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eHam Forums => Antennas and Towers and more => Topic started by: W7VO on June 29, 2011, 06:03:24 PM



Title: Vertical on metal roofed pole barn?
Post by: W7VO on June 29, 2011, 06:03:24 PM
I have just acquired a used 14AVQ vertical, and am wondering how well it might work on top and in the middle of a 24 X 60 metal roofed pole barn? Anybody done this and had either good or bad results? I figured the huge metal sloping roof would probably make a wonderful ground plane......

73;

Mike, W7VO


Title: RE: Vertical on metal roofed pole barn?
Post by: VE3FMC on June 29, 2011, 06:20:03 PM
I have just acquired a used 14AVQ vertical, and am wondering how well it might work on top and in the middle of a 24 X 60 metal roofed pole barn? Anybody done this and had either good or bad results? I figured the huge metal sloping roof would probably make a wonderful ground plane......

73;

Mike, W7VO

Mike the roof might act as a ground plane. However the normal practice when roof mounting a vertical is to cut radials for each band. 4 per band would work. Lay them on the roof, if you use insulated wire.

Or, go ahead and see how it works without the radials, you can always add them later.


Title: RE: Vertical on metal roofed pole barn?
Post by: K7KBN on June 29, 2011, 07:31:32 PM
If the roof is one solid piece of metal it MAY work quite well.  However, if it consists of several overlapping pieces of metal, then you should bond them together, removing rust and galvanizing at the bonding points.  The idea is to make one seamless metallic surface for the RF to see.


Title: RE: Vertical on metal roofed pole barn?
Post by: K2DC on June 30, 2011, 02:41:10 AM
Mike,

   Good advice in both of the previous posts.  The metal roof will act as a good reflecting plane to help support a low take-off angle.  However, it can not be relied upon to act as "the other half of the antenna" for proper matching and efficiency.  Even if the metal segments of the roofing material are bonded together, an elevated vertical requires resonant radials.  Two quarter-wave radials per band is a good start, four or more is much better.

GL & 73,

Don, K2DC


Title: RE: Vertical on metal roofed pole barn?
Post by: WB6BYU on June 30, 2011, 08:52:04 AM
The roof makes a fine ground plane as long as the panels are well bonded together and to the coax
shield at the feedpoint.  I've used extra sheet metal screws to bond the panels if they appear at all
rusted - the roofing screws with neoprene gaskets are probably best.  At a minimum they should be
bonded to the adjacent panels at all 4 corners, and perhaps also in the middle of the long sides if
that is closer to the feedpoint than one of the corners.

There is no need for radials when the roof is properly bonded to the feedpoint.

Be aware, however, that any distance between the feedpoint and the roof becomes part of the
antenna.  Folks who mount their verticals on a tripod above the roof often find that they can't
adjust the antenna short enough to tune 10m because of the added length below the feedpoint.
Ideally the feedpoint would be within 6" of the roof, though it may be difficult to manage this
and still get a mechanically robust mount - you may need to guy the antenna as well.


Title: RE: Vertical on metal roofed pole barn?
Post by: W7VO on July 01, 2011, 11:06:55 AM
Thanks, guys. I had a special steel mount welded up at the exact roof pitch angle that attaches the base of the vertical antenna almost directly on the roof, about what one would see with a ground mount.

My roof consists of overlapping metal sheets that are tied down with lots of screws. It would probably be impossible to get them all bonded properly as this building was built in 1984. It is also 24 feet wide by 60 feet long, that is a LOT of sheet metal to try to deal with. Maybe what I will do is see if it works without the added radials, and if I see the SWR jump around from intermittent grounding issues I will then add them.

I have never used a vertical before, all my other antennas are either yagis or wires....I just happened to get the HyGain at a very good swapmeet price....

One can never have too many antennas! (or radios either, for that matter....) :o

73;

Mike, W7VO


Title: RE: Vertical on metal roofed pole barn?
Post by: KC4YJI on July 05, 2011, 04:02:16 AM
Let us know how it works out.  I have a shed with a medal roof and I have thought about doing something like that too.

73, Scott


Title: RE: Vertical on metal roofed pole barn?
Post by: K7KBN on July 05, 2011, 08:01:40 PM
Good luck - but don't be surprised if it's a bit noisier than you might expect, especially if there are other rf sources like radio/tv stations within a few miles.  Google "rusty bolt effect"...


Title: RE: Vertical on metal roofed pole barn?
Post by: WD6GLA on July 07, 2011, 10:09:31 PM
I keep reading this about metal roofs and verticals . Baloney ! People make way too much out of bonding the roof sheets together and discourage those that want to give it a try .  They are just repeating what they have read on here and I wonder how many have actually tried it .  Unless its really a cobbled together roof , ancient and very rusty , or in the tropics the sheets are going to make contact .  All the roofing screws in the last 50 years are plated and the sheets are galvinized steel or aluminum .  Even if only some of the screws make contact its going to work and if you are in doubt run a few new screws in each panel , it'll be obvious when you get up there to take a look .   Put the antenna on the roof and enjoy ,  dont worry about it .  I've put several verticals on corregated roofs and they always worked great . 

Bob   WD6GLA 


Title: RE: Vertical on metal roofed pole barn?
Post by: K1CJS on July 08, 2011, 05:26:23 AM
That isn't entirely true, Bob.  All you need is one poor connection on that metal roof and you could--COULD have a noise generator that will make you tear your hair out.  It does depend on many variables.  One person that does have such a roof may get on fine with their antenna system while another may get so fed up that they may scrap the idea--permanently.


Title: RE: Vertical on metal roofed pole barn?
Post by: WB6BYU on July 08, 2011, 08:57:35 AM
There is a lot of variation  - roofing screws are probably better than nails for bonding the panels
together, especially with painted panels where there won't be much electrical contact between
them otherwise.

But it needn't be a big chore - while you are up there installing the antenna, take a look at the
roof and see how it looks.  Check the DC resistance across a couple panels if in doubt:  that
isn't the perfect test for RF, but if the resistance is high then add some additional screws.


Title: RE: Vertical on metal roofed pole barn?
Post by: K7KBN on July 09, 2011, 11:57:25 AM
There's a whiole bunch of difference between "making contact" and "making ENOUGH SOLID contact", particularly at RF.