How to model on EZNEC
 

Does anyone know how I can model a coaxial sleeve antenna
on EZNEC ?

I know how to enter a standard Vertical 1/2 wave but not sure how
to represent the coax going up through the tubing(sleeve) in the lower
portion.

Thanks in advance.

In my humble opinion, EZNEC is a POS for anything other than a simple "wire
antenna". Try to do a true ground plane with bent radials? Try to do a
simple patch? Try to do a J? Try to do ANY configuration other than a wire
dipole and the sucker chokes.

Jim



"David" wrote in message
...
Does anyone know how I can model a coaxial sleeve antenna
on EZNEC ?

Jim,

What would be your alternate suggestion ?

Thanks

Regards

David

ERST Engineering wrote:
In my humble opinion, EZNEC is a POS for anything other than a simple "wire
antenna". Try to do a true ground plane with bent radials? Try to do a
simple patch? Try to do a J? Try to do ANY configuration other than a wire
dipole and the sucker chokes.

Jim



"David" wrote in message
...

Does anyone know how I can model a coaxial sleeve antenna
on EZNEC ?

On Fri, 7 Oct 2005 20:38:43 -0700, "RST Engineering"
wrote:

In my humble opinion, EZNEC is a POS for anything other than a simple "wire
antenna". Try to do a true ground plane with bent radials? Try to do a
simple patch? Try to do a J? Try to do ANY configuration other than a wire
dipole and the sucker chokes.

I suggest that it is your models that may be choking. EZNEC uses the
NEC engine for caculations and NEC can do all the items you mention
above.

Danny, K6MHE

email: k6mheatarrldotnet
http://users.adelphia.net/~k6mhe/

"David" wrote in message
...
Does anyone know how I can model a coaxial sleeve antenna
on EZNEC ?

I know how to enter a standard Vertical 1/2 wave but not sure how
to represent the coax going up through the tubing(sleeve) in the lower
portion.

Thanks in advance.

Just model a vertical dipole. The presence of a coaxial cable, within the
lower conductor, will not effect its performance. For your model both upper
and lower conductors should be the same diameter. Dissimilar diameters in a
model can produce erroneous results.

NEC has its limitations, but alternative, FEM based, programs can cost tens
of thousands of dollars.

Regards,

Frank

On Sat, 08 Oct 2005 13:36:37 GMT, "Frank"
wrote:

"David" wrote in message
...
Does anyone know how I can model a coaxial sleeve antenna
on EZNEC ?

I know how to enter a standard Vertical 1/2 wave but not sure how
to represent the coax going up through the tubing(sleeve) in the lower
portion.

Thanks in advance.

Just model a vertical dipole. The presence of a coaxial cable, within the
lower conductor, will not effect its performance.

But the presence of the coax below the antenna sure will.

RST Engineering wrote:
In my humble opinion, EZNEC is a POS for anything other than a simple "wire
antenna". Try to do a true ground plane with bent radials? Try to do a
simple patch? Try to do a J? Try to do ANY configuration other than a wire
dipole and the sucker chokes.

I've modeled ground planes with bent radials and J antennas
using EZNEC and got reasonable results. Never tried a patch.
EZNEC's limitations are well known and well documented so
knowledgeable users can avoid those pitfalls. Of course,
nothing is foolproof.
--
73, Cecil http://www.qsl.net/w5dxp

Just model a vertical dipole. The presence of a coaxial cable, within the
lower conductor, will not effect its performance.

But the presence of the coax below the antenna sure will.

As an experiment I modeled a #14 AWG, 133 segment,134 ft free space dipole.
The input impedance at 3.575 MHz is 74.01 - j 0.749 ohms. Adding an
additional 25 ft wire at one end -- ends separated by 1.2" -- the input
impedance becomes 74.155 - j1.97 ohms. There is no discernable effect on
the radiation pattern.

While this test is not precisely equivalent; the presence of a, non
connected, axial extension appears to have only a minimal effect on the
antenna parameters.

