Yuri Blanarovich wrote:
Good point, Richard. Why isn't anyone arguing that the current on
each side of a loading coil in an antenna tuner is equal? It can
easily be proven to be different using a Smith Chart.



I mentioned way back too, question for Rauchians: How come we get RF current
drop across the RF choke, hmmm?
Or Are you going to argue that it is the same at both ends?
Extreme case but proves the point.
Get your "books" out, say it ain't so and look even more foolish.

I like the Hahastick :-) Yea, should have been Hamstick.

Yuri, K3BU.us
Viva Bush!




Since when has anyone claimed it's impossible to make a coil that
has a non-constant current distribution? You guys sure go out of
your way to pat yourselves on the back for proving something no
one has ever argued about. For those who really want to learn
about loading coils on small antennas, go to Tom
Rauch's web page and learn how a real engineer deals with
the problem.
73,
Tom Donaly, KA6RUH

For those who really want to learn
about loading coils on small antennas, go to Tom
Rauch's web page and learn how a real engineer deals with
the problem.
73,
Tom Donaly, KA6RUH


Yea, that current across the coil is constant.
Can you specify what engineering degree Tom has, from what school?

Yuri

Yuri Blanarovich wrote:

For those who really want to learn
about loading coils on small antennas, go to Tom
Rauch's web page and learn how a real engineer deals with
the problem.

Yea, that current across the coil is constant.
Can you specify what engineering degree Tom has, from what school?

Not only that, can he defend this assertion of Tom Rauch in his
response to your posting on eHam.net?

"If you look at HOW an inductor works, the current flowing in one
terminal ALWAYS equals the current flowing out the other terminal."

Has the definition of "ALWAYS" changed while I wasn't looking?????
--
73, Cecil http://www.qsl.net/w5dxp


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"If you look at HOW an inductor works, the current flowing in one
terminal ALWAYS equals the current flowing out the other terminal."

I think that is true. If you define current as electron flow, then the fields
and radiation that a large coil may be subjected to, will not increase or
decrease the number of electrons that the coil contains. As such, the amount
of electrons entering the base of the coil, will equal the same number exiting
the coil, with time displacement.
Consider a large physically long capcitor, with multiple plates. One can use
this as a loading element. There is no electron flow between plates. However
there is "displacement" current between the plates that has no physical
meaning. Now what? The capacitor will be just affected as a coil.
So, from the conservation of electron flow I don't know what to believe.

73 Gary N4AST

"If you look at HOW an inductor works, the current flowing in one
terminal ALWAYS equals the current flowing out the other terminal."

I think that is true. If you define current as electron flow, then the fields
and radiation that a large coil may be subjected to, will not increase or
decrease the number of electrons that the coil contains. As such, the amount
of electrons entering the base of the coil, will equal the same number exiting
the coil, with time displacement.

I think you've just proven that all antennas must have a constant
current distribution on their driven element... the same argument can
probably be made about a piece of straight wire!

More generally: I'd like to propose a thought experiment, which I
think may cause you to reconsider your conclusions.

The experiment: start with a straight length of wire 1/4 wavelength
long (minus a bit) at a frequency of interest. Install it over an
infinite ground plane and feed it at the base. You've got a resonant
"1/4 wavelength" monopole.

I think most people will agree that the net-current distribution in
said monopole is tolerably close to being a cosine function - highest
at the feedpoint, and lowest near the tip.

Mark two positions on the wire, 1/3 and 2/3 of the way along its
length. Consider the three sections of wire to be the "base", "mid",
and "tip" sections.

I think most people will agree that the net currents at the two ends
of the "mid" section are not equal. We haven't changed the
cosine-like current distribution by simply marking the third-of-the-
way points.

Now... take the "2/3" point, and pull it back (or down) towards the
base of the antenna, by some small amount... say, 1% of the length of
the "mid" section. Leave the "1/3" point right where it was. There's
now a small amount of slack in the "mid" wire. Shape the "mid"
section into a small-diameter helix, with uniform spacing between the
turns, so that the helixing of the wire just takes up the slack.

The antenna has now been shortened slightly, and some inductance has
been added to the "mid" section. Add or subtract wire at the end of
the "tip" to bring the antenna back into resonance.

Now... are the net currents at the "1/3" and "2/3" points suddenly
equal? Or, are they still unequal (but perhaps different from what
they were when the mid section was straight)? If unequal, by how much?

