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[TowerTalk] antenna sling for tramming

To: "Tower" <>
Subject: [TowerTalk] antenna sling for tramming
From: "Dick Green WC1M" <>
Date: Sun, 11 May 2008 21:35:16 -0400
List-post: <">>
Hi all,


I've trammed antennas 7 times over the past 18 months: a 40-2CD up and down
(the latter just today), plus three 4-el SteppIRs up and one down and back
up again. I'm still not satisfied with the sling technique I've been using
to support the antenna while tramming, and I'd like to hear what techniques
others are using.


What I do is take a couple of 4' nylon climbing loops (22kN) and secure them
to the boom as far from the center as I can reach. I wrap each loop around
the boom, passing one end of the loop through the other and pull until the
strap is tight against the boom. Then I connect the two over the center of
the boom with a carabiner, which is where the trolley and pull rope or
come-along attach. I adjust the distance of each strap from the center until
the antenna is balanced. For some antennas I could use a single strap at the
center of the boom, between the boom plate u-bolts, but I feel the two
widely separated straps distribute the load better.


My techniques works OK on a relatively light antenna like the 40-2CD, but I
found the heavier SteppIRs have a tendency to rotate in the straps i.e., the
boom rotates) When that's happened, I've had to secure the straps with hose
clamps, but I think this is a bad idea because hose clamps have sharp edges.
I'd like to find a better way to secure the straps to the boom. Also, I'd
like to have the center carabiner as close to the top of the boom as
possible (now that the tower is fully populated, antenna booms have to tram
over the elements of other antennas, so the close the boom is to the tram
line, the better.)


Soon I'll be tramming the heaviest antenna I've attempted: a Cal-AV 2D-40A,
at 17 sq ft wind load and 165 lbs. Needless to say, I'll wait for a calm
day. But with such a large antenna, I want to make sure the sling technique
is as sound as possible.


Please let me know how you sling your antennas for tramming.


73, Dick WC1M



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