I find it amazing that the only argument you guys can come up with is
an ad hominem attack. That's usually the last resort of someone who has
lost the argument. If I am so technically incorrect, is one iota of
technical proof too much to ask? It is, of course, if this is a good-
old-boys EM religion discussion rather than a technical discussion.
--
73, Cecil http://www.qsl.net/w5dxp

Cecil,
I admire your patience and civility, I will try to learn that.
In the mean time, it is almost amusing, if not sad, to observe some educated
idiots :-)

Yuri, K3BU.us

Gene Fuller wrote:
I was going to drop this discussion, but I will respond to your request
to share physics knowledge.

Thanks, Gene, Please be patient with me.

1) I will repeat. E-fields, H-fields, voltages, and currents are all
related through some very profound equations. However, shout THEY ARE
NOT INTERCHANGEABLE. /shout

Is the H-field around a wire proportional to the RF current in the wire?
Is the E-field around a wire proportional to the RF voltage between the
wires? Is the ratio of E-field to H-field fixed by Z0? Do I^2*R losses
affect the E-field and H-field by equal amounts?

This is not just a matter of semantics. These entities have different
physical meanings, different units, and different dimensionalities.

Of course that's true. However, they are not unrelated.

2) I offered a physics-based explanation for your proposed "current
drop" in the 440 MHz RG-58 example a few days ago. Did you not read that
message before responding to it?

Yes, and I have been thinking about an example that would better illustrate
what I was asking. A 1000 wavelength dipole located in outer space would
have less current at the ends than at the source. Since there is no other
path for current, what is the explanation for the decrease in the current
at the ends?

3) What is not correct is the assertion that the coil
exhibits a phase shift consistent with, for example, 20 feet of wire
used to make the coil.

Because nobody has made that assertion since the original eHam article, it
appears to be a straw man. The coil occupies whatever number of degrees
that it occupies and it does NOT occupy zero degrees.

For instance, using a particular EZNEC segment model of a coil, the
current at the bottom is 1.0 amp and the current at the top is 0.5
amp. Assuming the cosine distribution of standing-wave current is
accurate, the coil occupies about 60 degrees. The whip would occupy
about 30 degrees, the rest of the 1/4WL.

Nobody has attempted to explain how one can obtain 90 degrees of a
1/4WL antenna on 4 MHz using a ten foot (15 degree) whip. That is
one hell of a velocity factor. If the bottom-loading coil really
occupies zero degrees, then the ten foot whip would be forced to
occupy 90 degrees. That is so impossible as to be laughable.

The notion that a coil replaces some sizable
portion of the total phase shift in an antenna has been shown to be
incorrect. Experiments reported by Roy and Tom R. convincingly
demonstrate the phase shift behavior of coils.

The total current undergoes virtually no phase shift since it is a
standing wave. That's in the textbooks and nobody is arguing that
point so it's just another straw man.

It's the forward current and reflected current that is undergoing a
phase shift through the coil just like they do on a wire standing-
wave antenna. Nobody has measured those two current components so
the jury is still out on that subject. There is no argument about
the phase of the total current that Roy and Tom measured. Please,
there are enough arguments already without having to introduce
straw men.

If you will look at my phasor diagrams of forward and reflected
currents at:

http://www.qsl.net/w5dxp/current.htm

you will see that the phase of the total current is exactly the same
in both cases. That's the phase that Roy measured. Since it is a
standing wave current, the phase of the standing-wave current is almost
constant. It is the magnitude of the standing-wave current that
changes and it changes as a cosine function of electrical length
in degrees. The coil has an electrical length in degrees. That's
what causes the current to be different at the bottom and at the
top in a 1/4WL antenna. Assuming the phase shift from the feedpoint
current to the tip of the antenna is 90 degrees, if an accurate
measurement of the current at the top and bottom of a bottom-loaded
antenna coil is made, the number of degrees occupied by the coil can
be calculated from

arccos(Itop/Ibottom)

just as it can be calculated between two points on a wire. This
assumes that Ibottom is an Imax point on the standing wave.
--
73, Cecil http://www.qsl.net/w5dxp


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Cecil,

1) Only the total current matters. I have never found a detailed
treatment of antennas that was based on anything other than the total
current (or total current density) at each point on the antenna. Have you?

Current components may be useful for discovering the total current or
for handwaving explanations, but they have no further role in antenna
analysis.

