RadioBanter - Current across the antenna loading coil

RadioBanter (https://www.radiobanter.com/)

- Antenna (https://www.radiobanter.com/antenna/)

- - Current across the antenna loading coil - from scratch (https://www.radiobanter.com/antenna/91163-current-across-antenna-loading-coil-scratch.html)

Current across the antenna loading coil - from scratch

Tom Donaly wrote:
Not everyone is happy with the term "displacement current." Albert
Shadowitz, in his book _The Electromagnetic Field_, has a chapter
entitled "The So-called Displacement Current." The term isn't in
the index to Feynman's _Lectures on Physics_. (At least I couldn't
find it.) All that is academic to the fact that AC current seems to
be able to make its way through a capacitor with no more opposition
than the capacitive reactance. Fortunately, no one on this
newsgroup has any objection to the way the term is commonly used.

Here's an associated quote from "Electromagnetic Engineering"
by R.W.P King: "an adequate representation of the reactance
of a coil with a nonuniformly distributed current is NOT
POSSIBLE in terms of a coil with a uniform current [a lumped-
element inductance] connected in parallel with a lumped
capacitance."
--
73, Cecil http://www.qsl.net/w5dxp

Current across the antenna loading coil - from scratch

Cecil Moore wrote:

Gene Fuller has kindly explained the difference but W8JI and W7EL
seemed to have ignored his explanation.

Cecil,

Give it up on this line of baloney. There is not the slightest bit of
disagreement on the nature of traveling waves and standing waves.

The only person who was ever appeared to be confused was you. I am happy
that you seem to now have at least partial understanding.

73,
Gene
W4SZ

Current across the antenna loading coil - from scratch

Gene Fuller wrote:
"This is incorrect, and even Terman never said such a thing."

I had written:
"Displacement current which is the a-c current through a capacitor, that
has no a-c conduction, is not the "ONLY" thing that allows a conductor
to have a current taper." It was Tom, W8JI who shouted: "The ONLY thing
etc." I just said displacement current is NOT the only thing. Energy
level often declines between ends of a wire or coil due to losses from
radiation or dissipation in the wire or coil. Tom is mistaken.

I don`t find the subject of "displacement current" listed in my Terman`s
index. I think its definition is accepted. but I gave mine in case
someone did not understand what it is.

J.C. Maxwell unlocked the secret of radiation when he speculated
displacement current would produce magnetic lines of force the same as
conduction current does, thus a traveling E-field produces an H-field
and vice versa. It`s been proved correct.

Terman writes on page 1 of his 1955 edition:
"Electrical energy that has escaped into free space exists in the form
of electromagnetic waves. These waves, which are commonly called radio
waves, travel with the velocity of light and consist of magnetic and
electric fields that are at right angles to each other and at right
angles to the direction of travel."

Terman writes on page 866 of his 1955 edition in his chapter on
"Antennas":
"A wire antenna is a circuit with distributed constants; hence the
current distribution on a wire antenna that results from application of
a localized voltage follows the principles discussed in Chapt. 4,
(titled"Transmission Lines") and depends upon the antenna length;
mesured in wavelengths; the terminations at the ends of the antenna
wire; and the losses in the system."

Nothing I wrote conflicts with Terman. That`s not the kind of fool I am.

Best regards, Richard Harrison, KB5WZI

Current across the antenna loading coil - from scratch

Yuri Blanarovich wrote:
Check my article that describes the controversy, shows some proof of reality
and then efforts of the "gurus" to deny it and "reason" why it can't be so.
http://www.k3bu.us/loadingcoils.htm

Yuri,

I know you aren't going to like to hear this, but your article
incorrectly claims the current difference (you call it current drop) is
related to the electrical degrees the coil replaces.
That is not accurate.

ON4UN's book was initially incorrect.

Consider a short vertical antenna. If the current is uniform through
toploading, radiation resistance is higher and current lower throughout
the radiator.

If it is base loaded, current becomes nearly triangular in
distribution. Current into the vertical actually doubles so we have the
same number of ampere-feet. It always requires the same number of
ampere feet to radiate the same power as EM radiation.

The job of the inductor in either system is simply power factor
correction, to bring voltage and current into phase. We have a large
voltage drop across the coil, but current does not change. phase shift
and delay of current through the inductor will also be very small, zero
in a perfect coil.

That is in an ideal antenna with very small stray capacitance to the
outside world compared to the antenna area above the coil.

If we have a physically large coil, the coil MIGHT have significant
capacitance compared to the antenna area above the coil. In this case
there would be a difference in current between the bottom and top
terminal of the coil, and there would be phase difference in the
current entering and leaving the coil, but it is a result of current
being shunted off through displacement currents.

The exact amount would depend on the physical size of the coil and the
capacitance compared to the antenna above the coil.

There is not any magic to any of this, and we don't need to have
standing waves. It is incorrect to consider the coil behavior and
antenna currents by making the coil "act like" it has the missing
electrical dgrees or replaces a section current curve in the antenna.

I can have one antenna and use a good coil design that has essentially
no current difference at each terminal, and replace it with a very
large (or poorly designed) diameter coil that has large differences in
current at each end. Probably the ultimate in poor coil design for base
loading is a linear loading system or stub, while the best would be a
compact coil with nearly equal diameter to length.

The very fact we can change distribution all over the place with only a
change in loading inductor design proves your theory incorrect.

Please try to not extract certain sentences from long explainations to
distort the overall picture of what really happens, and of what I am
describing.

