"Richard Clark" wrote in message
...
On Tue, 15 Sep 2009 11:52:19 +0100, "christofire"
wrote:

No, you have it wrong again - the current must be zero at the ends, there
is
nowhere for it to go, and there cannot be acceleration of charge is
there's
no current. Please go away and read some books and the NEETS module to
which I provided the link.

Chris

Hi Chris,

This mistake is being compounded daily, so it seems. The "absence" of
current on any particular portion of the antenna is the superposition
of two currents flowing - hence the term "standing wave antenna."
Hence there is something of a paradox that where two currents reside
(the metal elements are continuous and conductive) it is said no
current flows. There is a correlation between this superposed
solution and the pattern of the far-field pattern but that does not
lead to the conclusion that there is no "acceleration" of charge at
the ends. After-all, the abundant alternating voltage at those same
ends is also charge, n'est pas? It could be as easily argued that
superposed voltage nodes also define the pattern of the far-field
pattern.

73's
Richard Clark, KB7QHC


Well, the moment of a section of a dipole is proportional to the average net
current on it and it's the integral of the moments at a point of inspection
that yields the radiation pattern. In my simplistic way of thinking, if the
moment of the end sections is zero, or as close as makes no difference, then
there's no contribution to the pattern from there, so there's no radiation
from there. Someone else who posted here a while ago used the term
'unopposed' current which is useful because it's the basis of why twin-wire
transmission line, driven differentially, is a poor radiator - put another
way, the moment at any point is close to zero. Alternatively, if there's no
radiation from a 'source' then there can't be any unopposed current there.

I wouldn't contradict what you say about there being a collection of charge
at the ends of a dipole during each cycle, especially when it has added
capacitance (e.g. a 'hat' or the top of a 'Tee'), but the current in a
symmetrical hat is fully opposed and, as I noted before, the current at the
end of the conductor must be zero - by the definition of conduction.

I believe there is danger in trying to relate radiation to voltages rather
than currents, arguing that displacement current causes radiation. Therein
lies the fallacy of the CFA, E-H antennas, and associated efforts at
re-writing of Maxwell's equations, which are all being demonstrated as bunk.
Also, this appears to be the basis of Mr. Bialek's lecture series. If you
wish to argue 'that superposed voltage nodes also define the (pattern of
the...sic) far-field pattern' then I won't stand in your way ... but I
probably won't believe you.

Chris

On Tue, 15 Sep 2009 21:25:29 +0100, "christofire"
wrote:

Well, the moment of a section of a dipole is proportional to the average net
current on it and it's the integral of the moments at a point of inspection
that yields the radiation pattern.

Hi Chris,

I have already offered that what you say above is not disputed. I
merely add that it is not the only perspective and says nothing of the
"absence" of current throughout the entire radiator.

In my simplistic way of thinking, if the
moment of the end sections is zero, or as close as makes no difference, then
there's no contribution to the pattern from there, so there's no radiation
from there.

That was the logical basis for Art's claims of length efficiency:
those portions that did not support current (read contribute to
radiation) were thus ancillary (redundant as the Briticism would go)
and unneeded. Art would then expand this logic to perform his Ritual
Antenna Bris and lop off a portion to reduce the length (increase the
efficiency). I've already commented on this reductio ad absurdum.

Far field patterns are created from the phase relationships and time
relationships, and distance relationships (all the same thing,
mathematically) from all points of the radiator to any single point of
the characteristic lobe. In the teachings of radiation as light, a
wave front can be considered to be an infinite number of points of
radiation along a curved line (that front).

Interference (with its product being the shape of a lobe) is the
combination of all their phases, distances, and times.

Someone else who posted here a while ago used the term
'unopposed' current which is useful because it's the basis of why twin-wire
transmission line, driven differentially, is a poor radiator - put another
way, the moment at any point is close to zero. Alternatively, if there's no
radiation from a 'source' then there can't be any unopposed current there.

This is not the same sense of current in a single wire that gives rise
to a structure known as a "standing wave antenna."

If you ran a twin line up into the air to an open connection, then you
would have two closely space radiators. The open would enforce a both
a longitudinal and transverse standing wave. They would both radiate
like twin fire hoses. The key point here is that in the distance of
their separation, that distance is an incredibly small fraction of the
wavelength they are radiating. Their two currents (the standing waves
on each wire being immaterial) impose an 180 degree relationship
throughout their entire length. Both waves' phases, distances, and
times cancel to within the degree of that space of separation. This
is very easy to demonstrate by observing how they become efficient and
productive non-canceling radiators as you draw them apart to form the
V antenna. The only thing that has changed is the distance which
imparts a phase (or time, or distance - all the same thing
mathematically) shift apparent at a great distance. They will still
have the same SWR along their length, and the same currents (apart
from what is imposed through the radiation resistance).


