colinear representation in NEC
 

Tom Donaly wrote:
Jim Lux wrote:
. . .
No it doesn't do prop delay. It does a steady state model. The TL is
just another two port that gets dumped into a giant matrix which is
solved as a system of linear equations. Think of TL as a special case
of NT.

What kind of two port does NEC use, Jim? What is "just another two port?"
73,
Tom Donaly, KA6RUH

NEC network objects are two port networks described by a set of Y
parameters -- see the NEC-2 documentation on the NT "card". When a
transmission line is specified via a TL "card", the Y parameters
appropriate for the specified line length and Z0 are calculated for a
standard Y parameter network which is then used in the model. In the
code, this is done in the NETWK subroutine between line labels 16 and 17.

EZNEC v. 5.0 allows the user to specify a skin-effect proportional
transmission line loss. It accomplishes this internally by appropriately
modifying the network Y parameters.

Roy Lewallen, W7EL

colinear representation in NEC
 

Cecil Moore wrote:
Jim Kelley wrote:
Cecil Moore wrote:

Could it be that a monopole is a "STANDING WAVE ANTENNA"?

The supposition is true, so the intended implication must be that only
standing wave current can be measured on monopole antennas. And Roy
therefore would have to have measured standing wave current (whatever
that is).

I must decline to agree. :-)

About 90% of the total current on an open-ended 1/4WL
monopole is standing wave current with close to unchanging
phase. That's why a 1/4WL monopole is called a "standing
wave antenna".

Presumably they're not called that because of 'standing current'. A
standing wave is just the stationary pattern that results from the
interference of waves. It doesn't really have a 'life' of it's own.

This is such a simple concept - I don't see the problem
in understanding that a wave with the following equation
doesn't change phase with position (x).

Cecil - as the equation is written, the phase term IS position. The
phase of the sine function changes with x.

The phase is the
same over 90 degrees of length no matter what fixed x and
fixed t are chosen. EZNEC supports that fact of physics.
Here's the standing wave equation from "Optics", by Hecht:

The phase of a time varying function changes with time except in the
special case of a 'standing wave' function, where it changes with position.

E(x,t) = 2E01*sin(kx)*cos(wt) quoting "Optics", by Hecht:

"[Standing wave phase] "doesn't rotate at all, and the resultant
wave it represents doesn't progress through space - its a standing
wave."

Right. He could (and should) have gone on to say that standing waves
don't really *DO* anything at all.

Another interesting thing about the standing wave equation
is that the sign of (wt) can be reversed, i.e. standing waves
don't move in either direction - they just stand there. EM
waves cannot stand still so "EM standing wave" is an oxymoron.

Quoting one of my college textbooks, "Electrical
Communication", by Albert:

"Such a plot of voltage is usually referred to as a
*voltage standing wave* or as a *stationary wave*.
Neither of these terms is particularly descriptive
of the phenomenon. A plot of effective values of
voltage, appearing as in Fig. 6(e), *is not a wave*
in the usual sense. However, the term "standing wave"
is in widespread use."

From "College Physics", by Bueche and Hecht:

"These ... patterns are called *standing waves*, as
compared to the propagating waves considered above.
They might better not be called waves at all, since
they do not transport energy and momentum."

Right. All of which deepens the mystery of why you would continue to
insist on claiming that Roy measured standing wave current.

One can use EZNEC's VERT1.EZ to view the essentially
unchanging phase on a standing wave monopole. Just look
at the difference in phase between the feedpoint and a
point 45 degrees up the antenna. In 45 degrees of antenna,
the current phase changes by 3.65 degrees. That is the
current Roy used to measure phase shift through a coil
in order to support w8ji's 3 nS delay "measurements".

I still need you to explain what standing wave _current_ is, and, just
as importantly how it phase shifts by *TRAVELING* through a coil.

73, ac6xg

colinear representation in NEC
 

Tom Donaly wrote:
What's the Z0 of a loading coil, Cecil?

Z0 and VF depend upon the geometry of the coil
*and the frequency*. A 75m Texas Bugcatcher coil
has a Z0 of ~3800 ohms and a VF of ~0.02. The
coil that w8ji used for his 3 nS "measurements"
has a Z0 of ~5300 ohms and a VF of ~0.033. I've
generated an EXCEL file that does the calculations:

http://www.w5dxp.com/CoilZ0VF.xls

I've also got a web page that explains why the
current phase in a standing-wave antenna cannot
be used to measure delay.

http://www.w5dxp.com/current2.htm

I have done the suggested bench experiments myself
and the results are nowhere near w8ji's results.
When traveling wave current is used instead of
standing wave current, the delay is obvious on a
dual-trace O'scope.

This is nothing new. It is based on the information
in the IEEE paper which someone presented years ago:

http://www.ttr.com/TELSIKS2001-MASTER-1.pdf
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com
"Government 'help' to business is just as disastrous as government
persecution..." Ayn Rand

colinear representation in NEC
 

Roy Lewallen wrote in
:
....

NEC network objects are two port networks described by a set of Y
parameters -- see the NEC-2 documentation on the NT "card". When a
transmission line is specified via a TL "card", the Y parameters
appropriate for the specified line length and Z0 are calculated for a
standard Y parameter network which is then used in the model. In the
code, this is done in the NETWK subroutine between line labels 16 and
17.

EZNEC v. 5.0 allows the user to specify a skin-effect proportional
transmission line loss. It accomplishes this internally by
appropriately modifying the network Y parameters.

I suspected as much from model behaviour.

My question is then, can the 'stub' in figure a) be replaced by a TL
element for a valid model of a)?

Owen

colinear representation in NEC
 

Jim Kelley wrote:
[A standing wave] doesn't really have a 'life' of it's own.

My point exactly, Jim. We may be closer than you think.

Cecil - as the equation is written, the phase term IS position. The
phase of the sine function changes with x.

My point exactly, Jim. We may be closer than you think.
Tom and Roy did NOT use position to determine the phase.
That is the entire point of my posting.

The phase of a time varying function changes with time except in the
special case of a 'standing wave' function, where it changes with position.

Again, my point exactly - something that (apparently)
neither w8ji or w7el wants to admit.

Right. He could (and should) have gone on to say that standing waves
don't really *DO* anything at all.

My point exactly! Now try to tell it to w8ji and w7el
who used primarily standing wave current to prove their
points.

I still need you to explain what standing wave _current_ is, and, just
as importantly how it phase shifts by *TRAVELING* through a coil.

My point exactly, Jim. We may be closer than you think.
I am the one who is saying that it doesn't phase shift
while traveling through a wire or a coil. W8JI and W7EL
apparently think that it does phase shift through a coil
and can therefore be used to measure the delay through
a coil. I am the one who disagrees with that concept.

