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