Date: Thu, 22 Oct 2015 23:10:44 -0400
From: "Roger (K8RI) on TT" <K8RI-on-TowerTalk@tm.net>
To: Grant Saviers <grants2@pacbell.net>, towertalk@contesting.com
Subject: Re: [TowerTalk] [Bulk] Re: Phillystran
The 1200# test makes a good truss material except for very large
antennas, or a shallow truss where the center is relatively close to
the boom. I've had no problems using the 1200# test well within its
ratings. I wish I had replaced the Al tube truss on the 7L C3i 6-meter
Yagi with the 1200# Phillystran when I first put it up. True, it's not
a huge monobander, but at a couple inches shy of 30 feet it does need a
truss. A flock of Cormorants using the antenna as an over night roost
broke the tube truss.
There was mention of pretensioning of the truss. That would not be
possible on most antennas, however once the cables are cut to length and
properly terminated, they can be pretensioned in an external fixture,
but as the tension in use will likely be less than the usual 10%
operating tension I doubt there would be any need to do so.
73
Roger (K8RI)
### I believe in a lot of cases, for a boom truss, that the truss does not
terminate
high enough above the boom ! Say you had a 40 ft boom, with a truss on either
side, and terminated 2 ft above the boom. Lets take the same 40 ft boom, and
toss
20 ft of it away.....one half. Then lets flip the boom so it stands
vertical..sitting on the
ground. You would not guy a 20 ft tall mast, with guy lines that are only 2
ft out from the
base, more like 16 ft or 80% of the height. Im not suggesting to raise the
truss 16 ft above
the tower, but another 1-3 ft higher would reduce the stress on both the boom
and the truss
line material. In some cases, esp on long booms, you would be better off to
use 2 truss lines
on either side, like 10 ft on either side of the tower, and again at 20 ft on
either side of the tower.
## The old way of a double truss, with a short horizontal cross member mounted
a few ft up the
mast, with 2 truss lines on either side..terminating to the far ends of the
boom. The thought at
the time was the assy would provide for some lateral support, from winds that
are broadside to the
boom, they don’t. The 3 point truss, like m2 and klm used, will provide for
lateral support. Even them,
the 3 x truss supports were several feet long each.
## I have never used philly for truss material. 5/32 winch cable in either
galvanized or SS works just
fine. Then use nicropress crimps at the far ends of the boom..and cable
clamps + turnbuckles at the
mast end of the truss.
Jim VE7RF
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