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-   -   EMT as antenna mast? (http://www.diychatroom.com/f18/emt-antenna-mast-45098/)

KE2KB 05-23-2009 05:07 PM

EMT as antenna mast?
 
Hi;
I am going to install an amateur radio/scanner antenna. This antenna is fairly small and light, being constructed from 1/2" copper pipe and is about 60" long.

I want to use a 10 ft mast, and thinking that 1-1/4" or maybe 1-1/2" EMT would do. It's a lot less expensive and I think a much better conductor of electricity (for grounding) than the painted steel mast sold at Radio Shack, and I wouldn't have to scrape the enamel from the pipe before attaching the ground clamp.

Do you think that EMT would withstand the wind loading caused by this small antenna? I estimate wind loading to be very low, considering that this is basically a single element vertical antenna with no ground plane radials.

I live in New Jersey, where we don't see many really bad storms, and I can remove the whole assembly in the event we do get a TS or hurricane.

Thanks

FW

InPhase277 05-23-2009 07:11 PM

I have a home made windmill with a 10' diameter supported from 1-1/2" EMT. I have three guy wires from the last 1/4 or so. It holds up amazingly well with a high load on it.

I don't see why you couldn't put a static load on it with some guy wires just to be sure.

KE2KB 05-23-2009 07:42 PM

Quote:

Originally Posted by InPhase277 (Post 277554)
I have a home made windmill with a 10' diameter supported from 1-1/2" EMT. I have three guy wires from the last 1/4 or so. It holds up amazingly well with a high load on it.

I don't see why you couldn't put a static load on it with some guy wires just to be sure.

A windmill! Do you generate your own electric, and if so, can you sell any of it back to POCO?

I can't guy my antenna install, since it's going on the wall of the house, next to an attic window, but considering that EMT is steel, just like the more expensive mast pipe sold by RS, and my antenna is minimal loading, I shouldn't have a problem.
I'm just not sure that the wall thickness on the EMT is comparable to the mast pipe, but I'm not going to sweat it (but I will be sweating the copper pipe; ha ha). It should be up there until the house comes down, or a neighbor complains<g>.

FW

InPhase277 05-23-2009 08:18 PM

My windmill is experimental, but I suppose that I could sell excess power back to the utility in the future. But not right now.

If you are concerned about the wall thickness, why not use a stick of rigid conduit?

KE2KB 05-23-2009 08:38 PM

Quote:

Originally Posted by InPhase277 (Post 277578)
My windmill is experimental, but I suppose that I could sell excess power back to the utility in the future. But not right now.

If you are concerned about the wall thickness, why not use a stick of rigid conduit?

I'll have to make that determination when I go to buy the stuff. Rigid is more expensive, so I don't want to use it unless I really think I'll need it.
I'm trying to keep the cost of this thing down too. That's why I'm building the J-pole out of copper instead of buying a Cushcraft Ringo Ranger, which would cost me over $100 (but it's a better antenna).
I just need something to get some use out of my 2 meter ham rig, and to double as a scanner antenna for listening to the railroads. Wouldn't need the outdoor antenna for the cops... they use high power repeaters. Trains don't.

On a slightly different subject:
What if I wasn't mounting the antenna to the house. What if it were on a tower in the back yard. Would I still need to run a continuous grounding conductor from the electrode at the base of the tower to the one at the SE?

FW

InPhase277 05-23-2009 09:55 PM

The EMT ought to be plenty sturdy for your antenna, especially mounted to the house, and a single 10' length. The grounding issue, I don't really know, and I no gotty me Code book, and me no wanny looky on the web.:whistling2:

kbsparky 05-23-2009 10:56 PM

My TV antenna is supported with a section of 1" EMT. It's been on the end of my house for over 17 years, with no problems. And this is a rather large TV antenna, complete with a rotor assembly on the top of the mast.

As long as you have the EMT supported at the bottom, and a few feet up, it should be able to do the job.

As for grounding, I installed a pipe grounding clamp near the bottom, and ran a ground wire to a ground rod. There is also an interconnecting bonding wire that runs from there to my main ground at the electrical service.

theatretch85 05-24-2009 01:37 AM

One thing about the EMT is it will rust if you don't spray it with a protective paint. Get some rustoleum spray paint and paint it to match the house color. Or if you like, just get some gray spray paint, basically about what the EMT looks like un-painted. I don't believe the spray paint is enough to mess with the proper grounding properties, if you are concerned about it, spray a section of it and let it dry, then check it for continuity with a multimeter.

Speedy Petey 05-24-2009 07:35 AM

I used 1" EMT for my two dual band (UHF/VHF) antennas and for my scanner antenna. It is almost the same size as those cheap painted gold antenna masts, and even stronger. For something big I'd go up to 1-1/4" like KB used.

For one I am using a gable end mount made out of deep Unistrut, one long piece and one short, and 1" strut straps.

Unless it is in an environment where it might get scratched EMT should not rust. It is coated/plated for corrosion resistance.

KE2KB 05-24-2009 08:37 AM

I am considering a coat of Rust-Oleum, but would probably install the ground clamp first, then mask it so as not to coat the terminal for the GC.
Luckily, my SE is on the same side as the antenna will be, so I only need to bring the GC down to its electrode. The system is bonded to the water pipe as well.

FW

theatretch85 05-24-2009 10:25 AM

I think the biggest areas I had issues with rust is where you drill the holes at in the conduit and typically the very ends of the conduit. Plus I can't imagine a piece of silvery/gray conduit blending in with the house very well, might look a little un-sightly to your neighbors.

Speedy Petey 05-24-2009 10:32 AM

Quote:

Originally Posted by theatretch85 (Post 277772)
Plus I can't imagine a piece of silvery/gray conduit blending in with the house very well, might look a little un-sightly to your neighbors.

*#@% the neighbors!!

:laughing: JK :laughing:

The antennas are ugly enough, the mast is the last thing you'll notice.
I definitely do agree, any cuts or drills do need to be painted.

KE2KB 05-24-2009 04:37 PM

Maybe I'll paint the whole thing; antenna and mast a sky blue, or maybe even sky blue and cloud white, so it would blend in with the sky.
OTOH, maybe I should just add fake leaves, like they do for cell towers:laughing:

FW

kbsparky 05-24-2009 07:19 PM

Even if it does eventually rust, it ain't worth the time and effort to rust-proof. A piece of EMT should last 20 years or more, and if it does rust out, it's cheaper to replace it than all this other muss and fuss, IMO.

KE2KB 05-26-2009 10:23 AM

Quote:

Originally Posted by kbsparky (Post 277978)
Even if it does eventually rust, it ain't worth the time and effort to rust-proof. A piece of EMT should last 20 years or more, and if it does rust out, it's cheaper to replace it than all this other muss and fuss, IMO.

Agreed.

FW


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