Doing the necessary planning and work in the US before I set up a station
outside the US and I've finished five side-mounted swing arm assemblies for my
Rohn 55. The design of the swing arms is what I've used in the past..."Z"
shaped, about 2 feet high and about 33 inches wide made of 1.5 inch "L' angled
aluminum. The rotor shelf and the thrust bearing shelf are also constructed
from the same material and are constructed in the typical "criss-cross"
pattern to create the shelf. The criss-cross distributes the load across all
the legs of the tower. The swing arms will of course cover around 300 degrees.
The station will employ 3 stacked tribanders, all will be side mounted on swing
arms and will be placed just above the three guy points of the tower. Two will
have a second WARC duobander above them about 10 feet higher. The duobanders
are Cushcraft A-3WS eachwith around a 3.5 sq ft windload. Due to clearance
issues, most commercial tribanders can not be mounted on swing arms and clear
the tower. The three antennas under consideration are the KT34 (16ft boom and
around 4.5 windload), KT36 (32 ft boom and 9.5 windload), and the Skyhawk (24
ft boom, 8.5 windload).
Here's my thoughts on the rotors and choice of antennas. I'm planning to go
with Yaesu 2800s for all three rotors. On paper the KT36 and a Cushcraft
would be no issue, but it is a side mount and of course there is considerably
more torque of the rotor...and the tower. The slightly smaller Skyhawk again
coupled with the Cushcraft on paper looks good until you consider it is side
mounted...same issue. The even smaller KT34 obviously is even less of an issue.
I don't want to undersize the antenna, but on the other hand I don't want to
tear up the rotor and/or the tower.
The safe bet would be the KT34 by M2. My previous experience with swing arms
leads me to think I would be just fine with forces on the tower and rotor. I'm
not sure of the Skyhawk and my gut feeling is I'd be asking for trouble using
the KT36 with a longer boom (lots of torque) and the 9.5 windload.
So, bottom line, I need some feedback before i commit big bucks to antennas and
rotors. What do you all think?
73 Bill K4XS/KH7XS
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