Tdonaly wrote:
Interesting. Still trying to divert the argument to your own
frame of reference.

Still trying to engineer solutions instead of murmuring
mantras about how impossibly difficult everything is.
--
73, Cecil http://www.qsl.net/w5dxp



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Here's an interesting quote from _Transmission Lines, Antennas, and Wave
Guides_, by King, Mimno, and Wing:

"The amplitude of the current is not the same at different points along
a conductor, because electric charge is deposited all along the surface
of the conductor. Superficially it may appear that an antenna consisting
of a straight conductor that is an appreciable fraction of a wavelength
long and with a generator at its center may be looked upon simply as an
open-end transmission line with the parallel conductors bent to lie
along the same axis instead of being parallel to each other. Although
there is considerable similarity between the two cases from the point of
view of the approximate distribution of current, *they are nevertheless
fundamentally different*. The transmission line may be analyzed to a
good approximation in terms of ordinary electric-circuit theory, because
equal and opposite currents are very close together. This is not true of
the antenna and ordinary electric-circuit theory cannot be applied. *It
is fundamentally incorrect to treat a center-driven antenna as though it
were the bent-open ends of a two-wire line.*

Circuits that satisfy the condition for the near zone, either because
they are sufficiently small or because they have equal and opposite
currents everywhere so close together that the currents in widely
separated parts of the circuit exert a negligible effect on one another,
are analyzed correctly by the methods of ordinary electric-circuit
theory. All other circuits must be investigated in terms of
electromagnetism. This nearly always involves a study of the
electromagnetic field as a useful intermediate step in determining
distributions of current and charge."

The above text surrounded by asterisks is printed in italics. The quote
begins on p. 85 of the paperback 1965 Dover reprint. I highly recommend
reading Chapter II, of which the quote is a part.

Roy Lewallen, W7EL

Cecil Moore wrote:
Tdonaly wrote:

Universally recognized principles of electromagnetics are obfuscation?


Complicating a simple measurement task beyond belief is obfuscation.

You changed the geometry. But even if you hadn't, you might be able to
say the changing electrical fields are greater at the ends of a
dipole, but not the voltages, because the voltages aren't uniquely
defined.


When a dipole is bent into an open loop, the relative voltage between
the ends is uniquely defined just like the voltage across a transmission
line is uniquely defined. If I poke two wires through two holes in a
faraday cage and ask you to measure the 10 MHz voltage between them
with 10% accuracy, would you say it can't be done?

You'll give some people the impression that things are as simple as
you say they are when things are not simple
at all.


The measurement may be extremely challenging, but the *concepts* are
simple.
All you need to do is note the similarity of the transmission line
impedances
on an SWR circle to a wire antenna. If the spacing on a transmission
line is
an appreciable percentage of a wavelength, the transmission line will
radiate.
That's all a center-fed wire antenna is - a transmission line with large
spacing between the conductors and it radiates.

"Cecil Moore" wrote in message
...
Tdonaly wrote:
But, for the rest of us, all the books,
the research, the mathematics, and the thinking of people
from Faraday to Feynman, actually mean something.

I don't recall Faraday or Feynman ever saying that the impedance
of an antenna wire is constant up and down the wire.
--
73, Cecil http://www.qsl.net/w5dxp



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ARGH! another thread that will never die... time to 'ignore' this one also.
don't you guys realize you will never agree on anything on here? you talk
in circles around and around the same dogmatic circles never seeing that you
are all saying the same thing in different terms and arguing around nits
that don't matter in the real world.

Roy Lewallen wrote:
Here's an interesting quote from _Transmission Lines, Antennas, and Wave
Guides_, by King, Mimno, and Wing: *It
is fundamentally incorrect to treat a center-driven antenna as though it
were the bent-open ends of a two-wire line.*

Funny, I thought Maxwell's equations worked for either case. Did you also
know that *It is fundamentally incorrect to treat a wolf like a dog.*

If you slowly increase the spacing and angle between the two conductors
of a transmission line, at exactly what spacing and angle does it magically
cease being a transmission line and become an antenna requiring a completely
different treatment? Please be specific as to the exact spacing and angle at
which it becomes "fundamentally incorrect" to treat the configuration as a
transmission line. Incidentally, I don't usually use circuit theory for
transmission lines.

Your current distribution curve displayed by EZNEC for a 1/2WL dipole
looks exactly like Fig 1, page 2-2, ARRL Antenna Book, 15th edition. I thought
you or Walt probably wrote that section. If you had displayed both the current
and the voltage distribution in EZNEC, what would it look like for a 1/2WL dipole?

We can easily measure the impedance at any point along a 1/2WL section of
transmission line with reflections or the feedpoint impedance at any point
along a 1/2WL dipole. As you know, those impedances are the ratio of net
voltage to net current. At the impedance minimum on a transmission line,
the voltage is minimum and the current is maximum. Same for a feedpoint
impedance minimum on an antenna. At the impedance maximum on a transmission
line, the voltage is maximum and the current is minimum. Same for a feedpoint
impedance maximum on an antenna. We can deduce the ratio of the voltage to
the current from the feedpoint impedance - or is that one of the rules of
physics that a transmission line obeys but an antenna disobeys?
--
73, Cecil http://www.qsl.net/w5dxp



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Roy Lewallen wrote in message ...
Here's an interesting quote from _Transmission Lines, Antennas, and Wave
Guides_, by King, Mimno, and Wing:

"The amplitude of the current is not the same at different points along
a conductor, because electric charge is deposited all along the surface
of the conductor. Superficially it may appear ...