You and I are on the same side, Jim. This reminds me of
the time someone else realized the gurus were wrong and
simply stopped posting in order to save guru face and
to avoid proving them wrong.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com
"Government 'help' to business is just as disastrous as government
persecution..." Ayn Rand

colinear representation in NEC
 

Owen Duffy wrote:
Roy Lewallen wrote in
:
...
NEC network objects are two port networks described by a set of Y
parameters -- see the NEC-2 documentation on the NT "card". When a
transmission line is specified via a TL "card", the Y parameters
appropriate for the specified line length and Z0 are calculated for a
standard Y parameter network which is then used in the model. In the
code, this is done in the NETWK subroutine between line labels 16 and
17. . .

I suspected as much from model behaviour.

My question is then, can the 'stub' in figure a) be replaced by a TL
element for a valid model of a)?

Owen

No, it can't. The NEC two-port network object can't have any common mode
current -- the current out of one terminal of a port is always exactly
equal to the current into the other terminal of that port regardless of
external connections, which means that common mode current is zero by
definition. The wire stub, on the other hand, couples to external fields
which can cause common mode current on the wires.

The only time you can substitute a transmission line (network) object
for a wire transmission line is when the transmission line is carrying
no common mode current. An example would be a transmission line
connected to the center of a symmetrical dipole and positioned
symmetrically with respect to the dipole so it gets equal coupling from
both legs.

A coaxial line can be modeled as a combination of a transmission line
(network) object and a wire, the former carrying the differential mode
current and the latter the common mode current, as described in the
EZNEC manual. This is possible because the two components are physically
separated on a coax line. However, I don't know of any way to do the
equivalent thing with a parallel-wire line because the two components
aren't physically separated as they are on coax.

Roy Lewallen, W7EL

colinear representation in NEC
 

Cecil Moore wrote:
Jim Kelley wrote:
[A standing wave] doesn't really have a 'life' of it's own.

My point exactly, Jim. We may be closer than you think.

Cecil - as the equation is written, the phase term IS position. The
phase of the sine function changes with x.

My point exactly, Jim. We may be closer than you think.
Tom and Roy did NOT use position to determine the phase.
That is the entire point of my posting.

The phase of a time varying function changes with time except in the
special case of a 'standing wave' function, where it changes with
position.

Again, my point exactly - something that (apparently)
neither w8ji or w7el wants to admit.

Right. He could (and should) have gone on to say that standing waves
don't really *DO* anything at all.

My point exactly! Now try to tell it to w8ji and w7el
who used primarily standing wave current to prove their
points.

I still need you to explain what standing wave _current_ is, and, just
as importantly how it phase shifts by *TRAVELING* through a coil.

My point exactly, Jim. We may be closer than you think.
I am the one who is saying that it doesn't phase shift
while traveling through a wire or a coil. W8JI and W7EL
apparently think that it does phase shift through a coil
and can therefore be used to measure the delay through
a coil. I am the one who disagrees with that concept.

You and I are on the same side, Jim.

That's true more than you know, which is why I can't figure out why you
keep claiming that someone has measured standing wave current phase
shifts (whatever they are).

73, ac6xg

colinear representation in NEC
 

Jim Kelley wrote:
That's true more than you know, which is why I can't figure out why you
keep claiming that someone has measured standing wave current phase
shifts (whatever they are).

I previously published the currents in a 20m dipole
with 21 segments. Here they are again. Can you comprehend
why there is only a maximum phase shift of 4.54 degrees
in 180 degrees of antenna? That is NOT the characteristic
of traveling wave current. That is the characteristic of
primarily standing wave current which has constant phase.

Roy reported that the phase shift across a loading coil wasn't
measurable which is a true statement because the standing wave
current indeed doesn't change phase across a coil or through a
wire. But he then used that same evidence to support w8ji's
ridiculous 3 nS delay through a 75m mobile loading coil when
there is no relationship between standing wave current phase
and the delay through a loading coil. Traveling wave current
must be used to measure the delay through a loading coil,
something I have been saying for years.

EZNEC+ ver. 4.0

20m dipole 3/23/2009 8:43:06 PM

--------------- CURRENT DATA ---------------

Frequency = 14.2 MHz

Wire No. 1:
Segment Conn Magnitude (A.) Phase (Deg.)
1 Open .09631 -4.54
2 .2561 -4.25
3 .39868 -3.93
4 .5289 -3.60
5 .64603 -3.25
6 .74868 -2.86
7 .83539 -2.43
8 .90483 -1.94
9 .95592 -1.38
10 .98795 -0.68
11 feedpoint 1 0.00
12 .98795 -0.68
13 .95592 -1.38
14 .90483 -1.94
15 .83539 -2.43
16 .74868 -2.86
17 .64602 -3.25
18 .5289 -3.60
19 .39868 -3.93
20 .2561 -4.25
21 Open .09631 -4.54
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com
"Government 'help' to business is just as disastrous as government
persecution..." Ayn Rand

colinear representation in NEC
 

Roy Lewallen wrote in
treetonline:

Owen Duffy wrote:
....
My question is then, can the 'stub' in figure a) be replaced by a TL
element for a valid model of a)?

Owen

No, it can't. The NEC two-port network object can't have any common
mode
....

Thanks Roy.

Is NEC capable of modelling the configuration shown at
http://www.vk1od.net/lost/King-22.3b.png (which is the same type of
problem as my figure b)?

My attempts to model b) by modelling a plain conductor and inserting a
load in the segment where the open end of the coax stub would otherwise
be, does not result in an in-phase current distribution.

King discusses the coaxial stub and suggests that the conductors need to
be significantly large in diameter, and the stub length would be less
than a quarter wave for in-phase radiator currents.

Owen

colinear representation in NEC
 

Owen Duffy wrote:

Thanks Roy.

Is NEC capable of modelling the configuration shown at
http://www.vk1od.net/lost/King-22.3b.png (which is the same type of
problem as my figure b)?

My attempts to model b) by modelling a plain conductor and inserting a
load in the segment where the open end of the coax stub would otherwise
be, does not result in an in-phase current distribution.

King discusses the coaxial stub and suggests that the conductors need to
be significantly large in diameter, and the stub length would be less
than a quarter wave for in-phase radiator currents.

Owen

Your description of the model is correct. Technically, the wire
representing the outside of the coax (which in the model is located
where the coax line is) should be the diameter of the shield, as we've
discussed before. The stepped wire diameter error of NEC-2 might,
however, result in less accurate results by doing this than by leaving
the diameter the same as the other wires. Experiments with your earlier
b) model showed that the transmission line object characteristics have
almost no effect on the wire currents when it's inserted at a point of
very low current, and that it doesn't result in in-phase current
distribution. That will be true here also at frequencies where the
current is very low near the open end of the stub.

Roy Lewallen, W7EL

colinear representation in NEC
 

Cecil Moore wrote:
Tom Donaly wrote:
What's the Z0 of a loading coil, Cecil?