The fact is, we cannot model or predict the behavior of a loading
system without knowing the displacement currents. Neither wave theory
nor "missing antenna length" theory will paint the correct picture of
what is going on, and neither will give an accurate answer to a wide
variety of real world systems.

By the way, this did not start with Belrose and it is not a QST or
Handbook problem. The Antenna Engineering Handbook by Jasik and dozens
of other college or engineering textbooks all deal with the problems
the same way. If you are looking to libel anyone, you need to go all
the way back to James C. Maxwell in the 19th century. It was before the
Civil War that the "big error" you and Barry found started.

I guess it all comes down to if Barry and Yuri are right, or if nearly
every professor, scientist, and engineer from Maxwell to today are
correct. I can measure ANY antenna and prove things behave as I
described. Can you do the same?

73 Tom

Current across the antenna loading coil - from scratch

Mike,

The question changes continuously. As soon as one myth is exploded Cecil
slides right into another.

The original topic dealt with currents in a loading coil for a mobile
antenna. However, the technical part of that discussion ended a long
time ago. Only the sniping remains.

73,
Gene
W4SZ

Michael Coslo wrote:
Not that I could fan the flames any more anyhow, but just what was the
original discussion about anyhow?

As in Cecil says what, and those disagreeing with him say what?

I'm curious how something that doesn't seem that complex can
generate so many weeks of acrimony and vitriol! I don't know the answer
- but then again, I'm not really sure what the question is. But I do
know where to look it up....

- 73 de Mike KB3EIA -

Current across the antenna loading coil - from scratch

Gene Fuller wrote:

Cecil Moore wrote:
Gene Fuller has kindly explained the difference but W8JI and W7EL
seemed to have ignored his explanation.

Give it up on this line of baloney. There is not the slightest bit of
disagreement on the nature of traveling waves and standing waves.

On the contrary, you must not have read W7EL's recent posting where
he again presented his coil delay "measurements" using the standing
current phase as a measurement reference. Remember, the current you
said contains no phase information? Maybe you should share your
knowledge with W7EL?

The only person who was ever appeared to be confused was you. I am
happy Regarding the cos(kz)*cos(wt) term in a standing wave:

When you made your posting, you reinforced my argument better
than any other reference. I am very happy with your posting
and cannot thank you enough. I will continue to use it as
one of my best references for the invalidity of W7EL's coil
delay measurements.

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

Current across the antenna loading coil - from scratch

Gene Fuller wrote:
The question changes continuously. As soon as one myth is exploded Cecil
slides right into another.

Would you rather discuss something for which no disagreement
exists, or discuss the real point of disagreement?

It is apparent to me that the problem is not with coils. The
same point of disagreement exists whether a coil is present
or not. That point of disagreement involves standing waves,
not coils. Take away the coil and the misconception still
exists when discussing only a straight wire.

W8JI is still maintaining that the current cannot drop to
zero at a standing wave current node when the forward
current and reflected current are of the same magnitude.

That is obviously the point of misconception and it has
been clear ever since he refused to discuss zero amps
at the bottom of the coil and 2 amps at the top of the
coil. Replace the coil with a straight wire and W8JI
still has that same misconception. So you see the coil
is not the source of the disagreement.
--
73, Cecil http://www.qsl.net/w5dxp

Current across the antenna loading coil - from scratch

Hi Richard,

My point is in complete agreement with Tom, W8JI. The only thing that
allows "current taper" is displacement current.

Conservation of charge is one of the most fundamental laws in nature.
The historical basis for referring to storage of charge in a capacitor
as "displacement current" is considered incorrect today. However, the
underlying physical science remains intact. "Current taper" means that
charge stops moving as current and becomes stored in a capacitor.
(Everything has capacitance; there is no requirement for a little lump
with two leads on it.) It is this charge storage phenomenon that is
known as displacement current.

Energy levels and losses have nothing to do with this question.

73,
Gene
W4SZ

Richard Harrison wrote:
Gene Fuller wrote:
"This is incorrect, and even Terman never said such a thing."

I had written:
"Displacement current which is the a-c current through a capacitor, that
has no a-c conduction, is not the "ONLY" thing that allows a conductor
to have a current taper." It was Tom, W8JI who shouted: "The ONLY thing
etc." I just said displacement current is NOT the only thing. Energy
level often declines between ends of a wire or coil due to losses from
radiation or dissipation in the wire or coil. Tom is mistaken.

Current across the antenna loading coil - from scratch

Cecil,

Your own calculations would appear to support Tom's assertion.

I believe after a long series of EZNEC models and RRAA messages you came
to the conclusion that the 75 meter bugcatcher coil at 4 MHz had a
traveling wave phase shift of around 10 degrees. I won't get into the
discussion about whether this has any bearing on a standing wave
antenna; let's just assume it does.

This same coil resonated an antenna with a whip length of 10 feet or so.
A quarter wavelength at 4 MHz is around 60 feet. The phase shift that
could be attributed to the whip is therefore around 15 degrees. The
phase shift of the missing 50 feet of wire for a plain quarter wave
antenna would be around 75 degrees.

Is 10 degrees the same amount as 75 degrees? Is this problem stated
incorrectly? Why is Tom wrong?

73,
W4SZ

Cecil Moore wrote:
wrote:

I know you aren't going to like to hear this, but your article
incorrectly claims the current difference (you call it current drop) is
related to the electrical degrees the coil replaces.
That is not accurate.

The current drop in a wire with standing waves is indeed related
to the number of degrees occupied by the wire. Why shouldn't the
same thing be true for a coil?