Cecil Moore wrote:
Owen Duffy wrote:
Thinking some more about it, my current thinking is that my analysis
was flawed. I was using the standing wave currents, when I should be
using the travelling wave components.

That's exactly the flaw committed by w8ji and w7el when
they tried to measure the delay through a 75m loading
coil using standing wave current which doesn't appreciably
change phase through a loading coil or through the entire
90 degree length of a monopole. Using standing wave
current, w8ji measured a 3 nS delay through a 10 inch
long coil, a VF of 0.27.

http://www.w8ji.com/inductor_current_time_delay.htm

W7EL reported: "I found that the difference in current
between input and output of the inductor was 3.1% in
magnitude and with *no measurable phase shift*, despite
the short antenna... The result from the second test was
a current difference of 5.4%, again with *no measurable
phase shift*."

Of course, phase shift is not measurable when one is
using standing wave current with its almost unchanging
phase. EZNEC supports that assertion. Bench measurements
support that assertion.

When traveling waves are used to measure the delay through
a 75m loading coil, the correct delay through w8ji's 10
inch coil turns out to be about 26 nS (~37 degrees) at 4 MHz
with a more believable VF of 0.033.

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

Cecil, if I ever have a dead horse on my hands, I won't let you
near it because you'll beat it even deader.
73,
Tom Donaly, KA6RUH

On Mar 17, 1:31*am, Owen Duffy wrote:
K7ITM wrote :

...

Yes--and then if they were exactly equal, would that not imply only
transmission line current on the stub? *Obviously, they are exactly

Thinking some more about it, my current thinking is that my analysis was
flawed. I was using the standing wave currents, when I should be using
the travelling wave components.

I suspect that when NEC models the conductor arrangement at my fig a), it
correctly accounts for propagation delay and the phase relationships
compute correctly.

If we replace the stub with a TL element, I suspect that NEC reduces the
TL to a two port network and loads a segment of the vertical with an
equivalent steady state impedance of the s/c stub network. If that is
done, the reduction to a lumped load means that there is zero delay to
travelling waves, and the computed currents (amplitude and phase) in the
vertical will be incorrect. This means that you cannot replace a resonant
stub with a high value of resistance, it doesn't work.

If that is the case, it suggests that NEC cannot model such phasing
schemes using TL elements.

Owen

Of course, if the TL model doesn't "know about" the antenna field
(which I believe is in fact the case), there will be no common-mode
current on it because of that field. It's pretty clear to me that the
common-mode current is very important to correctly simulating the
situations you are interested in. In fact, figure (B) of your
original posting puts the stub in a position where it does not see the
antenna field, and I would expect it to behave much differently from
the perpendicular stub of figure (A).

One of the things I did in my simulation playing last night was to
delete the stubs, leaving just the three 1/2 wave elements end-to-end
with a bit of gap between them. (0.01m gap between 0.5m elements, 1mm
diameter, 11 segments each.) I'm sure you know what that pattern and
current distribution look like. Then I added sources at the centers
of the outer elements. I set all the sources to 1 amp, in-phase. The
pattern was somewhat sharper (though just marginally more gain) than
the stub-coupled case. What I didn't try, but will as I have a
chance, is to put sources at the centers of the outer elements and set
them to the values (magnitudes and phases) I see in the stub-coupled
collinear, and see how much the current distribution near the ends
looks like the stub coupled case. I suppose it will be pretty close,
and the antenna pattern will look very similar to the stub coupled
pattern.

Thanks for bringing this subject up. I'm learning something from it.

Cheers,
Tom

"Tom Donaly" wrote in
:

....
Why would NEC reduce a TL two-port to a lumped load? Two-port
parameters can handle transmission line problems quite well without
the simplifying assumption that all components are of zero length.

Hi Tom,

I expect that NEC does model the propagation delay from end to end on a
transmission line. My comment was that NEC reduces a s/c TL stub to a
lumped load for the stub input end which is inserted in the vertical.

The problem here perhaps is our viewing the phasing section as a s/c stub
of two wire line, when perhaps is it better described as a single wire TL
of a half wave length.

With that thought in mind, I have constructed a model where the phasing
section is configured in a double triangular shape, but with the same
conductor length, and NEC suggests in-phase currents. In fact, it has
slightly better pattern symmetry than a).

CM
CE
GW 1 15 0 0 0 0 0 5 0.0005
GW 5 30 0 0 5.1 0 0 15 0.0005
GW 10 7 0 0 5 1.47 0 5. 0.0005
GW 11 10 1.47 0 5. 0 1.47 5. 0.0005
GW 12 15 0 1.47 5. 0 -1.47 5.1 0.0005
GW 13 7 0 -1.47 5.1 -1.47 0 5.1 0.0005
GW 14 15 -1.47 0 5.1 0 0 5.1 0.0005
GE 1
GN 1
EK
EX 0 1 1 0 1.0 0
FR 0 0 0 0 15 0
EN

Owen

On Mar 17, 12:41*pm, Owen Duffy wrote:
"Tom Donaly" wrote :

...

