(snip...)
>I'm planning to install a free-standing U.S. Tower MA-550 crank-up tower
>with the manual crank option. The MA-550 is the XYL's requirement.
Welcome to the club (not just the tower, the XYL too!) I know it's
expensive, but you might want to reconsider that manual crank option and get
the motorized version instead. It takes hundreds of turns of the crank to
raise and lower the tower. If you plan on cranking the tower down more than
a couple of times a month, you will quickly tire of it. Not planning on
cranking it down much? Well, once she sees the beam on the top, the XYL may
not think the "mast" has such an acceptable profile and may insist on it
being cranked down when not in use. And then there's the wind (see below)...
>2. If I go with the MAB mount, and put the rotator atop the tower, what's
>the maximum safe length of mast I can use and not overstress the rotator's
>bearings and other parts when I crank the tower over for antenna
>maintenance. I'm planning on a Force 12 C3SS beam. What would be your
>recommendation for the minimum rotator for this installation? Would I be
>better off going to the next one up the capacity chain?
Additional mast height will gain virtually nothing and will cost you in
windload capacity. I would mount the C3SS no more than a couple of feet
above the rotator. In fact, I'm wondering if there's any reason not to just
shove the beam right down against the top of the rotor clamps or maybe push
it up just a few inches above the clamps (anyone know?) I did that on a
rooftop tower once, with no problems. My TH7 is shoved almost all the way
down to the top of my tower (base mounted-rotor), so there's no additional
mast height to worry about. If you want more height, get one of the bigger
towers (MA-770 or MA-850).
About the wind: I don't have the figures for the C3SS, but since the C3 and
C3S are in the 5-6 sq. ft. range, I assume the C3SS is somewhere in the same
ballpark. That's a very reasonable load for that tower, but remember that
the tower's max windload of 10 sq. ft. is for 50 MPH, not 70 MPH. The
tower's windload rating derates incredibly at 70 MPH. For example, my
MA-770MDP is (conservatively) rated by U.S. Tower engineers at about 2 sq.
ft. at 70 MPH! I suspect the numbers would be similar for your tower (I'm,
not sure -- the wind profile is smaller than mine, but the base section is
smaller as well.)
This suggests that you may not want to leave your tower fully extended all
the time, especially if you are not home. 70 MPH winds are rare in most
locations, but if they happen to come up when your tower is up, it could
come down in a hurry. I never leave my tower fully extended when I'm not
home. I leave it at 50 feet most of the time, where the windload rating
improves considerably. I have an anemometer with a windspeed alarm (usually
set for 20-25 MPH) and monitor weather forcasts religiously. Whenever the
winds get above 25 MPH or so, or are forecast to do so, the tower goes all
the way down. It may be overkill, but I paid a lot for that tower and beam
and I don't want to lose 'em. Now, I do have a higher tower and a much
bigger antenna (TH7) than you are planning, but I don't think the advice is
overly cautious (wait 'til you see how much that tower sways in a stiff
breeze!)
That's why I think you might want to consider the motorized version -- it
saves a heck of a lot of work and time. The remote control is a good option
as well if the tower is not right next to the house (who wants to go outside
to lower the tower in a raging blizzard?)
By the way, about that tiltover option... I have it and have used it for
maintenance a few times. It works reasonably well. You have to remember that
the antenna boom will not allow the tower to be tilted to the horizontal.
You'll need a stepladder to reach the antenna and rotor. The Pythagorean
Theorum will help you figure out how high the ladder has to be. Shouldn't be
too bad with the CS3SS boom. Mounting the antenna from the tiltover position
takes some doing. It's a long story, which I'll be glad to relate to anyone
who wants to hear it.
Tilting the base-rotated model takes quite a bit of prep work. The tiltover
fixture cannot be left in place permanently because the raising motor would
slam into it when the tower rotates. I'm not sure, but the same might be
true of the manual-winch base-rotated model (the winch might hit the
fixture.) You have to untie all your cables, mount the tiltover fixture
(mine weighs 80 lbs and has to be lifted several feet off the ground),
attach the winch cable, disconnect the rotor, undo a bunch of bolts, and
crank for a long time to lower the tower. Then you have to do it all in
reverse.
I have some work to do on my tower this year, and am preparing to use an
alternatate method: an extension ladder. One Tower Talkian (a professional
installer) told me of a method whereby the ladder is leaned against the
tower and secured at bottom and top (kinda shaky until that top gets
secured, so help holding the ladder is essential.) Another Tower Talkian
told me of strapping the ladder vertically to the bottom section and
climbing it like a regular tower. Of course, the tower is fully retracted in
both cases. A safety belt is required for either method. I haven't tried it
yet, but I think it's going to be much better for certain kinds of work,
including lowering and raising the beam should that become necessary. I'll
let the reflector know how it goes.
