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My shack is on the second floor, 4m from the ground. My main antenna is a base loaded vertical, using the metal roof (10x6m) as a ground plane.

When I operate in 20 and 40 meters, it's pretty acceptable. I don't seem to have RF in the shack. But on 80m I do: I have a small power supply with a digital readout and I see the current indicator go wild when I transmit.

Does this mean my earthing is not good enough? What can be done to improve it? Will grounding the roof with the shortest possible ground strap help with this situation?

rclocher3
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hjf
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1 Answers1

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Very similar question to this one.

The difference might be the size of your metal roof. The RF field from your vertical antenna element is "looking" for a counterpose element. If your metal roof is too small for the transmitted wavelength to act as a semi-resonant counterpose, the vertical RF field might try to use something else for its counterpose: the wiring in your shack, the A/C power line, ground, internet or telephone wiring to your shack, etc.

So I might try adding some longer counterpose wires, suitable lengths for 80M, to your metal roof, so the vertical antenna is more likely to use those, instead of stuff nearer to you, for its primary counterpose.

Additionally, you might want to try to "cut" the feed line, A/C power wiring, etc., at the RF frequency, by adding RF chokes spaced so the distance between the chokes makes those wire segments an unsuitable length to act as good counterposes or as nicely resonant director or reflector parasitic antenna elements.

hotpaw2
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