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How do I determine the amount of space needed between the end of a wire antenna and the mast?

Edit: End-Fed Antenna Steel pipe one each end

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    $\begingroup$ What is your mast made of? If that's nonconducting, no spacing is needed at all. If it is made of something conductive, you'll want to place it such that it interacts with the antenna the least, but that depends on wavelength, orientation/polarisation, ground properties, and desired directions. $\endgroup$ Commented Apr 12, 2023 at 7:07
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    $\begingroup$ Also please edit your question to say what kind of antenna/mast arrangement you have. The required spacing is very different at the centre of an inverted V, to the tips of a wire dipole. $\endgroup$
    – tomnexus
    Commented Apr 12, 2023 at 15:08
  • $\begingroup$ Sightly off topic but I would guess it would be a bad thing if your conducting masts were some multiple of quarter wavelength. $\endgroup$ Commented Apr 14, 2023 at 20:21
  • $\begingroup$ @quanglewangle that really depends on the relative position and orientation of masts and antenna. If the mast is a perfect antenna, but for the polarization that's orthogonal to that of the "intended" antenna, then you only need to make sure to be in the far field (that sets a minimal mast-antenna distance, indeed), and you'd have zero problems. $\endgroup$ Commented Apr 15, 2023 at 20:27

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This is exactly what you can model in EZNEC I presume you are using vertical masts to support the ends of a largely horizontal antenna; and if that's the case, I think the length of the masts will have as much or more impact on radiation patterns than the proximity to the antenna, within reason.

If the masts are a multiple of 1/4 wave length, you will likely get some absorption and/or reflection.

The other thing to note is that when antennas get beyond 1/2 wave length, they develop more directional patterns.

Horizontal long-wire patterns: Horizontal long-wire patterns

Read more here.

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