RadioBanter - Current across the antenna loading coil

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Current across the antenna loading coil - from scratch

John Popelish wrote:

If we assume the coil is an idealized lumped inductance with no stray
capacitance at all (not a real inductor) then it would have the same
instantaneous current at each end and that current would be zero, since
it has zero size. In other words it would fit entirely in the point
that holds the node.

Real inductors with stray capacitance and imperfect magnetic coupling
for all parts of its internal current path, would have a phase shift in
the current at opposite ends, so they would have current at their ends
that was 180 degrees out of phase, if they were centered on the node
points. For half of each cycle, current would be entering each end, and
for the other half of each cycle, current would be leaving each end.
Both those currents would detour out the sides f the inductor into
displacement current through the stray capacitance of the surface of the
inductor to its surroundings.

I think (with very little actual knowledge of the software) this
conceptual model is how EZNEC handles current through a modeled inductor
and how it can have different currents at the inductor ends, without
being aware of whether those currents are driven by traveling or
standing waves. It is all based on current through inductor segments
and voltage across capacitive segments. If the segments are small
enough, it is a good approximation of a distributed solution.

There are two ways of modeling an inductor in EZNEC. One is by using an
inductive "load". This is a pure lumped inductance, which takes up zero
physical space and whose currents are equal at its two terminals. It
does not couple or react at all to its surroundings other than via its
terminals, and its voltage-current characteristics are dictated by that
of a pure inductance, v = L di/dt. For a number of reasons discussed
many times here, this isn't a good model for many or most typical
loading coils.

The other way of modeling an inductor in EZNEC is by making it from
conductors -- "wires" -- arranged in a polygonal helix. (EZNEC v. 4.0
provides an automated way to generate this structure.) These wires are
treated exactly the same as all other wires in the model. As long as the
turns aren't too close together (conservatively, closer than several
wire diameters, but in practice good results are usually obtained with
spacing as close as one diameter air space between wires), it does a
very good job of calculating the inductor currents and radiation. (It's
a little generous about loss if the turns are close because it doesn't
account for proximity effect.)

EZNEC calculates the total current by first calculating the self and
mutual impedances of every segment in the model from a fundamental
equation, then using Ohm's law to find the total current in each segment
from those impedances and the voltages from the user specified
sources.(*) It's not aware of traveling or standing waves. The presence
or absence of standing waves -- that is, a changing magnitude of current
with position -- can be seen by viewing its output. Displacement current
is a consequence of mutual coupling between segments -- in a dipole, the
dominant coupling is to the other half of the dipole, and in a grounded
monopole, to ground. However, each segment couples to every other, even
on its own wire, and it's this coupling which brings about the current
distribution that ultimately occurs.

EZNEC deals only with total currents and makes no effort to detect, use,
or break up total current into individual traveling waves. It isn't
aware of whether currents are "driven by traveling or standing waves" if
for no other reason that no currents are ever "driven by" traveling or
standing waves. Voltage differences cause currents which can be
described as traveling waves. When multiple traveling waves are summed
to find a total current, the amplitude of the sinusoidal current varies
with position along the line, and this envelope is called a "standing
wave". A standing wave is simply a description of the magnitude
distribution of the total current along a wire or transmission line. It
doesn't drive or cause anything -- it's a description of an effect, not
a cause. All the fuss about standing waves is a diversion which confuses
the issue and deflects attention from the salient issues involved in
understanding the topic under discussion.

(*) This is a simplified explanation. For details, see Part I of the
NEC-2 manual.

Roy Lewallen, W7EL

Current across the antenna loading coil - from scratch

This is freakin unbelievable.
You think you are making fool of me and rest of us? You are not answering
questions, nor engaging in the exchange. You keep pulling out crap, like
first the current is equal, then
"" I can change current difference at each end of the inductor all over
the place depending on the design of the loading coil, with NO change
in the loading coil position or antenna lengths."

You are getting tangled in your own webs!!!
Tell us what is wrong with W9UCW setup and results. Where did he screw up,
what is wrong, and show what you have measured in THE SAME type of setup.
Not freakin W8JI coils, not at the base, no weird frequency, not twist and
dance.
Just take 40m shorted vertical, make it resonant with DECENT coil like he
has about 2/3 up the mast, stick the RF ammeters at both ends and give us
the readings. You have the pictures, you should be able to replicate the
setup.
Then you tell us that the current is the same at both ends, show us the
pictures and describe your setup, meters, frequency and results.
This goes for the rest of the "gurus" that insist on the same.
Then model the loading coil as a solenoid or loading stub of same inductance
in EZNEC and show us what you get. Cecil did it, and the silence is
deafening!!! Can you explain what is "wrong" with Cecil's examples?

Looks like Belrose should get another pHDuuhh for starting all this
misconception and misinformation in ham literature. Pathetic is that some of
the "gurus" that should know better, are on the same bandwagon to la-la
land.
Stop crap and twist and dance, answer the freakin questions or say nothing.
We are not idiots that you BS with "you don't know what I mean by
impedance".
So what happened to impedance? Now you know what it is, or is pink electron
displacement capacitance current phasor phase mumbo jumbo?

wrote in message
ps.com...

