Date: Thu, 28 Jan 2016 10:43:10 -0500
From: "Larry" <lknain@nc.rr.com>
To: <towertalk@contesting.com>
Subject: Re: [TowerTalk] Klm 40m-1
I had a Force12 80M rotatable dipole which is a bit bigger (65 feet as I
recall). It used loading wires that also served as a support truss. The mast
ends of the truss were attached to the ends of a 3 foot piece of tubing
centered on the mast and was nominally about 3 feet above the boom. That
gives both vertical and some horizontal support. It survived the little ice
we get here once in a great while. I have seen drawings of that kind of
truss in ON4UN's book I think or perhaps it was the Physical Design book.
73, Larry W6NWS
## I have the same F-12 EF-180B....its 68 ft long. The original ones only had
a 3-4 ft long x 1 inch od, double walled horizontal tube, which was attached
on the mast, 24-30 inchs up the mast, above the 80m rotary dipole. These
earlier
types required the optional cw/ssb relay box at the feedpoint, to even be
able to
operate down at 3502 khz. Later versions used an 8 ft long, double walled
tube,
24-30 inchs above the 80m dipole, to hold up the LL wires. Then the dipole
would
operate down at 3502 without having to use the optional relay box, if so
desired.
## That 8 ft horizontal tube, on paper looks like it would provide for some
horizontal support.
In fact, it provides no additional Horz support. It might provide some H
support, if it was mounted 1-2
inches higher than the dipole. But with typ 2-4 ft mounting above the 80m
rotary dipole, it provides
zero Horz support.
## If the oem LL wires are replaced with T bars, coils, tornado tuner etc,
etc, then some form of truss
has to be used. A single 1/4 or 5/16 inch dacron line will suffice,
terminated 3-5 feet above the dipole.
Or phillystran can be used. Gerald is correct though, the terminating point
has to be high enough above the
dipole ( or boom, if trussing a boom), to be of any use. Mount it too low, and
with a lot of weight on the dipole
(boom), the tubing will compress. You wouldn’t install guy anchors on a
tower that were only out 15% of the
height of the tower...vs the normal 80%.
## KLMs oem 3 point boom truss will work..used on their 58 ft booms. Then it
will provide for Horz support.
A better method these days, used by some ant makers, like optibeam etc, is to
use two truss lines out each side
of the mast, with the 1st truss terminating part way out each side of the
boom. The 2nd truss terminates
way further out, towards the ends of the boom. All 4 truss lines terminate on
the mast. No Horz bar required.
Jim VE7RF
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