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

Cecil Moore 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?

I agree but who would be stupid enough to measure just a single
point?

Electronic components are exactly that stupid. They have no conception
of traveling or standing waves. They react simply to the voltages and
currents they experience at their terminals.

As far as current is concerned, that means the simple movement of charge
past a single point.

You see a larger picture of the whole antenna, so you can choose many
different ways to theorize about it. But your theory cannot be correct
if it requires that components behave in different, special ways
according to the way you happen to be thinking about it at the time.



--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

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

Roy Lewallen wrote:
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.

And there's no such thing as current imbalance based on standing
wave currents being different at each end of a loading coil.
"Current imbalance" is a concept that doesn't apply to standing
waves. "Phase rotation with position" is a concept that doesn't
apply to standing waves. Standing wave current is NOT ordinary
current. It is the superposition of two ordinary currents.
--
73, Cecil http://www.qsl.net/w5dxp

Cecil Moore wrote:

And there's no such thing as current imbalance based on standing
wave currents being different at each end of a loading coil.
"Current imbalance" is a concept that doesn't apply to standing
waves. "Phase rotation with position" is a concept that doesn't
apply to standing waves. Standing wave current is NOT ordinary
current. It is the superposition of two ordinary currents.

You two are so close to agreement. Standing waves have a current that
varies with position. The fact that the EZNEC simulation of a loading
coil shows differing current in a situation that is a fairly pure
standing wave situation (more energy bouncing up and down the antenna
than is radiating from it) means that the RMS current will vary along
the standing wave. And, since the simulation shows a different
current magnitude at the two ends of the coil, a significant part of a
standing wave cycle must reside inside the coil (more than the
physical length between the two ends of the coil would account for).

In one case (the highest frequency one) the phase of the current even
reverses from one end of the coil to the other, as well as an
amplitude variation, indicating that a standing wave node occurs some
where inside the coil, and the two ends are on opposite ends of that
node. If the two currents had been equal, but 180 degrees out of
phase, the node would have been in the center of the coil.

John Popelish wrote:

You two are so close to agreement. Standing waves have a current that
varies with position. The fact that the EZNEC simulation of a loading
coil shows differing current in a situation that is a fairly pure
standing wave situation (more energy bouncing up and down the antenna
than is radiating from it) means that the RMS current will vary along
the standing wave. And, since the simulation shows a different current
magnitude at the two ends of the coil, a significant part of a standing
wave cycle must reside inside the coil (more than the physical length
between the two ends of the coil would account for).

No, you're misinterpreting what you're seeing. Imagine an LC L network
with theoretically lumped series L and shunt C. If you look at the
currents at the input and output of the perfect inductor, you'll find
that they're exactly the same. If, however, you look at the currents in
and out of the *network* you'll see that they're different, because of
current going to ground through the C. And, as I said before, you can
even pretend it's a transmission line and measure forward and reverse
traveling waves and a standing wave ratio. But with zero length, there
can be no standing waves inside the inductor. Yet the terminal
characteristics of the network are the same as a transmission line. You
don't need to imagine standing waves residing inside the inductor in the
LC circuit, and you don't need to imagine them inside the inductor in
Cecil's model, either.

When you look at the currents reported by EZNEC for the model on Cecil's
web page, the current at the top of the coil is the equivalent to the
*network* current described above. It's the current flowing through the
inductance minus the current being shunted to ground via the C between
the coil and ground. You can tell just how much this is by looking at my
modified model and subtracting the current going into the coil from
ground from the current going into ground from the added wire. They're
not the same -- the difference is the displacement current through the C
from the inductor to ground. When I removed the ground, you could then
see the current flowing through the inductor, by itself, without the
current being shunted off. And lo and behold, it's nearly the same at
both ends of the inductor, showing that the inductor is behaving very
much like a lumped L. Only in conjunction with the C to ground does the
combination mimic a transmission line -- just like any other lumped LC
circuit.

Of course, at some length and/or poorness of interturn coupling, a coil
will start behaving in a way we can't adequately model as a lumped L.
But that's not the case here.

. . .

Roy Lewallen, W7EL

Roy Lewallen wrote:
If, however, you look at the currents in
and out of the *network* you'll see that they're different, because of
current going to ground through the C.

The main effect in a standing wave environment are the forward
and reflected phasors rotating in opposite directions. The
standing wave current is ZERO when those phasors are 180 degrees
out of phase. The standing wave current is maximum when those
phasors are in phase. "Current going to ground through the C"
is not even required.

But with zero length, there
can be no standing waves inside the inductor.

You keep saying stuff like this as if a zero length inductor
actually existed in reality. Wake up, Roy, and smell the
roses. That zero length inductor exists only in human minds.


When you look at the currents reported by EZNEC for the model on Cecil's
web page, the current at the top of the coil is the equivalent to the
*network* current described above. It's the current flowing through the
inductance minus the current being shunted to ground via the C between
the coil and ground.

Huh? How do you explain the current at the top being greater than
the current at the bottom of the coil? Is the coil sucking current
from the ground?
--
73, Cecil http://www.qsl.net/w5dxp

Roy Lewallen wrote:
John Popelish wrote:

No, you're misinterpreting what you're seeing. Imagine an LC L network
with theoretically lumped series L and shunt C.

Okay, I am imagining an idealized, network made of perfect, impossible
components that is simple to analyze. Got it.

If you look at the
currents at the input and output of the perfect inductor, you'll find
that they're exactly the same.

Right.

If, however, you look at the currents in
and out of the *network* you'll see that they're different, because of
current going to ground through the C.

Got it. Same for any pi, T, or more complicated LC network.

And, as I said before, you can
even pretend it's a transmission line and measure forward and reverse
traveling waves and a standing wave ratio.

Yes. Under some specific conditions.

But with zero length, there
can be no standing waves inside the inductor.

Yes. There are no waves in a single ideal lumped component, so there
can be no waves inside any of them, only a phase shift between the
voltage across them and the current through them. But a network made
of them can mimic lots of processes that internally involve
propagation of waves, including the phase shift between voltages
across the terminals and current into the terminals, and even group
delay, but only over narrow frequency range. It is a model with this
severe limitation.

Yet the terminal
characteristics of the network are the same as a transmission line. You
don't need to imagine standing waves residing inside the inductor in the
LC circuit, and you don't need to imagine them inside the inductor in
Cecil's model, either.
(snip)

Whether or not we need to imagine them to picture what is happening at
the terminals is not the question at hand. The question in my mind is
what is the actual mechanism, inside the device in question that is
causing the effects we see at the terminals. I am not interested in
the full range of models that predict the effect, but in the actual
cause. I accept that my motivation is not necessarily the same as yours.