Z0 and VF depend upon the geometry of the coil
*and the frequency*. A 75m Texas Bugcatcher coil
has a Z0 of ~3800 ohms and a VF of ~0.02. The
coil that w8ji used for his 3 nS "measurements"
has a Z0 of ~5300 ohms and a VF of ~0.033. I've
generated an EXCEL file that does the calculations:

http://www.w5dxp.com/CoilZ0VF.xls

I've also got a web page that explains why the
current phase in a standing-wave antenna cannot
be used to measure delay.

http://www.w5dxp.com/current2.htm

I have done the suggested bench experiments myself
and the results are nowhere near w8ji's results.
When traveling wave current is used instead of
standing wave current, the delay is obvious on a
dual-trace O'scope.

This is nothing new. It is based on the information
in the IEEE paper which someone presented years ago:

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

Still using the Tesla coil fella's ideas, are you? A frequency
dependent Z0 is a good trick. What happens when you double the
length of the coil? Does the Z0 stay the same? What if the coil is
infinite? Can you make a quarter wave shorted stub with it? If you
make it a half wavelength long - keeping in mind the velocity factor -
will the impedance looking into the coil equal the impedance of
the load? How do you attach a load to it?
73,
Tom Donaly, KA6RUH

colinear representation in NEC
 

Roy Lewallen wrote in
treetonline:

Owen Duffy wrote:
....
Is NEC capable of modelling the configuration shown at
http://www.vk1od.net/lost/King-22.3b.png (which is the same type of
problem as my figure b)?

A point made by King is that if the three half waves are in phase,
radiation resistance will be quite high (one third current required for
same distant field strength), around 316 ohms against 105 ohms for three
half waves not-in-phase. Presumably these figures are for free space.

This effect is certainly observable in models using my Fig a) (though
half the respective resistances due to the vertical over perfect ground).

The feedpoint impedance looks like it might provide a hint as to whether
currents are actually in-phase.

Exploring that thought, an example (to some extent) of King's Fig 22.3b
is the W5GI Mystery Antenna (see
http://www.w5gi.com/images/w5gimster...aschematic.gif ) which claims
to be three half waves in phase at 14.2MHz. It is very similar to the
diagram above in King though I note that the phasing sections are 105° in
electrical length.

The W5GI is fed with a half wave (at 14.2MHz) of 300 ohm line, then 34'
of RG8X. W5GI reports impedance looking into the RG8X as 42+/-j18. That
suggests the load on the RG8X is 31+j2 or 70-j18. The feedpoint impedance
should be about the same value due to the half wave of 300 ohm low loss
line. Neither impedance is within a bull's roar of 316+j0, and are so low
as to question whether the three half waves are indeed in-phase. (The
highest impedance that would yeild 42+/-j18 on a short length of RG8X
would be around 80+j0, closer to the not-in-phase configuration than the
in-phase configuration).

W5GI's reported feed impedance seem inconsistent with three half waves in
phase, and questions whether the phasing arrangement works as suggested.

Thoughts?

Owen

colinear representation in NEC
 

Tom Donaly wrote:
Still using the Tesla coil fella's ideas, are you?

The title of the article is "RF Coils, ..." The block
diagram of a Tesla coil with a top hat is identical
to a 160m mobile antenna with top hat.

A frequency dependent Z0 is a good trick.

It's no trick - just based on empirical measurements
as explained in the IEEE paper. Measurements proved
that the Z0 of a coil varies with wavelength so
wavelength is included in the empirical formula.
I observed that phenomenon during my own experiments.

What happens when you double the length of the coil?

Same thing as doubling the length of a stub. At a fixed
frequency, the delay through the coil is (roughly) doubled.

Does the Z0 stay the same? What if the coil is infinite?

Length of the coil does not appear in the empirical
formula for Z0 of a coil. Coil diameter, TPI, and
wavelength are the variables. Wire diameter would
obviously have some effect but is not included in
the empirical formula.

Can you make a quarter wave shorted stub with it?

Yes, but you need a ground plane close by. Mininec ground will do.
Here's a 75m Texas Bugcatcher coil loaded with its Z0 impedance
modeled over Mininec ground.

http://www.w5dxp.com/coil505u.EZ

The current phase shift through the coil is clearly visible
by displaying "Load Dat". The delay through the coil (EZNEC)
is roughly proportional to the phase shift, i.e. about 38
degrees. The coil is 0.5 feet long with a calculated VF
of 0.02 so the calculated phase shift (without EZNEC) is
about 36 degrees. That's pretty close agreement.
If you make it a half wavelength long - keeping in mind the velocity
factor -
will the impedance looking into the coil equal the impedance of the load?
How do you attach a load to it?

Here's the Texas Bugcatcher coil modeled at the first (1/4WL)
self-resonant frequency of 7.96 MHz:

http://www.w5dxp.com/coil505s.EZ

I have not experimented with 1/2WL self-resonance. The above
file seems to be 1/2WL self-resonant at about 19.2 MHz but
the 75m Texas Bugcatcher coil, at 19.2 MHz, does not meet
the guidelines for validity given in the IEEE article.

Reference:
http://www.w5dxp.com/current2.htm
http://www.w5dxp.com/current.htm
http://www.w5dxp.com/CoilZ0VF.xls
http://www.ttr.com/TELSIKS2001-MASTER-1.pdf
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com
"Government 'help' to business is just as disastrous as government
persecution..." Ayn Rand

colinear representation in NEC
 

Owen Duffy wrote:
The feedpoint impedance looks like it might provide a hint as to whether
currents are actually in-phase.

At a 1/4WL monopole's resonant frequency, the forward antenna
current and reflected antenna current are in phase. The two
component voltages are 180 degrees out of phase. The feedpoint
resistance is [|Vfor|-|Vref|]/[|Ifor|+|Iref|] where these are
antenna voltages and currents on a standing-wave antenna.

If the feedpoint impedance is purely resistive it appears
that the two component waves must be in phase or 180 degrees
out of phase.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com
"Government 'help' to business is just as disastrous as government
persecution..." Ayn Rand

colinear representation in NEC
 

Cecil Moore wrote:

Roy reported that the phase shift across a loading coil wasn't
measurable which is a true statement because the standing wave
current indeed doesn't change phase across a coil or through a
wire.

He wasn't measuring "standing wave current", whatever that is. You
should probably examine his test setup more carefully.

But he then used that same evidence to support w8ji's
ridiculous 3 nS delay through a 75m mobile loading coil when
there is no relationship between standing wave current phase
and the delay through a loading coil. Traveling wave current
must be used to measure the delay through a loading coil,
something I have been saying for years.

And after all those years you still haven't provided any measurements
that support what you've been saying. And as far as I know, neither has
anyone else. But I'm happy to stand corrected.

73, ac6xg

colinear representation in NEC
 

Jim Kelley wrote:
He wasn't measuring "standing wave current", whatever that is.

Sorry Jim, of course he was, since standing wave current
is the primary current that exists on standing wave
antennas like the antenna Roy used to measure his currents.

