[Top] [All Lists]

[Towertalk] US Tower MA-Series Maintenance

To: <>
Subject: [Towertalk] US Tower MA-Series Maintenance
From: (Dick Green)
Date: Thu, 28 Feb 2002 09:54:12 -0500
Thanks for the info, Jerry. It reinforces my non-professional opinions about
cable maintenance. Also, thanks for the hint on exercising the tower and
moving the resting point. It's made me rethink my strategy.

I've always kept the tower well below full height (50' instead of 70')
except when contesting or occasionally chasing rare DX. I used to put it all
the way down whenever the wind kicked up over about 25 MPH. That's partly as
a safety measure (you never know when a freak windstorm will come up) and
partly because the lower the tower the less it flexes. I think repeated
flexing can't be very good for the cable. There's certainly evidence that
the cable stretches over time -- I've had to tighten the pull-down side
about once a year to keep it from flapping over and getting caught on the
pulleys. I suspect some of that stretching is caused by the extended tower
swaying in the breeze and some is caused by the weight of the tower sections
over time.

I used to crank the tower up and down a lot because it had my main
antenna -- a TH-7 (right at the max rated windload.) But a couple of years
ago I installed a guyed portable military mast with another tribander and
have kept the crankup fully retracted except for contests and chasing rare
DX. I replaced the TH-7 with a 20M monobander, which has much lower windload
and weight. I think keeping the tower retracted is good for minimizing
stretch, but it also tends to put the cable in exactly the same position for
extended periods of time, which as you point out can't be good. Seems to me
that I need to exercise the tower more frequently, say once a week, then
park it at a random point between fully retracted and ten feet higher.

This has another benefit -- this winter I discovered for the first time that
the limit switches can freeze during an ice storm. The "full-down" switch
can get stuck in that position for long periods of time, well past the ice
storm. If you then raise the tower it can't be lowered because the limit
switch is already in the "full-down" position. I was lucky enough to be able
to reach the switch with a pole from the ground and exercise it enough to
break the ice, and could lower the tower. The problem is that the limit
switch arm rests against the small piece of track that triggers it in the
full down position. By raising the tower a little above this position after
fully retracting it, the switch can't freeze in the full-down position.

By the way, on the access issue I was referring to access for the purpose of
lubing the cables, not replacing them. That's a different issue altogether.
The U.S. Tower tubular cables can be replaced relatively easily, except on
the big MA-89 -- the lowest movable section is too heavy to remove without a
special jig (at least, that's what the manufacturer says.) It's not a
two-hour project -- you have to tilt your tower, remove your beam and
disassemble the tubes. On the 70-foot model it's probably a two-man job
since the lowest movable section weighs about 100 lbs. Unfortunately, U.S.
Tower does not provide a cable stringing guide, so it's important to study
the route very carefully before disassembly -- some digital pictures would
be a good idea! Several years ago the president of U.S. Tower told me they
had an engineer and a lawyer working on a comprehensive installation and
maintenance manual for the tubular towers, including multi-color
cable-routing diagrams. As far as I know, no such manual was ever published.

On the climbing issue, I certainly wouldn't climb a triangular crankup,
although there are some who say you can block the movable sections with wood
or steel beams to make that safe. However, I find that climbing a tubular
tower isn't nearly as dangerous (although much caution is still advisable.)
Many installers lean an extension ladder against the tower, then have
someone hold it at the bottom while they climb up and secure the top. Some
use a "tree" attachment at the top of the ladder to keep it from slipping
off before it's secured. I don't like these methods for a number of reasons,
including the requirement for a helper and sloping ground next to my tower
compromising the placement of the ladder feet. I prefer to strap an
extension ladder right against the tower. This puts the feet of the ladder
on the concrete slab. I use high-strength cargo straps to secure the ladder
to the tower (always fully retracted for this operation) and space the
straps closely -- every 3-6 feet. The result is a very tight bond between
the ladder and tower. I also use a climbing belt with standard and
fall-arrest lanyards and don't free-climb the ladder. It's only 20 feet, but
no sense taking chances.

I've found that this procedure is *much* faster than tilting the tower. The
tilting procedure requires a lot of steps, especially for the motorized,
rotating tubular towers. The tilt-over fixture can't be left in place (the
motor housing would hit it during rotation), so that 80-lb hunk has to be
transported to the tower, lifted into place and installed (takes about a
half hour or more just for that.) The rotor has to be disconnected, the
cables have to be untied and several bolts have to be removed (a step ladder
is required for that.) I also have a wire cage around the bottom of the
tower that has to be removed (it prevents the coax from getting hung up in
the rotor area.) These steps have to be executed very carefully (for
example, if you forget to remove the pin bolts from the tiling base they
will get sheared off.) Further it's difficult to get to the apex of the
tower when it's tilted because the antenna boom prevents the tower from
tilting all the way to the ground. A step ladder can be used but it has to
be over 10 feet high (15 feet in my case) and the ground under the apex of
my tilted tower slopes rather steeply. All the steps have to be done in
reverse to raise the tower back to vertical. All this takes a heck of a lot
of time -- not worth it just to replace the coax run or tighten the
pull-down cable.

Speaking of the pull-down cable, there is an elaborate tightening procedure
that involves cranking the tower up and down many times. You have to do that
to release the tension on the cable, use a come-along to tighten the cable,
then do all that cranking again to tighten the tension spring. Using the
tiltover procedure to get to the top of the cable presents the step ladder
problem and would make it at least a four hour project, maybe more.

