<< I have recently completed construction of a moderately large antenna -
48 foot boom with 5 elements for 20m and 2 heavily beefed up 402CD elements.
This weighs about 250 pounds.
The problem is that when I lift the boom with a sling, the antenna wants
to roll around the boom so the elements are vertical.... snip... All seven
elements are mounted on the bottom of the boom. There is a boom strut above
the boom with 3/16 EHS guys and real galvanized turnbuckles.....snip>>
Terry,
Wow! I'd call that a MAHnstah!
I'll throw out three suggestions for you.
1) Vertical lift. Perhaps you could simply lift from the truss lines or the
top of the strut above the boom. This puts your lift point above the center
of gravity for super stability. If not, Rig for your vertical lift as
planned, with two slings from either side of the boom balance point up to
the suspension point. Then, add a third, vertical sling from the suspension
point straight down to the boom, such that it passes by the overhead strut
assembly. Then secure the strut to this third sling with another rope. Once
tied together, the boom cannot spin about its long axis since the strut
assembly is secured to the sling. This method adds no extra weight to the
haul.
2) Tram 1. If you can rig for a tram, do so, and use a tiller on the haul
line, pointed toward the tower. Secure the leading end of the tiller to the
tram line with a carabiner, such that it can slip along the tram line, but
prevents the whole works from rotating.
3) Tram 2. Rig the tram as usual, and add an extra, long tiller arm with
counterweight, pointed straight down. This works just the way a keel does on
a sailboat. This tiller can be a long piece of aluminum angle, drilled at
one end for a U-bolt to clamp it to the boom. You will have to experiment
with the amount of counterweight to keep the antenna properly oriented. The
longer a tiller you make, the less counterweight you will need. You can also
skip the couterweight and add a tag line to this tiller, with a person on
the ground providing only the necessary downpull to maintain orientation
during the ride up the tram.
good luck!
--...MARK_N1LO...--
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