2) Where did this 90 degree phase shift requirement come from? There is
virtually no phase shift in the current of a half-wave dipole (or
quarter-wave monopole) from feedpoint to tip. I am looking at figure 9.6
on page 370 in Kraus "Antennas" (2nd Ed.), and it shows perhaps a few
degrees phase variation over the entire length of the dipole antenna.
This figure is located in the chapter on the Moment Method for
calculating cylindrical antennas, in case you do not have the second
edition.

I suspect you may be confusing the argument (AKA, the phase) of the
cosine function presumed to describe the behavior of the current
amplitude. However, current amplitude and current phase are not at all
the same thing.

Have you been seduced by your math models?

73,
Gene
W4SZ


Cecil Moore wrote:

[snip]


Because nobody has made that assertion since the original eHam article, it
appears to be a straw man. The coil occupies whatever number of degrees
that it occupies and it does NOT occupy zero degrees.

For instance, using a particular EZNEC segment model of a coil, the
current at the bottom is 1.0 amp and the current at the top is 0.5
amp. Assuming the cosine distribution of standing-wave current is
accurate, the coil occupies about 60 degrees. The whip would occupy
about 30 degrees, the rest of the 1/4WL.

Nobody has attempted to explain how one can obtain 90 degrees of a
1/4WL antenna on 4 MHz using a ten foot (15 degree) whip. That is
one hell of a velocity factor. If the bottom-loading coil really
occupies zero degrees, then the ten foot whip would be forced to
occupy 90 degrees. That is so impossible as to be laughable.

The notion that a coil replaces some sizable portion of the total
phase shift in an antenna has been shown to be incorrect. Experiments
reported by Roy and Tom R. convincingly demonstrate the phase shift
behavior of coils.


The total current undergoes virtually no phase shift since it is a
standing wave. That's in the textbooks and nobody is arguing that
point so it's just another straw man.

It's the forward current and reflected current that is undergoing a
phase shift through the coil just like they do on a wire standing-
wave antenna. Nobody has measured those two current components so
the jury is still out on that subject. There is no argument about
the phase of the total current that Roy and Tom measured. Please,
there are enough arguments already without having to introduce
straw men.

If you will look at my phasor diagrams of forward and reflected
currents at:

http://www.qsl.net/w5dxp/current.htm

you will see that the phase of the total current is exactly the same
in both cases. That's the phase that Roy measured. Since it is a
standing wave current, the phase of the standing-wave current is almost
constant. It is the magnitude of the standing-wave current that
changes and it changes as a cosine function of electrical length
in degrees. The coil has an electrical length in degrees. That's
what causes the current to be different at the bottom and at the
top in a 1/4WL antenna. Assuming the phase shift from the feedpoint
current to the tip of the antenna is 90 degrees, if an accurate
measurement of the current at the top and bottom of a bottom-loaded
antenna coil is made, the number of degrees occupied by the coil can
be calculated from

arccos(Itop/Ibottom)

just as it can be calculated between two points on a wire. This
assumes that Ibottom is an Imax point on the standing wave.

Gene Fuller wrote:
1) Only the total current matters. I have never found a detailed
treatment of antennas that was based on anything other than the total
current (or total current density) at each point on the antenna. Have you?

Check out my tag line, Gene. Balanis says we can use the component
currents If and Ib to analyze a standing-wave antenna. Kraus says
essentially the same thing when he says: "A sinusoidal current
distribution may be regarded as the standing wave produced by two
uniform (unattenuated) traveling waves of equal amplitude moving in
opposite directions along an antenna." This was in regards to the
"Fields of a thin linear antenna with a uniform traveling wave."

Just because there is no "detailed treatment" doesn't mean that it
should be forbidden to discuss. We are out on the edge of what has been
detailed (so far) so don't be afraid to think outside of the box. The
opposite phase shift between If and Ib is the cause of the decrease in
coil current in a typical mobile antenna. It happens even if there is
zero loss in the coil and zero radiation from the coil. It also
happens in a lossless transmission line. There is a decrease in standing
wave current on each side of a current maximum point even when the
transmission line is lossless. The same thing applies to a lossless
coil with dimensions larger than a point.

Current components may be useful for discovering the total current or
for handwaving explanations, but they have no further role in antenna
analysis.

Check my tag line again, Gene. They are absolutely useful for transmission
line analysis and are therefore useful for standing-wave antenna analysis.

2) Where did this 90 degree phase shift requirement come from? There is
virtually no phase shift in the current of a half-wave dipole (or
quarter-wave monopole) from feedpoint to tip.

