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Metal roof for 40m ground plane
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by W5GA on January 23, 2006
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I have a approx. 3000sq. ft. metal roof that I would like to use as the counterpoise for a 40m GP. Is this practical? Do I need to bond each and every roof panel, and if so, with what? The panels are held together with sheet metal screws as it is. Would this be sufficient or should I add jumpers.
And is 1 wire per panel sufficient?
Thanks!
Doug
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RE: Metal roof for 40m ground plane
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by WB6BYU on January 23, 2006
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Try it and see. I know of several places where this has
been done. In one case, we just put some extra sheet metal
screws through the roofing panels where they overlapped
(as they were pretty rusty). One screw in each corner
is probably good enough unless you find you have some
particular problems.
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RE: Metal roof for 40m ground plane
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by W5DXP on January 23, 2006
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Add some insulated wire to your ohm-meter leads and test the DC continuity from side to side and top to bottom. Not a perfect test for RF, but one data point at least.
--
73, Cecil http://www.qsl.net/w5dxp
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RE: Metal roof for 40m ground plane
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by WB2WIK on January 23, 2006
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>Metal roof for 40m ground plane Reply
by W5GA on January 23, 2006 Mail this to a friend!
I have a approx. 3000sq. ft. metal roof that I would like to use as the counterpoise for a 40m GP. Is this practical?<
::Is the roof flat, or sloping? When you say "metal," what's the material? Any coating, anodizing, galvanizing, etc?
>Do I need to bond each and every roof panel, and if so, with what? The panels are held together with sheet metal screws as it is. Would this be sufficient or should I add jumpers.<
::How many panels are there? Do they overlap? Again, what's the actual material, including any protective coating it may have? If you gently (loosely) touch a couple of Ohmmeter probes (X1 scale) to two adjacent panels, do you read continuity? Low resistance continuity (like 1 Ohm or less)? What about if you press the probes harder against the material?
>And is 1 wire per panel sufficient?<
::This makes me think there aren't many panels. If there are only a small number of roof panels, like four, can you mount the vertical antenna at their intersection? You normally don't want "wire" in series with the counterpoise connection -- that will add reactance (series inductance) that will alter resonance and make the counterpoise less effective. If you must have an interconnecting material, I'd use very wide flashing, aluminum or copper, depending upon what the roof panel material's made of.
-WB2WIK/6
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RE: Metal roof for 40m ground plane
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by N6AJR on January 23, 2006
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I should work ok, and better if you bond the panels. also keep us posted.
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RE: Metal roof for 40m ground plane
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by K6AER on January 23, 2006
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I have my 40 meter SteppIR mounted to the metal roof of the horse barn. The roof is 40 by 60 feet. The panel overlap is separated by paint only and the measured overlap on a 20 foot panel is over 10,000 pF. This is more than enough for 40 meters. Typical roof panels are attached with self tapping metal screws through overlapping panels and my roof is less than 10 ohms from end to end.
Metal roofs make a great ground plane.
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RE: Metal roof for 40m ground plane
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by W5GA on January 24, 2006
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I'll have to check the continuity between sections as it sits. The roof consists of many, many panels. They are approx. 3'x 20' or some fraction thereof, depending on what area of the roof you look at. The metal is painted, formed steel (28ga. I think), with the ends being formed to overlap the adjacent panel.
On second thought, it'd probably be easier to put some radials up.
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RE: Metal roof for 40m ground plane
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by KB4EMF on January 24, 2006
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I tend to think a perfect DC continuity is NOT important. Because of their size and the fact some part of the panels are overwrapped, there should be quite a sufficient capacitive coupling between panels making it "connected" RF wise.
I would just make sure the wire that connection from the antenna to one of the panels are as good as it can be.
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RE: Metal roof for 40m ground plane
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by W3LK on January 24, 2006
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Doug:
My metal roof is somewhat larger - 23k sq ft - and I have no idea if the panels have DC continuity or not, and I really don't care. I have my Butternut HF6-V mounted in the middle of it and it works fine.
Put up the antenna and see what happens.
73,
Lon - W3LK
Baltimore, Maryland
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RE: Metal roof for 40m ground plane
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by AG4DG on January 25, 2006
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A large metal roof sounds quite close to an ideal ground plane. It's like having an infinite number of long radials.
If you are concerned about continuity among panels, you can "bond" them together with aluminum foil duct tape or strips of aluminum foil attic insulation. To hold the foil in place, use water-filled jugs as anchors to hold it down. Or you can tape the foil down.
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