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Roof Antenna Mounting

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Hon1nbo

Wed Nov 25 2009, 07:13PM

Registered Member #902 Joined: Sun Jul 15 2007, 08:17PM
Location: Pacific Northwest USA
Posts: 1042

hello all,
I have gotten a radio club started at my school, and I am currently working out a roof antenna system with the school facilities director. We plan on first having a dipole, and maybe installing a vertical. For mounting the dipole, I planned on two tripods with the dipole between them. To fix the tripods to the roof is where I find my questions.
I planned to use a Gunpowder Actuated Tool to drive nails into the roof for securing the tripods. My nailer can take up to a 3 inch nail. Should I use a washer or any other hardware? The point is we don't want to have to take a drill up there and drill for bolts if we can avoid it, because we want to minimize our time spent up there.

any ideas?

73!, ke5tuz, Jimmy

Dr. Slack

Wed Nov 25 2009, 07:59PM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

If I was your Facilities Director, I would say "you ain't firing no nails through my roof". There aren't many bits of a roof that aren't either structural or meant to be/stay waterproof. Or I'd be telling you precsiely how and where you could fix them.

Can you lash stuff to any fixings that are there? Can you place 3 drums that can subsequently be filled with water as heavy enough weights to stay put with the wind under your antenna?

Just some thoughts

Hon1nbo

Wed Nov 25 2009, 09:27PM

Registered Member #902 Joined: Sun Jul 15 2007, 08:17PM
Location: Pacific Northwest USA
Posts: 1042

I understand that there are few places that are suitable for the nail gun, but there are some - mainly stone areas or that section. I would use something like sandbags or water drums but that becomes a little more unsightly than they'd prefer, but it remains an option. Also, if we did the water drums we would have to make sure that they are sealed and the like not only because of water leaking (not a big deal) but because mosquitoes in the area are unimaginably horrific. We also thought of making it cross the little courtyard to the other covered walkway (which is made of Concrete) - I am pretty sure that the main location where there definitely will be a mount is mostly stone and concrete like the rest, or at least has a layer of metal... however, there is a covering on it so I will have to check. Even if we were not sure, the test to see if the material is safe with a nail actuator is very simple. Otherwise, we might just go with sand bags or water - also, since this covered walkway meets with a couple of walls that run up along it, we might anchor into those

I'm also going to try to map things out on an overlay on a google earth view to see what is best

Sulaiman

Wed Nov 25 2009, 10:24PM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3141

Since you're installing on a public building your FIRST concern should be safety;

this will probably mean that each tripod will need a lightning conductor to earth
and some arrangement allowing the dipole/feeder to be earthed is also required.
This makes a quick installation unlikely.

I'm not a structural engineer but I doubt that nails would be a long term stable solution due to wind-induced vibrations and flexing and the legal liabilities are scary.

Maybe a quotation from a qualified local installer would give some cost perspective and free advice.

Hon1nbo

Thu Nov 26 2009, 12:23AM

Registered Member #902 Joined: Sun Jul 15 2007, 08:17PM
Location: Pacific Northwest USA
Posts: 1042

Sulaiman wrote ...

Since you're installing on a public building your FIRST concern should be safety;

this will probably mean that each tripod will need a lightning conductor to earth
and some arrangement allowing the dipole/feeder to be earthed is also required.
This makes a quick installation unlikely.

I'm not a structural engineer but I doubt that nails would be a long term stable solution due to wind-induced vibrations and flexing and the legal liabilities are scary.

Maybe a quotation from a qualified local installer would give some cost perspective and free advice.

of course safety comes first, what I meant by quick installation was the actual mounting etc, not the details like grounding and cable management.

as for the nailer, it isn't a simple one nail per leg mounting, the tripod would be mounted to a plane which would have many points of attachment to the roof - but we might go with something else, it was just an idea because it is available. These also are not regular nails, they are pretty beefy but I understand your point for concern

as for hiring a service, there is no way the school is going to pay for that but I might talk to some of them for ideas

-Jimmy

Proud Mary

Mon Nov 30 2009, 08:57PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Hey Jimmy, you haven't said what the frequency bands are, so how can we possibly recommend any particular antenna? - Stella

Dave Marshall

Mon Nov 30 2009, 10:29PM

Registered Member #16 Joined: Thu Feb 02 2006, 02:22PM
Location: New Wilmington, PA
Posts: 554

Jimmy,

Got a photo of your tripod or a sketch of the design? Might be able to help you out in that way.

Nailing to a flat asphalt roof isn't impossible,but the nail has to be properly sealed with liquid asphalt or some kind of appropriate sealant (roofing caulk is available at hardware stores). Covering over the nail with a waterproof cap after the fact isn't a bad idea either.

-Dave

Hon1nbo

Tue Dec 01 2009, 11:48PM

Registered Member #902 Joined: Sun Jul 15 2007, 08:17PM
Location: Pacific Northwest USA
Posts: 1042

as for the antenna, it is simply going to be a dipole for the time being, but we have decided to wait until after Christmas to mount it since mid-terms are coming fast and by then we might be able to do something else

as for the tripod, I currently do not have a sketch or the like but if you picture it, it is simple three metal pipes with a few cross members and welded at the top to a tube that will act as a mast. There will be either one or two of these for the dipole depending on the final configuration, our sponsor suggested an inverted V configuration, in which case we would only have one

the dipole is a "multi-band" dipole from MFJ - surprisingly it has a very good SWR on three bands without a tuner! (20-40-80 meters)

-Jimmy

Proud Mary

Sat Dec 05 2009, 06:18PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Don't forget the lightning arestors, Jimmy.

Hon1nbo

Sun Dec 06 2009, 10:32PM

Registered Member #902 Joined: Sun Jul 15 2007, 08:17PM
Location: Pacific Northwest USA
Posts: 1042

Proud Mary wrote ...

Don't forget the lightning arestors, Jimmy.

I won't forget the lightning arrestors : - )
however, even though we plan to install them the antennas will always be disconnected from anything when not in use, and if there was bad weather we likely wouldn't be operating at the school

anyways, since mid-terms have snuck up on us any design or construction of an antenna system is being put on hold until after winter break, and there is a chance that we might just stick with setting up an antenna on demand when wanted.
I'll make sure to post how everything works out

-Jimmy, ke5tuz

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