You keep saying "whatever that is" when it is well
defined in most any antenna book. That you don't
understand standing wave current on standing wave
antennas is just a statement of ignorance - no
offense intended - apparently Roy is just as ignorant.

Perhaps you should study and understand the
difference between a standing wave antenna like
a dipole and a traveling wave antenna like a
terminated Rhombic. Balanis has a good discussion
of such. Here's a quote: "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..."

An inverted-V dipole can be converted from a
standing wave antenna to a traveling wave antenna
by terminating the ends with a load connected to
mininec ground. Here is an inv_V and a terminated
inv_V modeled in EZNEC. Please look at the "Currents"
display until you understand the meaning of the
phase angles.

http://www.w5dxp.com/inv_v.EZ (standing wave antenna)

Phase angle of the current varies by 2.72 degrees
along each 90 degrees of antenna. This is the current
that Roy used.

http://www.w5dxp.com/inv_vT.EZ (traveling wave antenna)

Phase angle of the current varies by 90 degrees
along each 90 degrees of antenna. This is the current
that Roy should have used.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com
"Government 'help' to business is just as disastrous as government
persecution..." Ayn Rand

colinear representation in NEC
 

Cecil Moore wrote:
Jim Kelley wrote:
He wasn't measuring "standing wave current", whatever that is.

Sorry Jim, of course he was, since standing wave current
is the primary current that exists on standing wave
antennas like the antenna Roy used to measure his currents.

The only current flowing on an antenna is the current traveling from one
end to the other.

You keep saying "whatever that is" when it is well
defined in most any antenna book.

I have the ARRL Antenna Book. Where might I find 'Standing Wave
Current' defined, or at least a description of how to measure it?
Perhaps it's in a section about 'Standing Wave Power'?

That you don't
understand standing wave current on standing wave
antennas is just a statement of ignorance - no
offense intended - apparently Roy is just as ignorant.

Sounds authoratative. I wonder if anyone is buying it?

73, ac6xg

colinear representation in NEC
 

Jim Kelley wrote:
The only current flowing on an antenna is the current traveling from one
end to the other.

Since standing waves cannot exist without the underlying
component traveling waves, to avoid conceptual blunders,
one needs to deal directly with the component traveling
waves. Your statement is based on a purely mathematical
shortcut which exists only in the human brain, not in
reality, and obscures the actual speed-of-light physics
necessary for an EM wave to even exist.

The current can be artificially parsed the way you
are doing it but that parsing leads to the very
misconception under which you are laboring. The same
thing happened with w8ji's and w7el's "measurements"
involving delays through loading coils. The actual
component physics, as explained in any reasonably
technical antenna book is:

Total current = forward current + reflected current

Itot = Ifor + Iref (phasor addition)

Reference: "Antenna Theory", Balanis, 2nd edition

Balanis, page 488:
"The sinusoidal current distribution of long open-ended
linear antennas is a standing wave constructed by two
waves of equal amplitude and 180 degrees phase difference
at the open end traveling in opposite directions along
its length. ... The current and voltage distributions
on open-ended wire antennas are similar to the standing
wave patterns on open-ended transmission lines."

Balanis, page 489:
"Standing wave antennas, such as the dipole, can be
analyzed as traveling wave antennas with waves
propagating in opposite direstions (forward and
backwards) and and represented by traveling wave
currents, If and Ib in Figure 10.1a."

In a standing wave antenna, e.g. a 1/2WL dipole, there
exists a forward wave that gives up about 10% of its
energy content to radiation. The remaining 90% of the
wave encounters the open end of the antenna and is
reflected. So, just as in the case of an open-circuit
stub, we have a forward current component flowing in
one direction and a reflected current component flowing
in the other direction. Many of the mistakes and mis-
conceptions about antennas are based on your false
assertion above.

I have the ARRL Antenna Book.

:-) The ARRL Antenna Book doesn't even have "traveling
wave antennas" in its index. It does state: "Unterminated
long-wire antennas are often referred to as 'standing
wave antennas'". Please reference a reasonably technical
antenna book like "Antennas", by Kraus. "A sinusoidal
current distribution (on a standing wave antenna) may be
regarded as the standing wave produced by two uniform
(unattenuated) traveling waves of equal amplitude moving
in opposite directions along the antenna."

I wonder if anyone is buying it?

It doesn't matter if anyone is buying it. What matters
is technical validity. Your first statement above is
technical invalid. Given the free space description of
standing waves of light given by Hecht in "Optics", your
assertion above would lead one to believe that the photons
comprising the standing wave of light must be at rest even
though that's an impossibility (except in the human mind).

Here's what a couple of references say about standing waves.
"Electrical Communication", by Albert:

"Such a plot of voltage is usually referred to as a
*voltage standing wave* or as a *stationary wave*.
Neither of these terms is particularly descriptive
of the phenomenon. A plot of effective values of
voltage, appearing as in Fig. 6(e), *is not a wave*
in the usual sense. However, the term "standing wave"
is in widespread use."

"College Physics", by Bueche and Hecht:

"These ... patterns are called *standing waves*, as
compared to the propagating waves considered above.
*They might better not be called waves at all*, since
they do not transport energy and momentum."
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com
"Government 'help' to business is just as disastrous as government
persecution..." Ayn Rand

colinear representation in NEC
 

Jim Kelley wrote:
The only current flowing on an antenna is the current traveling from one
end to the other.

Let's assume you are correct. Here are a few questions:

1. Given a 90 degree monopole fed against an infinite
ground plane, what would be the phase at the top of the
antenna compared to the phase at the feedpoint for any
instant in time?

2. Why would the feedpoint impedance of a 1/4WL monopole
be more than a magnitude less than the feedpoint impedance
of an infinite monopole?

3. Where does the above current go when it hits the open-
circuit at the top of the monopole?

4. Why is the total energy in the E-field at the top of the
monopole so high?
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com
"Government 'help' to business is just as disastrous as government
persecution..." Ayn Rand

colinear representation in NEC
 

Owen Duffy wrote:
Roy Lewallen wrote in
treetonline:

Owen Duffy wrote:
...
Is NEC capable of modelling the configuration shown at
http://www.vk1od.net/lost/King-22.3b.png (which is the same type of
problem as my figure b)?

A point made by King is that if the three half waves are in phase,
radiation resistance will be quite high (one third current required for
same distant field strength), around 316 ohms against 105 ohms for three
half waves not-in-phase. Presumably these figures are for free space.
. . .

I looked up the section in King, Mimno, and Wing and was pretty
disappointed. It's one of my favorite references, and I usually find the
explanations clear. But the description of that antenna is pretty vague,
with considerable hand waving ("[Operation of coaxial stubs] is much
less satisfactory than that with the open-wire stubs. . ." without
explaining why). And in the explanation of the open-wire stubs, the
authors seem to state that the wires must carry purely differential
currents. And their models (Fig. 22-4) do show purely differential
coupling from the antenna to the stubs.

