Current through coils
 

For what it's worth --

I've avoided this discussion for two primary reasons. One is that it
saddens me to see this "controversial" topic being brought up yet again
after having been discussed at great length a number of times before.
There's no reason I can see for it other than Cecil's religious zeal and
dogged determination.

The second reason is that I hate to be reminded how easily some people
can be manipulated to wholly ignore well known physics and embrace
alternate theories which are devoid of the ability to produce
predictions or numerical results to demonstrate their validity. We live
with it every day in our ordinary lives, seeing the astrology column in
the newspaper (and learning that it's been a driving force behind top
level government decisions), homeopathic remedies at the drug store, and
so forth. It's hard to see it keep surfacing here also.

Fortunately, some very good, honest, and knowledgeable people have been
doing a very good job of presenting the facts. These include Tom, W8JI;
Ian, G3SEK; Wes Stewart, N7WS; and Gene Fuller, W4SZ. Anyone who is
truly interested in understanding the topic (which is fundamentally very
simple) would do well to read what those folks have written and are
writing. Because they're dealing with facts and well known phenomena,
they can back up what they say with numbers and the ability to explain
the phenomena you see.

I'd like to add one note to particularly pay attention to Ian's postings
on March 6 and 8 explaining the difference between an inductor and
inductance. When I and others have spoken of a "physically small coil"
we're talking about something resembling a pure inductance. As Ian and
others have said, the first step in understanding this topic is to
understand how the idealized component works. Only after that can you
add the effects of coupling to external fields, which explain the
current difference you typically do see between the ends of a real
inductor loading an antenna. The red herring in this discussion is the
attempt to attribute this effect to something fundamental about
inductances, rather than the effect of external fields interacting with
a real inductor of significant physical size. Part of this is
understandable, because an inductor can be surprisingly small and still
exhibit substantial current difference from one end to the other when in
the field of a short antenna, because the field from the antenna is very
intense. The field from the inductor is also quite large, making
noticeable capacitive coupling nearly always present, which also
provides a path for displacement current. So it's somewhat natural to
assume that the current difference between ends is more fundamental than
it really is. But the argument has been taken well beyond reason by the
zeal to explain every phenomenon by means of reflecting waves and
packets of average power. It's not necessary at all, and all that does
is to provide a confounding factor to obscure the simplicity of what's
really happening. Since the basis for this approach is largely contrived
and devoid of the ability to produce quantitative results, it's easy to
make pronouncements which can't be verified.

It's pretty obvious that objects in motion come to rest naturally
without any external force. You reach this conclusion by failing to
separate the external force of friction from the inherent inertia of the
object. The problem here is exactly the same -- people are failing to
separate the phenomenon of external coupling from the inherent
properties of inductance, and concluding that observed current
differences between the ends of loading inductors are caused by some
inherent property of inductance.

I can imagine people arguing about the basic property of objects to
spontaneously come to rest long after Newton proved it otherwise.
Actually, I wouldn't even be surprised if there's some Newtonian Cecil
who's still arguing about it.

Roy Lewallen, W7EL

Current through coils
 

"Roy Lewallen" wrote:
A physically small inductor such as a toroid will
function exactly the same in both cases. (I limited it to being
physically small, since a larger inductor will interact with the
antenna's field.)

You're missing the point, Roy. It indeed does function the
same way in both cases but if there are reflections present,
your lumped circuit analysis rules are known to fail.Your
analysis of both cases may be equally wrong in both
cases.

What is the traveling wave current delay through the coil in
degrees? That's easy to measure. That current delay is the
degrees that the coil supplies to the antenna. You can ignore
any measurements involving standing wave current as being
essentially meaningless. What is important is the traveling-
wave current delay through the coil. Please measure it and
report what it is for your 'physically small toroid'.

Your lumped circuit analysis pre-assumes a zero delay
through the coil. That delay is certainly not zero in the real
world.
--
73, Cecil, W5DXP

Current through coils
 

wrote:
1.) Cecil wants everyone to start using reflection wave models to
analyze every antenna system in the world.

No, I simply want you and others to stop using a known invalid
model for every standing wave antenna system in the world.
This is a quote from the first web page below: The capital
letters are where the author used bold italics for emphasis.

