[Elecraft] OT - anyone have experience with effects of metal roofs on antenna performace?

[Mel Farrer]

Hello Paul, 

I have not had any bad experience with metal roof with one exception.  I had a garage with a metal roof and while I did not see any pattern or tuning issues, I did notice that on a couple of galvanized panels where the connection was marginal, some discoloration  where they touched.  I was using a 14AVQ at power near the roof.  RF currents?  With insulated panels that are screwed together, or galvanized ones with sheet metal screws probably will never give you any problems. 

On my barn which is 46 x 54 feet I have used a vertical with the Galvanized panel roof as a ground plane.  Worked great.

Mel, K6KBE




________________________________
 From: Jim Bennett <w6jhb at mac.com>
To: Paul Taenzer <ptaenzer at gmail.com> 
Cc: elecraft at mailman.qth.net 
Sent: Thursday, July 4, 2013 10:31 AM
Subject: Re: [Elecraft] OT - anyone have experience with effects of metal roofs on antenna performace?
 

Paul,

Our home is about 25 miles east of downtown Sacramento, CA. It is a two story home and until May of 2012 had a wood shake roof - very common in this part of the state. It was the original roof, about 21 years old, and was getting pretty nasty. We had it replaced with a metal roof: the "Barcelona" style of powder coated steel roofing made by Gerard.

My primary antenna is an 88 foot long doublet made with #26 wire. It is supported in the center (at 45 feet) by a long fiberglass windsurfing mast. The ends run through some trees to the north and south. The roof is only about 15-20 feet from quite a bit of the antenna. I did not notice ANY differences in performance of this antenna when we had the roof replaced.

Note that with the wood shake roof, my feeder was 600-ohm line that I had simply lying on the wood shakes. I knew that was not a good idea with a metal roof, so I replaced the 600-ohm feeder with 450-ohm ladder line and routed that along the side of the house, running about 120 feet from the shack window to the antenna. Other than my K3's internal tuner having to re-learn tuning algorithms for each band/frequency, all was good.

I never bothered to mess with my eznec radiation pattern stuff, as (1) the patterns from a doublet are really whacky to begin with, and (2) I had no other options, so I knew "it is what it is!". :-)

IMHO, you may see "some" difference, but I doubt it's going to be significant.

Jim / W6JHB
Folsom, CA (not the prison!)


On   Thursday, Jul 4, 2013, at  Thursday, 9:19 AM, Paul Taenzer wrote:

> Hello,
> 
> We live on a very windy Island (with an industrial wind farm) and have been
> loosing shingles off the roof due to severe wind storms.
> 
> We've been considering having a metal roof, but I'm wondering about the
> possible impact of the metal roof on the radiation pattern and efficacy of
> nearby antennas.
> 
> There's a SteppIR on a tower about 20 feet from a corner of the roof. The
> antenna is about 30 feet higher than the highest point of the roof.
> 
> I'd appreciate learning from anyone with relevant experience or technical
> expertise related to this.
> 
> Many thanks.
> 
> 73s,
> 
> Paul
> VA3LX
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