In a message dated 97-05-28 00:07:42 EDT, you write:
> To hide the beam, it has to be a crankup (of course, it would show when I'm
> operating, but only when there's really rare DX on or a big contest --
> mostly nights and the occasional weekend.) For convenience, it has to be
> motorized (I'm not running up and down the hill twice every time I want to
> use the radio!) For aesthetic appeal when it is raised (minimum
> impact on the XYL) and safety (there are children) I'd like it to be a
> tubular tower (holy cow!) U.S. Towers looks like the only game in town.
I'm
> willing to spring for a self-supporting (not house-bracketed), tilt-over,
> motorized tubular with the rotator at the bottom. The two most appealing
> options are the 55' 3-section model and the 71' 4-section model.
Hi, Dick --
Sounds like a fun project. You'll get good input from other
TowerTalkians.
First of all, Grafton County is only a 70 MPH wind zone but it is within
100 miles of a hurricane oceanline and it sounds like you have a spot with
higher wind exposure and potential wind speeds so you might want to consider
80 MPH as your system planning wind speed. Besides if you do, it'll let you
sleep better when those big storms come rolling through.
A 50 MPH wind (to which the tower is rated) exerts 10 PSF wind pressure.
A 70.7 MPH wind exerts 20 PSF wind pressure. You can see the problem already.
You'll have to take the factory rating and cut it in half to get a 70 MPH
wind load capacity. With your potential for horrific wind and other wx
conditions, even that might not be enough for longterm reliability. You
really need a much bigger tower especially with bigger antenna loads like the
KT34XA.
Are you going to get a permit? A crank-up can make the process more
difficult.
BTW, you probably want to have a copy of an article that Roger Cox,
WB0DGF, of Hy-Gain wrote several years ago entitled "Match Your Antenna To
Your Tower". It covers various crank-up capacities vs. wind speed scenarios.
TOWER TECH has copies of the article for an SASE.
>
> However, a friend says that I'd be nuts to go with a tube over 50' and
> should put up nothing bigger than a medium-sized beam. He suggests the 55'
> model with the TH5Mk2.
Sounds like reasonable advice to me. Another alternative would be to look
at the Force 12 antennas. They are lighter and have less wind load (resulting
in less stress on the system) than similar designs by other manufacturers.
>
> Assuming I'm willing to bear the $1000+ cost difference to get the better
> performance of the larger installation, what should I do? Am I buying a
lot
> of potential headaches? What are the risks? Is there a chance the 71'
tower
> could get stuck in the raised position all winter until I can get a crane
> down there to remove it? My wife would never forgive such a gaff.
You'll probably need a crane to install it BTW. You can get "positive
pulldown" with many of the US Towers which means that they'll always retract.
Crank-ups have their own foibles but since that's all you can entertain
for your installation, you're stuck with them.
>
> Please, folks, your opinions. I'd most like to hear from anyone with
> personal experience with the two U.S. tower models, TH7DX, and/or KT-34XA
> in a similar installation. Also, I need a recommendation on whether to go
> with the heavy-duty boom option on the KT-34XA.
>
At this point, the HD boom is the least of your concerns.
Congratulations though on planning ahead for your project.
73, Steve K7LXC
TOWER TECH -- professional tower supplies for amateurs
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