Regards,

Frank

On Sat, 08 Oct 2005 16:31:17 GMT, "Frank"
wrote:

While this test is not precisely equivalent; the presence of a, non
connected, axial extension appears to have only a minimal effect on the
antenna parameters.

Hi Frank,

And did resonance go unperturbed?

73's
Richard Clark, KB7QHC

"Richard Clark" wrote in message
...
On Sat, 08 Oct 2005 16:31:17 GMT, "Frank"
wrote:

While this test is not precisely equivalent; the presence of a, non
connected, axial extension appears to have only a minimal effect on the
antenna parameters.

Hi Frank,

And did resonance go unperturbed?

73's
Richard Clark, KB7QHC

Hi Richard,

A nominal 2.5 kHz shift, at 3.575 MHz (0.07%), is about all I can detect.

73,

Frank

On Sat, 08 Oct 2005 16:45:24 GMT, "Frank"
wrote:

A nominal 2.5 kHz shift, at 3.575 MHz (0.07%), is about all I can detect.

Hi Frank,

Is this shift constant over all axial lengths, or variable?

73's
Richard Clark, KB7QHC

I just took the ARRL antenna modeling course and bought EZNEC+ V4.0 to
provide the tools to do the examples. One chapter was devoted to
limitations and common shortcomings of the software. I think the
course is great and I would select the same software if I was doing it
again. I wonder if you are referring to the free demo package?

On Fri, 7 Oct 2005 20:38:43 -0700, "RST Engineering"
wrote:

In my humble opinion, EZNEC is a POS for anything other than a simple "wire
antenna". Try to do a true ground plane with bent radials? Try to do a
simple patch? Try to do a J? Try to do ANY configuration other than a wire
dipole and the sucker chokes.

Jim



"David" wrote in message
...
Does anyone know how I can model a coaxial sleeve antenna
on EZNEC ?

A nominal 2.5 kHz shift, at 3.575 MHz (0.07%), is about all I can detect.

Hi Frank,

Is this shift constant over all axial lengths, or variable?

73's
Richard Clark, KB7QHC

Hi Richard,

Axial extension 1.2" from antenna end -- Results as follows:

Extension Length (ft) Resonant Freq. (MHz)

0 3.5765
5 3.576
10 3.575
20 3.574
50 3.5725
100 3.5720

For a total shift of 4.5 kHz (0.125%) from zero to 100 ft

73,

Frank

On Sat, 08 Oct 2005 06:58:43 -0700, Wes Stewart
wrote:

On Sat, 08 Oct 2005 13:36:37 GMT, "Frank"
wrote:

"David" wrote in message
...
Does anyone know how I can model a coaxial sleeve antenna
on EZNEC ?

I know how to enter a standard Vertical 1/2 wave but not sure how
to represent the coax going up through the tubing(sleeve) in the lower
portion.

Thanks in advance.

Just model a vertical dipole. The presence of a coaxial cable, within the
lower conductor, will not effect its performance.

But the presence of the coax below the antenna sure will.

Let me expand on this. If---big if---the sleeve is the correct length
and lossless, so that it acts as a quarter-wave choke, then in theory
it does decouple the coax from the radiator.

A few points however:

1. The Vp of the choke will depend on the effective dielectric
constant of the air/outer jacket combination. The choke so formed
will likely be fairly lossy as the outer jacket is probably not the
lowest loss dielectric around.

2. Since the choke Vp will be lower than an air-dielectric one, it
must be physically shortened to optimize the choking function. This
combined with the usual diameter differences between the sleeve and
the upper radiator (rod) makes the vertical dipole asymmetric, i.e.
unbalanced, when the rod length is adjusted for resonance. In effect
the feedpoint is moving up and down as the rod length is adjusted. In
practice, this is no big deal but offered for completeness.