Why would NEC reduce a TL two-port to a lumped load? Two-port
parameters can handle transmission line problems quite well without
the simplifying assumption that all components are of zero length.

Hi Tom,

I expect that NEC does model the propagation delay from end to end on a
transmission line. My comment was that NEC reduces a s/c TL stub to a
lumped load for the stub input end which is inserted in the vertical.

The problem here perhaps is our viewing the phasing section as a s/c stub
of two wire line, when perhaps is it better described as a single wire TL
of a half wave length.

....

I'm not sure why you want to reduce it to something less complex than
it is. Transmission lines like this support both even and odd mode
propagation, I guess what we'd normally call "transmission line
currents" and "antenna currents." It seems perfectly OK to me to let
both exist on the line at the same time. It also seems to me there is
value in doing that, because I believe there's insight to be gained
from understanding how each of those currents contributes to the net
performance of the antenna. It's important that the stub be in the
field of the antenna so that antenna current is excited on it, and
it's also important that the stub be shorted a quarter wave away from
where it attaches to the collinear elements, so that the differential
transmission line currents do the right thing.

On the other hand, you may well discover some insights looking at it
in a different way, so I hope my comments won't discourage you from
doing that!

Cheers,
Tom

K7ITM wrote in
:

On Mar 17, 12:41*pm, Owen Duffy wrote:
"Tom Donaly" wrote
innews:QoQvl.13889$8_3.3071@f
lpi147.ffdc.sbc.com:

....
On the other hand, you may well discover some insights looking at it
in a different way, so I hope my comments won't discourage you from
doing that!

My real objective is to model b) in NEC.

Trying to understand a) and to deconstruct it is part of an approach to
finding a solution to b).

The 'stub' in a) cannot simply be replaced by a s/c TL element, so that
suggests that a s/c TL element is not a solution for b) either.

The last configuration with the triangular / diamond configuration of the
phasing line seems to work in an NEC model, and the deconstruction
suggests that having a half wave of conductor is fundamental, and that it
need not be in the form of a two wire TL.

I have also tried removing the 'stub' from a) and using a half wave TL to
drive segments each side of the gap from each other. If the segments are
close to, but not the last, this does produce a current distribution that
is not 180° out of phase, but it does not produce the almost perfect in-
phase outcome of modelling the wire structure. Nevertheless, playing with
the length of that TL, being very close to half wave in length is
essential to overriding the natural tendency to out of phase currents.

This hasn't solved the problem of modelling a coaxial configuration,
expecially where the coaxial section was coax cable, apart from excluding
some approaches as invalid.

Owen

Owen Duffy wrote:
K7ITM wrote in
:

...
Yes--and then if they were exactly equal, would that not imply only
transmission line current on the stub? Obviously, they are exactly

Thinking some more about it, my current thinking is that my analysis was
flawed. I was using the standing wave currents, when I should be using
the travelling wave components.

I suspect that when NEC models the conductor arrangement at my fig a), it
correctly accounts for propagation delay and the phase relationships
compute correctly.

If we replace the stub with a TL element, I suspect that NEC reduces the
TL to a two port network and loads a segment of the vertical with an
equivalent steady state impedance of the s/c stub network. If that is
done, the reduction to a lumped load means that there is zero delay to
travelling waves, and the computed currents (amplitude and phase) in the
vertical will be incorrect. This means that you cannot replace a resonant
stub with a high value of resistance, it doesn't work.

If that is the case, it suggests that NEC cannot model such phasing
schemes using TL elements.

Owen

It's easy to reason yourself into traps by dividing currents into
"standing wave" and "traveling wave" components. They're different
things and don't add or superpose. Results of attempts to make this
differentiation can be seen in a vast number of postings on this forum
in the past.

Rather, I recommend considering a current to be a single value or, at
most, made of differential and common mode components which *can* be
added to obtain the total current.

In a steady state single frequency analysis, which is what NEC performs,
there is no such thing as delay. All time relationships can be expressed
as phase difference, which can't be tied to a unique delay -- you can't
even tell if the phase difference was due to time delay or magical
prescience-caused time lead. In a steady state analysis there is no way
to distinguish a half wave lossless transmission line from a 1-1/2 wave
line; they act exactly the same in all ways. So does a magical -1/2
wavelength line whose output appears a half cycle *before* the input
appears. Only in a time-domain analysis will you be able to tell the
difference. So yes, NEC models the transmission line as a two port
network. It does force the correct voltage and current amplitude and
phase relationships between the input and output. And it's
indistinguishable in the steady state analysis from an ideal
transmission line which effects the phase difference by means of delay.
The NEC transmission line model is equivalent to a real (but lossless)
transmission line on which the current is purely differential, e.g., a
coax line with a large number of ferrite cores on the outside. The model
is accurate within the constraints of a steady state analysis. If you're
interested in looking at the effects of delay in a transient system,
you'll need to use an analysis tool other than NEC. But if you let your
transient analysis run until steady state is reached, the results will
be the same as NEC.