Yes, you are talking about the standing-wave current which is the
superposition of the forward and reflected currents. A 1/4WL wire
is 90 degrees of a traveling-wave antenna. The forward current rotates
by 90 degrees and the reflected current rotates by 90 degrees.

I am looking at figure 9.6
on page 370 in Kraus "Antennas" (2nd Ed.), and it shows perhaps a few
degrees phase variation over the entire length of the dipole antenna.

Yes, that is true for the superposed forward and reflected currents and
is shown to be true by my phasor diagrams on my web page. The forward
current is a traveling wave. The reflected current is a traveling wave.
I'm sure you are familiar with the change in phase undergone by traveling
waves in perfectly matched systems. Apply that knowledge to the separate
forward and reflected current traveling waves and you will understand
the magnitude variation in If+Ib caused by their respective phase shifts
in the opposite direction even if their magnitudes remain constant.

I suspect you may be confusing the argument (AKA, the phase) of the
cosine function presumed to describe the behavior of the current
amplitude. However, current amplitude and current phase are not at all
the same thing.

Nope, I fully agree that the superposed net current has almost zero
phase shift because it is a *standing wave*. Traveling waves, OTOH,
experience phase shifts when traveling along a wire. The forward
current and reflected current on a standing-wave antenna are
*traveling waves*.

This is an onion-type problem, Gene. Please peal back the net current
layer and look at the component currents underneath even if you feel
presently that it will be a waste of time.

Incidentally, I bounced most of this stuff off of Dr. Balanis when
I was working with him on a joint Intel/ASU project. He agreed so
far (1995) and my extensions since 1995 are logical. If you will
take it step-by-step, I think you will agree. If you find any error
at all on my part, you will, no doubt, call my attention to it and
I will learn something.
--
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,

Thanks. You just validated my point. Kraus absolutely does not use
component currents for any serious analysis; he uses only total current.
Likewise, it appears that Balanis is merely waving his hands as well.
The quote you provided comes from Chapter 10, on traveling wave
antennas, not from a chapter on simple dipole antennas. Does he actually
load these components into equations and carry out the analysis in detail?

Subcomponents of the current may be useful for handwaving explanations,
but they are not superior to the standard net current model. Any
modeling results must agree with the standard model (widely used for
more than 100 years) or else the simple handwaving model is likely to be
bogus.

Soooo, we are back to the beginning. There is minimal current phase
shift in a dipole or monopole antenna, certainly nothing like the the 30
to 60 degree "replacement" phase shift you have been claiming. There is
no mysterious "current drop". Any reduction in measured (or modeled)
current can (and must) be accounted by shunt currents.

What's left?

Bye,
Gene
W4SZ


Cecil Moore wrote:


Check out my tag line, Gene. Balanis says we can use the component
currents If and Ib to analyze a standing-wave antenna. Kraus says
essentially the same thing when he says: "A sinusoidal current
distribution may be regarded as the standing wave produced by two
uniform (unattenuated) traveling waves of equal amplitude moving in
opposite directions along an antenna." This was in regards to the
"Fields of a thin linear antenna with a uniform traveling wave."

Gene Fuller wrote:
Thanks. You just validated my point. Kraus absolutely does not use
component currents for any serious analysis; he uses only total current.

Let me get this straight. Just because Kraus didn't use component
currents for any serious analysis prohibits future thinkers from
doing so? Do you really believe that anything Kraus didn't choose to
include in his book should not be considered by human beings like
you and me? (I don't recall him saying anything about sex.) :-)

If you consider Kraus' book to be an Antenna Bible, then you are
guilty of bringing metaphysics into physics.

Likewise, it appears that Balanis is merely waving his hands as well.
The quote you provided comes from Chapter 10, on traveling wave
antennas, not from a chapter on simple dipole antennas.

"Handwaving - anything that disagrees with your present EM religion"

Does that prohibit you from considering the component currents? If
so, what are you afraid that you will discover? You are perfectly
free to put on the blinders, but to what purpose?

Subcomponents of the current may be useful for handwaving explanations,
but they are not superior to the standard net current model.

Is the "standard net current model" so perfect that it will never
be modified? Please think outside of the box on this one, Gene. You
are essentially saying that all the human knowledge that has been
accumulated on this subject is all that will ever be discovered. That
reminds me of the patent clerk who, around 1900, declared that the
patent office should be closed because all possible discoveries had
already been made.

Any
modeling results must agree with the standard model (widely used for
more than 100 years) or else the simple handwaving model is likely to be
bogus.

