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antenna height
Topic Started: Saturday, 5. September 2015, 08:56 (1,281 Views)
Lowflyer
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108 Charlie Tango 036

Hardly a surprise to find some differences in models as there are so many variables that can affect the plots, ground type, conditions, wire thicknesses, insulation, diameters etc.
I played about with a 1/4 wave model the other night that had 4 radials on it at 45 degrees, and the 2nd lobe did the same thing at 6m and produced more gain than the primary lobe, which also screwed the TOA numbers but this does not happen with every model !
Im pretty sure if you ask Henry when that page was written you will find it was quite some time ago, and that it was published up for illustration purposes, just like any theoretical modelling.
The graph I posted up previously for the vertical was also purely to illustrate the relationship between the ground influence, and the peaking and fluctuating of the gain at 1/2 WL intervals.

Maybe you should download yourself the demo copy of EZNEC Geoff. Its pretty easy to use and although restricted in segment numbers, you can still model and play about with most verticals and get reasonably accurate results. If nothing else its a great tool to visualize with.

Edit, Ok I need to apologise, I just checked what model I used for the graph which I claimed was a vertical and realised that the model was actually a Horizontal 1/2 wave dipole. Ohps. Sorry about that guys.


Edited by Lowflyer, Tuesday, 8. September 2015, 10:44.
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RadioDaze
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Quite a difference between a horizontal dipole and a ground plane based 1/2 wave coil loaded vertical for sure.It explains why the TOA is bad at low height, verticals tend to fair better given low height.

Last night I started thinking about a Silver Rod on the gate and a GM in the air as high as I can with an antenna switcher. This should cover many possible angles. Overkill though and just more work, there are limits so it will probably never happen and interactions between the 2 might render it pointless.

I think you can only get a demo for free on that software.
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Lowflyer
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108 Charlie Tango 036

The demo version is fully functioning with the NEC2 engine, but it is restricted by the number of segments that can be used which makes it inaccurate at modelling the currents on complex models with multiple wires. Otherwise it is perfectly fine to use for simple antennas like verticals and dipoles and even simple beams, and quads etc. The other draw back is that the NEC2 engine isn't very accurate at determining the swr curve so if you build the antenna, the swr isn't often where you expect it to be compared to the model and you have to make adjustments, but im not talking miles off the mark here. As an educational tool the demo is super to use and free. I however have the pro version so no restrictions on segments, but that's all there is between the two. Well worth the tiny download that it is.


Link to download Eznec v6 demo

Edited by Lowflyer, Tuesday, 8. September 2015, 16:50.
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The DB
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I, personally, prefer 4NEC2, which has several advantages over the free version of EzNEC. For example, its free, and still supports an unlimited number of segments. It also has more views than EzNEC to show the same data, and it can show a wider range of data as well, including some things that a very expensive EzNEC Pro does. It also uses the stock NEC2 files, and fully supports third party updates to the NEC2 code, some of which have both fixed known bugs and runs much faster. It also support the NEC4 engine if you are willing to pay for that...

I'm not saying not to use EzNEC, I'm simply saying that if you want to get into modeling you should try both. Find the one that is easier for you to use and has the features you need/want, and use that. It is possible to port data back and forth between the two programs as well...

Also, there are other third party programs out there, some of which are based on the NEC2 engine, and some based on the MiniNEC engine, which has both advantages and disadvantages over NEC2, depending on what it is you are modeling.


The DB
Edited by The DB, Tuesday, 8. September 2015, 17:41.
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RadioDaze
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Thanks for the information all worth looking into.
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