Quoted from an e-mail exchange I am having:

However, I'd like you to reconsider your position concerning inductances in
series with a line that has both forward and reverse currents flowing, as in
short mobile antennas. As a result of two currents from the same source flowing
in opposite directions, a standing wave is inevitable, hence different values of
current at different points along the wire in the inductor.

That is incorrect for the conditions we are outlining, and it is
misleading Cecil. It has him lost in a world of reflections. You have
gone outside the limits of the model by assuming, incorrectly, the
inductor has no or little flux linkage from end-to-end and has large
stray capacitance to the outside world compared to load impedance. The
conductor used to build a inductor does not have current slowly winding
its way along that path.

There is no virtually no difference in phase delay in current at each
end of a relatively compact inductor. It is very easy to measure that.
It also have very little group delay compared to the group delay one
would expect from a transmission line or antenna the same length. I
know that because I have measured it hundreds of times.

I have repeated a url below that Cecil posted on the rraa. The material in that
url agrees with my position, and specifically states that circuit analysis is
invalid when the model contains distributed currents, and admonishes that anyone
who disbelieves this has forgotten the warning about the situation given in
sophmore EE courses.

The Tesla coil, by definition of how it works, violates all boundaries
of the examples myself and others are giving Cecil. It does not apply
to the discussion at all.

The Tesla coil is intentionally of exceptionally long form factor. It
has virtually an open circuit at the end, and is by operation
self-resonant at the operating frequency. It has a very large amount
of distributed capacitance compared to termination impedance, since the
termination is an open. It is not operated at a fraction of
self-resonance as people SHOULD know a good mobile loading coil is.

It has no bearing at all on the discussion, any more than it would if I
started measuring the plate choke from an AL1200 amplifier at the
self-resonant frequency with an open termination, or a loading coil for
a 75 meter antenna at the self-resonant frequency.

Everyone (except Cecil) has been very careful to give the boundaries
and describe the effects. The Tesla coil does not fit the boundaries
described, and the secondary inductor in the Tesla coil behaves nothing
like an inductor operated well below self resonance.

http://www.ttr.com/corum/index.htm

The very first paragraph of that reference should have been a red flag
that it does not apply to this discussion. Here is what it says:

"Can one model the physical operation of a Tesla coil appropriately
with only lumped-element circuits? If not, why not? It was pointed out
long ago that, at its operating frequency, a Tesla coil is NOT a
lumped-element induction coil. Forget the quest for "many turns of fine
wire". In fact, a Tesla coil has more in common with a cavity resonator
than it does with a conventional inductor."

The key words they use, and they even drew attention to the words by a
type style change, "at its operating frequency, a Tesla coil is NOT a
lumped-element induction coil". They were very clear about that, and go
on to describe how it does behave like a normal induction coil.

Everyone in the conversation has been very careful to clearly establish
the boundary conditions that the behavior we are talking about is
significantly below self-resonance, an inductor of compact form factor,
and an inductor of good design.

I can't understand why anyone would attempt to reference an article
that, in the very opening, states the inductor is operating at
self-resonance! I can't understand why anyone would reference an
article that violates the boundaries of termination impedance outlined
in the discussion, where it has been stated over and over again the
inductor must be terminated in an impedance that is low compared to
leakage impedances.

I can't imagine anyone using a lossy Tesla coil as an antenna or part
of an antenna system. Please read the opening paragraphs of the article
you reference.

73 Tom

wrote :
That is incorrect for the conditions we are outlining, and it is
misleading Cecil. It has him lost in a world of reflections.

What is causing the misleading part is: THE LUMPED-CIRCUIT
MODEL FAILS IN THE PRESENCE OF STANDING WAVES!

There is no virtually no difference in phase delay in current at each
end of a relatively compact inductor.

Is a 75m bugcatcher coil a "relatively compact indictor"? If you say
yes, you are stuck with its measured delay. If you say no, then we
are not discussing the typical amateur radio mobile loading coil.

Of course, one turn on a toroid is going to exhibit the characteristics
you are presenting. But that is not a typical bugcatcher coil either.

The Tesla coil, by definition of how it works, violates all boundaries
of the examples myself and others are giving Cecil. It does not apply
to the discussion at all.