I wouldn't contradict what you say about there being a collection of charge
at the ends of a dipole during each cycle, especially when it has added
capacitance (e.g. a 'hat' or the top of a 'Tee'), but the current in a
symmetrical hat is fully opposed and, as I noted before, the current at the
end of the conductor must be zero - by the definition of conduction.

Well, to this point there has been no discussion of end loading.
Doesn't matter, all the key issues are discussed above.

I believe there is danger in trying to relate radiation to voltages rather
than currents, arguing that displacement current causes radiation.

This is an engineering shorthand. It works with great precision. But
the simple fact of the matter is there is no current without a
potential gradient. Radiation could as easily be described by it.
Without regard for patterns, radiation is a function of Ohm's law and
we have three variables there. You cannot ignore any element or
assess some distinction of one at the cost of the other(s).

Therein
lies the fallacy of the CFA, E-H antennas, and associated efforts at
re-writing of Maxwell's equations, which are all being demonstrated as bunk.
Also, this appears to be the basis of Mr. Bialek's lecture series. If you
wish to argue 'that superposed voltage nodes also define the (pattern of
the...sic) far-field pattern' then I won't stand in your way ... but I
probably won't believe you.

So I gather. It is merely a shift in perspective of conventions, not
an up-ending of them. You may note that none of my discussion above
demands any new physics, nothing new in math, no novel methods. I've
used only two wires both close together and drawn farther apart under
the most simple of terms to reveal on one hand a transmission line,
and on the other hand a V antenna. The math of phase, distance, and
time is drawn from NEC; or rather, NEC leans heavily upon it and drew
it from Optics and I state my case in the strict terms of a method of
moments.

To cut to the chase: The full length of the radiator contributes to
radiation and the evidence of this is found in any characteristic lobe
displayed in the far field.

73's
Richard Clark, KB7QHC

On Sep 15, 5:44*pm, Richard Clark wrote:
To cut to the chase: *The full length of the radiator contributes to
radiation and the evidence of this is found in any characteristic lobe
displayed in the far field.

In practical and provable terms, how much of that characteristic, far-
field radiation pattern can be attributed to the linear, unloaded,
center-fed dipole radiator lengths as exist less than ~10% distant
from the endpoints of that dipole?

Just wanting to learn.

RF

On Tue, 15 Sep 2009 16:53:55 -0700 (PDT), Richard Fry
wrote:

On Sep 15, 5:44*pm, Richard Clark wrote:
To cut to the chase: *The full length of the radiator contributes to
radiation and the evidence of this is found in any characteristic lobe
displayed in the far field.

In practical and provable terms, how much of that characteristic, far-
field radiation pattern can be attributed to the linear, unloaded,
center-fed dipole radiator lengths as exist less than ~10% distant
from the endpoints of that dipole?

The math behind this has been terribly abused by Cecil in the past,
but we shouldn't let that poison the well. It is based in optics, a
field that predates RF by several centuries.

"... S1 and S2 are two point sources of light each
emitting a sinusoidal wave of the same angular
frequency omega. They have position vectors r1
and r2. The field point P where we evaluate the
intensity [flux density] has position r. The electric
field at P resulting from the two sources is assumed
to be of the form....
"The total relative phase Psi0 between the two waves
at P thus consists of two parts: a part Phi2 - Phi1
coming from the relative phases at the two sources,
and a part -Dell coming from the different
retardation in phase suffered by the two
beams resulting from the propagation
from S2 to P and from S1 to P.
"An important special case occurs when
A1 == A2. Then we can write
I = 2·I1·(1 + cos(phi2 - phi1 - Dell))"

Every point along the radiator is considered to be a point source with
the same frequency. However, each point is not at the same phase by
virtue of its distance from the feedpoint and its distance from other
points. Each point is not at the same distance from P (a point in the
far field) which gives rise to a retardation of that altered phase.
Thus the phase accumulates over two distances: one from the excitation
source to the point on the radiator; and, two, from the point on the
radiator to the point of the lobe where we are observing all of the
effects of the combined illumination from all point sources along the
length of the radiator. The extract above speaks to the contributions
of only two points, an antenna comprises many, many more.