3. You can model this antenna to some extent. Below are some
coordinates for a model I used. The wire size was #12, all lengths in
inches and the frequency was 100 MHz. I used Multinec invoking EZNEC 4
for the calculations. In Multinec I made the Z a variable and could
vary the height above ground programmatically. The sleeve is
represented by four stubs; more would perhaps more accurately
represent a cylinder, but I don't believe it's necessary. Since the
"coax" connects to ground, MiniNEC ground (avg) was used. To observe
NEC limitations, all segments are (very nearly) the same length and
adjacent segments are aligned. The sleeve length was adjusted to
minimize the current on the "coax" below the antenna (wire #4) and the
rod length adjusted for zero reactance.


End 1 End 2
X Y Z X Y Z Dia Segs.

Source wire
0.00 0.00 354.09 0.00 0.00 355.09 #12 1

Upper radiator (rod)
0.00 0.00 355.09 0.00 0.00 382.47 #12 29

"Coax" inside sleeve
0.00 0.00 326.84 0.00 0.00 354.09 #12 29

"Coax" below sleeve
0.00 0.00 0.00 0.00 0.00 326.84 #12 337

Top of sleeve
0.00 0.00 354.09 0.00 2.00 354.09 #12 2
0.00 0.00 354.09 0.00 -2.00 354.09 #12 2
0.00 0.00 354.09 2.00 0.00 354.09 #12 2
0.00 0.00 354.09 -2.00 0.00 354.09 #12 2

Sides of sleeve
0.00 2.00 326.84 0.00 2.00 354.09 #12 29
0.00 -2.00 326.84 0.00 -2.00 354.09 #12 29
2.00 0.00 326.84 2.00 0.00 354.09 #12 29
-2.00 0.00 326.84 -2.00 0.00 354.09 #12 29



4. If SWR is your criteria for "goodness", you will be in for a big
surprise. The above example places the midpoint of the antenna at 3
wavelengths above ground. The feedpoint Z is a nice 56.6 +j0 but the
elevation for maximum radiation is 71 degrees above the horizon. If
satellite work is your goal, this is your antenna.

5. Despite the "choke", the transmission line is part of the antenna.
Skeptics of the model above can remove the sleeve and put a trap at
end 2 of the coax and see similar results.

On Sun, 09 Oct 2005 03:39:32 GMT, "Frank"
wrote:

Axial extension 1.2" from antenna end -- Results as follows:

Extension Length (ft) Resonant Freq. (MHz)

0 3.5765
5 3.576
10 3.575
20 3.574
50 3.5725
100 3.5720

For a total shift of 4.5 kHz (0.125%) from zero to 100 ft

Hi Frank,

Thanx.

Was this for a coaxial line running from the drivepoint, then parallel
to the lower leg, down? Was the parallel separation 1.2" as you
describe above?

Was this line modeled as a third wire connected at the drivepoint and
dropping as I describe?

73's
Richard Clark, KB7QHC

"Richard Clark" wrote in message
...
On Sun, 09 Oct 2005 03:39:32 GMT, "Frank"
wrote:

Axial extension 1.2" from antenna end -- Results as follows:

Extension Length (ft) Resonant Freq. (MHz)

0 3.5765
5 3.576
10 3.575
20 3.574
50 3.5725
100 3.5720

For a total shift of 4.5 kHz (0.125%) from zero to 100 ft

Hi Frank,

Thanx.

Was this for a coaxial line running from the drivepoint, then parallel
to the lower leg, down? Was the parallel separation 1.2" as you
describe above?

Was this line modeled as a third wire connected at the drivepoint and
dropping as I describe?

73's
Richard Clark, KB7QHC

Hi Richard,

My model is only valid providing the coax has no current on the exterior of
the shield. All I did was extend one leg of the dipole by the length
specified, but not actually connected to it; with a 1.2" gap. As per the
following sketch.

----------o---------- ----------
dipole extension

Do you think it makes sense? It is the only way I could think of modeling
it with NEC.

