"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

On Wed, 3 Nov 2004 09:25:20 -0600, (Richard
Harrison) wrote:

[snip]

|"For present purposes" we may declare anything so long as we don`t
|define our purposes, but Fig 9-22 on page 9-15 of ON4UN`s "Low-Band
|DXing" is significant and no one has said his pictures are wrong and
|given reasons.

There are multiple editions of this book. Could you describe in more
detail what the "pictures" are saying.

They are probably the same as in my third edition, just on different
pages with different figure numbers.

I should wait for your answer, but I'm going out on a limb and
guessing that they are the ones showing current distribution and "area
under the curve."

If my guess is correct, then I submit that using them in the current
context (no pun intended) is not applicable.

This whole "shootout" nonsense pertains to antennas with (unloaded)
electrical lengths well under 0.1 lambda. Devoldere shows no examples
of loaded antennas that are this short.

If I guessed wrong, then I will standby for clarification.

"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!

On 03 Nov 2004 15:01:47 GMT, oUsama (Yuri Blanarovich)
wrote:

|
| If you're really interested in the "AREA under the current curve,"
|you'll have to figure out how to make an efficient, continuously loaded,
|short antenna. You'll find, though, that the difference between a
|continuously loaded antenna and an antenna with the loading coil,
|say, halfway up from the feedpoint won't amount to a hill of beans.
| There's still no such thing as a "current drop."
|73,
|Tom Donaly, KA6RUH
|
|
|You are flying in a dreamland. Check the results of shootouts comparing
|Haasticks and other continuously loaded antennas vs. Bugcatchers or top loaded.
|You guys get your noses out of the books and check the reality.

When someone posts the results of a "shootout" where the *same*
vehicle, in the *same* location, with the test antenna located at the
*same* position on the vehicle, fed with the *same* transmitter and
where the *same* receiver is used for field strength then *maybe* I'll
give some credence to the results. Otherwise, it's all hogwash.

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

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

Yes, but Tom modified his statement shortly thereafter.

Are you guys actually interested in antennas, or is this just some sort
of ****ing contest?

(Clearly a rhetorical question.)

73,
Gene
W4SZ

Cecil Moore wrote:


Tom, W8JI claimed such in the following quote from 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."

Reg Edwards wrote:
"My patience is getting thin" was also a joke. Seems it fell flat.

Oops, sorry Reg. I'm guilty of what I accused you of.
--
73, Cecil http://www.qsl.net/w5dxp


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Tom Donaly wrote:
Go to Tom's home page and read _everything_ he wrote about loading
coils and come back here and tell us what he really thinks.

Once again, the argument is not about what is on Tom's web page. The
argument is about what Tom asserted in his argument with Yuri on
eHam.net. Diverting attention to his web page is just, well, an
obvious diversion of the issue.

If I say there is no God on eHam.net and don't say it on my web page
does that prove I never said it?

You said:
Since when has anyone claimed it's impossible to make a coil that
has a non-constant current distribution?

When was August 10, 2003:

In Search of 'The Perfect Mobile Antenna':
Reply by W8JI on August 10, 2003
Yuri, You are like to call names, insult people, and argue rather than
take the time to learn basic electronics. This is in any book, including
the ARRL Handbook. If you look at HOW an inductor works, the current
flowing in one terminal ALWAYS equals the current flowing out the other
terminal. THE VOLTAGE can be (and is) different on each end of the inductor,
NOT the current.

During that argument, W8JI presented the lumped inductance in EZNEC as proof
of the above statement.
--
73, Cecil http://www.qsl.net/w5dxp


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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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