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