73,

Frank

On Sun, 09 Oct 2005 09:17:31 -0700, I wrote a fairly detailed
analysis:

[snip]

Apparently, I wasted my time.

On Mon, 10 Oct 2005 09:54:51 -0700, Wes Stewart
wrote:

On Sun, 09 Oct 2005 09:17:31 -0700, I wrote a fairly detailed
analysis:

[snip]

Apparently, I wasted my time.

Hi Wes,

I wouldn't say so. I took the time to enter your data into EZNEC and
confirm your results. I haven't closely examined the implications of
construction variations for the skirt wires, much less the "choking"
action that is notably missing.

73's
Richard Clark, KB7QHC

On Mon, 10 Oct 2005 16:05:16 GMT, "Frank"
wrote:

My model is only valid providing the coax has no current on the exterior of
the shield. All I did was extend one leg of the dipole by the length
specified, but not actually connected to it; with a 1.2" gap. As per the
following sketch.

----------o---------- ----------
dipole extension

Do you think it makes sense? It is the only way I could think of modeling
it with NEC.

Hi Frank,

No. The extension lies in the null of the dipole. As such, it would
be no mystery that it has so little influence.

To model it correctly requires some form of cage or skirt of wires as
Wes has provided in this thread.

73's
Richard Clark, KB7QHC

I have tried entering the model shown in EZNEC 4

The "View" of the antenna looks fine but when I try to run the
simulation it reports that it cannot because the gain is negative.

I then changed from azimuth to elevation simulation but this time it
reported the maxim 500 segments were exceeded.

I then reduce the segments slightly but now the program reports Runtime
error M6201: Math Sqrt Domain error.

ie. Cannot get the model to work using EZNEC. I'll see if it will run in
MNANA.

Richard Clark wrote:
On Mon, 10 Oct 2005 16:05:16 GMT, "Frank"
wrote:


My model is only valid providing the coax has no current on the exterior of
the shield. All I did was extend one leg of the dipole by the length
specified, but not actually connected to it; with a 1.2" gap. As per the
following sketch.

----------o---------- ----------
dipole extension

Do you think it makes sense? It is the only way I could think of modeling
it with NEC.


Hi Frank,

No. The extension lies in the null of the dipole. As such, it would
be no mystery that it has so little influence.

To model it correctly requires some form of cage or skirt of wires as
Wes has provided in this thread.

73's
Richard Clark, KB7QHC

On Mon, 10 Oct 2005 22:52:51 GMT, David wrote:

Cannot get the model to work using EZNEC.

Hi David,

Sounds like you got a wire crossed somewhere.

73's
Richard Clark, KB7QHC

Some ninkum poop (me) had the units set to wavelengths instead of inches.

It does run now. Thanks for the model, it gives me a starting point to
"play" with the thing.

Richard Clark wrote:
On Mon, 10 Oct 2005 22:52:51 GMT, David wrote:


Cannot get the model to work using EZNEC.


Hi David,

Sounds like you got a wire crossed somewhere.

73's
Richard Clark, KB7QHC

----------o---------- ----------
dipole extension

Do you think it makes sense? It is the only way I could think of modeling
it with NEC.

Hi Frank,

No. The extension lies in the null of the dipole. As such, it would
be no mystery that it has so little influence.

To model it correctly requires some form of cage or skirt of wires as
Wes has provided in this thread.

73's
Richard Clark, KB7QHC

I did not notice that somebody had attempted what you suggest. I translated
the coordinates into regular NEC2, and it does run. It appears to violate
some NEC2 criteria, but not sure how critical the model is. Obviously I
cannot use the "Minninec" ground, so have substituted an average S/M ground
with the coax end about an inch above the ground. I had assumed the antenna
was for HF, so it is probably impractically high, causing multiple lobing.
A free space model might provide more meaningful results.

73,

Frank

Does it matter that the outer sleeve and radiator element are connected
together in the model ?

