Ed,
I have had an MA-770MDP with rotating base supporting my TH-7 for just about
two years now and have been generally very pleased with it. Some
observations:
1. If you can afford it, get the taller tower. When carrying close to the
maximum windload, these towers sway quite a bit in strong winds. Although
I'm sure the tower will live up to its rating of 10 sq. ft. at 50 MPH, I
don't like the way the fully extended tower jerks around when the wind gusts
get over 20-25 MPH. Consequently, I normally leave it at 50 ft except when
contesting or chasing rare DX (the TH-7 still works very well at 50 ft.) It
is very stable at 50 ft, even with gusts up to 25-30 MPH, and I'm sure it
would stand up to our local maximum of 70 MPH. But I always lower the tower
all the way when the gusts get up to the 30-35 MPH range because that
usually happens during thunderstorms that could have violent microbursts
with much higher windspeeds.
2. I monitor weather forecasts religiously, both by radio and Internet. I
use a weather radio that sounds an alarm when there are storm warnings. I
also have a wind speed gauge with an alarm that I normally set for 25 MPH. I
never leave the tower at 70 ft when leaving the house, and lower it all the
way to 22 ft whenever leaving the house overnight.
3. Obviously, there's enough raising and lowering that the motor drive is
essential (not to mention the fact that my tower is 250 ft from the house.)
It takes literally hundreds of turns of the winch crank to raise and lower
one of these towers by hand. People without the motor have told me that this
tends to make them lazy about lowering the tower when they should. I would
*strongly* recommend that you get the motor if you can afford it. Get the
remote control package, too. I modified mine to eliminate the 120VAC control
signals. If you're curious about that, just ask. The motor setup has been
working well for me so far. Takes about 2 1/2 minutes to raise the tower
from 22 feet to 70 feet.
4. When building the concrete base, don't tighten the anchor bolts too
tightly to the wooden template. The plywood can bend or crack and throw off
the spacing of the bolts.
5. The tiltover winch was essential for installing the tower initially, and
we used it for installing the antenna, too. But since then I have found it
much more convenient to lash an extension ladder to the tower for climbing.
You must use a safety belt and there are some tricks and techniques for
this, so ask if you want to know. The tiltover winch is still the best way
to get to the ends of the antenna boom, but I tend to avoid it otherwise
because the tiltover procedure is very time consuming. The big problem is
that the winch cannot remain installed during normal operation when you have
both the rotating base and the motor package. It turns out that the motor
and its relay cabinet would hit the winch fixture when the tower is rotated.
So, you have to take the 80 lb winch fixture off when using the tower. To
tilt the tower over, it has to be remounted, the cable has to be threaded
through a pulley on the tower, the rotor has to be disconnected from the
tower drive shaft, and about six bolts must be removed. It takes a while. I
guess I would still recommend getting the tiltover winch (otherwise you'll
probably need a crane to install the tower), but it isn't as useful as I'd
hoped.
6. The way the steel raising cables are threaded on these towers makes it
difficult or impossible to fully lubricate them. That's because the cables
go down into the tubes where you can't reach them when the tower is
retracted. You can get at most, but not all, of the main cable when the
tower is extended, but the upper cables can't be reached. The same isn't
true of the triangular crankups because you can get to the cables through
the crossmembers. According to Joel at First Call, the tubular towers have a
higher cable failure rate than the triangular towers, and I think this might
be the reason (although a lot of amateurs don't lube the cables at all,
which might be the real explanation.)
7. The rotating base works very well with my Tailtwister, and I highly
recommend it. This configuration places less weight at the top of the tower,
puts less strain on the rotor, and makes removing the rotor for repair a
snap -- even in the winter! However, I had terrible problems getting my
tower to rotate without binding when I first installed it. After several
days of frustration, I finally discovered that there are some tricks you
need to know when installing the tower to make it rotate correctly. The most
important is to allow the pipe coupling the rotor to the tower driveshaft to
move freely. This requires a careful rotor mounting procedure which I can
detail for you. Also, some grease is required on the upper "bearing"
surface. Tthe factory made a few mistakes which made the problem worse: 1)
the base wase slightly shorter than spec, 2) the rotor shelf was shipped
upside down, and 3) there were no written instructions on installing the
tower.
8. That last comment is important to understand. Unless things have changed
in the last two years, U.S. Tower does not document installation of these
towers. Unless you know what you are doing, I would recommends hiring an
expert who has installed this type of tower before. I'm sure Joel at First
Call will get in touch with you to recommend installers affiliated with his
company.
9. I had a great deal of trouble with the pull-down cable on my tower
popping off the two upper pulleys through which it is threaded. When it pops
out, the cable gets caught between a pulley wheel and its bracket, as well
as behind a bolt, causing cable abrassion. There's a procedure for
tightening the cable that involves using a come-along and tightening a
tension spring (and repeatedly running the tower up and down.) I found it to
be only partly effective, and the cable kept popping off. U.S. Tower added
these pulleys a few years ago to keep the cable from slapping against the
tower, and may have created a problem where there wasn't one before. They
recommended removing the two upper pulleys. I did that and haven't had a
problem with the pull-down cable since. I've never seen the cable get close
to slapping into the tower, even with the tower fully extended and the wind
blowing.
10. If you use the motorized winch and remote control, great care is
required in setting up the coax standoffs and routing the coax. I very
nearly had a terrible accident when the cable snagged on the motor housing
shortly after I installed the tower. Luckily, the TH-7 balun exploded and
the coax came free before the tower pulled itself apart or the motor burnt
out. The solution was to add two more coax standoffs to the lowest section,
relocate the standoffs to be exactly opposite the motor, switch from stiff
LMR400UF to RG-213, and build a cage out of hardware cloth around the base
of the tower to prevent snags in the rotor area.
I hope this helps. Please feel free to ask more questions if you need to.
73, Dick WC1M
> Hi,
>
> I am thinking about putting up a US Tower MA series crank-up. Does anyone
> have experience with the MA series, particularly the 550 and 770, with or
> without the motor drive? Mine would have to be free-standing, that is, no
> house
> bracket. I would probably use the rotator base. Any comments including
pros,
> cons, alternatives, lessons learned, etc. would all be appreciated
--
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