I speculate that they really didn't understand how these antennas
worked, had discovered that the coaxial sleeve versions didn't work or
at least didn't work as well -- and didn't show the proper impedance --,
but didn't fully understand why. King, in particular, was and is one of
the giants of antenna theory, and leaves us a lifetime of brilliant
insight and rigorous mathematical analysis. But at least at the time
that book was published, they lacked the modeling tools we have today.

This effect is certainly observable in models using my Fig a) (though
half the respective resistances due to the vertical over perfect ground).

The feedpoint impedance looks like it might provide a hint as to whether
currents are actually in-phase.

It surely does. Given the currents on and locations of the end wires,
the modification to the center wire can be calculated from mutual
coupling considerations. And I think this is a clue that led King,
Mimno, and Wing to conclude that something was amiss with the coaxial
version.

Exploring that thought, an example (to some extent) of King's Fig 22.3b
is the W5GI Mystery Antenna (see
http://www.w5gi.com/images/w5gimster...aschematic.gif ) which claims
to be three half waves in phase at 14.2MHz. It is very similar to the
diagram above in King though I note that the phasing sections are 105° in
electrical length.

The W5GI is fed with a half wave (at 14.2MHz) of 300 ohm line, then 34'
of RG8X. W5GI reports impedance looking into the RG8X as 42+/-j18. That
suggests the load on the RG8X is 31+j2 or 70-j18. The feedpoint impedance
should be about the same value due to the half wave of 300 ohm low loss
line. Neither impedance is within a bull's roar of 316+j0, and are so low
as to question whether the three half waves are indeed in-phase. (The
highest impedance that would yeild 42+/-j18 on a short length of RG8X
would be around 80+j0, closer to the not-in-phase configuration than the
in-phase configuration).

W5GI's reported feed impedance seem inconsistent with three half waves in
phase, and questions whether the phasing arrangement works as suggested.

Thoughts?

I doubt that it does.

Roy Lewallen, W7EL

colinear representation in NEC
 

Hi Roy,

Roy Lewallen wrote in
treetonline:

Owen Duffy wrote:
Roy Lewallen wrote in
treetonline:

Owen Duffy wrote:
...
Is NEC capable of modelling the configuration shown at
http://www.vk1od.net/lost/King-22.3b.png (which is the same type
of problem as my figure b)?

A point made by King is that if the three half waves are in phase,
radiation resistance will be quite high (one third current required
for same distant field strength), around 316 ohms against 105 ohms
for three half waves not-in-phase. Presumably these figures are for
free space. . . .

I looked up the section in King, Mimno, and Wing and was pretty
disappointed. It's one of my favorite references, and I usually find
the explanations clear. But the description of that antenna is pretty
vague, with considerable hand waving ("[Operation of coaxial stubs] is
much less satisfactory than that with the open-wire stubs. . ."
without explaining why). And in the explanation of the open-wire

This lesser mortal was encouraged that he noted the difference, but there
really was no explanation. My feeling is that to note the difference but
to be unable to explain it, other than nebuluous conditions like the
coaxial tubes must be large diameter ratio, is incomplete... a problem
yet to be solved.

I have come to the conclusion that the coaxial tubes are not simply a
relocation of a TL as popularly explained. Over the years, I have
accumulated a few projects that were works of art, but didn't work
properly... and they all used coaxial phasing sections.

stubs, the authors seem to state that the wires must carry purely
differential currents. And their models (Fig. 22-4) do show purely
differential coupling from the antenna to the stubs.

I speculate that they really didn't understand how these antennas
worked, had discovered that the coaxial sleeve versions didn't work or
at least didn't work as well -- and didn't show the proper impedance
--, but didn't fully understand why. King, in particular, was and is
one of the giants of antenna theory, and leaves us a lifetime of
brilliant insight and rigorous mathematical analysis. But at least at
the time that book was published, they lacked the modeling tools we
have today.

Understood... but, I think after our discussion on this, NEC is not up to
the task, it may take a more advanced EM field modelling tool.

My suspicion is that NEC's shortfall is that a TL element does not
properly represent the coaxial stub and its interaction with the other
elements near resonance, though well away from resonance, it is possible
that it may be quite ok. King raises the issues of diameter ratios, and
the difference with whether the stub is inboard or outboard of the o/c
end... but it is not resolved quantitatively.


This effect is certainly observable in models using my Fig a) (though
half the respective resistances due to the vertical over perfect
ground).

The feedpoint impedance looks like it might provide a hint as to
whether currents are actually in-phase.

It surely does. Given the currents on and locations of the end wires,
the modification to the center wire can be calculated from mutual
coupling considerations. And I think this is a clue that led King,
Mimno, and Wing to conclude that something was amiss with the coaxial
version.

Exploring that thought, an example (to some extent) of King's Fig
22.3b is the W5GI Mystery Antenna (see
http://www.w5gi.com/images/w5gimster...aschematic.gif ) which
claims to be three half waves in phase at 14.2MHz. It is very similar
to the diagram above in King though I note that the phasing sections
are 105° in electrical length.

The W5GI is fed with a half wave (at 14.2MHz) of 300 ohm line, then
34' of RG8X. W5GI reports impedance looking into the RG8X as
42+/-j18. That suggests the load on the RG8X is 31+j2 or 70-j18. The
feedpoint impedance should be about the same value due to the half
wave of 300 ohm low loss line. Neither impedance is within a bull's
roar of 316+j0, and are so low as to question whether the three half
waves are indeed in-phase. (The highest impedance that would yeild
42+/-j18 on a short length of RG8X would be around 80+j0, closer to
the not-in-phase configuration than the in-phase configuration).

W5GI's reported feed impedance seem inconsistent with three half
waves in phase, and questions whether the phasing arrangement works
as suggested.

Thoughts?

I doubt that it does.

Now W5GI does introduce his antenna with the statement "A multi-band wire
antenna that performs exceptionally well even though it confounds antenna
modeling software".

I know that is almost always a harbinger of bunk, the proverbial "Danger
Will Robinson...", but in fairness, it does appear that one modelling
package, NEC, cannot adequately model the coaxial arrangement near
resonance, though in his antenna, the coax section would be resonant
around 12MHz and King suggests it ought to be much shorter (resonant well
above 14MHz).

That is not to say there aren't other BS warnings in the W5GI explanation
of operation, or claims of performance.

Thanks for your comments, I find this an interesting subject.

Owen

colinear representation in NEC
 

Owen Duffy wrote:
. . .
Understood... but, I think after our discussion on this, NEC is not up to
the task, it may take a more advanced EM field modelling tool.

I don't agree with this.

My suspicion is that NEC's shortfall is that a TL element does not
properly represent the coaxial stub and its interaction with the other
elements near resonance, though well away from resonance, it is possible
that it may be quite ok. King raises the issues of diameter ratios, and
the difference with whether the stub is inboard or outboard of the o/c
end... but it is not resolved quantitatively.