False: A 75m bugcatcher coil used as a 1/4WL resonator on
9-10 MHz meets the minimum requirements for a Tesla coil.
It uses 1/6 wavelength of wire on 75m. I'll bet it would
certainly arc at a kilowatt.

The typical minimum Tesla system is a coil with a top hat sphere.
It looks a lot like your 160m mobile antenna. :-)

It is not operated at a fraction of
self-resonance as people SHOULD know a good mobile loading coil is.

A 75m bugcatcher coil is operating close enough to its self-resonant
frequency that the self-resonant effects are certainly present.

A 75m bugcatcher coil can be considered to be a lumped circuit
impedance at 60 Hz but certainly not at 4000000 Hz. In fact,
that is the whole question. At what frequency can the lumped
circuit model be validly used on a 75m bugcatcher coil? I'm
willing to bet that frequency is lower than 1000000 Hz.

It has no bearing at all on the discussion, ...

Wishful thinking on your part.
..
In fact, a Tesla coil has more in common with a cavity resonator
than it does with a conventional inductor."

A 75m bugcatcher coil has more in common with a cavity resonator
than it does with your lumped circuit inductance.

"at its operating frequency, a Tesla coil is NOT a
lumped-element induction coil".

Neither is a 75m bugcatcher coil.

Everyone in the conversation has been very careful to clearly establish
the boundary conditions that the behavior we are talking about is
significantly below self-resonance, an inductor of compact form factor,
and an inductor of good design.

A 75m bugcatcher coil used on 4 MHz is NOT significantly below
the self-resonant frequency of 9-10 MHz.

THE LUMPED-CIRCUIT MODEL FAILS IN A STANDING
WAVE ENVIRONMENT! In the face of that simple technical fact,
all other discussion is moot. Anyone wishing to validly model a
75m bugcatcher coil used on a mobile antenna is forced to choose
a model that does not presuppose faster than light wave travel
through a 75m bugcatcher coil. It's as simple as that.

Tom, with a straight face, I want you to assert that the RF waves
on a 75m bugcatcher mobile antenna are traveling faster than
the speed of light. If it takes 125 nanoseconds for the forward
current wave to make it from the end of the antenna and back
to the feedpoint, then the lumped-circuit model yields invalid
results. TDR anyone?
--
73, Cecil, W5DXP

Cecil Moore wrote:
A 75m bugcatcher coil used on 4 MHz is NOT significantly below
the self-resonant frequency of 9-10 MHz.

Yes it is, but no so far as to have perfectly equal currents at each
end an zero phase shift in current. It is in the neither land between a
Tesla coil (which is still nothing like my mobile antenna, but at least
getting closer) and a idealized lumped component.

THE LUMPED-CIRCUIT MODEL FAILS IN A STANDING
WAVE ENVIRONMENT! In the face of that simple technical fact,
all other discussion is moot. Anyone wishing to validly model a
75m bugcatcher coil used on a mobile antenna is forced to choose
a model that does not presuppose faster than light wave travel
through a 75m bugcatcher coil. It's as simple as that.

Nonsense. You are ignoring the coupling mechanisim inside the inductor.


Tom, with a straight face, I want you to assert that the RF waves
on a 75m bugcatcher mobile antenna are traveling faster than
the speed of light. If it takes 125 nanoseconds for the forward
current wave to make it from the end of the antenna and back
to the feedpoint, then the lumped-circuit model yields invalid
results. TDR anyone?

They are not travelling faster than light.

What you (and the one or two others who seem to agree with you)
repeatedly ignore or forget is magnetic flux couples one turn to
another. A real inductor is always someplace between the two extremes
of something like a radial mode helice (helically loaded whip) and an
ideal lumped component.

Since you have taken the path of totally forgetting or ignoring flux
coupling, you are reaching incorrect conclusions. Using the Tesla coil
model is a good example.

Everyone is freely admitting there is *some* transmission line effect
going on. There is some distrbuted component (a series of inductors
shunted by capacitors) going on.

Everyone (except you) is being careful to qualify remarks by specifying
the inductor is operating well below self-resonance.