I will add here that the intensity variable now draws in the
discussion of the superposed forward and reflected currents. This is
the remaining part of the analysis which is more instructive for your
very simple example. Clearly, from a very small dipole to a half
wave, there is little variation in the far field pattern and it is
appealing to infer that the differences in length suggest that that
additional length suggests nothing is going on in the ends. However,
when we add only a slightly longer length (by proportion*), this
negates the appealing suggestion. The superposed current distribution
change accounts for this and we are still talking about simple linear
elements (and there is still zero current at the ends).

If we were to succumb to the argument of "length efficiency" as
offered in the practice and Art of Antenna Bris, then the additional
gain of that proportionate smaller length addition would have been
lost to that invalid proposition.

The NEC method of moments is by definition the application of the
formula above to the middle of EVERY segment to EVERY point in three
space. The resulting curve is an abstraction of that fog of numbers
that is reduced to a planar curve (or to a solid model in the 3D
representation).

[* What is this proportional and proportionate mean? For a dipole of
0.05 WL to a dipole of 0.5WL, the far field change for that 10:1
variation is negligible. However, for a dipole of 0.5WL to a dipole
of 1.25WL, the far field change for that 2.5:1 (a smaller proportion)
variation is very noticeable.]

73's
Richard Clark, KB7QHC

"Richard Clark" wrote
...
On Tue, 15 Sep 2009 16:53:55 -0700 (PDT), Richard Fry
wrote:

On Sep 15, 5:44 pm, Richard Clark wrote:
To cut to the chase: The full length of the radiator contributes to
radiation and the evidence of this is found in any characteristic lobe
displayed in the far field.

In practical and provable terms, how much of that characteristic, far-
field radiation pattern can be attributed to the linear, unloaded,
center-fed dipole radiator lengths as exist less than ~10% distant
from the endpoints of that dipole?

The math behind this has been terribly abused by Cecil in the past,
but we shouldn't let that poison the well. It is based in optics, a
field that predates RF by several centuries.

"... S1 and S2 are two point sources of light each
emitting a sinusoidal wave of the same angular
frequency omega. They have position vectors r1
and r2. The field point P where we evaluate the
intensity [flux density] has position r. The electric
field at P resulting from the two sources is assumed
to be of the form....
"The total relative phase Psi0 between the two waves
at P thus consists of two parts: a part Phi2 - Phi1
coming from the relative phases at the two sources,
and a part -Dell coming from the different
retardation in phase suffered by the two
beams resulting from the propagation
from S2 to P and from S1 to P.
"An important special case occurs when
A1 == A2. Then we can write
I = 2·I1·(1 + cos(phi2 - phi1 - Dell))"

Every point along the radiator is considered to be a point source with
the same frequency. However, each point is not at the same phase by
virtue of its distance from the feedpoint and its distance from other
points. Each point is not at the same distance from P (a point in the
far field) which gives rise to a retardation of that altered phase.
Thus the phase accumulates over two distances: one from the excitation
source to the point on the radiator; and, two, from the point on the
radiator to the point of the lobe where we are observing all of the
effects of the combined illumination from all point sources along the
length of the radiator. The extract above speaks to the contributions
of only two points, an antenna comprises many, many more.

"Every point along the radiator is considered to be a point source with
the same frequency".
But the intesity of radiation is not the same. Electron at the end of the
open circuit are extremally compressed. Intensity of radiation is
compression dependent. Of course radiation means alternate electric field
(Art's "Gauss law with time").

I will add here that the intensity variable now draws in the
discussion of the superposed forward and reflected currents. This is
the remaining part of the analysis which is more instructive for your
very simple example. Clearly, from a very small dipole to a half
wave, there is little variation in the far field pattern

Antenna is the last part of the open circuit. If it has the half wave or
less such dipole antenna has only one intesive source of radiation on one
radiator.

and it is
appealing to infer that the differences in length suggest that that
additional length suggests nothing is going on in the ends.

See abowe.

However,
when we add only a slightly longer length (by proportion*), this
negates the appealing suggestion.

If "visible" part of an antanna is longer than the 1/4 WL the next source
appears.

The superposed current distribution
change accounts for this and we are still talking about simple linear
elements (and there is still zero current at the ends).