The actual antenna only connects the sleeves to earth braid and the
centre conductor does not touch anything ?


Frank wrote:
----------o---------- ----------
dipole extension

Do you think it makes sense? It is the only way I could think of modeling
it with NEC.

Hi Frank,

No. The extension lies in the null of the dipole. As such, it would
be no mystery that it has so little influence.

To model it correctly requires some form of cage or skirt of wires as
Wes has provided in this thread.

73's
Richard Clark, KB7QHC


I did not notice that somebody had attempted what you suggest. I translated
the coordinates into regular NEC2, and it does run. It appears to violate
some NEC2 criteria, but not sure how critical the model is. Obviously I
cannot use the "Minninec" ground, so have substituted an average S/M ground
with the coax end about an inch above the ground. I had assumed the antenna
was for HF, so it is probably impractically high, causing multiple lobing.
A free space model might provide more meaningful results.

73,

Frank

On Tue, 11 Oct 2005 01:05:32 GMT, David wrote:

Some ninkum poop (me) had the units set to wavelengths instead of inches.
-YOW!-
It does run now. Thanks for the model, it gives me a starting point to
"play" with the thing.

Hi David,

I provided no model so you should revisit the thread to offer those
thanks where they are due.

73's
Richard Clark, KB7QHC

On Tue, 11 Oct 2005 02:57:44 GMT, "Frank"
wrote:

I did not notice that somebody had attempted what you suggest.

Hi Frank,

You need to revisit the posters to the thread. Wes, N7WS, went to
some trouble to provide a comprehensive response.

A free space model might provide more meaningful results.

It will certainly be different results - all depends on what your
goals are.

73's
Richard Clark, KB7QHC

On Tue, 11 Oct 2005 03:20:51 GMT, David wrote:

Does it matter that the outer sleeve and radiator element are connected
together in the model ?

Hi David,

ALL connections contribute to radiation. Their combination is what
builds the familiar lobe characteristic.

The actual antenna only connects the sleeves to earth braid and the
centre conductor does not touch anything ?

That's one way, the convention - could be t'other way 'round too; and
perhaps more interesting.

73's
Richard Clark, KB7QHC

On Tue, 11 Oct 2005 02:57:44 GMT, "Frank"
wrote:

----------o---------- ----------
dipole extension

Do you think it makes sense? It is the only way I could think of modeling
it with NEC.

Hi Frank,

No. The extension lies in the null of the dipole. As such, it would
be no mystery that it has so little influence.

To model it correctly requires some form of cage or skirt of wires as
Wes has provided in this thread.

73's
Richard Clark, KB7QHC

I did not notice that somebody had attempted what you suggest. I translated
the coordinates into regular NEC2, and it does run. It appears to violate
some NEC2 criteria, but not sure how critical the model is.

Which criteria?

Obviously I
cannot use the "Minninec" ground, so have substituted an average S/M ground
with the coax end about an inch above the ground. I had assumed the antenna
was for HF, so it is probably impractically high, causing multiple lobing.

The multiple lobes are what you should see and are exactly my point.

A free space model might provide more meaningful results.

If you can operate your antennas in free space then they would be
meaningful.

If you can't/won't buy Roy's fine EZNEC program, then may I suggest
4nec2 at zero cost or MultiNEC at nominal cost as alternatives to bare
NEC.

On Tue, 11 Oct 2005 03:20:51 GMT, David wrote:

Does it matter that the outer sleeve and radiator element are connected
together in the model ?

The actual antenna only connects the sleeves to earth braid and the
centre conductor does not touch anything ?

In the model I supplied, the first wire (cleverly labeled "Source
Wire") contains the source. By modeling convention, a source must be
"on" a wire, so the wire connecting the upper radiator to the
skirt/sleeve is equivalent to the transmitter (coax center conductor)
and is *not* a short circuit.

