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Old 04-11-2017, 08:19 AM   #11
wa8yxm
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The big problem with a 9' Whip on top of a trailer is this
Say the trailer is 10 feet, the whip adds 9 feet that's 19 feet.. you are going to be hitthing bridges, traffic signals, and may well earn yourself the attention of the police less you fold it down when in motion.
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Old 04-11-2017, 11:15 AM   #12
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Originally Posted by Gashog View Post
As for wind load, I think if you did the math, you'd see that a 9' whip has a bit more wind load than an aerodynamic AC unit sticking up 12" off the roof.
Depends on what you call "a bit more".

Aerodynamically, it's a difficult question. There will be some wind load on the A/C unit, but it will be minimal because the air moving down the top surface is slowed by friction on that surface and by any other protrusions on that surface; and the wind load will be further reduced by any turbulence in the flow. Basically the wind load on the A/C ought to be quite small.

The whip, on the other hand, is in undisturbed laminar flow, sometimes at perhaps 70 to 80 mph. The wind load will be much larger, and is applied about 5 feet from the mount. That's enough moment (torque) at the mount to tear a petty big hole in the roof, or at least wrinkle the skin considerably. So you need a reinforcing plate, on which the whip is mounted, large enough to distribute that load. I'd think a four-foot square of 1/4" 6061-T6 aluminum plate would probably handle it OK.

Indeed, that "a bit more" would really be "a heck of a lot more".
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Old 04-11-2017, 07:20 PM   #13
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Height does not matter it is the surface area that produces wind load. Leverage maybe I have a 21 foot dual band fastened to my tower 40 feet up with hose clamps. No metal in my 14X14's makes it's too hard to fasten vent screws to.
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Old 04-11-2017, 07:31 PM   #14
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Replace the vent with a 14X14 aluminum plate and mount any vertical. This thing is going to be parked any way, you in a tornado area? If so I think the last place in would want to be in is a trailer.
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Old 04-12-2017, 06:41 AM   #15
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Replace the vent with a 14X14 aluminum plate and mount any vertical. This thing is going to be parked any way, you in a tornado area? If so I think the last place in would want to be in is a trailer.
It'll be parked in the black dirt region in Pine Island/Goshen NY.
We've only had two tornadoes in 40 years that I can recall.

When I move it, the antenna will come down obviously.

Is there any down side to guying it?
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Old 04-12-2017, 07:58 AM   #16
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I have fiberglass poles like 24' of them for my rotatable dipole, at 17 meters it's 36' I made a walk up device fastened to the rear bumper of the camper and in that case guying is a must. I have an R7 it's off the ground about 8' Cushcraft says it's OK not guyed they do however make a kit to guy it! Mine is guyed because winds off the mountains have exceed 60 MPH here. I really don't think you would have a problem with 9' of antenna We have 2 18+ feet of single point mount antennas at our club repeater site @ 1600 feet.
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