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?

  • $\begingroup$ Lots of similar questions have been asked and answered here before. Maybe you'll find that your question has already been answered. Check it out. $\endgroup$
    – Mike Waters
    Oct 8 '19 at 21:01
  • $\begingroup$ It seems that you have already asked this before. If this is new information, then kindly update your original question. $\endgroup$
    – Mike Waters
    Oct 8 '19 at 21:04
  • $\begingroup$ I am closing this as a duplicate. If you feel that this is unwarranted, kindly let me or another moderator know. $\endgroup$
    – Mike Waters
    Oct 8 '19 at 21:07
  • $\begingroup$ @MikeWaters In my opinion, this question isn't a duplicate; it seems to me to be more about grounding (or earthing) the station from the second floor than about the metal roof. $\endgroup$
    – rclocher3
    Oct 8 '19 at 21:40
  • $\begingroup$ @MikeWaters this question is related to the previous one. In the previous one I asked about options, and executed one of the options given by the people there. But now I've ran across the problem of RF in the shack which I think it's due to a lack of proper grounding, which I'm trying to address, because it only seems to happen in one band. $\endgroup$
    – hjf
    Oct 8 '19 at 22:36

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.

  • $\begingroup$ Adding counterpoise wires isn't really possible as this is a city property (attached houses. I could extend a bit from the roof but not really 20 meters. I've read about ground tuning units (coils that make random wires resonant at ground), but I'm not sure they will help in my case? $\endgroup$
    – hjf
    Oct 9 '19 at 19:21
  • $\begingroup$ You might try attaching some counterpose wires to the far corners of your metal roof, and letting them drop to the ground (insulated). Perhaps extend them out a bit on flagpoles, if possible. How well inductive loading might work on counterpose wires and non-buried ground radials might make a good separate question. $\endgroup$
    – hotpaw2
    Oct 10 '19 at 21:14

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