I did not notice that somebody had attempted what you suggest. I
translated
the coordinates into regular NEC2, and it does run. It appears to violate
some NEC2 criteria, but not sure how critical the model is.

Which criteria?

This is from L. B. Cebik. "Basic Antenna Modeling: A Hands-On Tutorial",
page 2-9 published by Nittany Scientific; "Among the most important
conventions to adopt is to begin at one end of each antenna element and to
proceed from that end to the other without changing directions in
mid-stream". I have seen array pattern reversals when this is not followed.
There will also be current discontinuities. To be honest, with such a high
segmentation this will probably not effect the pattern of such a stucture,
or for that matter the input impedance. Just for curiosity I will give it a
try, and see if it makes much difference. Also, although it should not
cause any problems, I would not have used a single segment for the source,
just the end segment from the upper element.

Obviously I
cannot use the "Minninec" ground, so have substituted an average S/M
ground
with the coax end about an inch above the ground. I had assumed the
antenna
was for HF, so it is probably impractically high, causing multiple lobing.

The multiple lobes are what you should see and are exactly my point.

I had assumed the antenna was to be used on HF, still comparing models with
similar parameters will provide meaningful information.

A free space model might provide more meaningful results.

If you can operate your antennas in free space then they would be
meaningful.

True, but the pattern is much simplified. Even so, in free space, I do see
evidence of minor patter ripple. I have also read (Cebik again) where the
Mininec ground can produce eroneous results.

If you can't/won't buy Roy's fine EZNEC program, then may I suggest
4nec2 at zero cost or MultiNEC at nominal cost as alternatives to bare
NEC.

I use Nittany Scientific's (www.nittany-scientific.com) NEC-Win Pro, which
seems to be a fairly good implementation of NEC2. The program does contain
simplified (spread sheet) data entry, but I prefer to enter in basic code,
which is apparently not available in EZNEC.

73,

Frank

Frank wrote:
... I prefer to enter in basic code,
which is apparently not available in EZNEC.

EZNEC data can be entered from an ASCII file. I regularly
generate ASCII files using MS Professional Basic for entry
into EZNEC. Here's a quote from the EZNEC help file:

"Wire coordinates can be imported from an ASCII file in a simple
format, either replacing or adding to the existing model. This
can be used to import coordinates from another program."
--
73, Cecil http://www.qsl.net/w5dxp

On Tue, 11 Oct 2005 19:20:35 GMT, "Frank"
wrote:

I did not notice that somebody had attempted what you suggest. I
translated
the coordinates into regular NEC2, and it does run. It appears to violate
some NEC2 criteria, but not sure how critical the model is.

Which criteria?

This is from L. B. Cebik. "Basic Antenna Modeling: A Hands-On Tutorial",
page 2-9 published by Nittany Scientific; "Among the most important
conventions to adopt is to begin at one end of each antenna element and to
proceed from that end to the other without changing directions in
mid-stream". I have seen array pattern reversals when this is not followed.
There will also be current discontinuities. To be honest, with such a high
segmentation this will probably not effect the pattern of such a stucture,
or for that matter the input impedance. Just for curiosity I will give it a
try, and see if it makes much difference. Also, although it should not
cause any problems, I would not have used a single segment for the source,
just the end segment from the upper element.

With the exception of the sleeve wires, the model follows this
convention and a trial with different end-to-end connections for the
sleeve gives identical results.

If someone doubts that the sleeve is effective or the model of same is
invalid, as I said before, remove it and place a parallel resonant
trap at the top of the "coax" running from ground to the bottom of the
antenna. The results will be very (but not exactly) similar.

With a one amp source, there will be a current standing wave on the
"coax" with a peak amplitude of approximately 1/2 amp. Changing the
height above ground changes this dramatically and the angle of maximum
radiation above ground changes dramatically as well.

Those wanting to spend more time with it can try adding wires to each
end of the sleeve, tying the wires together; changing the length of
the sleeve and re-resonating the rod, and so forth.

