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[TowerTalk] Re: Metal roof & antenna patterns

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Subject: [TowerTalk] Re: Metal roof & antenna patterns
From: (
Date: Tue, 2 Oct 2001 23:10:39 +0200
When I was living in Upperaustria we had a house and antenna similar to your 
description. Our building had two stories with a flat metal roof and the 
antenna was mainly a 5 element tribander. The size of the roof was about 6 
meters times 15 meters. So it was a rather big metallic surface beyond the 
antenna. The Tribander itself was on a 17 meters high mast, about 5 meters away 
from the building.

We changend the antenna several times (building some homemade quad-antennas and 
later the commercial tribander) but we never noticed any influence of the 
metallic roof. The commercial tribander worked exactly with the dimensions of 
the supplier.

We also measured the radiation diagramm of one quad at zero elevation angle, 
which seemed okay. Of course a metallic surface beyond the antenna can change 
your elevation angle and we never had the possibility to test the antennas 
without the roof (or without the building, hi). But from my point of view I 
would not worry to much about a metallic roof, which is almost a wavelength 
away from your antennas.

By the way, we even were very happy to have the (flat) metallic roof, as we 
installed a quarterwave vertical for 40 meters on the roof. Because of the good 
conductivity of the metallic surface, this antenna worked very well without 
radials. From your antenna-description I see, you don´t have an antenna for 30 
meters. Perhaps a vertical on a metall roof would make you as happy on 30 as we 
were on 40.

For lightning protection the roof must be grounded. We used several ground-rods 
for this purpose and also connected it to the groundsystem of the mast (which 
was a steel-wire of about 1 cm diameter and about 20 meters long, buried about 
60 cm deep in the garden). In almost all cases a lightning strike will hit your 
tower and not the roof.


Juergen - OE5CWL

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