Can you prove that the "standard model" is perfect? If not, is there
a chance that it is not perfect? Are you opposed to discovering
imperfections in the "standard model"? Do you have the cahones to
defend the standard model in a rational technical discussion?

Soooo, we are back to the beginning.

No, we are back to your EM metaphysics. I am begging you, Gene, please,
please, allow yourself to think outside of the box. What do you have
to lose except your religious-like beliefs? If your beliefs are correct,
it should be relatively easy to prove me wrong. If your beliefs are
incorrect, don't you want to change them? What, exactly, are you afraid of?

The mere fact that you resort to an argumentum ad verecundiam (diversionary
appeal to authority) argument tells me that you are afraid to consider
anything new.

So are you going to sandbag behind an omniscience flag, or are you going
to engage in a rational technical discussion where the outcome is unknown?

I am not trying to be difficult. In a one-on-one discussion, I will
either be proven right or wrong. I'm not afraid of that - are you?
--
73, Cecil http://www.qsl.net/w5dxp


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What's left?

Bye,
Gene
W4SZ

Take the RF ammeters, stick them at ends of coil and SEE wasaaaap!

Bye, bye!
Yuri, K3BU.us

Gene Fuller wrote:

Kraus absolutely does not use
component currents for any serious analysis; he uses only total current.
Likewise, it appears that Balanis is merely waving his hands as well.
The quote you provided comes from Chapter 10, on traveling wave
antennas, not from a chapter on simple dipole antennas. Does he actually
load these components into equations and carry out the analysis in detail?

Subcomponents of the current may be useful for handwaving explanations,
but they are not superior to the standard net current model.

True. Although it's worth noting that the traveling waves, or
subcomponenets as you call them, are actually the source of radiation.
The fields generated by forward and reverse waves of course superpose to
produce the net field. Obviously in practice it's considerably simpler
to just superpose the currents in order to obtain the net field, but the
result should be the same either way.

Any
modeling results must agree with the standard model (widely used for
more than 100 years) or else the simple handwaving model is likely to be
bogus.

Soooo, we are back to the beginning. There is minimal current phase
shift in a dipole or monopole antenna, certainly nothing like the the 30
to 60 degree "replacement" phase shift you have been claiming. There is
no mysterious "current drop". Any reduction in measured (or modeled)
current can (and must) be accounted by shunt currents.

What's left?

I have a question. If a loading coil only makes a physically short
antenna look like it's an electrical quarter wavelength reactively, why
does its position along the radiator make such an apparent difference in
performance?

73, Jim AC6XG

"Jim Kelley" wrote in message
...
deletia....

I have a question. If a loading coil only makes a physically short
antenna look like it's an electrical quarter wavelength reactively, why
does its position along the radiator make such an apparent difference in
performance?

73, Jim AC6XG


My first reaction is to point out that this was (is?) a question on the
Extra exam.
Now how can I explain qualitatively why this is?
Consider an end-fed wire antenna.
An electromagnetic wave goes through the conduction electrons down to the
end and reflects back.
At 1/4 wavelength, the reflected wave is exactly in phase with the source so
the load looks minimal and resistive, loss plus radiation. As the antenna
gets shorter the radiation resistance gets lower and the reflected wave gets
back to the feed point sooner (becomes capacitive). We need to add
inductance to slow down the wave so it gets back in phase. We cannot, alas,
raise the radiation resistance; this is a short antenna. If I place the
inductor at the feed point all the current must flow through it, maximizing
loss. If I place it at the top little current flows through it, minimizing
effectiveness. If I distribute it the antenna's resonance is broader, but at
what cost? Lower Q. The signal strength is less. So I make the coil as short
as I can, put it in the middle and it's juuust right.

73, H. NQ5H

If I place the
inductor at the feed point all the current must flow through it, maximizing
loss. If I place it at the top little current flows through it, minimizing
effectiveness. If I distribute it the antenna's resonance is broader, but at
what cost? Lower Q. The signal strength is less. So I make the coil as short
as I can, put it in the middle and it's juuust right.

73, H. NQ5H

Simple rule, as mentioned in ON4UN book, the efficiency of the antenna is
proportional to the area under the current curve. When you model the antenna
and view the current distribution and compare various cases with coil
positioned at bottom, middle, top, it is obvious why. It also shows why it is
important to understand the role of the loading coil and its effect on the
current distribution along the radiator. This effect gets magnified when using
loaded elements in parasitic beam designs. If you use "zero" size inductance in
modeling, the results are "too good" and correlation with reality is way off.
That's what is all about.

Yuri, K3BU.us