Because the top of the sleeve is a multiwire junction I prefer to use
a separate wire to hold the source.


Obviously I
cannot use the "Minninec" ground, so have substituted an average S/M
ground
with the coax end about an inch above the ground. I had assumed the
antenna
was for HF, so it is probably impractically high, causing multiple lobing.

The multiple lobes are what you should see and are exactly my point.

I had assumed the antenna was to be used on HF, still comparing models with
similar parameters will provide meaningful information.

A free space model might provide more meaningful results.

If you can operate your antennas in free space then they would be
meaningful.

True, but the pattern is much simplified. Even so, in free space, I do see
evidence of minor patter ripple. I have also read (Cebik again) where the
Mininec ground can produce eroneous results.

If you can't/won't buy Roy's fine EZNEC program, then may I suggest
4nec2 at zero cost or MultiNEC at nominal cost as alternatives to bare
NEC.

I use Nittany Scientific's (www.nittany-scientific.com) NEC-Win Pro, which
seems to be a fairly good implementation of NEC2. The program does contain
simplified (spread sheet) data entry, but I prefer to enter in basic code,
which is apparently not available in EZNEC.

Since I'm a long time client of Roy's and a beta tester for MultiNEC,
I use EZNEC with MultiNEC as a shell. I get the best of both worlds
and MultiNEC will also invoke Arie's fine program, which I use for the
neat full-color 3-D plotting. EZNEC keeps me honest with all of the
segment length checking, antenna viewing and other fine features.

MultiNEC offers full spreadsheet entry, and other features too
numerous to mention. It writes EZNEC input files just dandy. It will
do the same with your Nec-Win.

On Tue, 11 Oct 2005 17:46:18 -0700, Wes Stewart
wrote:

MultiNEC offers full spreadsheet entry, and other features too
numerous to mention. It writes EZNEC input files just dandy. It will
do the same with your Nec-Win.

Also Antenna Model and GNEC too!

Dan Maguire did one hell of job with that program!

Danny, K6MHE

email: k6mheatarrldotnet
http://users.adelphia.net/~k6mhe/

With the exception of the sleeve wires, the model follows this
convention and a trial with different end-to-end connections for the
sleeve gives identical results.

If someone doubts that the sleeve is effective or the model of same is
invalid, as I said before, remove it and place a parallel resonant
trap at the top of the "coax" running from ground to the bottom of the
antenna. The results will be very (but not exactly) similar.

With a one amp source, there will be a current standing wave on the
"coax" with a peak amplitude of approximately 1/2 amp. Changing the
height above ground changes this dramatically and the angle of maximum
radiation above ground changes dramatically as well.

Those wanting to spend more time with it can try adding wires to each
end of the sleeve, tying the wires together; changing the length of
the sleeve and re-resonating the rod, and so forth.

Because the top of the sleeve is a multiwire junction I prefer to use
a separate wire to hold the source.

Checking your lines of code more carefully, I see that they are all in the
same direction, except for the small radials connecting the top of the
sleeves. What I noticed is that the card sequence is not in order, which
was why I was confused. Not sure how important this is.

What I have noticed is that similar structures (GP with depressed radials,
for example) produce erroneous TRP results. It will be interesting to try
such computations on variants of your sleeve antenna. My results did not
show significant current on the outer shield of the coax. This may be due
to my inability to implement the "Mininec" ground.

Since I'm a long time client of Roy's and a beta tester for MultiNEC,
I use EZNEC with MultiNEC as a shell. I get the best of both worlds
and MultiNEC will also invoke Arie's fine program, which I use for the
neat full-color 3-D plotting. EZNEC keeps me honest with all of the
segment length checking, antenna viewing and other fine features.

MultiNEC offers full spreadsheet entry, and other features too
numerous to mention. It writes EZNEC input files just dandy. It will
do the same with your Nec-Win.