Roy Lewallen, W7EL

Tom Donaly wrote:
Cecil, if I ever have a dead horse on my hands, I won't let you
near it because you'll beat it even deader.

The horse is alive and well - the nonsense that I quoted
is still on W8JI's web page.
--
73, Cecil http://www.w5dxp.com
"Government 'help' to business is just as disastrous as
government persecution..." Ayn Rand

Roy Lewallen wrote:
If you're
interested in looking at the effects of delay in a transient system,
you'll need to use an analysis tool other than NEC. But if you let your
transient analysis run until steady state is reached, the results will
be the same as NEC.

But in NEC, if you load a transmission line with its
characteristic impedance, reflections are eliminated
and the delay along the wire is proportional to the
phase shift *even during steady-state*.
--
73, Cecil http://www.w5dxp.com
"Government 'help' to business is just as disastrous as
government persecution..." Ayn Rand

Cecil Moore wrote:
Owen Duffy wrote:
Thinking some more about it, my current thinking is that my analysis
was flawed. I was using the standing wave currents, when I should be
using the travelling wave components.

That's exactly the flaw committed by w8ji and w7el when
they tried to measure the delay through a 75m loading
coil using standing wave current which doesn't appreciably
change phase through a loading coil or through the entire
90 degree length of a monopole. Using standing wave
current, w8ji measured a 3 nS delay through a 10 inch
long coil, a VF of 0.27.

http://www.w8ji.com/inductor_current_time_delay.htm

W7EL reported: "I found that the difference in current
between input and output of the inductor was 3.1% in
magnitude and with *no measurable phase shift*, despite
the short antenna... The result from the second test was
a current difference of 5.4%, again with *no measurable
phase shift*."

Of course, phase shift is not measurable when one is
using standing wave current with its almost unchanging
phase. EZNEC supports that assertion. Bench measurements
support that assertion.

When traveling waves are used to measure the delay through
a 75m loading coil, the correct delay through w8ji's 10
inch coil turns out to be about 26 nS (~37 degrees) at 4 MHz
with a more believable VF of 0.033.

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

I agree that electromagnetic traveling waves are the kinds of waves that
propagate on and cause radiation to emanate from an antenna. But your
claims about 'standing waves not changing phase along the antenna'
provoke the following questions:

1.) what relation (if any) do you believe the wavelength of the standing
wave has to the wavelength of the radio frequency waves traveling on an
antenna? And,

2.) what relation (if any) does the phase of a sinusoidal wave have to
its amplitude?

73, ac6xg

Jim Kelley wrote:
I agree that electromagnetic traveling waves are the kinds of waves
that propagate on and cause radiation to emanate from an antenna. But
your claims about 'standing waves not changing phase along the antenna' ...

Jim, I thought you have EZNEC. Here are the currents at all of
the segments along a 20m dipole with 21 segments from end to end.
Please note that in a dipole that is 180 degrees long, the phase
of the (mostly standing-wave) current varies by less than 3 degrees.
How can the current in a 180 degree antenna vary by less than 3 degrees?

Quoting my web page: "Standing wave current cannot be used to directly
measure either a valid amplitude change or a valid phase shift through
a loading coil. All of the reported conclusions based on loading coil
measurements using standing-wave current on standing-wave antennas are
conceptually flawed." Owen had an epiphany of a sort when he realized
that fact of physics.

20m dipole 3/18/2009 5:28:50 PM

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

Frequency = 14.2 MHz

Wire No. 1:
Segment Conn Magnitude (A.) Phase (Deg.)
1 Open .0836 -2.75
2 .23595 -2.57
3 .37707 -2.38
4 .50791 -2.17
5 .62692 -1.95
6 .73226 -1.71
7 .82218 -1.44
8 .89511 -1.13
9 .94979 -0.78
10 .98539 -0.37
11 1 0.00
12 .98539 -0.37
13 .94979 -0.78
14 .89511 -1.13
15 .82218 -1.44
16 .73226 -1.71
17 .62691 -1.95
18 .50791 -2.17
19 .37707 -2.38
20 .23595 -2.57
21 Open .0836 -2.75
--
73, Cecil http://www.w5dxp.com
"Government 'help' to business is just as disastrous as
government persecution..." Ayn Rand

P.S. I posted this reply but it didn't show up on my server.
I apologize if it is a duplicate.