If you weren't so pig-headed you could look at the measured data at:

http://www.w8ji.com/mobile_antenna_c...ts_at_w8ji.htm

....and see that as inductors move towards self-resonance they do begin
to display characteristics of transmission lines.

It's too bad in three years you have claimed others made a measurement
error, when in fact the error is in thinking all of the current in a
loading coil slowly winds its way around turn by turn and the magnetic
field linking turns does not cause charges in other turns to move long
before current traveleing at light speed would wind through the copper
path.

Until you stop, put the beer away, and think about this a while you'll
continue to butt your head up against people who KNOW how inductors
behave.

73 Tom

wrote:

Cecil Moore wrote:
A 75m bugcatcher coil used on 4 MHz is NOT significantly below
the self-resonant frequency of 9-10 MHz.

Yes it is, but not so far as to have perfectly equal currents at each
end an zero phase shift in current. It is in the neither land between a
Tesla coil (which is still nothing like my mobile antenna, but at least
getting closer) and a idealized lumped component.

That's about a 99% change in attitude from when we started this
discussion a couple of years ago. At that time you were claiming
that a 75m bugcatcher coil modeled as a lumped inductance with
EZNEC showed zero change in current magnitude and phase and that
was that. I'm glad to see the truth winning for a change.

I think you are going to have to go a *LOT* lower in frequency
than 4000000 Hz before a 75m bugcatcher coil can be treated as
a lumped-inductance.

THE LUMPED-CIRCUIT MODEL FAILS IN A STANDING
WAVE ENVIRONMENT! In the face of that simple technical fact,
all other discussion is moot. Anyone wishing to validly model a
75m bugcatcher coil used on a mobile antenna is forced to choose
a model that does not presuppose faster than light wave travel
through a 75m bugcatcher coil. It's as simple as that.

Nonsense. You are ignoring the coupling mechanisim inside the inductor.

That coupling mechanism works, at best, a lot
lower than the speed of light and only on the voltage. In
a high-Q inductor, the current is known to lag the voltage
by a phase angle approaching 90 degrees. Do you have any
idea what the velocity factor of a 75m bugcatcher coil is?
I'll bet Reg can tell us.

If the voltage is indeed traveling at the speed of light, the
current is known to lag the voltage by a large number of degrees
approaching 90 degrees for an ideal coil. The laws of physics
strikes again. How can you bring yourself to ignore them? The
voltage cannot travel faster than the speed of light and the
current is lagging by, e.g. 60 degrees. It's hard not to suffer
a 40 nS current wave delay through the coil on 4 MHz. I've told
this to you before but you have avoided the subject like a plague.

What you (and the one or two others who seem to agree with you)
repeatedly ignore or forget is magnetic flux couples one turn to
another. A real inductor is always someplace between the two extremes
of something like a radial mode helice (helically loaded whip) and an
ideal lumped component.

You are talking about the E-field, not the H-field. I can agree with
the E-field propagating at the speed of light but the H-field is
known to lag the E-field by an angle approaching 90 degrees in the
limit for an ideal inductor. Or is that another law of physics that
you simply choose to ignore?

Everyone is freely admitting there is *some* transmission line effect
going on. There is some distrbuted component (a series of inductors
shunted by capacitors) going on.

Are you admitting that a 75m bugcatcher coil can be modeled as a
transmission line with a Z0 and a VF? If so, you are giving up
on your lumped-constant model. Actually, since the lumped-constant
model is a subset of the distributed-network model, the lumped-
constant model is very often wrong when the distributed-network
model is correct. OTOH, it is impossible for the lumped-constant
analysis to be right while the distributed-network analysis is
wrong. So much for your choice of models.

Everyone (except you) is being careful to qualify remarks by specifying
the inductor is operating well below self-resonance.

A 75m bugcatcher coil is NOT operating "well below" self-resonance.
It is operating at 1/2 the self-resonant frequency. If one adds one
foot at a time to the stinger above a 75m bugcatcher coil, at exactly
what frequency does it cease to act like a "velocity inhibited
slow-wave helical" and start acting like a lumped inductance? I
propose that frequency is considerably lower than 1000000 Hz.