Now, continue repeating this process... pull the "2/3" point back
towards the base by the same amount you did before (1% of the original
length of the "mid" section), re-coil the "mid" section into a helix
to take up the slack, adjust the length of the "tip" to re-resonate
the antenna, and re-evaluate the net currents at the "1/3" and "2/3"
points. You can do this "shorten and re-resonate" step a total of 100
times, at which point the "mid" section has no physical length and is
a "pure" inductance. [Let me know what page you find it on in the
Digi-Key catalog, please!]

You may use any strategy you wish for deciding how many turns are in
the helix at each step, and what its diameter is at each step, as long
as you're consistent and as long as all of the slack is used up each
time.

So... we now have a total of 101 sets of measurements... all the way
from "mid is a straight length of wire" to "mid is a pure inductance
having no physical length". We could graph "difference in net current
between points 1/3 and 2/3" on the Y axis, and "number of shortening
steps taken" along the X axis.

Question: exactly how many shorten/re-coil/re-trim steps must we go
through, before the net currents at the two ends of the mid-section /
helix / coil become the same (mathematically identical, assuming zero
resistance in the wire)?

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

Gary,

There is not the slightest bit of mystery in the "conservation of
electron flow". An important relationship in electromagnetics is the
so-called continuity equation. In simple terms this is an expansion of
Kirchhoff's current law. It says that any current imbalance at a point
in space must be compensated by a change in the stored charge at that
point in space. You can see the exact equation in any mid-level text on E&M.

This is how capacitors work. Current flows in but does not pass through
the gap between the plates. Instead, charge is stored on the plates. It
is sometimes convenient to describe this behavior in terms of
displacement current through the gap, but of course no electrons
actually pass between the capacitor plates.

Antennas work the same way. Any change in current along the antenna must
be accompanied by a change in stored charge. The antenna acts as a
capacitor. Everyone talks about high voltage at the tips of a dipole
antenna, but perhaps fewer people understand there is a buildup of
stored charge as well.

73,
Gene
W4SZ

JGBOYLES wrote:
"If you look at HOW an inductor works, the current flowing in one
terminal ALWAYS equals the current flowing out the other terminal."


I think that is true. If you define current as electron flow, then the fields
and radiation that a large coil may be subjected to, will not increase or
decrease the number of electrons that the coil contains. As such, the amount
of electrons entering the base of the coil, will equal the same number exiting
the coil, with time displacement.
Consider a large physically long capcitor, with multiple plates. One can use
this as a loading element. There is no electron flow between plates. However
there is "displacement" current between the plates that has no physical
meaning. Now what? The capacitor will be just affected as a coil.
So, from the conservation of electron flow I don't know what to believe.

73 Gary N4AST

Gene Fuller wrote:
Antennas work the same way. Any change in current along the antenna must
be accompanied by a change in stored charge.

The net (total) current on a standing-wave antenna is the phasor sum
of the forward current and reflected current and can change simply
because it is part of a standing wave. The change in net current at
the tip of a standing-wave antenna simply means that the energy has
moved from the H-field into the E-field.
--
73, Cecil http://www.qsl.net/w5dxp
"The current and voltage distributions on open-ended wire antennas are
similar to the standing wave patterns on open-ended transmission lines ...
Standing wave antennas, such as the dipole, can be analyzed as traveling
wave antennas with waves propagating in opposite directions (forward and
backward) and represented by traveling wave currents If and Ib ..."
_Antenna_Theory_, Balanis, Second Edition, Chapter 10, page 488 & 489


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Cecil,

I cannot speak directly for Tom Donaly, but you and I are about 99% in
DISagreement over physics.

One more time:

Current, charge, voltage, E-field, and H-field are different physical
entities. They are related, but they are not interchangeable.

No amount of E-field, H-field, or voltage can create or destroy charge.
Current is the movement of charge. At any point in space that charge
must either keep moving (Kirchhoff's current law) or it must be stored
(continuity equation). There is absolutely no other choice, period.

Your traveling wave/standing wave model is intuitive, but otherwise
useless. Many authors reference such a model, but no one seems to use it
for serious calculations.

You have started quoting Balanis:

"The current and voltage distributions on open-ended wire antennas are
similar to the standing wave patterns on open-ended transmission lines ...
Standing wave antennas, such as the dipole, can be analyzed as traveling
wave antennas with waves propagating in opposite directions (forward and
backward) and represented by traveling wave currents If and Ib ..."
_Antenna_Theory_, Balanis, Second Edition, Chapter 10, page 488 & 489


I do not have easy access to the Balanis book at this time. Does he go
on to actually perform antenna calculations such as actual current
distributions and radiated fields? I found the table of contents for
this edition of his book, and it appears that Chapter 10 is a chapter on
traveling wave antennas, not basic dipoles. If so, then it is likely
that Balanis is merely trying to tie the entire world of antennas
together to give a warm and fuzzy feeling to the reader.