"... - no wave interferrence and no standing waves can be
present on lumped elements. The problem has been that many
experimenters working with self-resonant helices have
PURSUED THE CONCEPT OF COIL SELF-
CAPACITANCE WITHOUT REALLY UNDERSTANDING
WHERE THE NOTION COMES FROM OR WHY IT WAS
EVER INVOKED BY ENGINEERS. For that, they will have
to go read R.W.P. King's wonderful old book, "Electromagnetic
Engineering, McGraw-Hill, 1945. ... On page 465, the Harvard
Professor points out that, for coils whose *wire length* exceeds
1/6 wavelength, ...'an adequate representation of the reactance
of a coil with a nonuniformly distributed currentr is NOT
POSSIBLE in terms of a coil with a uniform current [a lumped
element inductance] ...' Period. Resonant FIELDS present
surprises to engineers with limited training."

Certainly sounds like he is talking about you, Tom. "Electronic
Engineering" was written before you were born. Why are you
ignorant of the technical facts presented in it?

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

http://www.ttr.com/TELSIKS2001-MASTER-1.pdf

The .pdf paper is a pier-reviewed publication by the IEEE. Here's
what it says about the model you have chosen to use.

"Of course, the uniform current assumption has no validity for coils
operating anywhere near self-resonance!"

"The failure of any limped element circuit model to describe the
real world lies at its core inherent *presupposition*: the speed of
light is presumed to be infinite in the wave equation. ... Consequently,
lumped element circuit theory does not (and cannot) accurately
embody a world of second order partial differential equations in
space and time."

"The concept of coil "self-capacitance" is an attempt to circumvent
transmission line effects on small coils when the current distribution
begins to depart from its DC behavior."

"There are a great number of formulae for coil self-capacitance.
None are of particular value for quarter-wave helical resonators
anywhere near the 90 degree point."

"The delusion is that the short coil is then made to operate in the
lumped element regime ...".

That you refuse to give up on an invalid method in the face of
overwhelming evidence is amazing.

What he wants me or others to do is a moot point.

Afraid of what you will find? The first web page above says:
"Lumped circuit theory isn't absolute truth, it's only an analytical
theory - and in these resonators we have the case where this
sophmore theory fails experimentally." Do the experiment, Tom,
and discover exactly how sophmorish you are being.

I am concerned about the commonly held but very incorrect view that
current travels through an inductor turn-by-turn, and that a loading
inductor somehow shifts the phase of and/or level of current to "make
up for missing degrees".

Tom, that's what any matching network does. Loading coils are no
exception.

My only concern is people not understanding how an inductor and short
antenna actually behaves.

I am concerned about you not understanding, Tom. Don't
you believe the information posted on those web pages above. Don't
you think a peer-reviewed IEEE publication that disagrees with you
is worth a second thought from you. Don't you think ignoring the
knowledge published by experts in the field is a little naive?
--
73, Cecil, W5DXP

Current through coils
 

"Roy Lewallen" wrote:
I've avoided this discussion for two primary reasons. One is that it
saddens me to see this "controversial" topic being brought up yet again
after having been discussed at great length a number of times before.
There's no reason I can see for it other than Cecil's religious zeal and
dogged determination.

The reason is that you are wrong and I have provided expert testimony
that you are wrong. I'm trying to stop you from speading false information
so don't fault me for that. The fact that you refuse to have a technical
discussion with me in spite of the numerous expert postings that
prove you are using an invalid model, speaks volumes. The results
of the spreading of lumped-circuit analysis myths is that you are
hoodwinking the uninitiated.

Fortunately, some very good, honest, and knowledgeable people have been
doing a very good job of presenting the facts. These include Tom, W8JI;
Ian, G3SEK; Wes Stewart, N7WS; and Gene Fuller, W4SZ.

This is an argumentum ad verecundiam, a well known logical
diversion and not a technical argument. I have quoted just as many
experts and you have ignored them. In particular, R.W.P. King is
quoted from "Electromagnetic Engineering": ... for coils whose
*wire length* exceeds 1/6 wavelength, an adequate representation
of the reactance of a coil is *NOT POSSIBLE* in terms of a coil
with a uniform current [a lumped-element inductance]..."