I believe that NEC can do a fine job of modeling any of the variations
we've been discussing. But like all modeling systems, it has to be used
properly -- the transmission line object isn't an adequate model for
either a coaxial structure or an open wire stub, if either is carrying
any common mode current. And in these antennas it is, so you can't
insist on using nothing more than a transmission line object and then
bemoaning that the result isn't correct. The wire stub variation can be
correctly modeled as wires. The coaxial structure can be correctly
modeled as a combination of a wire and transmission line object. In
either case I have high confidence that carefully and accurately
measured results will agree closely with NEC predictions.

Now W5GI does introduce his antenna with the statement "A multi-band wire
antenna that performs exceptionally well even though it confounds antenna
modeling software".

I know that is almost always a harbinger of bunk, the proverbial "Danger
Will Robinson...", but in fairness, it does appear that one modelling
package, NEC, cannot adequately model the coaxial arrangement near
resonance, though in his antenna, the coax section would be resonant
around 12MHz and King suggests it ought to be much shorter (resonant well
above 14MHz).

It doesn't appear this way to me at all. What has led you to the
conclusion that it isn't possible to accurately model it with NEC?
Again, it's certainly impossible if you use only a transmission line
object to represent a structure which has common mode current. There are
many ways to build a model which doesn't accurately represent the
antenna being modeled. But just because it's possible to make a bad
model doesn't mean it's impossible to make a good one.

What is the evidence that results from a properly designed NEC model
disagree with careful measurements of pattern, current, or impedance of
an actual antenna of these types? You've noted that the W5GI antenna
impedance isn't consistent with a correctly phased collinear. I'd be
surprised if the impedance isn't close to what a correct NEC model
predicts -- or that the phases of the currents aren't also what NEC
predicts.

That is not to say there aren't other BS warnings in the W5GI explanation
of operation, or claims of performance.

Thanks for your comments, I find this an interesting subject.

Me too, and thanks for bringing it up. I'd never taken a really close
look at this class of antenna before, and the results have been interesting.

Roy Lewallen, W7EL

colinear representation in NEC
 

Roy Lewallen wrote in
:

Owen Duffy wrote:
....
I believe that NEC can do a fine job of modeling any of the variations
we've been discussing. But like all modeling systems, it has to be
used properly -- the transmission line object isn't an adequate model
for either a coaxial structure or an open wire stub, if either is
carrying any common mode current. And in these antennas it is, so you
can't insist on using nothing more than a transmission line object and
then bemoaning that the result isn't correct. The wire stub variation
can be correctly modeled as wires. The coaxial structure can be
correctly modeled as a combination of a wire and transmission line
object. In either case I have high confidence that carefully and
accurately measured results will agree closely with NEC predictions.

Taking the W5GI as an example, here is a deck that models the coaxial
stub section as a conductor of 5mm dia, whilst the wires for the other
sections are 2mm diameter. I have calculated the impedance looking into
16.5' of RG8X (W5GI's specified stub) as 14.5-j179 at 14.2MHz, and
inserted that load in both of the segments where the o/c end of the stub
is located. I have not used a TL element, rather I have separately
calculated the input Z of the stub using the technique used at
http://www.vk1od.net/calc/tl/tllc.php , that should be more accurate than
using a lossless TL element.

The model assumes an effective balun, ie that there is no common mode
feedline current since I have not provided such a path.

CM W5GI Mystery Antenna
CM Extended thin wire kernel used
CM
CE
GW 1 31 -5.033 0.000 10.563 5.033 0.000 10.563 0.001000
GW 2 15 -10.067 0.000 10.563 -5.033 0.000 10.563 0.002500
GW 3 15 -15.100 0.000 10.563 -10.067 0.000 10.563 0.001000
GW 4 15 5.033 0.000 10.563 10.067 0.000 10.563 0.002500
GW 5 15 10.067 0.000 10.563 15.100 0.000 10.563 0.001000
GE
EK
FR 0,1,0,0,14.200
EX 0 1 16 0 1 0
LD 5 0 0 0 5.7E7
LD 4 1 1 1 14.505 -191.739 0
LD 4 1 31 31 14.505 -191.739 0
GN 2 0 0 0 13 0.005
XQ
EN

This model indicates out of phase operation of the antenna, a multi lobed
pattern and feedpoint Z of 115-j179. (Although there is a half wave of
300 ohm line in between, this feedpoint Z would cause VSWR=8 on the 50
ohms line.

I think that I have dealt with the common mode path properly.

Try as I might changing stub lengths etc, I cannot get this configuration
to deliver in-phase operation of the radiator.

I suspect the model is not valid.

Owen

colinear representation in NEC
 

I'm very naive in these matters. Could a coaxial stub be modeled as a
cage of wires around the center conductor? Would the orders of
magnitude difference between shield/center distance and wire lengths
cause problems?

73
Jon LA4RT, Trondheim, Norway

colinear representation in NEC
 

Roy,

I have spent a lot of time exploring different modelling options over
recent weeks.

One view that one might take re my fig a) is that at connection of the
stub with the main vertical, the stub offers low impedance to common mode
current and high impedance to differential current. It leads to thinking
of it as a kind of mode trap that guides the system into in-phase
operation.

I have played around with ways of trying to represent that without using
the wire segments of the stub.

One method was to place a transformer with only one centre tapped
winding. The top and bottom of the winding connect to the upper half wave
and the lower quarter wave respectively, and the centre tap connects to a
horizontal quarter wave. My thinking was that this structure provides low
impedance to common mode current on the horizontal section, but a high
impedance to differential input to the top and bottom of the transformer
winding.

The model achieves reasonably good in-phase operation, but works best
with about 0.35 wave horizontal. I have used an NT card to insert the
transformer windings in the two segments. Here is the deck.

CM
CE
GW 1 15 0 0 0 0 0 5 0.005
GW 2 15 0 0 5 0 0 15 0.005
GW 3 15 0 0 5 7.2 0 5 0.005
GE 1
NT 1 15 2 1 0 0.01 0 -0.01 0 0.01
GN 1
EK
EX 0 1 1 1 0
TL 1 15 2 1 100 0
FR 0 0 0 0 15 0
EN

I then tried changing the horizontal section to two opposed radial wires,
and found that worked well with each radial being about 0.2 wave long.

CM
CE
GW 1 15 0 0 0 0 0 5 0.005
GW 2 15 0 0 5 0 0 15 0.005
GW 3 15 0 0 5 4 0 5 0.005
GW 4 15 0 0 5 -4 0 5 0.005
GE 1
NT 1 15 2 1 0 0.01 0 -0.01 0 0.01
GN 1
EK
EX 6 1 1 1 0
FR 0 0 0 0 15 0
EN

One can achieve similar outcome by wiring an appropriately phased zero
length TL between the segments each side of the horizontal wire.

If these models indicate that the common mode path on the horizontal wire
is important, one loses control of the length of that in the case of the
coaxial configuration because there isn't an o/c end indpendent of the
vertical conductor.

