Hello,

(pse excuse my english)

I have some questions about GPA and vertical dipole
(vertical quarter wave with four horizontal radials and half wave center
feed vertical)

With a modelling software (MMANA) and antennas calculated in free space
conditions, at resonance,I get 72 Ohms for the dipole (correct), but only 22
Ohms for the GPA as I expected 36;

does anybody know the reason ?


Another question, The radiation patterns seem to be identical for both
antennas, so I expected the same gain with GPA or dipole, but the soft give
2.13 dBi for the dipole (correct) but only 1.57 dBi for the GPA.

Not due to the fact that the currents are greater in the GPA, as the soft
was working in 'no loss' conditions for the wires.

Tnx if you have solutions,

73

André
F5AD
--------------------------
http://f5ad.free.fr/

I believe that MMANA is a MININEC-based program. If that's correct, then
there will be an error wherever wires connect at an angle, as they do in
the ground plane antenna. The error can be minimized by making the
segments of both wires very short near the connection point, either by
greatly increasing the number of segments or by "tapering" the segment
length. A capability to do the "tapering" automatically might be built
into MMANA -- it was a feature of MININEC-based ELNEC 15 years ago. I
don't know if that's the reason for your results, but that's where I'd
start looking.

Roy Lewallen, W7EL

André wrote:
Hello,

(pse excuse my english)

I have some questions about GPA and vertical dipole
(vertical quarter wave with four horizontal radials and half wave center
feed vertical)

With a modelling software (MMANA) and antennas calculated in free space
conditions, at resonance,I get 72 Ohms for the dipole (correct), but only 22
Ohms for the GPA as I expected 36;

does anybody know the reason ?


Another question, The radiation patterns seem to be identical for both
antennas, so I expected the same gain with GPA or dipole, but the soft give
2.13 dBi for the dipole (correct) but only 1.57 dBi for the GPA.

Not due to the fact that the currents are greater in the GPA, as the soft
was working in 'no loss' conditions for the wires.

Tnx if you have solutions,

73

André
F5AD
--------------------------
http://f5ad.free.fr/

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

"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

André wrote:
"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, you might find this interesting:

http://www.cebik.com/gp/gp3.html
On Ground Planes

73,

Chuck
NT3G

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"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