|
GPA vs Vert dipole
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/ |
GPA vs Vert dipole
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/ |
GPA vs Vert dipole
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 |
GPA vs Vert dipole
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 |
GPA vs Vert dipole
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 |
GPA vs Vert dipole
"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/ |
GPA vs Vert dipole
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 |
GPA vs Vert dipole
"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 |
GPA vs Vert dipole
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 ----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
GPA vs Vert dipole
"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 |
GPA vs Vert dipole
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 |
GPA vs Vert dipole
"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/ |
GPA vs Vert dipole
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 |
GPA vs Vert dipole
On Fri, 19 Jan 2007 14:41:46 -0800, Roy Lewallen
wrote: 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 I will spend more time here. The last model I worked out with a perfect ground appeared to produce a 0 degree take off angle. Mornings are best for me to push my gray matter! John Ferrell W8CCW |
GPA vs Vert dipole
John Ferrell wrote:
I will spend more time here. The last model I worked out with a perfect ground appeared to produce a 0 degree take off angle. . . . That is the correct result. The pattern is exactly the same as half the pattern of a vertical dipole, which has a maximum at zero degree elevation angle, except that the gain of the vertical is 3 dB greater because the same power is concentrated in only one hemisphere. Roy Lewallen, W7EL |
GPA vs Vert dipole
On Fri, 19 Jan 2007 14:41:46 -0800, Roy Lewallen
wrote: 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 Varying the parameters of the free space vertical, reading the EZNEC help file and computing various scenarios with the G4FGQ program RADIAL_3 has satisfied my curiosity for the moment. I will next look at the physical problems of erecting a vertical for use on 40/80/160. Initially I will start with my 28 foot radiator over a radial field of 16 seventy foot radials fed with the SG-237 tuner. If I can work out the matter of keeping that up with acceptable guys I can step up to a 48 foot radiator out of my existing aluminum supply. Based on that experience, I will consider buying a little more aluminum to get to the 66 foot height. That is the reason for the 70 foot radial length. Most of the problems will be mechanical for a while. John Ferrell W8CCW |
| All times are GMT +1. The time now is 03:42 PM. |
Powered by vBulletin® Copyright ©2000 - 2025, Jelsoft Enterprises Ltd.
RadioBanter.com