Hello Roy,

Tnx for advices;
I Have tried automatic "tapering" With a good convergence, but with the same
results.
I have no other modelling software, so I can not verify if it is due to
MMANA;
if anybody has the possibility to test a GPA in free space with another
soft, I should be interested by the results.
Vertical element 10.6m
radials 10.6m at 90°
radius 1.5mm
freq 7.06 MHz

73

André

Hi Roy,

I was sure to know you call sign, I was searching in my logs to see if wee
already had a contact on decametrics when I saw your email...

I have the reason now!

73

André

André wrote:
if anybody has the possibility to test a GPA in free space with another
soft, I should be interested by the results.
Vertical element 10.6m
radials 10.6m at 90°
radius 1.5mm
freq 7.06 MHz

EZNEC agrees closely with your previous values.
--
73, Cecil http://www.w5dxp.com

"Cecil Moore" a écrit dans le message de news:
qW5rh.32215

EZNEC agrees closely with your previous values.
--
73, Cecil http://www.w5dxp.com


OK Cecil, thank you for the test.

The question now, is, why a GPA in free space does not present a 36 Ohms
impédance ?


I use a full sized GPA on 40m, 6 meter high and a quasi 1/1 SWR with 50 Ohms
coax line;
with 36 Ohms in free space I had 14 Ohms for losses in the ground and 36
Ohms for my correspondant;
but now, it is 28 Ohms for the ground and 22 for the QSO...


To night, I can not open your page www.qsl.net/w5dxp/dipvsver.htm

I was interested to see if you get the same results,
I use also a half wave dipole 16m high and the GPA, with a slight advantage
for the GPA during the night and distant stations, and the opposite during
the day time and short distances;
the ground is very poor here.


73

André
http://f5ad.free.fr/

André wrote:
The question now, is, why a GPA in free space does not present a 36 Ohms
impédance ?

I'm sorry, I don't know. Maybe W7EL will jump in
and answer the question.

Tonight, I can not open your page www.qsl.net/w5dxp/dipvsver.htm

Yes, I am converting over to a new web page at
http://www.w5dxp.com

www.qsl.net is free and unfortunately one gets
what one pays for.
--
73, Cecil http://www.w5dxp.com

"Cecil Moore" wrote in message
. net...
André wrote:
The question now, is, why a GPA in free space does not present a 36 Ohms
impédance ?


The question is why is he modeling antenna in free space??
Planning to go there anytime soon???
Why would anyone model especially vertical antennas in free space (besides
trying to see how the donut looks)?
Verticals especially work with ground in forming the pattern and impedance.
I use and model my verticals on earth. JMO

73 Yuri, K3BU

On Wed, 17 Jan 2007 11:26:18 -0500, "Yuri Blanarovich"
wrote:


The question is why is he modeling antenna in free space??
Planning to go there anytime soon???
Why would anyone model especially vertical antennas in free space (besides
trying to see how the donut looks)?
Verticals especially work with ground in forming the pattern and impedance.
I use and model my verticals on earth. JMO

73 Yuri, K3BU

On my "Things to do List" I plan to spend some time with EzNec and a
ground plane in free space.

What I hope to better understand is the effect of the the quality of
the ground plan in the are between a modeled "real ground" and a
modeled "perfect ground".

I don't know the free space model will be valid, but I hope to learn
from the exercise.

I could just ask another series of "dumb questions" here but I fear
some of those who are so generous will tire of my noise!

When I modeled the vertical with a perfect ground I was expecting half
a vertical dipole and that is not what I got!

John Ferrell W8CCW

John Ferrell wrote:

On my "Things to do List" I plan to spend some time with EzNec and a
ground plane in free space.

What I hope to better understand is the effect of the the quality of
the ground plan in the are between a modeled "real ground" and a
modeled "perfect ground".

I don't know the free space model will be valid, but I hope to learn
from the exercise.

I could just ask another series of "dumb questions" here but I fear
some of those who are so generous will tire of my noise!

When I modeled the vertical with a perfect ground I was expecting half
a vertical dipole and that is not what I got!

John Ferrell W8CCW

If you model a vertical connected to perfect ground, you should get
almost exactly half the impedance of a dipole of twice the length in
free space, with the same radiation pattern except 3 dB greater in
amplitude and of course with the lower half missing. If you use an odd
number of segments and a single source for the dipole, there will be a
small difference because of the difference in source placement between
the dipole and vertical. This difference will become less as the number
of segments is increased in both models.

However, you can make the models virtually identical by using a "split
source". Here's an example you can even do with the demo program:

Open the EZNEC example file Vert1.ez or d_Vert1.ez. Click Src Dat to see
that the source Z is 36.65 + j2.971. (It's using MININEC type ground, so
the source Z is the same as for perfect ground.) Then change the Ground
Type to Free Space. Add a second wire with end coordinates 0, 0, 0 and
0, 0, -10.3 meters, 40 mm diameter, 10 segments, to be an exact mirror
image of the vertical. Then open the Sources Window and change the
source type to SV (split voltage) or SI (split current) and click Src
Dat. The reported Z is now 73.3 + j5.942, exactly twice the Z of the
vertical. To compare patterns, you'll need to use Perfect ground for the
vertical rather than MININEC type ground.

Roy Lewallen, W7EL

"André" wrote in
:


"Cecil Moore" a écrit dans le message de news:
qW5rh.32215

EZNEC agrees closely with your previous values.
--
73, Cecil http://www.w5dxp.com


OK Cecil, thank you for the test.

The question now, is, why a GPA in free space does not present a 36
Ohms impédance ?

Where does the 36 ohms come from? Is it for a quarter wave monopole
mounted on a perfect ground plane?

Is the radiation pattern of a quarter wave monopole mounted over 4
quarter wave radials the same as a quarter wave monopole mounted on a
perfect ground plane?

Though you might use the term GPA to refer to a quarter wave monopole
mounted over 4 quarter wave radials, it is not the same as a quarter wave
monopole mounted on a perfect ground plane.

Owen

"Owen Duffy" a écrit dans le message de news:


Where does the 36 ohms come from? Is it for a quarter wave monopole
mounted on a perfect ground plane?


yes


Is the radiation pattern of a quarter wave monopole mounted over 4
quarter wave radials the same as a quarter wave monopole mounted on a
perfect ground plane?


at first, it seems it is the same, but in fact there are some slight
differences, and it explains the difference in gain and radiation
resistance.

Though you might use the term GPA to refer to a quarter wave monopole
mounted over 4 quarter wave radials, it is not the same as a quarter wave
monopole mounted on a perfect ground plane.

right!
and it was the reason.

73 Owen and thank you

André
http://f5ad.free.fr/