The tiltover fixture was very helpful for installing the tower, although I'm
sure the right machinery could have place the tower in the vertical position
without the fixture. It is very useful for replacing the cables without
dismounting the tower (can be done in the tiltover position on all but the
MA-850.) However, I'm not so sure it's a very useful accessory for routine
maintenance on base-rotated towers.
>3. How do you go about ensuring that the base will be level, and the tower
>plumb, as you are pouring the concrete and letting it set? Can you shim
>the base in some manner after the concrete has cured? Will these questions
>be answered in the U.S. Tower planning information packet?
This is easier than you might think. U.S. Tower supplies four 24" long by 1"
diameter anchor bolts for you to embed in the concrete pad. There are nuts
welded on one end of each bolt to prevent it from pulling out of the
concrete (they used to supply J-bolts, but don't anymore.) The tower base
consists of a square vertical member welded to a square base plate that has
four 1" diameter holes drilled in the corners. You screw a nut onto each
bolt, drop a washer on top of it, then lower the tower base onto the bolts
so that the base plate it sits on the washers and nuts. Then you drop
another washer on each bolt and loosely thread another nut on the top side
of the base plate. To level the base, you simply run the bottom nuts up and
down until the base is level, then secure with the top nuts.
However, it's important to note that plumbing the base vertical member will
not necessarity plumb the tower mast. After installing the tower mast, the
base should be re-leveled so that the mast is plumb -- it doesn't matter if
the vertical member is plumb or not.
As for installing the bolts in the concrete, U.S. Tower provides a plywood
template with a hole pattern for the anchor bolts. You screw a nut on to
each anchor bolt, drop a washer on the nut, insert the anchor bolt in the
template, and drop on another washer, and secure it with the remaining nut.
I can't remember whether U.S. Tower supplied washers or if I went out and
bought some. Once the bolts and template are assembled, you nail the
template to a 2x4. You lay the 2x4 on top of the wooden frame used to form
the top of the concrete pad, suspending the bolts and template over the
hole. Then fill the hole with concrete. You have to be careful not to let
the template/bolt assembly move too much when the concrete is poured.
Alternatively, I think you can just shove the bolts down into the concrete
after it has been poured (I didn't do it that way.)
Either way, you also have to be careful that the plywood template doesn't
crack or warp under pressure from the concrete. I think I had the nuts
screwed down a little too tightly, which caused one corner of the template
to flex a little. That threw off one bolt by about 1/8 inch. I was able to
slip a PVC pipe over the threads and tap it into alignment with a hammer.
The tower base slipped on relatively easily and was a snap to level.
You can specify that the base template be shipped ASAP when you place your
order. That way, you can have the pad and bolts installed and ready when the
tower arrives. Then, the machine you use to unload it from the truck can be
used to carry it to the tower site and place it on the tower base. Allow 28
days for the concrete to fully cure (although many would say it's safe after
a couple of weeks.)
If things at U.S. Tower are still the same as last year, this procedure is
covered in a bare-bones fashion in the literature you will receive with your
order confirmation.
>4. If anyone has recently purchased a MA-series tower, how long did it
>take from order to receipt.
Pleasantly, less time than they originally quoted. I ordered mine on about
July 12, 1997, and was told the tower would ship on 10/09/97 (about 12
weeks.) You have to add at least another 10 days for trans-continental
shipment. The tower shipped somewhere around 9/16/97, and arrived on
9/26/97. In all, about three weeks early. Luckily, I didn't dawdle getting
the concrete in and it was ready when the tower arrived.
By the way, the biggest logistical problem for me was coordinating the
people and machinery to unload the tower, carry it 400 feet down a hill to
the tower site, and install it on the base. You should think this through
very carefully.
>
>5. Does U.S. Tower provide, or not provide, an installation instruction
>manual? I've seen both answers in prior posts.
Again, if things have not changed since last year, there is virtually no
documentation with the tower. I was fortunate to receive from a Tower
Talkian a Xerox of a somewhat more detailed old set of instructions on
installing an MA-850MDP. They're sparse, too, but better than what I got. I
thought they had accidentally omitted the installation manual, but when I
called U.S. Tower they told me that they do not supply installation
instructions and that I should use a qualified professional installer (they
provide a list.) Later, Bruce, the owner of the company, told me that he had
an engineer and a lawyer working on an extensive installation manual for the
tower and that I would get one when it is completed. Still no manual.
Anybody get one yet?
Installation is pretty intuitive, but if you have a professional installer
nearby and can afford it, I'd recommend it. At a minimum, try to get advice
from someone who has done it before. Initially, I had severe problems
getting my tower to rotate. It took a number of lengthy phone calls to U.S.
Tower to resolve the problems (Bruce personally handled my case, in a very
courteous and efficient manner.) It turns out that there are a some tricks
you have to know... a few simple written instructions would have saved me
hours of frustration and hassles!
Hope this helps,
73, Dick, WC1M
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