Roy, my 75m bugcatcher coil, made from 44 feet of wire, is more
than 1/6 wavelength of wire. R.W.P. King says your lumped-circuit
analysis is *NOT POSSIBLE*. He used bold print and underlined the
words, *NOT POSSIBLE*. Ignoring the quotations from the true
experts is just going to leave you ignorantly spreading old wives'
tales. Is that really how you want to be remembered here?

Why are all of you alleged "experts" unwilling to discuss technical quotes
like R.W.P. King's above? Are you afraid that readers will discover
your common mistake which Dr. Corum calls "sophomoric"?

As Dr. Corum says: "There are no standing waves on a lumped
element circuit component. (In fact, lumped-element circuit theory
inherently employs the cosmological presupposition that the speed
of light is infinite, as every EE sophomore should know."

Why do you choose to absolutely ignore that technical knowledge?
--
73, Cecil, W5DXP

Current through coils
 

Summary of design of a short loaded vertical antenna.

There is a 90-degree phase shift between the feedpoint and the tip of
the antenna.

With a short antenna most of the 90 degree phase shift is due to the
loading coil which is, in effect, a transmission line.

The transmission line has Zo, velocity, phase-shift and some
attenuation due to radiation resistance plus wire loss resistance.

Radiation resistance and phase-shift are directly proportion to coil
length, as are L and C and wire resistance.

Q = Omega*Total Inductance / Total R as is usual. Bandwidth =
Resonant Freq / Q.

Radiating efficiency takes into account wire resistance below the
coil, coil resistance, resistance of the wire above the coil, plus
ground loss resistance, plus the sum of the three radiation
resistances. All resistances are referred to the antenna feedpoint.

With short coils, radiation resistance of the coil is usually much
less than that due to the length of the wires above and below it. With
a helical antenna, wire loss resistance is always greater than its
radiation resistance.

At low HF, with a good set of ground radials, the loss resistance of
coil wire usually predominates. At high HF, the ground loss usually
predominates but the radiation resistance becomes important.

The whole business is calculable. There are few rules of thumb. The
only thing which is missing is the radiation pattern. If you don't
already know what the radiation pattern is in the vertical plane then
Eznec will attend to that. Actually, in the vertical plane, radiation
is approximately proportional to the cosine of the elevation angle.
The horizontal groundwave is stongest.

Some of the parameters need not be explicitly calculated.

EXAMPLE:

Starting data:
Height of antenna below coil = 2 metres = 79 inches.
Diameter of antenna below coil = 25mm = 1 inch.
Length of antenna above coil = 1 metre = 39 inches.
Diameter of antenna above coil = 10mm = 0.4 inches.
Length of coil = 152mm = 6 inches.
Diameter of coil = 76mm = 3 inches.
Overall antenna height = 3.152 metres = 124 inches = 10.3 feet.
Ground electrode loss resistance = 5 ohms.
Frequency = 3.8 MHz.

Calculated data:
Number of turns on coil = 53
Wire gauge = 13 or 14 awg.
Radiating efficiency = 10 percent.
Loss relative to full-size 1/4-wave vertical = 9.4 dB.
Self-resonant frequency of the coil = 8.2 MHz.
For maximum efficiency the coil is located at 50% of the overall
antenna height.
But there's not much extra loss by using base loading.

For other calculated data use program LOADCOIL which is about 6 years
old and I think I have lost the source code.
----
.................................................. ..........
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
.................................................. ..........

Current through coils
 

wrote in message
oups.com...

Cecil Moore wrote:

What is the traveling wave current delay through the coil in
degrees? That's easy to measure. That current delay is the
degrees that the coil supplies to the antenna. You can ignore
any measurements involving standing wave current as being
essentially meaningless. What is important is the traveling-
wave current delay through the coil. Please measure it and
report what it is for your 'physically small toroid'.

Your lumped circuit analysis pre-assumes a zero delay
through the coil. That delay is certainly not zero in the real
world.

