past a given point, and nothing more.

A phasor is not a real thing, but a mathematical abstraction that
relates how the sinusoidal change in current magnitude and direction
relate to a reference periodic cycle in time. Since, in both standing
waves and traveling waves, current at a point, changes magnitude and
sign in exactly the same way (at a point, they are indistinguishable),
they can both be described with phasor notation.

The difference between a traveling wave and a standing wave is how the
phasor representing the current at one point differs from the phasor
representing the current at a neighboring point.

For traveling waves, the phasor of a neighboring point has the same
amplitude but a different phase shift (passes through zero at a
different time).

For standing waves, the phasor of a neighboring point has the same
phase shift, but a different amplitude, unless the neighboring point
is on the other side of a current node. Then it has the opposite phase.

But at any point along both standing waves and traveling waves, there
certainly is a phasor that represents the current at that point.

You need to get past this misconception that standing waves are not
current and are not describable by phasors. I think your concepts are
correct in lots of ways and recently improving, but this is a
recurring snag that keeps detouring your adversaries into straw men
that you offer them on a platter.

John Popelish wrote:
Since, in both standing
waves and traveling waves, current at a point, changes magnitude and
sign in exactly the same way (at a point, they are indistinguishable),
they can both be described with phasor notation.

Limiting oneself to a point measurement is handicapping onself. When
the equation for standing wave current is compared to the equation
for traveling wave current, the real differences are obvious.

For standing waves, the phasor of a neighboring point has the same phase
shift, ...

Exactly! Therefore, it cannot be used to measure the phase shift
through a coil or even through a wire.

But at any point along both standing waves and traveling waves, there
certainly is a phasor that represents the current at that point.

For the standing wave current it is a phasor that doesn't rotate
all up and down the wire. You have to admit, that's a weird phasor.
It's more akin to DC than anything else.

You need to get past this misconception that standing waves are not
current and are not describable by phasors.

Standing waves current is the superposition of two essentially equal
currents traveling in opposite directions. If it was equal DC
currents traveling in opposite directions, what would the net current
be?
--
73, Cecil http://www.qsl.net/w5dxp

Cecil Moore wrote:
John Popelish wrote:

Since, in both standing waves and traveling waves, current at a point,
changes magnitude and sign in exactly the same way (at a point, they
are indistinguishable), they can both be described with phasor notation.


Limiting oneself to a point measurement is handicapping onself. When
the equation for standing wave current is compared to the equation
for traveling wave current, the real differences are obvious.

I was just making sure we were using the same definitions for things
like current and phasors. You are jumping ahead. :-)

For standing waves, the phasor of a neighboring point has the same
phase shift, ...


Exactly! Therefore, it cannot be used to measure the phase shift
through a coil or even through a wire.

I agree, unless you use phase measurement to hunt for the location of
the current nodes that have moved as a result of adding the coil.
Finding a phase reversal at opposite ends of the coil, for instance,
implies that an odd number of nodes reside in the coil.

But at any point along both standing waves and traveling waves, there
certainly is a phasor that represents the current at that point.

For the standing wave current it is a phasor that doesn't rotate
all up and down the wire.

A phasor rotates at the reference frequency, and with a phase angle
that represents the angular difference between the value in question
and the reference cycle. Pick a point on the conductor, and if it
carries either a standing or traveling wave (or any combination of
traveling waves at the reference frequency), the current at that point
is describable as a phasor (having a specific magnitude, and a
specific phase with respect to the reference cycle).

You have to admit, that's a weird phasor.
It's more akin to DC than anything else.

This is your mental block. A phasor describes the activity at a
point, not whether that activity is a result of an energy wave moving
past in one direction, the other, or some combination of those.

You need to get past this misconception that standing waves are not
current and are not describable by phasors.


Standing waves current is the superposition of two essentially equal
currents traveling in opposite directions.

No. Currents do not travel. Current is the movement of charge past a
point. Cyclic current is a sloshing back and forth of charge at some
frequency. If you want to picture that process with respect to time,
you can refer to it as a cycle or wave, but it is a wave on a scope
trace or time graph, not a physical wave of something moving along a
wire. The physical wave is charge slushing back and forth along the wire.