Yuri Blanarovich wrote:
Let's back off one more giant step back to measurements. Show where
W9UCW
was "cheating" in his test setup, pictures and comments at
http://www.k3bu.us/loadingcoils.htm
where he shows clearly that RF current drops significantly across
(through)
the loading coil, just like it drops across (through) the resonant
antenna
(piece of wire or tubing) from max at the base, to zero at the tip.

Displacement currents in the inductor and the very high reactance of
the very short antenna above the coil explain current difference.

Current cannot vanish Yuri. It has to have an alternative path.

Have you heard of standing waves?

I can change current difference at each end of the inductor all over
the place depending on the design of the loading coil, with NO change
in the loading coil position or antenna lengths.

That is the progress, first current can't change, now you can make it.

It is the theory you have, that the current is tied to the "missing
degrees", that is wrong.

Without displacement currents there is no current difference at each
end of the coil, it is not caused by "missing degrees. It is caused by
the capacitance above the coil being very low and the capacitance of
the coil to the outside world being much larger. The current is not all
gone in the first few turns either. It is a series reactance/shunt
reactance problem.

73 Tom

PRICELESS!!!!!
So WHAT IS THE CURRENT AT THE TOP OF THE RESONANT 90 deg (any) VERTICAL?
Same as at the base, because "Current can not vanish Yuri"?
You are jerking our chain or have a real problem.

Suggestion: do some reading on impedance, resonance, standing waves, current
and voltage distribution along the antennas, and look at the current curves
in books and as produced by EZNEC. Looks like you have no clue how antennas
work.

You can have another "last word" that will "show" that you "know" what you
are talking about.

73 Yuri

Current across the antenna loading coil - from scratch

Roy Lewallen wrote:
EZNEC deals only with total currents and makes no effort to detect, use,
or break up total current into individual traveling waves.

Then, without effort, EZNEC accurately reports the presence
of traveling waves or standing waves as can be seen from
the graph of the EZNEC results at:

http://www.qsl.net/w5dxp/travstnd.GIF

The graph on the left is for traveling wave current. Its
magnitude is fixed and its phase varies with wire length.
Traveling wave phase can be used to determine the phase
shift through the wire (or through a coil).

The graph on the right is for standing wave current. Its
phase is fixed and its magnitude varies with wire length.
Standing wave magnitude can be used to determine the phase
shift through the wire (or through a coil) by taking the
arc-cosine of the magnitude.
--
73, Cecil http://www.qsl.net/w5dxp

Current across the antenna loading coil - from scratch

Yuri Blanarovich wrote:

Just take 40m shorted vertical, make it resonant with DECENT coil like he
has about 2/3 up the mast, stick the RF ammeters at both ends and give us
the readings. You have the pictures, you should be able to replicate the
setup.

What is it you are after?

I already posted, years ago, measurements at:

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

Then you tell us that the current is the same at both ends, show us the
pictures and describe your setup, meters, frequency and results.

I think what is happening here is you are getting angry and not paying
attention to what people are saying. I've already said it is possible
to have different currents at each end of a loading coil.

What I disagree with you about is you seem to attribute that difference
to some magical property related to the distribution of current based
on electrical degrees the loading coil replaces or standing waves, and
that is very simply and clearly wrong.

Current cannot "drop" or be "dropped". It can be divided between paths,
but it cannot vanish into thin air. The mechanism that allows current
to change in an antenna is displacement current, and it comes from
capacitance.

The only thing wrong with Barry's setup is he uses large meters
compared to the size of the coil, and they are invasive. The meter
requires cutting the leads and adding a fairly large bulk into the
system. I'd never use thermocoupler meters to measure high impedance
systems, magnetic-field coupling systems can be smaller, have less
distributed capacitance, and don't require rerouting leads. Current
transformer systems are also more accurate and can have much better
resolution, and can even be used to determine phase.

Let's not let the measurement method overshadow the real disagreement,
however.

The real disagreement is you seem to be saying the missing area of
antenna replaced by the inductor and standing wave patterns of current
distribution in the antenna are what causes the loading coil to behave
as it does. Barry also proposed that, if I am not mistaken.

That is not true.

The single thing that allows an inductor to have a current difference
and phase shift in current along the coil or at each terminal is the
capacitance of the coil to the outside world. That is why we would have
to be very careful NOT to disturb the coil by mounting other large
measurement devices on the coil.

This goes for the rest of the "gurus" that insist on the same.

The "gurus" you despise go back to Maxwell, who described displacement
current:

http://maxwell.byu.edu/~spencerr/websumm122/node72.html

The term displacement current is not an invention of those you call
"gurus". It is part of physics dating way back to the 19th century.
THAT is why so many people are trying to tell you about displacement
currents, it isn't to make you feel bad.

You have to include displacement currents in any model, or you cannot
have a current taper along the length of a conductor.

Then model the loading coil as a solenoid or loading stub of same inductance
in EZNEC and show us what you get. Cecil did it, and the silence is
deafening!!! Can you explain what is "wrong" with Cecil's examples?