The problem with people doing work to verify this is even if several
people measure something, Cecil will ignore results.

I will accept what you find as long as long as the method to
obtain the results is valid.. Roy's earlier measurements are
virtually meaningless since he was measuring standing wave
current which doesn't even flow (phase is constant and
fixed around zero degrees). You guys always seem to
make measurements that support your preconceived
notions and avoid measurements that don't

But you have already started what I am asking, Tom. You
measured a voltage phase shift of 60 degrees through a
100uH coil at 1 MHz. The current is known to lag the voltage
through a coil so the current phase delay is more than 60
degrees. I wouldn't be surprised to see it at 120+ degree
lag in the current. So your own experiment proves you are
wrong. How do you get away with such behavior without
anyone noticing?.

(Hint: there are a handful of knowledgeable lurkers who
have noticed.)

When you measured S12, was the load side of the coil
looking into 50 ohms?

In the web pages I previously posted, R.W.P. King, in
"Electromagnetic Engineering", asserts that you cannot
use a lumped circuit analysis on a coil containing 1/6
wavelength of wire. Your 100uH coil above exhibits
60 degrees of phase shift even for the voltage and that's
1/6 wavelength for voltage - even more for current. The
lumped-circuit model assumes that the voltage is traveling
at an infinite speed, faster than light. Since you believe so
strongly in the lumped-circuit model, wonder why your
measurement didn't reflect that fact? :-)
--
73, Cecil, W5DXP

Current through coils
 

Cecil Moore wrote:
I will accept what you find as long as long as the method to
obtain the results is valid.. Roy's earlier measurements are
virtually meaningless since he was measuring standing wave
current which doesn't even flow (phase is constant and
fixed around zero degrees).

Roy,

Shame on you for measuring current that doesn't flow through a current
transformer.

73 Tom

Current through coils
 

wrote in message
ups.com...
Cecil Moore wrote:
I will accept what you find as long as long as the method to
obtain the results is valid.. Roy's earlier measurements are
virtually meaningless since he was measuring standing wave
current which doesn't even flow (phase is constant and
fixed around zero degrees).

Shame on you for measuring current that doesn't flow through a current
transformer.

Standing wave net current doesn't flow back and forth
along the wire. That's why they call it a *standing* wave.
Why don't you know that already? At any point on the
wire, the H-fields and E-fields are exchanging energy at
the frequency of operation. That's certainly enough reason
for an inductive pickup to respond.

Why is that a surprise to you or Roy? Because you two
mistakenly thought net standing wave current flows and
ignorantly measured it? All you measured was the
orthogonal exchange of energy between the two fields.
Nothing was moving except the underlying forward and
reflected currents. Isn't this stuff taught anymore?

What have you guys done - gotten together and elected
yourselves into a club of omniscient gurus? Please take
a look at the laws of reflection physics. It appears that
you are ignorant of most of them.
--
73, Cecil, W5DXP

Current through coils
 

Current through coils
 

Cecil,

A few random comments:

* I have done a number of "peer reviews" for IEEE and AIP publications
as well as other publications. I have seen comments from the other
reviewers. In general peer review is better than nothing, but in many
cases it doesn't mean diddly.

* The Tesla coil crowd seems to contain an unusually large fringe. I
know nothing of the authors of your latest bible, but in any case I was
not particularly impressed with their credentials or their paper. I love
the part, "Lumped circuit theory isn't absolute truth, it's only an
analytical theory about lumped models". As if their work is somehow
absolute truth. (Back to the previous bullet: I have never seen any
serious peer-reviewed paper that would contain such a statement.)

* No one is his right mind would think that a Tesla coil with a
gazillion closely spaced turns is equivalent to a bugcatcher coil. No
one should think that an axial mode helical antenna is equivalent to an
ordinary loading coil either.

