"40' could be manhandled"? I want to be far away from that exercise!
I'm of the school of slow and safe (particularly when 807's are around),
so welded up a 5" channel H about 4' on the cross, 3' on the verticals
that had angled pipe sleeves at 4 corners for 36" concrete form stakes.
Pretty heavy, but this insures the base is stable. The H had custom
hinge pins for Rohn 25 both ends of the cross. 20' of Rohn 25 is walked
up as the fixed derrick (this could be 20' of 4" x 3/16 sq tube) and was
side and back guyed. Using 4:1 block and tackle with low stretch line,
it is easy to pull up 30' with mast, rotator, and tribander. Probably,
40' could be handled ok, never tried it. Fixed side guys are attached
on the tower being erected, again of very low stretch line. Layed out
properly, they are tensioned while the tower is on the ground (or
crutch) and thus are correctly tensioned for any elevation angle. A
tended back guy on the tower going up keeps the whole shebang stable
when vertical, then it is tied off. To me, the guy anchors in the
ground are the least reliable part of most any design for FD, trees and
vehicles have much to recommend them as guy anchors.
Even with 5" channel the cross was bending more than I liked so I welded
a plate on the channel bottom to make it a box, which is much stiffer.
I made 2 of these about 25 years ago and they are still being used for
FD at former former QTH club. Made a downsized version for FD 2012 for
a 30' aluminum tower and 6m/2m/70cm stacked yagis and used a 10 foot 2
1/2" x 1/8"sq tube as the fixed derrick. Worked slick, club took a first
in 1A. I built this one with a flex fixture for the tower end, so
whatever is available, mast, Rohn or ?? a hinged plate adapter can be
made. Hinge plates are much easier to get right than making hinge pins,
particularly for Rohn 25.
Grant KZ1W
On 2/1/2013 7:54 PM, Wilson Lamb wrote:
We put up several at FD.
40’ Rohn 25 on the back of my 16’ trailer.
Raised by elect. winch on front end.
Rested on wooden crutch to install ant.
30’ Rohn 25 manhandled, on a tilt base pinned down with rebar, same crutch to
install beam.
Both Rohns guyed with one set of 3/8” ropes, works fine, tied to 1” steel
stakes driven into hard ground.
I’m sure 40’ could be manhandled (walked up), but it’s somewhat more to deal
with. Painless with the winch.
The critical part is using the falling derrick to get started when the tower is
low.
Friend built 22’ trailer rig with outriggers for 55’ telescoping mast, works
great.
Another friend built trailer rig for homemade telescoping mast made with EMT
and winch to raise.
All four have rotors...500 contacts on 20m, with FIVE Watts!
I’d MUCH rather deal with 30’ of R-25 than any push up pole, so if you have a pickup or
trailer to carry the 10’ sections, you’re ready.
Wilson
W4BOH
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