I've also found that it's much faster and safer to mount and dismount a
large beam using a ladder plus block and tackle than it is to do it with the
tower tilted -- I've tried it both ways and there's no comparison. It took
six people to mount my TH-7 on the tilted tower and it was a dangerous
procedure for all concerned (especially the guy balancing on a stepladder at
the apex of the tower.) It only took two people to do it with the ladder. A
number of professional installers have told me they do it that way (one even
carries the beam up the ladder -- don't try this at home!) Again, these
comments apply only to the tubular towers and the usual tower-climbing
safety caveats apply.

73, Dick WC1M

> -----Original Message-----
> From: Jerry Devine []
> Sent: Thursday, February 28, 2002 2:52 AM
> To:
> Subject: Re: [Towertalk] US Tower MA-Series Maintenance
> On Thu, 28 Feb 2002 01:17:05 -0500 "Dick Green" <>
> writes:
> >Jeff,
> >
> >It's amazing -- U.S. Tower provides virtually no installation or
> >maintenance
> >instructions, and you get different answers to questions at different
> >times.
> >I asked the company president about cable lubrication and was told
> >it's not
> >necessary.
> They recommend total replacement every 6 yrs.  And no lube is needed
> if you do so.
> If you think about it, it is a smart way to ensure total in spec reliable
> operation.  Many other issues occur in a greater than 6yr old cable!
> Lube is
> a minor issue at this point of the service life.
> >Others on this reflector have asked the same question and
> >have
> >been told it is necessary. I think it depends on where you live -- if
> >you
> >live near saltwater or your atmosphere is caustic, you'll probably get
> >more
> >cable corrosion and need to lube them.
> IMHO a crack up tower's cable is it's weakest link!  You should
> plan on always throwing 100 bucks at it every six years or you can
> throw more at it if you opt not to do so.   The cable is the life line
> for everything installed on it.
> >I happen to have the manual for the old Wilson series of tubular
> >towers,
> >which was the predecessor of the U.S. Tower MA series. It's got loads
> >of
> >detail on installation, but not one word about lubricating the cables.
> Exactly,  It's a given that it should be replaced at regular intervals.
> Ask a tow truck operator how many years he gets out of his cable!  Then
> ask him the mode of failure usually experienced with it.  I'll bet he
> says
> it never fails. Because he replaces before that could occur.
> >The MA series of tubular towers is problematic in that a significant
> >portion
> >of the main cable is either inside the bottom tube or difficult to
> >access.
> Not true.  I've replaced many cables.  Usually only takes 3 hours and a
> half dozen new bolts/screws.  All items on tower excluded from time.
> Naturally they all need come off and then reinstalled.
> >It's not like the triangular towers where you can spray the cable
> >through
> >the lattice-work. It would take considerable effort to lube the entire
> >main
> >cable, and you still can't get to part of it. You can lube most of the
> >cable
> >by standing on a stepladder and spraying the cable as it goes into or
> >out of
> >the winch. That leaves the portion of the cable that was above the
> >winch
> >when the tower is full-down (on the pull-down side) and the portion of
> >the
> >cable that's above the winch when the tower is full-up (on the pull-up
> >side.) You can reach the pull-down side by tilting the tower when
> >retracted,
> >but you can't get to the pull-up side that way when the tower is
> >extended.
> >One approach would be to strap an extension ladder to the bottom
> >section in
> >order to reach both sides of the cable (some people tilt an extension
> >ladder
> >against the bottom section and have a friend hold it while they climb
> >up and
> >secure the top; others strap the ladder vertically against the bottom
> >section, securing it as they climb -- this requires a climbing belt.)
> I only lube cables when customers complain about noise.  I never ever
> climb a crankup tower.   They tilt over for any top side work need!
> If they won't, then they were inproperly installed.  Generally only the
> pully needs lubed on it's pin.
> >Unfortunately, there's still a section of the cable that's not
> >reachable --
> >the part that comes off the top pulley and goes down into the top of
> >the
> >bottom section (it lifts the first movable section.) That's a few feet
> >of
> >cable that can't be lubed. Further, the upper cable sets can't be
> >reached at
> >all. When the tower is retracted they are inside the tubing. When the
> >tower
> >is raised, they are out of reach. The MA-50 has one additional cable
> >set,
> >the MA-70 has two and the MA-89 has three. Although these cables
> >support
> >less weight, they can't be lubed at all.
> >I've had my MA-770MDP up for 4 1/2 years and have never lubed the
> >cables.
> >They look good, no sign of rust or fraying. That's probably because
> >the
> >atmosphere here isn't particularly caustic -- we're not near the ocean
> >and
> >humidity is pretty average. But I'll probably replace the cables in a
> >couple
> >of years just to be safe.
> Welcome to crankup towers.  Like cars, they too have a mileage service
> interval
> on the tires. I mean cables.  And like cars it's usually going to cost
> 100 bucks
> or more to change them.    The worst thing you can do to a crank up tower
> is to
> NOT exercise it!  The second worse thing you can do is leave dead weight
> in one
> spot of the cable for long periods.  With that said always change the
> height of it
> + - 5 - 10ft of useful height over every week randomly...  This will
> minimize
> a cable set risk.    After six years of proper use.  That 5-15 ft area of
> cable
> is probably weakened to now some 25-30% of new cable and should be
> replaced.
> If you've always parked in the same place, the your cable is yet worse
> shape sooner.
> See ya Dick
> 73,    Jerry                           
> [text|uuencode|59kb ea]   No RFC #2048
>          'Y2K ?   Because 1k is 3 decibels down in amplitude. 9991
> krr2ak'
> ________________________________________________________________
> Juno offers FREE or PREMIUM Internet access for less!
> Join Juno today!  For your FREE software, visit:

<Prev in Thread] Current Thread [Next in Thread>