Sure. His explanation of what is happening and the fact he picked a
very special conditions just to satisfy a twisted theory. Roy showed in
his models why Cecil's conclusions were wrong. Practical measurements
will show the same thing.

The ONLY thing that allows a conductor to have current taper along its
length is displacment current. That is a function of the capacitance
from that conductor to the world around that conductor compared to the
impedance presented by the system beyond that point. It is NOT
determined by standing waves. It is not determined by "missing length
replaxed by coil".

Looks like Belrose should get another pHDuuhh for starting all this
misconception and misinformation in ham literature. Pathetic is that some of
the "gurus" that should know better, are on the same bandwagon to la-la
land.

I'm not sure what motivates you to attack everyone, but at least you
universally seem to hate almost everyone. Jack Belrose is a great guy
and has contributed a great deal with his work. If you finmd something
wrong with what he is saying, tell us what it is. Don't attack the
person, point out the error.

Stop crap and twist and dance, answer the freakin questions or say nothing.
We are not idiots

I suppose everyone has a right to their own opinions on that topic.
I've done my best to answer the questions. I hope this post helps
clarify things. Calm down, there is no need to get upset.

Did this help answer your questions?

73 Tom

Current across the antenna loading coil - from scratch

wrote:
I already posted, years ago, measurements at:

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

Those are RMS standing wave measurements. To see what is wrong
with using RMS standing wave measurements please see:

http://www.qsl.net/w5dxp/travstnd.GIF

I think what is happening here is you are getting angry and not paying
attention to what people are saying. I've already said it is possible
to have different currents at each end of a loading coil.

And there phase information in those standing wave current
magnitudes. There is no phase information is standing wave
current phase.

What I disagree with you about is you seem to attribute that difference
to some magical property related to the distribution of current based
on electrical degrees the loading coil replaces or standing waves, and
that is very simply and clearly wrong.

No, it is your misconceptions about standing wave current
that are very simply and clearly wrong.

Current cannot "drop" or be "dropped".

RF current drops with the attenuation factor, just like RF
voltage does. Clinging to the lumped circuit model
presuppositions is what causes you to make silly assertions
like the above. Standing wave current periodically drops
to zero in unterminated transmission lines.

The single thing that allows an inductor to have a current difference
and phase shift in current along the coil or at each terminal is the
capacitance of the coil to the outside world.

Is capacitance to the outside world also what allows a wire
to have zero current at one point and two amps of current
90 degrees away. Of course not! The degrees of delay through
the coil is primarily responsible for the difference in
current. That, and where it is places on the standing wave
current curve.

You have to include displacement currents in any model, or you cannot
have a current taper along the length of a conductor.

We are talking about displacement current to earth ground and
there is zero displacement current to the outside world ground
yet there's SWR current taper on coaxial transmission lines.
Maybe it's time for you to learn how to add phasors?

Sure. His explanation of what is happening and the fact he picked a
very special conditions just to satisfy a twisted theory. Roy showed in
his models why Cecil's conclusions were wrong. Practical measurements
will show the same thing.

Roy used standing wave current phase to try to measure the
delay through a coil. That's an invalid measurement. None of
my conditions are special. They just seem special to your
lumped circuit model. The distributed network model works
for all conditions.
--
73, Cecil http://www.qsl.net/w5dxp

Current across the antenna loading coil - from scratch

Roy Lewallen wrote:
Jack Belrose, VE2CV, is a highly respected engineer and scientist with
an extensive and distinguished professional history.

So are a lot of people who disagree with you.

No one is always right, ...

You have known for a year now that standing wave current phase
cannot be used to determine the delay through a coil yet you
continue to post those invalid results. Guess you are proof
of your own statement.
--
73, Cecil http://www.qsl.net/w5dxp

Current across the antenna loading coil - from scratch

Tom, W8JI wrote:
"The ONLY thing that allows a conductor to have current taper along its
length is displacement current."

In a-c circuits, added to ordinary conduction current there is
displacement current, at right angles to the direction of propagation,
determined by the rate at which the field energy changes.

Also at right angles to the direction of propagation, and determined by
the rate at which energy changes, there is a changing magnetic field, in
addition to the changing electric field. Together the electric and
magnetic fields exchange energy and produce radiation.

Displacement current which is the a-c current through a capacitor, that
has no d-c conduction, is not the"ONLY" thing that allows a conductor to
have a current taper along its length.. A conductor can lose energy
through dissipation and radiation forever, not just relocate it
temporarily through storage in a reactance.

The dissipation line at the end of a rhombic antenna does not handle the
entire output of the transmitter at its other end. Most of the energy is
already radiated by the time it reaches the dissipation line.

Best regards, Richard Harrison, KB5WZI

Current across the antenna loading coil - from scratch

Cecil Moore wrote:

We are talking about displacement current to earth ground and
there is zero displacement current to the outside world ground
yet there's SWR current taper on coaxial transmission lines.
Maybe it's time for you to learn how to add phasors?

Cecil,

Sorry, you cannot pick and choose which displacement currents to consider.

It might be helpful to go back to review the fundamentals of Maxwell's
equations, including the continuity equation for current, before making
these inane comments.

73,
Gene
W4SZ