[TowerTalk] copper roofs?

[K4IA@aol.com]

I have a tin roof on my house.  I asked a lot of questions like yours and got 
darn few answers.  I think no one really knows.  It definitely isn't "ground" 
and you can't consider the roof a monolith because there are seams.  The 
seams are not electrically bonded and with a little corrosion may act like 
diodes and spin off all sorts of RFI.  Mine don't but it is possible in 
theory.

I think the roof is just a mess -- hard to model and hard to figure.  A roof 
slopes and the antenna may not be in the middle in all four directions.  How 
do you figure all that?  

I mounted a Cushcraft R7000 about five feet above the tin and it worked 
great.  A GAP Titan mounted the same way gave me fits with RFI until I ran 
the feedline straight down to the ground instead of across the roof.  Neither 
antenna has radials and neither was "grounded" to the tin roof.  A ladder 
line fed multiband dipole mounted away from the roof seems to do better than 
either of the verticals ever did.  Can you blame the roof?

I now have a TGM mini beam (quagi) about 15 feet above the roof.  It is 
probably 40 feet in the air and the roof slopes away from the base pretty 
steeply.  It works on 20 and above but I have can't compare it to the same 
antenna mounted in the clear.

I suspect this is like a lot of other antenna questions.  Just put the dang 
thing up and see what happens.  The K4IA antenna axiom is  "Any antenna in 
the air will get more QSOs and work more DX than every antenna on the drawing 
board."

Radio K4IA
Craig Buck
Fredericksburg, Virginia USA
QRP ARCI #2550  FISTS #6702 CC 788
K1 #470
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