Whilst working in Stockholm back in the mid 1980s, as SM0/G3JVC. I had a
Hygain 18AVQ/WB vertical clamped to a canopy on the roof of a 20 story
building just outside Stockholm, from that position you could see clear to
the horizon. The roof was covered with thick copper sheet, and I connected
the 18AVQ/WB radial connection to that. Over two years or more, I had no
adverse comment regarding RFI from the occupants living below the copper
roof ground plane. From the performance point of view the 18AVQ/WB was
outstanding, if I could hear it, then I could work it, running 50 watts 3.5
- 28 MHz. The only downside was the adverse effect when, during the winter,
the entire antenna became coated with ice during freezing rain storms.
73, John. G3JVC
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com] On Behalf Of Grant Saviers
Sent: 06 August 2011 17:02
To: Jim Hoge; towertalk
Subject: Re: [TowerTalk] Metal roofs and EMI/RFI
I've had two verticals on metal roofs, old galvanized barn and shed
roofs at that. A 80m hat loaded 40' vertical was terrific for DX,
particularly when using a Beveridge or dipole for lower noise receive.
An elevated vertical with a large metal ground plane is an excellent DX
antenna IMHO.
The antenna support structure, connectors, and coax PIM (passive
intermodulation) issues are an issue on cell towers with lots of full
duplex radios, but I think unlikely in common amateur service. Anyway,
you likely have many thousands of metal to metal joints in RG8 shields,
metal fences, tower parts, house wiring, audio systems, etc. etc.
There is an interesting application note from Andrews that compares
braid coax PIM with hardline, as an example.
Grant
KZ1W
On 8/5/2011 10:57 AM, Jim Hoge wrote:
> Are there any RF noise issues to consider when contemplating a residential
> reroof from composition to metal shingles? The last thing I want to do is
> increase my background noise level here in suburbia.
>
> Tnx, Jim W5QM
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