Both traveling energy waves and combinations of them (standing waves,
for example) involve energy traveling in various directions, but the
current does not travel. It occurs at a point, as charge moves back
and forth past that point. When you can separate the concept of
current from the concept of energy waves, you might see this snap into
focus.

I am not trying to be the guru, here. My earlier posts confused these
same concepts, when I mentioned current waves traveling in various
directions. I was mistaken, and have seen my error, and am trying to
get you to see it, also. I should have been speaking of charge waves
that produce current. Correct thinking requires correct speaking.
You cannot be sloppy with words and have (let alone express) clear
thoughts. This thread has done a lot to help me clear up both my
words and thoughts, and I thank you for that. I am not absolutely
sure that I have eliminated all mistakes from this way of talking
about the process under discussion, so I may have to make some more
corrections. That is the reason I am watching this thread.

If it was equal DC currents traveling in opposite directions,
what would the net current be?

Their algebraic sum, same as for non equal currents. Same for any
combination of currents that result from charge being shoved back and
forth by passing energy waves. Instantaneously the current is the
algebraic sum of all components passing through that point. If the
components are AC at the same frequency, the sum will be some
resultant instantaneous current that varies with that same frequency.

I think I agree with just about every conclusion you are making about
treating coils as slow wave transmission lines. The nits I am picking
is in the language you are using to describe these effects to justify
those conclusions. I think terminology is at the root of most of the
disagreements in this thread.

John Popelish wrote:

Cecil Moore wrote:
Exactly! Therefore, [standing wave phase] cannot be used to measure the phase shift
through a coil or even through a wire.

I agree, unless you use phase measurement to hunt for the location of
the current nodes that have moved as a result of adding the coil.
Finding a phase reversal at opposite ends of the coil, for instance,
implies that an odd number of nodes reside in the coil.

John, I didn't say the amplitude couldn't be used to determine
phase. The current nodes are associated wiht amplitudes, not phase.

A phasor rotates at the reference frequency, and with a phase angle that
represents the angular difference between the value in question and the
reference cycle. Pick a point on the conductor, and if it carries
either a standing or traveling wave (or any combination of traveling
waves at the reference frequency), the current at that point is
describable as a phasor (having a specific magnitude, and a specific
phase with respect to the reference cycle).

Yes, but the standing wave phasor doesn't change phase with position.
The traveling wave phasors change phase with position. That's a big
difference.

No. Currents do not travel. Current is the movement of charge past a
point.

So current doesn't flow and all the references to "current flow" are
wrong? If so, your task is a lot bigger than mine. May I suggest a
new thread titled, "Current Doesn't Flow".
--
73, Cecil http://www.qsl.net/w5dxp

Cecil Moore wrote:
John Popelish wrote:

Cecil Moore wrote:

I agree, unless you use phase measurement to hunt for the location of
the current nodes that have moved as a result of adding the coil.
Finding a phase reversal at opposite ends of the coil, for instance,
implies that an odd number of nodes reside in the coil.


John, I didn't say the amplitude couldn't be used to determine
phase. The current nodes are associated wiht amplitudes, not phase.

If you can measure phase, you can see that it is opposite on opposite
sides of a node. There is a 180 degree phase shift each time the
measurement passes over a node. Do you disagree?

A phasor rotates at the reference frequency, and with a phase angle
that represents the angular difference between the value in question
and the reference cycle. Pick a point on the conductor, and if it
carries either a standing or traveling wave (or any combination of
traveling waves at the reference frequency), the current at that point
is describable as a phasor (having a specific magnitude, and a
specific phase with respect to the reference cycle).


Yes, but the standing wave phasor doesn't change phase with position.
The traveling wave phasors change phase with position. That's a big
difference.

That's exactly the difference. But if you measure a single point, you
can't tell whether you are measuring a point on a traveling wave or a
standing wave. Agree?

No. Currents do not travel. Current is the movement of charge past a
point.


So current doesn't flow and all the references to "current flow" are
wrong?

Afraid so. The concept of current already includes the concept of
flow. Current is charge flow. Current flow is charge flow flow??

If so, your task is a lot bigger than mine. May I suggest a
new thread titled, "Current Doesn't Flow".

