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I live at the 15th floor and am interested on a pair of window-mount antennas for the 40 meters band: a top-fed vertical; and a loaded monopole, which I've already used with pretty decent results.

I'd like to run some simulations of both on 4nec2, especially the monopole, with which I'd like to experiment using alternative positions and sizes of inductors and a capacitive hat.

However, I believe it would be important to simulate the effect performed by the building wall over the far-field pattern.

Is it possible to simulate it using 4nec2, either directly or using some sort of trick, like a grid of lossy conductors? I've tried to find some info on the internet, with no success so far.

I experimented "rotating" my design and using the ground as if it were the building wall. However, I believe there is a more appropriate way and, besides, this wouldn't allow me to simulate the top-fed vertical, since its end will be closer to the ground and, therefore, it's going to be under effect of both the ground and the building wall.

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Welcome back after five years! The only way to know if a model is a good model is to make a model, and then compare its predictions to real-world measured results. If you live in a large building then I will guess that you don't know the exact construction of the wall, and that you're not allowed to drill holes to discover what is inside. So you will probably need to start with a model that is a rough guess.

Let's say that your building is made of concrete that is reinforced with steel rods. I don't know how I would model concrete, but the concrete is probably not as important to model as the steel rods and other conductors, such as electrical cables and metal pipes. If I had your problem, I would try making a model of the wall as a grid of lossy conductors as you suggest. I would give the simulated conductors the conductivity of steel, and I would make them the same diameter as rods that reinforce concrete, and I would space them the same distance apart as reinforcing rods are in typical concrete. I would add "copper" conductors for the electrical cables, and more "steel" conductors for pipes, and use that as my model.

If this model sounds too complicated, then you could try experimenting with a simpler model. If doubling the space between the "reinforcing rods" doesn't change the results of the model very much, then you probably don't need as many "reinforcing rods" in the model.

I think that this method will give a useful model that will help you see what will happen if you move your monopole antenna or add a capacitive hat. Good luck, and if you try this, please consider coming back and answering your own question to tell us what your results were.

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    $\begingroup$ I would start out modeling it without the building. Later, add the wall, etc. $\endgroup$
    – Mike Waters
    Jul 27 at 22:50
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    $\begingroup$ I can't argue with that approach, @MikeWaters. $\endgroup$
    – rclocher3
    Jul 27 at 23:35
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    $\begingroup$ @rclocher3 yeah there's no need to model this so accurately, I just need some estimate of gain and directivity. $\endgroup$ Jul 28 at 13:02
  • $\begingroup$ A nearby conductor might affect your gain a lot. Or it might not. The model is not much good unless you compare it to reality somehow to see if it is accurate or not. But ham radio is something we do for fun, so please build your model in whatever order you like best. Personally I would enjoy spending the time to make the entire model including the rebar and the electrical service cables, but that's just how I would like to do it. Other people think differently, and that is good. $\endgroup$
    – rclocher3
    Jul 28 at 18:23

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