Peter O. Brackett wrote:
Well, as we all "know" the current wave on a dipole antenna is exceedingly
close to sinusoidal, but not [exactly] sinusoidal, because if it were
exactly sinusoidal it wouldn't be radiating. That [small] difference
between the actual current distribution on an antenna and the actual current
distribution on a transmission line is the [tell-tale] residual that
separates us from an exact analytic expression for the driving point
impedance of a dipole.

Of course, but for conceptual purposes, both Balanis and
Kraus seem to give us permission to consider the current
distribution to be sinusoidal for "thin-wire" dipoles.
Kraus says: "... it is assumed that the current distribution
is sinusoidal. Current-distribution measurements indicate
that this is a good assumption provided that the antenna is
thin, i.e. when the conductor diameter is less than, say,
lambda/100." Balanis agrees: "If the diameter of each wire
is very small (d lambda), the ideal standing wave pattern
of the current along the arms of the dipole is sinusoidal
with a null at the end."

It would be interesting to compare how closely the input impedance of a 1/2
wave lossless feed line of appropriate Zo (Say 600 Ohms?) terminated in a 73
Ohm resistor would approximate that of a "real" dipole. At resonance it
would be 73 Ohms at least.

Of greater interest might be the construction of a stub using
resistance wire to simulate the "loss" to radiation plus all
the other losses. As one of gurus on r.r.a.a said, "One can
replace the resonant antenna with a dummy load without changing
anything." :-)
--
73, Cecil http://www.w5dxp.com

Richard:

[snip]
Beliefs. -sigh- Is this one of those transcendental statements about
navel gazing?
[snip]

No... it's not transcendental it's purely algebraic! (grin)

[snip]
Everywhere...
Even in the near field of an antenna.

No. Not even in the near field of an antenna.
[snip]

Where then is Zo = 377 Ohms?

[snip]
That is an antenna itself has no effect on the fundamental u and e of the
media in which it is immersed.

Wrong.
[snip]

Surely uo, eo, Zo and c (velocity of light) are fundamental and invariant
properties of "free space", no?

[snip]
After all the antenna is very small, and free space is very large (grin),
and so a tiny antenna cannot change u and e everywhere!

Abstracting from near space to everywhere is the source of your error.
[snip]

No, I'm "contracting" from outer space to near space... using the
contravarient tensor!

[snip]
The waves are not plane where the waves are not plane, but... Is this
a Zen "but?"
[snip]

If a tree falls in the forest and no one is there to hear it, does it make a
sound?

If an antenna radiates somewhere in the Universe and there are no receivers,
does it really radiate?

[snip]
There might just also be plane waves passing through identically the same
region of space, say emanating from a more distant antenna.

Wrong.
[snip]

Oh, and here I thought that at least tiny remnants of all radiation
eventually passes through every part of space, filling all of space as it
expands throughout the Universe..

[snip]
The ratio for
those plane E and H fields will indeed be 377 Ohms over the exact same
region of space where Zo is different because of simultaneous but
non-planar
waves.

Wrong.
[snip]

I know that Special Relativity [Maxwell's equations] is not supported in
full by General Relativity, but surely even though space is warped by mass,
superposition must still be supported. The radiation in your neighbourhood
is a superposition of suitably delayed and reduced (by path attenuation) of
all radiation, no?

[snip]
So in fact... the wave impedance of free space can have many values
simultaneously, one [universal?] constant value of ~377 Ohms for plane
waves, while it may have many other [arbitrary] values for waves passing
through the same region of space that are not plane.

Thoughts, comments?

Wrong.
[snip]

And here I thought I was going to be able to sell you a little corner of the
Universe [very near the Brooklyn Bridge] that has any Zo you want. What?

[snip]
Peter, are you trying to bust loose a seized bearing? Most of this
reads like the Molly Bloom citation from a technical translation of
"Ulysses."

73's
Richard Clark, KB7QHC
[snip]

Molly Bloom? How did she get into this... I thought she was still living in
the house on Eccles Street". What?

Now Ulysses, he's my man!

I miss Reg Edwards already :-(

Regards,

--
Pete K1PO
Indialantic By-the-Sea, FL

On Tue, 12 Sep 2006 18:39:25 GMT, "Peter O. Brackett"
wrote:

Where then is Zo = 377 Ohms?

Hi Peter,

To how many places? Your question is rather oblique when we are
discussing near fields and antenna as "transducer" [not a choice of
term I subscribe to].

I seriously doubt that you've unhinged from the origins of that value,
however, it bears only tangentially on the matter.

That is an antenna itself has no effect on the fundamental u and e of the
media in which it is immersed.

Wrong.
[snip]

Surely uo, eo, Zo and c (velocity of light) are fundamental and invariant
properties of "free space", no?

And some toothpaste makes our teeth whiter, no? Your reply does
nothing to answer your error, however.

[snip]
After all the antenna is very small, and free space is very large (grin),
and so a tiny antenna cannot change u and e everywhere!

Abstracting from near space to everywhere is the source of your error.
[snip]

No, I'm "contracting" from outer space to near space... using the
contravarient tensor!