The coaxial construction gives the opportunity to create a high impedance
to differential current between the adjacent segments, but lacks the
ability to create a low impedance common mode path independently of the
vertical structure.

Thoughts?

Owen

colinear representation in NEC
 

Cecil Moore wrote:
Jim Kelley wrote:
The only current flowing on an antenna is the current traveling from
one end to the other.

Let's assume you are correct. Here are a few questions:

1. Given a 90 degree monopole fed against an infinite
ground plane, what would be the phase at the top of the
antenna compared to the phase at the feedpoint for any
instant in time?

2. Why would the feedpoint impedance of a 1/4WL monopole
be more than a magnitude less than the feedpoint impedance
of an infinite monopole?

3. Where does the above current go when it hits the open-
circuit at the top of the monopole?

4. Why is the total energy in the E-field at the top of the
monopole so high?

In what way are any of the questions relevant to, or deterministic of
the assumption?

73, ac6xg

colinear representation in NEC
 

Jim Kelley wrote:
In what way are any of the questions relevant to, or deterministic of
the assumption?

Answering a question with a question is a well known
diversion. Please answer my questions and you will
automatically answer yours.

Here's some mo How can a current that changes
phase by 3 degrees in 90 degrees of wire be used
to measure the EM wave delay through the wire?

How can that current be used to measure the delay
through a coil positioned in the middle of that wire?

How fast does EM wave energy travel through a wire?
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com
"Government 'help' to business is just as disastrous as
government persecution..." Ayn Rand

colinear representation in NEC
 

Richard Clark wrote:
Returning to the process - through sub-optimization by adding
bafflegab, ...

As far as bafflegab goes, Richard, no one can hold a candle
to you. Your posting is a perfect example.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com
"Government 'help' to business is just as disastrous as
government persecution..." Ayn Rand

colinear representation in NEC
 

On Thu, 26 Mar 2009 08:20:07 -0800, Jim Kelley
wrote:

Cecil Moore wrote:
Jim Kelley wrote:
The only current flowing on an antenna is the current traveling from
one end to the other.

Let's assume you are correct. Here are a few questions:

1. Given a 90 degree monopole fed against an infinite
ground plane, what would be the phase at the top of the
antenna compared to the phase at the feedpoint for any
instant in time?

2. Why would the feedpoint impedance of a 1/4WL monopole
be more than a magnitude less than the feedpoint impedance
of an infinite monopole?

3. Where does the above current go when it hits the open-
circuit at the top of the monopole?

4. Why is the total energy in the E-field at the top of the
monopole so high?

In what way are any of the questions relevant to, or deterministic of
the assumption?

Ah Jim!

You have the essence of Cecil's (r) Sub-optimal Conjugated Hypothesis
Information Transform before you, the SCHIT (c) model.

He has taken the ordinary postulate of current flow, conjugated it
into a new hypothesis through his sub-optimization. By removing
random bytes, it becomes more intelligible (I will take a stab at it
here):
1. a 90 degree monopole fed against an infinite ground plane
2. the feedpoint impedance of a 1/4WL monopole
3. current go[es]
4. the total energy
now makes perfect sense and whitens your teeth at the same time.

Returning to the process - through sub-optimization by adding
bafflegab, the future deconstruction (posts that would follow the one
above and for which I have already deconvoluted) would find Cecil
eventually unwinding the original conjugation, proving he was right by
proving you right - except you were wrong in what you "thought" (the
information transform) because he thought you were wrong.

73's
Richard Clark, KB7QHC

colinear representation in NEC
 

Richard Clark wrote:
You must be flattered (an example of information transformation) at
this imitation of you then (your comment here so unabashedly basking
in the intended conjugate of these congratulations).

Just send me some of what you are smoking and I will die happy. :-)
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com
"Government 'help' to business is just as disastrous as government
persecution..." Ayn Rand

colinear representation in NEC
 

On Thu, 26 Mar 2009 12:32:15 -0500, Cecil Moore
wrote:

Richard Clark wrote:
Returning to the process - through sub-optimization by adding
bafflegab, ...

As far as bafflegab goes, Richard, no one can hold a candle
to you. Your posting is a perfect example.

You must be flattered (an example of information transformation) at
this imitation of you then (your comment here so unabashedly basking
in the intended conjugate of these congratulations).

[Gad this so easy, I should have gotten an AIG bonus for derivative
design!]
:-0

colinear representation in NEC
 

On Thu, 26 Mar 2009 14:59:21 -0500, Cecil Moore
wrote:

Richard Clark wrote:
You must be flattered (an example of information transformation) at
this imitation of you then (your comment here so unabashedly basking
in the intended conjugate of these congratulations).

Just send me some of what you are smoking and I will die happy. :-)

A double conjugation which reveals the source of this side thread.
Deconstructing the bafflegab by random byte dispersal gives us Cecil's
information transform:
what I am smoking isn't good enough.

[gad, this is so easy I could be double-dipping AIG bonuses and
getting favored IRS status too!]

colinear representation in NEC
 

Owen Duffy wrote in
:

....
I suspect the model is not valid.

I should have explained that the reason for that suspicion that the model
does not predict behaviour similar to W5GI's claims, most importantly three
half waves in phase on 20m.

Owen

colinear representation in NEC
 

Owen Duffy wrote in news:Xns9BDAEB77E6B1nonenowhere@
61.9.191.5:

NT 1 15 2 1 0 0.01 0 -0.01 0 0.01


Ouch, the signs of the Y values should be the opposite, so

NT 1 15 2 1 0 -0.01 0 0.01 0 -0.01

Leakage reactance is usually +ve, so Y11 should be -ve, etc.

It has a similar effect, but correct signs is better.

Apologies.

Owen

colinear representation in NEC
 

On Thu, 26 Mar 2009 09:35:06 +0100, Jon K Hellan LA4RT
wrote:

I'm very naive in these matters. Could a coaxial stub be modeled as a
cage of wires around the center conductor? Would the orders of
magnitude difference between shield/center distance and wire lengths
cause problems?

Hi Jon,

I offered that model long ago in this thread - as it was ignored, I
was condemned to use it myself.

I had given some thought ahead of plunging ahead into the model (it
was originally a thick radiator for which the model was perfectly
suitable). The concept of coaxial tube shielding proceeds along the
premise of the shield supporting separate conduction paths, isolated
by skin effect of the tube conductor. That is, the currents of the
shield on the inside surface are separate and distinct from those on
the outside surface. I knew full well that NEC would not maintain
that distinction for any wire in a cage simply because it lacks the
ability to report separate currents along the same wire as would be
found in this inside/outside tube surface.

The model I published and provided the link to here in this thread was
not strictly faithful to the concept of the cage model for a coaxial
tube, however. I enhanced it into roughly 1000 wires emulating a cage
10.5M long, 2M in diameter, with hoops every 33cM along its length,
and closed at both ends. Think of it as a roll of mesh with a 1 foot
grid capped at both ends with radial wires. Within it is a length of
wire that is roughly 10M long and isolated from the cage at both ends.

