[TowerTalk] Motorized Crank Up Towers

[Dick Green WC1M]

I have a somewhat different take on this issue. Though my own experience
with remote control lends a lot of credence to Steve's position, sometimes
the circumstances dictate a compromise. If you're interested, read on...

Back in 1997, I purchased the remote control option for my US Tower 72'
motorized tubular rotating crankup tower. I felt the remote control kit was
necessary because the tower is located about 250' from the shack, down a
steep hill (another compromise.) Knowing that these towers really don't have
much windload capacity (at the time, it was advertised as 10 sq ft at 50
MPH), and planning to put a 9.7 sq ft TH-7 on it, I decided that the tower
would be partly or fully retracted whenever it was not in use. The first
time I saw the fully-extended tower with TH-7 at the top violently swaying
in a 35-40 MPH wind convinced me that this was the right decision. Having
had some experience with our club's 40-foot version, I knew that
hand-cranking a 72-foot tower would require a lot of time and elbow grease.
I knew that I would likely avoid this effort, reducing the opportunities of
using the tower and dangerously increasing the likelihood that the tower
would remain up and be exposed to a sudden windstorm. So, I got the motor
option. But even with the motor, I knew that I would inevitably find reasons
not to make the trek to and from the tower, especially in winter when we can
have 4 feet of snow on the ground, and decided to get the remote control
option.

Unfortunately, the tower is fully screened from the shack by a large stand
of trees. Back when I installed the tower, it could not be seen above the
trees until it was extended at least 60 feet or so. But the significance of
this really didn't hit me until it was almost too late.

During installation, I dressed the coax and checked the raising and lowering
repeatedly, using the "local" up/down switch at the tower. At first I
attempted to secure the coax to the standoffs in order to have it come down
in big "loops", thus keeping the coax off the ground. I had seen a drawing
of this technique in an old Wilson manual. But the first time I tried this
it was immediately clear that the loops had a tendency to twist around
themselves, and if twisted tightly enough the coax might be damaged when
yanked by the tower on the way up. Worse, it looked very likely that the
loops could snag on the motor or pulley housings on the way up, even though
I put the standoffs on the side of the tower opposite the motor housing. So,
I abandoned that idea and rigged the coax to fall straight down on the
ground. Some people let it fall into a large box or barrel, where it can
have a tendency to wind neatly into the container, but I felt such a
container was likely to fill with sleet, slush, ice and snow, making a solid
mass out of the coax. There's a steep hill that falls away from the tower
base, so I let the coax sort of fall down that hill. This seemed to work
fairly well. I knew I would have to pull it out from under ice-covered snow
in the winter, but figured that wouldn't be so bad (and that's, indeed, the
way it has turned out.)

About a month after the installation, I was demonstrating raising the tower
to a friend. It was October, and most of the leaves were down, allowing us
to see more of the tower from the shack window as it extended. When the
tower got close to fully extended, it began to jerk back and forth very
violently -- and I mean *very* violently. It took a split second for this to
sink in, and just before I hit the off switch the tower gave one last
convulsive jerk. I rushed down to the tower, convinced that something
terrible had happened. When I got there, I was relieved to see the tower
still standing and the cables apparently intact. The coax, however was on
the ground. It was immediately obvious what had happened: the very stiff
coax (LMR400UF, which is not as "Ultra-Flexible" as advertised), had
migrated around the tower to the motor housing and had snagged on one of the
control box brackets. The plastic jacket and shield had been pulled apart at
the point of the snag, and the dielectric was still firmly lodged in the
bracket. At the other end of the coax, the plastic balun housing at the
antenna had literally exploded, releasing the SO-239 connector. This lucky
event saved the tower. Had the balun not let go of the coax, the cables
would surely have snapped, causing thousands of dollars worth of damage to
the tower and antenna.

I called US Tower about the incident, and they advised changing the cables.
They sent me a brand new set at no charge. However, after extensive
examination and testing, it did not appear that the cables had been
stretched or damaged during the incident. Since it is a major project to
change the cables, I elected not to do it. 10 years later that seems to have
been a reasonable gamble. It's likely that I'll change the cables within the
next five years or so, and have the spare set ready to go.

The cause of the incident was clear: there was nothing to prevent the coax
from migrating around the tower and catching on various protuberances.
Further, the stiffness of the coax made this more likely -- more flexible
coax would have a greater tendency to drop straight down and curl up at the
base of the tower. So, I made the following modifications to the
configuration, in order of importance:

1. I added coax standoffs above and below the motor. These are not standard
equipment with U.S. Towers, but they should be. The standoff above the motor
probably isn't necessary, but the one below it is essential to keeping the
coax from migrating around the tower and catching on the motor.

2. I switched the coax to RG-213, which is much more flexible than LMR400UF.
Later, I changed to Buryflex, which is even more flexible than RG-213 and
has much lower loss.