If we were to succumb to the argument of "length efficiency" as
offered in the practice and Art of Antenna Bris, then the additional
gain of that proportionate smaller length addition would have been
lost to that invalid proposition.

The NEC method of moments is by definition the application of the
formula above to the middle of EVERY segment to EVERY point in three
space. The resulting curve is an abstraction of that fog of numbers
that is reduced to a planar curve (or to a solid model in the 3D
representation).

[* What is this proportional and proportionate mean? For a dipole of
0.05 WL to a dipole of 0.5WL, the far field change for that 10:1
variation is negligible.

The both (0.05 WL to a dipole of 0.5WL have only the two sources at the both
ends.

However, for a dipole of 0.5WL to a dipole
of 1.25WL, the far field change for that 2.5:1 (a smaller proportion)
variation is very noticeable.]

Each "long wire antenna" has additional sources for each 0.5WL.

"The full length of the radiator" means the "vissible" and spaced part of
feeding line. Yor: "If you ran a twin line up into the air to an open
connection, then you would have two closely space radiators."

Step by step and the discussion should end with the full agreement (I am
sure).
S*

On Wed, 16 Sep 2009 11:24:16 +0200, Szczepan Bia?ek
wrote:

S*

Can you read English?

73's
Richard Clark, KB7QHC

Richard Clark wrote:
The math behind this has been terribly abused by Cecil in the past,
but we shouldn't let that poison the well.

NEC would be interested in your proof that the
method of moments is abuse and poison.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com

Richard Fry wrote:
In practical and provable terms, how much of that characteristic, far-
field radiation pattern can be attributed to the linear, unloaded,
center-fed dipole radiator lengths as exist less than ~10% distant
from the endpoints of that dipole?

For the MOM calculations inside NEC, the net segment
*current* determines the incremental far-field.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com

"christofire" wrote
...

"Richard Clark" wrote in message
...
On Tue, 15 Sep 2009 11:52:19 +0100, "christofire"
wrote:

No, you have it wrong again - the current must be zero at the ends, there
is
nowhere for it to go, and there cannot be acceleration of charge is
there's
no current. Please go away and read some books and the NEETS module to
which I provided the link.

Chris

Hi Chris,

This mistake is being compounded daily, so it seems. The "absence" of
current on any particular portion of the antenna is the superposition
of two currents flowing - hence the term "standing wave antenna."
Hence there is something of a paradox that where two currents reside
(the metal elements are continuous and conductive) it is said no
current flows. There is a correlation between this superposed
solution and the pattern of the far-field pattern but that does not
lead to the conclusion that there is no "acceleration" of charge at
the ends. After-all, the abundant alternating voltage at those same
ends is also charge, n'est pas? It could be as easily argued that
superposed voltage nodes also define the pattern of the far-field
pattern.

73's
Richard Clark, KB7QHC


Well, the moment of a section of a dipole is proportional to the average
net current on it and it's the integral of the moments at a point of
inspection that yields the radiation pattern. In my simplistic way of
thinking, if the moment of the end sections is zero, or as close as makes
no difference, then there's no contribution to the pattern from there, so
there's no radiation from there. Someone else who posted here a while ago
used the term 'unopposed' current which is useful because it's the basis
of why twin-wire transmission line, driven differentially, is a poor
radiator - put another way, the moment at any point is close to zero.
Alternatively, if there's no radiation from a 'source' then there can't be
any unopposed current there.

I wouldn't contradict what you say about there being a collection of
charge at the ends of a dipole during each cycle, especially when it has
added capacitance (e.g. a 'hat' or the top of a 'Tee'), but the current in
a symmetrical hat is fully opposed and, as I noted before, the current at
the end of the conductor must be zero - by the definition of conduction.

I believe there is danger in trying to relate radiation to voltages rather
than currents, arguing that displacement current causes radiation.
Therein lies the fallacy of the CFA, E-H antennas, and associated efforts
at re-writing of Maxwell's equations, which are all being demonstrated as
bunk. Also, this appears to be the basis of Mr. Bialek's lecture series.
If you wish to argue 'that superposed voltage nodes also define the
(pattern of the...sic) far-field pattern' then I won't stand in your way
... but I probably won't believe you.

So I will start "Mr. Bialek's lecture series" as a new topic.
The first will be on a "standing waves". A will try to explain the paradox:
"Hence there is something of a paradox that where two currents reside (the
metal elements are continuous and conductive) it is said no current flows
(R. Clark).
S*


Chris