With the wire loss set to perfect, the central wire was driven and it
was as though no shielding cage existed. Within tenths of a dB, the
radiation characteristic across HF was roughly the same as from a
simple wire dipole. Conceptually, it would appear that the Faraday
shield does not exist in the world of NEC.

When I introduced the copper setting for wire loss, this assemblage
exhibited the following "loss"
MHz
1 24.2
2 16.6
3 14.2
4 12.8
5 12.1
6 12.1
7 13.4
8 18.8
9 19.0
10 6.6
11 3.0
12 2.2
13 2.0
14 1.8
15 1.6
16 1.7
17 1.5
18 1.4

Following this, I connected the ends of the coaxial interior wire to
the caps at the tube ends (a complete short circuit). Losses in the
left column (where significant); lobe peak in the right column (where
significant):
MHz
1 56.1
2 39.4
3 29.3
4 21.9
5 15.8
6 10.5
7 6.0
8 2.4
9 0.2 1.8 dBi
10 2.7 dBi
11 2.8 dBi
12 2.7 dBi
13 2.5 dBi
14 2.3 dBi
15 0.2 2.1 dBi
16 0.5
17 0.7
18 1.1

So, to your question:
Could a coaxial stub be modeled as a
cage of wires around the center conductor?
No, not if my experience bears any relevance.

73's
Richard Clark, KB7QHC

colinear representation in NEC
 

Richard Clark wrote in
:

On Thu, 26 Mar 2009 09:35:06 +0100, Jon K Hellan LA4RT
wrote:

I'm very naive in these matters. Could a coaxial stub be modeled as a
cage of wires around the center conductor? Would the orders of
....
So, to your question:
Could a coaxial stub be modeled as a
cage of wires around the center conductor?
No, not if my experience bears any relevance.

Hi Jon, Richard,

I considered the same, and I did model some simpler structures to explore
some possible effects.

Although it would be possible to create a cylindrical structure of GW
elements, my concern was that it would not have the near complete
isolation of inner and outer surfaces of the outer conductor, that it
might need be be very large in diameter in terms of wavelength, and that
it moves further away from practical commercial coaxial lines.

I have been quiet here, but have been modelling and writing notes up on
the results. I have asked for comment on a draft model, and subject to
that, I will post the URL for further comments, hopefully in a day or
two.

The effort was really about understanding whether the stub in my fig a)
could simply be replaced by a pure differential mode transmission line,
and whether that could then be coaxially collinear with the main
radiator. I think the answer to the first question is NO, and that drives
the answer to the second question.

Owen

colinear representation in NEC
 

Cecil Moore wrote:
Jim Kelley wrote:
In what way are any of the questions relevant to, or deterministic of
the assumption?

Answering a question with a question is a well known
diversion. Please answer my questions and you will
automatically answer yours.

One could claim that the questions exemplify your point about diversion.
:-)

Here's some mo How can a current that changes
phase by 3 degrees in 90 degrees of wire be used
to measure the EM wave delay through the wire?
How can that current be used to measure the delay
through a coil positioned in the middle of that wire?

Assuming the antenna is 90 degrees in length, the relevant currents can
be measured, the maximum is known and the minimum is zero, then:
According to the plots that I've seen, the standing wave pattern will
show a discontinuous change in amplitude at positions where there is an
abrupt change in phase of the traveling waves. Since it's fair to
assume propagation velocity is the same in both directions, waves would
be phase delayed by the same amount in both directions at a
discontinuity, and the combined sum of the two delays would account for
the total delay and for the resulting change in amplitude. Since a
standing wave can be considered an amplitude vs phase plot (where both
phase and amplitude vary with position) and the amplitude is known on
both sides of the discontinuity, the amplitude on each side of the
discontinuity relates functionally to a corresponding phase on the
abscissa of the standing wave curve. The total change in phase is equal
to the difference in phase on the two sides of the discontinuity. The
phase delay for each traveling wave is then half the total phase change.
Whether all of the assumptions are true for the cited case, I don't
know. The assumptions that you've made are not always clearly or
completely communicated, but would obviously weight heavily in the
results. This is also true for EZNEC results.

Why not take some actual phase shift measurements for yourself?

73, ac6xg

colinear representation in NEC
 

Jim Kelley wrote:
Why not take some actual phase shift measurements for yourself?

I have already done that at my previous QTH and
reported it two years ago. Remember these graphs
from software that you recommended?

http://www.w5dxp.com/travstnd.gif

My dual-trace scope measurements agreed within
the accuracy to which I could measure.

Point is that the delay through a transmission
line, a wire, or a coil is the same no matter
what type of current (standing wave or traveling
wave) is flowing. EM waves are EM waves. If the
current is primarily standing wave current with
essentially unchanging phase, the phase shift
in the standing wave current is unrelated to the
delay through the T-line, wire, or coil. Yet
standing wave current phase is what was used to
"prove" a 3 nS delay through a 100T, 2" dia, 10TPI
coil on 75m. If traveling wave current had been
used, as I did on my 75m Texas Bugcatcher coil,
the delay would have been shown to be ~26 nS.

In a 1/4WL monopole or 1/2WL dipole, the total
current is about 90% standing wave current.

Did you take a look at the current phase in these
two inverted-Vs?

http://www.w5dxp.com/inv_v.EZ

http://www.w5dxp.com/inv_vt.EZ
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com

colinear representation in NEC
 

Jim Kelley wrote:

It's like having a conversation with a recorded message.

ac6xg

Exactly why I plonked him a few years ago. The relative silence is
refreshing, and I haven't missed a thing.

Roy Lewallen, W7EL

colinear representation in NEC
 

Cecil Moore wrote:
Jim Kelley wrote:
Why not take some actual phase shift measurements for yourself?

I have already done that at my previous QTH and
reported it two years ago. Remember these graphs
from software that you recommended?

http://www.w5dxp.com/travstnd.gif

My dual-trace scope measurements agreed within
the accuracy to which I could measure.

Point is that the delay through a transmission
line, a wire, or a coil is the same no matter
what type of current (standing wave or traveling
wave) is flowing. EM waves are EM waves. If the
current is primarily standing wave current with
essentially unchanging phase, the phase shift
in the standing wave current is unrelated to the
delay through the T-line, wire, or coil. Yet
standing wave current phase is what was used to
"prove" a 3 nS delay through a 100T, 2" dia, 10TPI
coil on 75m. If traveling wave current had been
used, as I did on my 75m Texas Bugcatcher coil,
the delay would have been shown to be ~26 nS.

In a 1/4WL monopole or 1/2WL dipole, the total
current is about 90% standing wave current.

Did you take a look at the current phase in these
two inverted-Vs?

http://www.w5dxp.com/inv_v.EZ

http://www.w5dxp.com/inv_vt.EZ

It's like having a conversation with a recorded message.

ac6xg