Every detailed professional treatment of antenna theory and modeling I
have found starts with Maxwell's equations, and quickly gets immersed in
integral equations, Green's functions, and other messy stuff. Why would
people do this if the mere application of a couple of traveling waves
would provide the correct answers?

Do you have a reference to an analytic treatment using the traveling
wave model that could give results comparable to NEC2? If so, I would
sure like to find that reference.

73,
Gene
W4SZ

Cecil Moore wrote:

Gene Fuller wrote:

Antennas work the same way. Any change in current along the antenna
must be accompanied by a change in stored charge.


The net (total) current on a standing-wave antenna is the phasor sum
of the forward current and reflected current and can change simply
because it is part of a standing wave. The change in net current at
the tip of a standing-wave antenna simply means that the energy has
moved from the H-field into the E-field.

You have to use some care in applying the conservation of charge to a
system that includes radiation or other manifestations of displacement
current. Imagine a capacitor with widely spaced plates. Charge flows
into one plate of the capacitor, and an equal amount of charge flows out
of the other plate. You have to include both plates in the system when
counting up the total amount of charge that's conserved. Similarly, in
the case of a radiating coil, you have to count the charge that flows on
all nearby and distant conductors as a result of the (field created by)
the charge flowing on the inductor. That is, some of the charge that
flows into a radiating inductor flows out of other nearby and distant
conductors.

In the absence of radiation, all the charge that flows into an inductor
has to flow out, a point I and (much more eloquently) Ian and others
have tried to make, but which is lost on some of the most vocal
contributors to the newsgroup. This concept doesn't seem to fit neatly
into some of the preconceived theories, so is simply being ignored. In
the end, any theory that truly explains observed phenomena has to work
with physically vanishingly small inductors, for which the currents in
and out must be equal, as well as larger ones.

Roy Lewallen, W7EL

JGBOYLES wrote:
"If you look at HOW an inductor works, the current flowing in one
terminal ALWAYS equals the current flowing out the other terminal."


I think that is true. If you define current as electron flow, then the fields
and radiation that a large coil may be subjected to, will not increase or
decrease the number of electrons that the coil contains. As such, the amount
of electrons entering the base of the coil, will equal the same number exiting
the coil, with time displacement.
Consider a large physically long capcitor, with multiple plates. One can use
this as a loading element. There is no electron flow between plates. However
there is "displacement" current between the plates that has no physical
meaning. Now what? The capacitor will be just affected as a coil.
So, from the conservation of electron flow I don't know what to believe.

73 Gary N4AST

Roy Lewallen wrote:
In the absence of radiation, all the charge that flows into an inductor
has to flow out, a point I and (much more eloquently) Ian and others
have tried to make, but which is lost on some of the most vocal
contributors to the newsgroup. This concept doesn't seem to fit neatly
into some of the preconceived theories, so is simply being ignored. In
the end, any theory that truly explains observed phenomena has to work
with physically vanishingly small inductors, for which the currents in
and out must be equal, as well as larger ones.

What a lot of people are missing is that a relatively constant forward
current flows into the bottom of the coil and out the top. That current
is reflected from the tip of the antenna and a relatively constant
reflected current flows into the top of the coil and out the bottom.
The current at the bottom and top of the coil is the phasor sum of
those two currents and cannot help but be different for the typical
mobile bugcatcher antenna.

The net total current is the sum of those two currents and even if the
component currents are constant, their phasor sum will differ because
the phase of the component currents are changing in opposite directions
across the bugcatcher coil.

The cosine current distribution on a standing-wave antenna is just a
standing wave caused by the superposition of forward and reflected
current.

For a vanishingly small inductor, the phase shift through the inductor
is near zero and indeed results in the same current on both sides of
the inductor so the theory works just fine.
--
73, Cecil http://www.qsl.net/w5dxp
"The current and voltage distributions on open-ended wire antennas are
similar to the standing wave patterns on open-ended transmission lines ...
Standing wave antennas, such as the dipole, can be analyzed as traveling
wave antennas with waves propagating in opposite directions (forward and
backward) and represented by traveling wave currents If and Ib ..."
_Antenna_Theory_, Balanis, Second Edition, Chapter 10, page 488 & 489


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