[TowerTalk] Measuring Cable Tension - W4XN Tower Progress

[Al Williams]

I suspect that rather than measuring the tension with an expensive device, 
one can calculate the tension after approximating the weight of what is 
being tilted up.  This calculation will require someone with more knowledge 
than me but hopefully there are those on this forum that can do so, if given 
the fundamentals:

1.  The tower with antennas weighs at most about 2000 pounds.
2.  The tilt fixture is about 7' tall and the tilt cable attaches to the 
tower about 7' from the bottom.
3.  The tower has a heavy 23' mast and antenna at the far end so one has to 
approximate the weight distribution.
4.  The HDX572 tilt fixture, if it like mine, has two pulleys at its top. 
The cable from the winch goes through one of these pulleys, out and around a 
pulley on the tower (7' from bottom); back to the second pulley at the top 
of the fixture, then back around the second pulley on the tower and on to 
attach to the tilt fixture.  This gives a mechanical advantage of 4?

Since only one cable comes out of the winch, intuition tells me that all of 
the tension is on this one cable of the four in use.  However the winching 
effort is greatly reduced by using four pulleys and I think that the tension 
is distributed somewhat equally to the four pulleys resulting in a cable 
capability of ~9800 lb x 4 (less efficiency of the pulleys).

With equal 7' heights the pulling force is at 45 degrees so that the lifting 
component required  initially  is 1.4 times the tension on the
cable.

 How does one determine the tension on the cable when the ~23' tower and 23 
mast extension is being pulled up at 7' from the bottom of the tower.  When 
the tower tip is just off the ground, then because the fulcrum is at 7' 
(towers pulleys at 7') it would appear that the unbalanced tower is trying 
to pull the cement block up!

My guess is that the tilting fixture can easily handle the tension?  The 
LM470 uses only two pulleys for the same load.

k7puc


----- Original Message ----- 
From: "Dr M J DiGirolamo" <DrD at 2020.com>
To: <towertalk at contesting.com>
Sent: Wednesday, May 02, 2007 2:41 PM
Subject: [TowerTalk] Measuring Cable Tension - W4XN Tower Progress


> Dear Colleagues,
>
> I am at the point of installing antennas on the 23' mast on the top
> of my US Tower HDX-572 (while it's on the ground).  I have the associated
> UST tilt over attachment, which uses a Fulton K2550 Standard Work Winch, 
> and
> the cable shown for this winch is 5/16" dia, 7x19 Aircraft (8mm) cable.
> When finished this tower will house 8 antennas on the mast, one being a
> heavy TH-11DX HF beam.
>
> I'm concerned about the tension put on the winch cable upon raising
> the system and would like to KNOW if I'm reaching dangerous cable tension
> limits.  The maximum breaking strength of this size cable is shown as 9800
> lbs (galvanized cable) on the CarlStahl website.
>
> What I would like to do is to obtain a device to measure the cable
> tension.  I've been to the Dillon Website
> (http://dillonqualityplus.com/pdf/quick-check_L.pdf) and found their
> "Quick-Check Tension Meter."
>
>  I'm wondering if we have anyone who has used this unit and, if so,
> I'd like to hear their opinion of it.  It's very expensive to purchase but
> it's not much more than the HF beam and one more antenna.
>
> I've tried to locate someone who rents them but to no avail.  I may
> consider purchasing one.  Any suggestions?
>
> 73,
>
> Mike DiGirolamo, W4XN
> DrD at 2020.com
> Charlottesville, VA
>
>
>
>
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