Nec-Win Pro does have a Pseudo built-in NEC-Win Plus interface, which allows
spread sheet entry, and it will also interface with Excel. I am not
familiar with MultiNEC, or EZNEC, although I do have ARRL's EZNEC version,
but have never used it. I understand that EZNEC is an excellent program,
thought it does not support NEC code entry, or the S/M ground.

73,

Frank

On Wed, 12 Oct 2005 13:32:16 GMT, "Frank"
wrote:
[snip]

Checking your lines of code more carefully, I see that they are all in the
same direction, except for the small radials connecting the top of the
sleeves. What I noticed is that the card sequence is not in order, which
was why I was confused. Not sure how important this is.

I don't see how the wires are numbered can be important; it's how they
connect, isn't it?

My rational for always (almost always) using wire 1 to hold the source
is that them I can add or subtract wires without having to change the
source wire designation.

What I have noticed is that similar structures (GP with depressed radials,
for example) produce erroneous TRP results.

Please explain "TRP".

It will be interesting to try
such computations on variants of your sleeve antenna. My results did not
show significant current on the outer shield of the coax. This may be due
to my inability to implement the "Mininec" ground.

Run it without any ground. Run it without any sleeve. Just put a
trap (or a high value resistor) at one end of a center-fed halfwave
vertical to represent the sleeve (choke) and then add various lengths
of wire on the other side of the trap. With no ground, the current on
the added wire will peak at multiples of 1/4 wavelength. So much for
the trap "isolating" the rest of the antenna.


Since I'm a long time client of Roy's and a beta tester for MultiNEC,
I use EZNEC with MultiNEC as a shell. I get the best of both worlds
and MultiNEC will also invoke Arie's fine program, which I use for the
neat full-color 3-D plotting. EZNEC keeps me honest with all of the
segment length checking, antenna viewing and other fine features.

MultiNEC offers full spreadsheet entry, and other features too
numerous to mention. It writes EZNEC input files just dandy. It will
do the same with your Nec-Win.

Nec-Win Pro does have a Pseudo built-in NEC-Win Plus interface, which allows
spread sheet entry, and it will also interface with Excel. I am not
familiar with MultiNEC, or EZNEC, although I do have ARRL's EZNEC version,
but have never used it. I understand that EZNEC is an excellent program,
thought it does not support NEC code entry, or the S/M ground.

I don't know what "S/M" ground is, but EZNEC supports perfect ground,
Sommerfeld-Norton and MiniNEC grounds. And I believe the object is to
*not* have to input files as NEC code.:-)

Wes Stewart wrote:
I don't know what "S/M" ground is, ...

Sado/Masochistic? :-)
--
73, Cecil http://www.qsl.net/w5dxp

I don't see how the wires are numbered can be important; it's how they
connect, isn't it?

You are probably right

My rational for always (almost always) using wire 1 to hold the source
is that them I can add or subtract wires without having to change the
source wire designation.

Good point.

What I have noticed is that similar structures (GP with depressed radials,
for example) produce erroneous TRP results.

Please explain "TRP".

"Total Radiated Power"

It will be interesting to try
such computations on variants of your sleeve antenna. My results did not
show significant current on the outer shield of the coax. This may be due
to my inability to implement the "Mininec" ground.

Run it without any ground. Run it without any sleeve. Just put a
trap (or a high value resistor) at one end of a center-fed halfwave
vertical to represent the sleeve (choke) and then add various lengths
of wire on the other side of the trap. With no ground, the current on
the added wire will peak at multiples of 1/4 wavelength. So much for
the trap "isolating" the rest of the antenna.

Ok.

I don't know what "S/M" ground is --

Oops, did I say S/M? What I meant was S/N (Sommerfeld/Norton).

-- but EZNEC supports perfect ground,
Sommerfeld-Norton and MiniNEC grounds. And I believe the object is to
*not* have to input files as NEC code.:-)

Ok, but I like to type it in cold, so see if I can get the cards in the
right order.

Frank