3. I used hardware cloth to build a cage around the bottom of the tower to
prevent the coax from getting into the rotor area.

As you might imagine, I checked and rechecked the movement of the coax
dozens of times before I felt comfortable doing so remotely. It turned out
that the measures were quite effective, and I have raised and lowered the
tower remotely, without being able to see it, probably hundreds of times for
nearly 13 years. I do periodically check how the coax is laying on the
ground, and have never had to rearrange it. Since I "walk" my antenna farm
before every contest, which is pretty-much the only time I raise the tower
(I have 110' of guyed Rohn 55 with better antennas), I do check the coax
before raising. I definitely do that if there's any snow on the ground, and
usually once a year, before ARRL DX CW in February, I have to pull it out
from under the crust on top of the snow.

If there has been any significant wind while the tower is extended, I check
the pulldown cable before retracting the tower. This is because early on I
found that if the tower twisted and swayed in the wind while fully extended,
the pull-down cable would pop off its pulley sheaves. The cable went over
the top of one pulley, which was no problem, but it would get caught between
the sheave and housing in the other pulley. Eventually, at US Tower's
recommendation, I removed the pulleys, which were not part of the original
tower design (a bad "improvement" by US Tower, IMHO.) Even with the pulleys
removed, if the tower twists and sways enough, the cable can get caught
behind the bolt through one of the main upper pulleys, abrading the cable.
It's not hard to undo this -- just yank on the cable while the tower is
fully extended -- but it's bad to retract the tower with the cable abrading
on that bolt head. I've done a three things to significantly reduce
occurrence of this problem:

1. Re-tensioned the pull-down cable. This is a big job that involves running
the tower up and down a bunch of times.

2. Moved the upper standoff of the pulldown cable a little further away from
the pulley

3. Significantly reduced the windload on the tower (it has a 4-el
monobander, which is about 1/2 the windload of a TH-7)

The point I wanted to make with all this is that the motor and remote
control ensure that I have access to the tower when needed, and will be able
to keep the tower retracted at all other times. It's not an ideal situation
as far as being able to see the tower when it's going up or down, but it's
what I have and I've tried to do my best to compensate for the inherent
problems.

73, Dick WC1M




-----Original Message-----
From: Jim McDonald [mailto:jim at n7us.net] 
Sent: Thursday, May 20, 2010 2:44 PM
To: towertalk at contesting.com
Subject: Re: [TowerTalk] Motorized Crank Up Towers

Though my tower has remote control (or did until my lightning strike), I
would only lower it from inside, and I did that when I knew no cables could
get caught in the tower.  It's especially prudent to control it at the tower
base for a tower with positive pull-down, which my previous Hy-Gain HG70HD
didn't have.

Even being outside watching it on the way up, I've caught a ladder line
feedline on an eave, and slopers and inverted vees can get caught too. 

I was always uncomfortable with my previous tower, the Hy-Gain, because I
couldn't get it down with the manual winch if the wind was blowing too hard,
which caused it to bind.

I wouldn't buy the remote control option again.

Jim N7US



-----Original Message-----

A little late comment Steve, but you make a very good point.  My HG-70HD
came with the motor control option but I never bothered to install it. And,
glad I did not. Last spring, after all the winter winds, I decided to hand
crank it back up to full height (it was at 2/3).  Did NOT notice that  a
section of the top drooping cable had evidently been blown hard enough to
hang up over the top coax arm.  Noticed the cranking was suddenly a little
hard, looked up and my coax arm was bent down at almost 45 degrees.
Necessitated cranking it back down all the way, climbing up and replacing
the coax arm. Hate to think what might have happened if I'd had the motor
attached and raised it from inside the shack. Lesson learned -  always do a
close inspection of the tower if its been cranked down awhile.

Don W7WLL


  ----- Original Message ----- 

  In a message dated 5/3/2010 12:01:23 P.M. Pacific Daylight Time,
towertalk-request at contesting.com writes:
    >  As to tower cables failing, in my 54 years of hamming, I have never
heard 
    first hand from anyone that has had cable failure although I am sure
this 
    has occurred, certainly there are enough stories floating around. I have
to 
    imagine that the majority of cases was because of poor maintenance 
    procedures, pushing a reasonable replacement time limit, or undersized
or 
    poor quality cable or improper eye swaging.

        Actually the 2 I've seen were none of the above. Both cable failures
were due to another external cable (coax, etc.) snagging on something on the
way up and unnoticed by the owner as the tower was moving. BIG noise as the
main haul cable snapped and everything collapsed into the tower bending
antenna booms and creating a bit of a problem repair-wise. 

        This is why I discourage using any kind of remote tower control and
strongly recommend you be at the tower watching everything whenever it's
moving. 

    Cheers,
    Steve   K7LXC
    TOWER TECH 
_______________________________________________



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