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.

Gene Fuller wrote:
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.



As usual, Cecil is very selective of his quotes. Balanis uses a
highly mathematical approach in most of his book, supplemented by
many graphs and charts. Cecil's quote, like his quote of Tom Rauch
on loading coils is only a very small part of the total.
73,
Tom Donaly, KA6RUH

Tom Donaly wrote:
Balanis uses a
highly mathematical approach in most of his book, supplemented by
many graphs and charts. Cecil's quote, like his quote of Tom Rauch
on loading coils is only a very small part of the total.

You want me to quote the total Balanis book?????? Why don't you,
instead, just pick one subject upon which you think you and I
disagree, and discuss it. The only thing I know for sure that
you and I disagree on is the current at each end of a bugcatcher
coil.
--
73, Cecil http://www.qsl.net/w5dxp


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Gene, W4SZ wrote:
"Do you have a reference to an analytic treatment using the traveling
wave model that could give results comparable to NEC2?"

NEC2 must agree with reality else it is worthless.

Terman agrees with Balanis and is only wrong when theory is revoked.
Terman says on page 866 of his 1955 edition:
"A wire antenna is a circuit with distributed constants; hence the
current distribution in a wire antenna that results from the application
of a localized voltage follows the principles discussed in Chap. 4, and
depends upon the antenna length, measured in wavelengths; the
terminations at the ends of the antenna wire; and the losses in the
system. The current distribution is also affected by the ratio of wire
length to diameter in situations where the antenna is unusually thick.
(see Kraus, Schelknoff, and Friis) Under most circumstances, the losses
are sufficiently low and the ratio of wire length to diameter
sufficiently great so that to a first approximation the current
distribution can be taken as that for a line with zero losses; it then
has the characteristics discussed in Sec. 4-5."

Sec. 4-5 is titled: "The Effect of Attenuation on Voltage and Current
Distribution - Lossless Lines" This is in Chapter 4, "Transmission
Lines".

Best regards, Richard Harrison, KB5WZI

Richard,

What in the world are you babbling about????

Nothing I wrote conflicts with Terman or Balanis. Did you see a ghost
message from me that I did not write?

73,
Gene
W4SZ

Richard Harrison wrote:
Gene, W4SZ wrote:
"Do you have a reference to an analytic treatment using the traveling
wave model that could give results comparable to NEC2?"

NEC2 must agree with reality else it is worthless.

Terman agrees with Balanis and is only wrong when theory is revoked.
Terman says on page 866 of his 1955 edition:
"A wire antenna is a circuit with distributed constants; hence the
current distribution in a wire antenna that results from the application
of a localized voltage follows the principles discussed in Chap. 4, and
depends upon the antenna length, measured in wavelengths; the
terminations at the ends of the antenna wire; and the losses in the
system. The current distribution is also affected by the ratio of wire
length to diameter in situations where the antenna is unusually thick.
(see Kraus, Schelknoff, and Friis) Under most circumstances, the losses
are sufficiently low and the ratio of wire length to diameter
sufficiently great so that to a first approximation the current
distribution can be taken as that for a line with zero losses; it then
has the characteristics discussed in Sec. 4-5."

Sec. 4-5 is titled: "The Effect of Attenuation on Voltage and Current
Distribution - Lossless Lines" This is in Chapter 4, "Transmission
Lines".

Best regards, Richard Harrison, KB5WZI

Gene Fuller wrote:
Nothing I wrote conflicts with Terman or Balanis.

And nothing I wrote conflicts with your physics.
--
73, Cecil, W5DXP

Richard Harrison wrote:

"A wire antenna is a circuit with distributed constants;

Terman, Kraus, Balanis, ... what do they know? :-)

Apparently, a lot of the otherwise knowledgeable people
on this newsgroup have forgotten that the formula for
the characteristic impedance of a single-wire transmission
line is 138*log(4h/d) where h is the height of the wire
above ground and d is the diameter of the wire. There's
no difference between that single-wire transmission line
and a lot of ham antennas. That single-wire transmission
line radiates just like an antenna.

1/2WL of #16 wire 24 feet in the air has a Z0 of 600 ohms.

If that center-fed dipole were terminated at each end with
a 600 ohm load, it would be a traveling-wave antenna with
a feedpoint impedance of 600 ohms. Take away the loads and
there's a match to 50 ohm coax at the feedpoint.

The only difference in those two antennas is that removing
the loads turned the antenna into a standing-wave antenna
and reflections are arriving back at the feedpoint, lowering
the feedpoint impedance.

Any coil installed in a standing wave antenna is going to
be subjected to both forward and reflected currents. There
is no hope of understanding the current in a loading coil
without understanding the component currents flowing both
directions through the loading coil.
--
73, Cecil, W5DXP

Forgotten? How can we forget a "fact" we learned wasn't true in the
first place?

According to the many references I have, the equation you quote is a
simplified equation that's valid for a single wire over a perfect
conducting ground plane, where the height is a very small fraction of a
wavelength (i.e., radiation is negligible). Even when you ignore the
relatively poor conductivity and the permittivity of real ground, the
equation is certainly not valid if the wire is high enough for
significant radiation to take place. There are several reasons for this:

1. The field shapes become different from the shapes assumed in deriving
the equation.
2. Radiation would make the impedance complex rather than purely real.
3. The voltage between the conductor and ground depends on the path
taken to measure it, so "characteristic impedance" takes on a whole
different meaning, if it has any at all in this context.

There is, of course, also the problem of ignoring the finite
conductivity of real ground, which will likewise impact the angle of the
impedance.

It's surely tempting to take a nice, simplistic equation like this and
build from it a whole theory of how things work. The seductive thing
about it is that it seems to work, sort of, for some special
applications. But it's a house of cards, and is at its root based on
invalid assumptions. So all the wonderful theories that follow from it
are fatally flawed and not to be trusted.

As apparently the only person on this newsgroup to have "learned" this
"fact", it would serve you well to un-learn it. That is, if you're
really interested in discovering how things really work rather than
clinging to possibly mistaken notions about how they do.

Roy Lewallen, W7EL

Cecil Moore wrote:

Apparently, a lot of the otherwise knowledgeable people
on this newsgroup have forgotten that the formula for
the characteristic impedance of a single-wire transmission
line is 138*log(4h/d) where h is the height of the wire
above ground and d is the diameter of the wire. There's
no difference between that single-wire transmission line
and a lot of ham antennas. That single-wire transmission
line radiates just like an antenna.

1/2WL of #16 wire 24 feet in the air has a Z0 of 600 ohms.

If that center-fed dipole were terminated at each end with
a 600 ohm load, it would be a traveling-wave antenna with
a feedpoint impedance of 600 ohms. Take away the loads and
there's a match to 50 ohm coax at the feedpoint.

The only difference in those two antennas is that removing
the loads turned the antenna into a standing-wave antenna
and reflections are arriving back at the feedpoint, lowering
the feedpoint impedance.

Any coil installed in a standing wave antenna is going to
be subjected to both forward and reflected currents. There
is no hope of understanding the current in a loading coil
without understanding the component currents flowing both
directions through the loading coil.
--
73, Cecil, W5DXP