If you weren't so pig-headed you could look at the measured data at:
http://www.w8ji.com/mobile_antenna_c...ts_at_w8ji.htm

You measured standing wave current, Tom. Your measurements are
meaningless! Standing wave current has the same constant phase
whether the coil exists or not. Your measurements prove absolutely
nothing that is not already known.
--
73, Cecil http://www.qsl.net/w5dxp

Cecil Moore wrote:
You measured standing wave current, Tom. Your measurements are
meaningless! Standing wave current has the same constant phase
whether the coil exists or not. Your measurements prove absolutely
nothing that is not already known.

Nothing I have said has changed from what I've said for years.

Now you have magnetic fields traveling slower than light speed in air,
and have gone right back to the same nonsense of standing wave current.

Please tell us all how you would measure the "traveling current" while
ignoring "standing wave current".

This ought to be good.....

wrote:
Please tell us all how you would measure the "traveling current" while
ignoring "standing wave current".

Good question. One would ideally do it in a system without
reflections. I am struggling with that concept right now.

The best thought I have come up with so far is simple:

coil
+----////----+
| |
source --- cap
| ---
| |
+--/\/\/\/\--+
resistor

I'm not a measurements guy so I could use some help.

What's wrong with just reporting the measured the delay
through your test coils? Your measured data already
shows the current on one side of the coil to be
different from the current on the other side of the
coil. All we have to worry about now is the delay
through the coils.

If I've got your attention, let me repeat something I
posted days ago.

The forward current through the coil can indeed be assumed
to be equal magnitude at both ends of the coil without much
error. That should make you happy.

The delay through the coil is whatever it is but it is
nowhere near zero. I assume that makes you unhappy.

The reflected current through the coil can indeed be
assumed to be equal magnitude at both ends of the coil
without much error. That should make you happy.

The delay through the coil is whatever it is but it is
nowhere near zero. I assume that makes you unhappy.

The standing wave is the phasor sum of the forward wave
and reflected wave. Its magnitude can vary from about
double the forward current at a current loop to close to
zero at a current node. I assume that makes you unhappy.

The standing wave phase is close to constant and fixed
near zero degrees within 1/4WL of the feedpoint. I assume
that makes you happy.

So three out of six results should make you happy and
that's about all any mere mortal can hope for. :-)
--
73, Cecil http://www.qsl.net/w5dxp

Cecil Moore wrote:


What's wrong with just reporting the measured the delay
through your test coils? Your measured data already
shows the current on one side of the coil to be
different from the current on the other side of the
coil. All we have to worry about now is the delay
through the coils.

What measurement are you talking about? The one I did over two years
ago that has been up on my web site since that time? Something on a
bench?

wrote:

That is incorrect for the conditions we are outlining, and it is
misleading Cecil. It has him lost in a world of reflections. You have
gone outside the limits of the model by assuming, incorrectly, the
inductor has no or little flux linkage from end-to-end and has large
stray capacitance to the outside world compared to load impedance. The
conductor used to build a inductor does not have current slowly winding
its way along that path.

There is no virtually no difference in phase delay in current at each
end of a relatively compact inductor. It is very easy to measure that.
It also have very little group delay compared to the group delay one
would expect from a transmission line or antenna the same length. I
know that because I have measured it hundreds of times.
(snip)

Real world inductors cover a wide range of construction from tiny
(with respect to wavelength) units that have tight flux linkage
between all turns, to extended things that fade into slow wave, high
inductance transmission lines (think of a straight conductor with
ferrite beads strung on it. Any discussion of inductors and waves
needs to either select an example inductor for discussion, or remain
general enough to cover anything that might be called an inductor.

Or else, endless and pointless arguments will ensue.

John Popelish wrote:
Any discussion of inductors and waves needs to either
select an example inductor for discussion,

e.g., 75m bugcatcher mobile loading coil.

or remain general enough to
cover anything that might be called an inductor.

e.g., Maxwell's equations. Certainly not a lumped-circuit
model that presupposes that EM waves travel through anything
and everything faster than the speed of light.

Or else, endless and pointless arguments will ensue.

Yep, notice how the inductors that Tom is talking keep
getting smaller and smaller with time. Pretty soon they
will indeed be point-sized inductors. :-)
--
73, Cecil http://www.qsl.net/w5dxp