What are the effects on signal propagation if this ground plane is just a metal object and what are the effects if the ground plane is actually grounded?

I am asking this question because someone wants to put a storage container under my 40m antenna and I want to know what the effects of this large metal object will be. Will it harm my radiation pattern?

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    $\begingroup$ I agree with Phil's answer. But let me ask, (1) What are the dimensions of this metal storage container? (2) How high is your dipole? and (3) will it be centered under and parallel with that dipole? $\endgroup$ – Mike Waters Jun 6 '19 at 19:18
  • $\begingroup$ Related question $\endgroup$ – Mike Waters Jun 6 '19 at 19:26

If the container is small relative to wavelength, then it won't have much effect at all.

If it's very large (say, infinite) then it will reduce ground losses by providing a more conductive ground plane. It doesn't matter if it's actually connected to the soil or not. This is a good thing.

The container will be closer to the antenna, which will change the spacing of the dipole and the image antenna under it, which may move the elevation of the main lobe up or down depending on the height of the dipole.

Since a storage container is probably neither very small nor very large relative to a 40m wavelength, you can expect effects somewhere between the extremes. In all, I'd say as long as the dipole isn't very close to the container you can expect no significant detrimental effects, and perhaps even some positive ones.

If you want to know more exactly what will happen, of course the thing to do is model the precise geometry of your situation.

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    $\begingroup$ Would it be correct to assume that a ground plane directly under a dipole would be good for NVIS operation but not be much of an improvement for DX operation? $\endgroup$ – Cecil - W5DXP Jun 6 '19 at 23:47
  • $\begingroup$ @Cecil-W5DXP A ground plane under a dipole is an improvement in any circumstance, as it reduces the resistive loss in the soil. Whether the antenna is good for DX or NVIS depends on the height of the antenna above the ground plane, not the ground plane conductivity. $\endgroup$ – Phil Frost - W8II Jun 7 '19 at 17:59

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