"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

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 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 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

----------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