Here's another interesting quote from exactly the same source, page
71, the very first two paragraphs of King's "Antennas" chapter.

CHAPTER II
ANTENNAS

Electric Circuit Theory and Electromagnetic Theory. -- In order to
understand the behavior of antennas and of electric circuits at
ultra-high frequencies, it is essential to recognize that phenomena of
a vastly more general nature are involved than are encountered in
conventional electric networks. Attention is seldom called to the fact
that electric-circuit theory which proceeds from Kirchhoff's laws is a
highly specialized form of a more general theory. In some respects,
the situation is like that in mechanics, in which the simple law of
gravitation due to Newton may be looked upon as a special case of a
more general law formulated in the theory of relativity. Much as
Newtonian mechanics is adequate for the mechanical engineer, ordinary
electric-circuit theory is accurate for the requirements of electrical
power engineering and for many requirements in communications. But
even as Newton's laws of motion are inadequate in dealing with atomic
phenomena and some astronomical problems, so ordinary electric-circuit
theory fails when applied to antennas and to most circuits that are to
be used at ultra-high frequencies. The reason is that the conditions
that limit the generality of Newton's laws on the one hand, or the
theorems of electric-circuit theory on the other, are not satisfied.
For those who have assumed that Kirchhoff's laws are perfectly
general, a series of surprises is in store. They may, in fact, feel
like Alice when the Red Queen was annoyed by her reluctance to believe
"six impossible things before breakfast." But presently they may
return through the Looking Glass and discover that they have been
living in the one-dimensional Wonderland of electric-circuit theory
and that Nature is as simple as this suggests only in sufficiently
small spaces.

It is difficult to understand the structure of general
electromagnetism without first learning the appropriate symbolism,
that of mathematics. But if one is willing to accept some things on
faith and to meet others with an open, perhaps even an adventurous
mind, a degree of familiarity with many electromagnetic phenomena can
be acquired from a qualitative discussion.

David Robbins wrote:


ARGH! another thread that will never die... time to 'ignore' this one also.
don't you guys realize you will never agree on anything on here? you talk
in circles around and around the same dogmatic circles never seeing that you
are all saying the same thing in different terms and arguing around nits
that don't matter in the real world.

I think that's the point. Cecil and his buds are doing this for
entertainment.

- Mike KB3EIA -

Mike Coslo wrote in message .net...
David Robbins wrote:


ARGH! another thread that will never die... time to 'ignore' this one also.
don't you guys realize you will never agree on anything on here? you talk
in circles around and around the same dogmatic circles never seeing that you
are all saying the same thing in different terms and arguing around nits
that don't matter in the real world.

I think that's the point. Cecil and his buds are doing this for
entertainment.

:-) Gee, I think Cecil is trying to carry this one by himself. I
don't see any of "his buds" on the list of contributors. Certainly
Tom, Ian, Roy and I are in very close agreement about this topic.

It is worth a step back from all this, though. If the lurkers can get
the single idea that it's the _current_ distribution on an antenna
structure that ultimately matters, not any voltages (whether we can
agree about them or not), then they'll have gained something of value.

If they also pick up some simple things like "electric fields are
always very nearly perpendicular to the surface of good conductors"
and "the potential between two points in general depends on the path
you take," that would be a nice plus. If they get curious and go
learn more about those things, that would be wonderful.

Cheers,
Tom

Mike Coslo wrote:
I think that's the point. Cecil and his buds are doing this for
entertainment.

Sure beats mowing the yard. :-)
--
73, Cecil http://www.qsl.net/w5dxp



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Tom Bruhns wrote:
:-) Gee, I think Cecil is trying to carry this one by himself. I
don't see any of "his buds" on the list of contributors. Certainly
Tom, Ian, Roy and I are in very close agreement about this topic.

I agree that *measuring* the voltage is a challenge.

It is worth a step back from all this, though. If the lurkers can get
the single idea that it's the _current_ distribution on an antenna
structure that ultimately matters, ...

It's hard to develop that H-field without an E-field. The feedpoint
impedance of a standing wave antenna gives a deductive clue to the
magnitude of the E-field and it is not the same as a traveling wave
antenna. It also varies up and down the standing wave antenna.
--
73, Cecil http://www.qsl.net/w5dxp



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Cecil Moore wrote:
Roy Lewallen wrote:

Here's an interesting quote from _Transmission Lines, Antennas, and
Wave Guides_, by King, Mimno, and Wing: *It is fundamentally incorrect
to treat a center-driven antenna as though it were the bent-open ends
of a two-wire line.*


Funny, I thought Maxwell's equations worked for either case. Did you also
know that *It is fundamentally incorrect to treat a wolf like a dog.*

If you slowly increase the spacing and angle between the two conductors
of a transmission line, at exactly what spacing and angle does it magically
cease being a transmission line and become an antenna requiring a
completely
different treatment? Please be specific as to the exact spacing and
angle at
which it becomes "fundamentally incorrect" to treat the configuration as a
transmission line. Incidentally, I don't usually use circuit theory for
transmission lines.

That question is a lot like asking for the exact speed an object has to
be moving before non-relativistic becomes invalid, or how small before
quantum theory has to be used.

I maintain that the authors of that book know more than you do about the
topic by at least an order of magnitude -- more likely about three. If
you really want to know the answer to your silly question, you should
study what they've written and try to understand it, rather than posting
it as a question to me on this newsgroup.

. . .

Roy Lewallen, W7EL