I am looking at putting up a decent hf antenna on my 17.5' Glen Martin roof 
tower.  Apart from yagis, I'm thinking about a Gem Quad or standard 2 element 
quad.  My question is, how much interaction with the roof will I have and how 
much will it degrade performance with the bottom of the loops being so close to 
the roof?  I figure the bottom of the 20m loop will be roughly 8' above the 
roof.  The house is typical wood construction with asphalt shingle roofing.  
I've been modeling with EZNEC and can accept the compromise in overall height 
(take off angle, etc.) but am just not sure what effect the close proximity 
with the roof will have.  Any help is appreciated.   Thanks.
 
N7XW
 
 
                                          
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