I wonder how long that thread would "flow".

John Popelish wrote:
If you can measure phase, you can see that it is opposite on opposite
sides of a node. There is a 180 degree phase shift each time the
measurement passes over a node. Do you disagree?

Yes, but you can tell that from the amplitude being zero.

That's exactly the difference. But if you measure a single point, you
can't tell whether you are measuring a point on a traveling wave or a
standing wave. Agree?

I agree but who would be stupid enough to measure just a single
point? One could wear a blindfold and use no hands and have an
even greater challenge.
--
73, Cecil http://www.qsl.net/w5dxp

John Popelish wrote:
. . .
That's exactly the difference. But if you measure a single point, you
can't tell whether you are measuring a point on a traveling wave or a
standing wave. Agree?


There seems to be some confusion about just what a standing wave is.

A standing wave is the result of, and the sum of, two or more traveling
waves. There aren't points which are "on" one or the other. If you can
separately measure or calculate the values of the traveling current
waves at any point, you can add them to get the total current (what
Cecil calls "standing wave current") at that point. If you add the
traveling current waves at each point along the line and plot the
amplitude of the sum (that is, of the total current) versus position,
you see a periodic relationship between the amplitude and position. It's
this relationship which is called a "standing wave". It's so called
because its position relative to the line stays fixed. It's simply a
graph of the total current (the sum of the traveling waves) vs. position.

Roy Lewallen, W7EL

John Popelish wrote:
. . .
I think I agree with just about every conclusion you are making about
treating coils as slow wave transmission lines. . .

A coil itself isn't a slow wave transmission line. In conjunction with
shunt C, it can be analyzed as a transmission line, but only in
conjunction with shunt C. Remove the shunt C and it ceases looking like
a transmission line. The earlier example of the modification to Cecil's
EZNEC model illustrated this -- when the ground (the other side of the
shunt capacitor) was removed, the current drop across the coil disappeared.

As far as considering a coil itself as a "slow wave structure", Ramo and
Whinnery treat this subject. It's in the chapter on waveguides, and they
explain how a helix can operate as a slow wave waveguide structure. To
operate in this fashion requires that TM and TE modes be supported
inside the structure which in turn requires a coil diameter which is a
large part of a wavelength. Axial mode helix antennas, for example,
operate in this mode. Coils of the dimensions of loading coils in mobile
antennas are orders of magnitude too small to support the TM and TE
modes required for slow wave propagation.

Roy Lewallen, W7EL

Roy Lewallen wrote:
A coil itself isn't a slow wave transmission line. In conjunction with
shunt C, it can be analyzed as a transmission line, but only in
conjunction with shunt C.

A 75m bugcatcher has its own shunt C called "distributed capacitance".
It's what causes the self-resonant frequency of my 75m bugcatcher coil
to be only 60% higher than the 4 MHz operating frequency.

Remove the shunt C and it ceases looking like a transmission line.

That's true *only* for a lumped-circuit inductance. It is NOT true
for a 75m bugcatcher which has it very own distributed capacitance
built in. It is *IMPOSSIBLE* to remove the distributed shunt
capacitance from a 75m bugcatcher coil.

The earlier example of the modification to Cecil's
EZNEC model illustrated this -- when the ground (the other side of the
shunt capacitor) was removed, the current drop across the coil disappeared.

That may be true but please tell us how to remove the ground from a
75m mobile bugcatcher mobile antenna installation.

Coils of the dimensions of loading coils in mobile
antennas are orders of magnitude too small to support the TM and TE
modes required for slow wave propagation.

Sorry Roy, Dr. Corum disagrees with your statement. You really should
read the details of the Dr. Corum web page references that I posted.

His test for the validity of his helix equations is:

5*N*D^2/lamda(0) = 1 where N is number of turns, D is diameter,
and lamda(0) is the self-resonant frequency.

That value for my 75m bugcatcher coil is 0.4 so his equation for
velocity factor is valid. The velocity factor for my 75m bugcatcher
coil calculates out to be 0.0175. Now that's what I call a "slow
wave" coil.

But I have offered all these references weeks ago. Are you too
arrogant to even have read them? (Another rhetorical question)
--
73, Cecil http://www.qsl.net/w5dxp