Then you have misapplied it, clearly. Arguing does not take the place
of easily demonstrable facts. AH! forgive me, wrong forum, arguing
is classic substitution. However, the entertainment value is rather
poorer this round.

There might just also be plane waves passing through identically the same
region of space, say emanating from a more distant antenna.

Wrong.
[snip]

Oh, and here I thought that at least tiny remnants of all radiation
eventually passes through every part of space, filling all of space as it
expands throughout the Universe..

Are "thoughts" related to "beliefs?" Bloated speculations of
background radiation don't change the basic assertion that in the near
field, there is nothing that remotely approaches the presumed 377 Ohm
specification. You've both (earlier) acknowledged this and (have
since) challenged it with a semantic fog such as:

I know that Special Relativity [Maxwell's equations] is not supported in
full by General Relativity, but surely even though space is warped by mass,
superposition must still be supported. The radiation in your neighbourhood
is a superposition of suitably delayed and reduced (by path attenuation) of
all radiation, no?

EZNEC demonstrates the violation of your "beliefs," yes?

I miss Reg Edwards already :-(

Certainly you're a poor substitute for Punchinello. (and Kelvin is
winding up a pitch to wing a chunk of chalk off your noggin.)

73's
Richard Clark, KB7QHC

Richard:

[snip]
To how many places? Your question is rather oblique when we are
discussing near fields and antenna as "transducer" [not a choice of
term I subscribe to].
[snip]

OK, ok... you've busted me...

I admit that circuit theory is on really shaky ground.

Although circuit theory was developed by Ohm, Kirchoff and others before
Maxwell presented the world with his celebrated equations, we can all agree
that circuit theory is a very poor (one dimensional) approximation to field
theory. Circuits are a thoroughly useless affair dealing only with poorly
understood approximations to the "real deal"...waves!

I admit it, there is no such thing as "voltage", which after all is only the
value V of a definite line integral of the vector field that depends upon
the somewhat arbitrary path of integration, chosen by the integrator,
through the appropriate E field, and so consequently there is no such thing
as a "real" driving point impedance Z = V/I. The only reality is the
characteristic or wave impedance! There I've said it!

So... youv'e got me... I agree... we should not really be messing about
trying to define phoney "transducer" functions between circuit theoretic
variables (V, I) and wave theoretic variables (E, H) since the former have
such an ephemeral existence.

Still in all... one wonders... do circuits and waves, charge particles
(electrons) and waves particles (photons) have any truck with each other
or... do they lead entirely separate lives? What would you call the
intermediaries between reality and approximation?

I'm very sorry to have brought up the subject... I've probably confused the
OP, and I am here and now prepared to recant my heresy, before you light the
kindling beneath my feet, heh, heh... I solemly swear that an antenna is not
a "transducer" between circuits and waves! (grin)

But... ahem... the sun still has spots!

Kathy, bring me another glass of that Rivaner!

Molly Bloom indeed!

--
Pete K1PO
Indialantic By-the-Sea, FL

I seriously doubt that you've unhinged from the origins of that value,
however, it bears only tangentially on the matter.

That is an antenna itself has no effect on the fundamental u and e of
the
media in which it is immersed.

Wrong.
[snip]

Surely uo, eo, Zo and c (velocity of light) are fundamental and invariant
properties of "free space", no?

And some toothpaste makes our teeth whiter, no? Your reply does
nothing to answer your error, however.

[snip]
After all the antenna is very small, and free space is very large
(grin),
and so a tiny antenna cannot change u and e everywhere!

Abstracting from near space to everywhere is the source of your error.
[snip]

No, I'm "contracting" from outer space to near space... using the
contravarient tensor!

Then you have misapplied it, clearly. Arguing does not take the place
of easily demonstrable facts. AH! forgive me, wrong forum, arguing
is classic substitution. However, the entertainment value is rather
poorer this round.

There might just also be plane waves passing through identically the
same
region of space, say emanating from a more distant antenna.

Wrong.
[snip]

Oh, and here I thought that at least tiny remnants of all radiation
eventually passes through every part of space, filling all of space as it
expands throughout the Universe..

Are "thoughts" related to "beliefs?" Bloated speculations of
background radiation don't change the basic assertion that in the near
field, there is nothing that remotely approaches the presumed 377 Ohm
specification. You've both (earlier) acknowledged this and (have
since) challenged it with a semantic fog such as:

I know that Special Relativity [Maxwell's equations] is not supported in
full by General Relativity, but surely even though space is warped by
mass,
superposition must still be supported. The radiation in your
neighbourhood
is a superposition of suitably delayed and reduced (by path attenuation)
of
all radiation, no?

EZNEC demonstrates the violation of your "beliefs," yes?

I miss Reg Edwards already :-(

Certainly you're a poor substitute for Punchinello. (and Kelvin is
winding up a pitch to wing a chunk of chalk off your noggin.)

73's
Richard Clark, KB7QHC

On Tue, 12 Sep 2006 19:55:52 GMT, "Peter O. Brackett"
wrote:

OK, ok... you've busted me...

Hi Peter,

Sure, and without being... elliptical.