* You are waaaay too hung up on the subject of standing waves vs.
traveling waves. You may have noticed that the standard treatments of
antennas in texts and other references barely mention the terms. They
merely discuss the actual current in the antenna. The fundamentally
important entity in radiation is accelerated charge, just as Tom noted.
At any point in an antenna, such as the loaded monopole discussed here,
there is simply a current, not a traveling wave or a standing wave. If
you could examine the antenna microscopically at a single point you
would find electrons sloshing back and forth. You could not tell if the
current was represented by a standing wave or a traveling wave. The
standing wave description relates to the overall amplitude
characteristic of the current when you look at the entire antenna. This
amplitude characteristic is certainly important in calculation of
details of the radiation field, but it does not change the fundamental
property of radiation or the physical processes ongoing in the antenna.
It is just plain silly to argue that a standing wave is totally inert
and does not flow back and forth.

* Distributed or network models are mathematically convenient for
treating complex problems. However, they add precisely zero new
information to the underlying physical reality described by Maxwell's
equations. They offer no new physics beyond lumped models. They can be
misapplied just the same as lumped models can be misapplied. It is
generally best to drive a nail with a hammer, but a monkey wrench will
also do the job. It is best to choose the most efficient tool, but that
does not mean others won't work.

73,
Gene
W4SZ


Cecil Moore wrote:
wrote:

1.) Cecil wants everyone to start using reflection wave models to
analyze every antenna system in the world.


No, I simply want you and others to stop using a known invalid
model for every standing wave antenna system in the world.
This is a quote from the first web page below: The capital
letters are where the author used bold italics for emphasis.

"... - no wave interferrence and no standing waves can be
present on lumped elements. The problem has been that many
experimenters working with self-resonant helices have
PURSUED THE CONCEPT OF COIL SELF-
CAPACITANCE WITHOUT REALLY UNDERSTANDING
WHERE THE NOTION COMES FROM OR WHY IT WAS
EVER INVOKED BY ENGINEERS. For that, they will have
to go read R.W.P. King's wonderful old book, "Electromagnetic
Engineering, McGraw-Hill, 1945. ... On page 465, the Harvard
Professor points out that, for coils whose *wire length* exceeds
1/6 wavelength, ...'an adequate representation of the reactance
of a coil with a nonuniformly distributed currentr is NOT
POSSIBLE in terms of a coil with a uniform current [a lumped
element inductance] ...' Period. Resonant FIELDS present
surprises to engineers with limited training."

Certainly sounds like he is talking about you, Tom. "Electronic
Engineering" was written before you were born. Why are you
ignorant of the technical facts presented in it?

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

http://www.ttr.com/TELSIKS2001-MASTER-1.pdf

The .pdf paper is a pier-reviewed publication by the IEEE. Here's
what it says about the model you have chosen to use.

"Of course, the uniform current assumption has no validity for coils
operating anywhere near self-resonance!"

"The failure of any limped element circuit model to describe the
real world lies at its core inherent *presupposition*: the speed of
light is presumed to be infinite in the wave equation. ... Consequently,
lumped element circuit theory does not (and cannot) accurately
embody a world of second order partial differential equations in
space and time."

"The concept of coil "self-capacitance" is an attempt to circumvent
transmission line effects on small coils when the current distribution
begins to depart from its DC behavior."

"There are a great number of formulae for coil self-capacitance.
None are of particular value for quarter-wave helical resonators
anywhere near the 90 degree point."

"The delusion is that the short coil is then made to operate in the
lumped element regime ...".

That you refuse to give up on an invalid method in the face of
overwhelming evidence is amazing.


What he wants me or others to do is a moot point.


Afraid of what you will find? The first web page above says:
"Lumped circuit theory isn't absolute truth, it's only an analytical
theory - and in these resonators we have the case where this
sophmore theory fails experimentally." Do the experiment, Tom,
and discover exactly how sophmorish you are being.


I am concerned about the commonly held but very incorrect view that
current travels through an inductor turn-by-turn, and that a loading
inductor somehow shifts the phase of and/or level of current to "make
up for missing degrees".


Tom, that's what any matching network does. Loading coils are no
exception.


My only concern is people not understanding how an inductor and short
antenna actually behaves.


I am concerned about you not understanding, Tom. Don't
you believe the information posted on those web pages above. Don't
you think a peer-reviewed IEEE publication that disagrees with you
is worth a second thought from you. Don't you think ignoring the
knowledge published by experts in the field is a little naive?
--
73, Cecil, W5DXP