Myself, I find Joyce rather a Mick awash in beer soaked imaginings in
comparison to Henry Miller and The Cosmodemonic Telegraph Company of
North America.

73's
Richard Clark, KB7QHC

Peter O. Brackett wrote:

Correct, but don't we all believe that the wave impedance of "free space" is
approximately 377 Ohms...

Everywhere...

Even in the near field of an antenna.

That is an antenna itself has no effect on the fundamental u and e of the
media in which it is immersed. u and e are defined only in terms of and as
affecting "plane wave" [TEM mode?] propagation, and...

After all the antenna is very small, and free space is very large (grin),
and so a tiny antenna cannot change u and e everywhere!

The fields E and H in the "near region" of an antenna where the waves are
not "plane" on the other hand may not be related by 377 Ohms, simply because
the waves emanating from the "near" antenna are not plane, but...

There might just also be plane waves passing through identically the same
region of space, say emanating from a more distant antenna. The ratio for
those plane E and H fields will indeed be 377 Ohms over the exact same
region of space where Zo is different because of simultaneous but non-planar
waves.

So in fact... the wave impedance of free space can have many values
simultaneously, one [universal?] constant value of ~377 Ohms for plane
waves, while it may have many other [arbitrary] values for waves passing
through the same region of space that are not plane.

Thoughts, comments?

I don't believe I've ever encountered the term "wave impedance of free
space", and its use is certain to cause confusion, as I sense here.

The *intrinsic* impedance of free space is 377 ohms. The *wave*
impedance of an EM wave in that medium is 377 ohms if it's a plane wave
in the far field of a radiator, and some other value if it's close to an
antenna or other conductor or dielectric. The *intrinsic* impedance of
free space is determined only by the conductivity, permittivity, and
permeability of the medium; the impedance of a wave is governed not only
by the intrinsic impedance of the medium but also other factors.

If you have a reference that defines and uses the term "wave impedance
of free space", I'd like to look it up to see how the author deals with
this potentially confusing combination of terms. If it does indeed "have
many values simultaneously", it's pretty useless in my opinion.

Roy Lewallen, W7EL

Peter O. Brackett wrote:
Circuits are a thoroughly useless affair dealing only with poorly
understood approximations to the "real deal"...waves!

What? No lumped inductors in reality? :-) What about
the measured 3 nS delay through a 100 uH coil?
--
73, Cecil http://www.w5dxp.com

Cecil:

[snip]
"Cecil Moore" wrote in message
. ..
Peter O. Brackett wrote:
Circuits are a thoroughly useless affair dealing only with poorly
understood approximations to the "real deal"...waves!

What? No lumped inductors in reality? :-) What about
the measured 3 nS delay through a 100 uH coil?
--
73, Cecil http://www.w5dxp.com
[snip]

Delay through a coil... what is that? Heh, heh...

Nickola Tesla would be rolling over in his grave if he could hear us
discussing a possible dichotomy between lumped and distributed systems.
Nickola "lived" in the intersticies between the wave theoretic and circuit
theoretic fabrics of reality.

It is interesting is it not, that the "only" element of circuit theory that
allows for "action at a distance" [a.k.a. "field effects"] is that of mutual
inductance "M".

Circuit theoretic elements; R, L, C, and M...

Other than "M" circuit/network theoretic concepts are devoid of the wave
theoretic aspects of the celebrated Maxwell/Heaviside partial differential
equations.

Funny what you can do with "M". Variometers, Tesla coils, and such...

--
Pete K1PO
Indialantic By-the-Sea, FL

On Wed, 13 Sep 2006 02:38:37 GMT, "Peter O. Brackett"
wrote:

It is interesting is it not, that the "only" element of circuit theory that
allows for "action at a distance" [a.k.a. "field effects"] is that of mutual
inductance "M".

Hi Peter,

What happened to... capacitance? The Leyden jar proved "action at a
distance," literally, long before folks started choking.

73's
Richard Clark, KB7QHC

Peter O. Brackett wrote:
Nickola Tesla would be rolling over in his grave if he could hear us
discussing a possible dichotomy between lumped and distributed systems.
Nickola "lived" in the intersticies between the wave theoretic and circuit
theoretic fabrics of reality.

Some very interesting information on that subject is contained
in: "Class Notes: Tesla Coils and the Failure of Lumped-Element
Circuit Theory" by K. L. Corum (KB1EUD) and J. F. Corum (K1AON)

http://www.ttr.com/corum/index.htm

More very good information on RF coils is found in an IEEE
paper by Drs. Corum at:

http://www.ttr.com/TELSIKS2001-MASTER-1.pdf

It's hard to look at the Figure 2 diagram of "a capacitively
tuned resonator" and not see a 75m mobile antenna with top hat.

Equations (32) for velocity factor and (51) for characteristic
impedance are of particular value to amateur radio operators.

Having a good approximation for characteristic impedance and
velocity factor for a bugcatcher mobile loading coil allows
an understandable analysis of a mobile antenna system. I'm
working on a web page based on those two papers.
--
73, Cecil http://www.w5dxp.com