In a message dated 7/23/2007 12:13:41 P.M. Pacific Daylight Time,
towertalk-request@contesting.com writes:
> I've always used a feedline "loop" that hangs out and down from the tower
leg that's half-way on the rotation circle, is attached to the boom a few
feet out from the mast, and is long enough that it doesn't impede antenna
rotation in either direction. I recently saw an installation with the
antenna mounted about 2 feet up the mast from the tower top, with the
feedline coiled about 2 turns loosely around the mast rather than hanging
down. The antenna end of the coax was attached at the bottom of the
mast-to-boom plate. The arrangement looked like those coils of cable that
the TV trucks deploy when they raise their microwave towers, but only a
couple of turns to the coil. When rotated in one direction the coil got
tighter to the mast, but not touching it. In the other direction the coil
got looser.
> My question is.... is this a good idea? I have never seen it before, so
maybe it isn't in widespread use, which makes me wonder why not.... as it
"appears" that it would put less stress on the coax than the usual U-shaped
arrangement.
You betcha. It's an alternate method that works FB and is a little more
foolproof than a conventional rotation loop. I think the reasons that it's
not used more is a) many people don't know about it and b) it takes a little
more thought and planning to do. If you've hauled up the feedline with your
beam, getting it around the mast a couple of times might not be easy. OTOH you
can spin the beam on the mast a couple of times to do it.
I've used it many times. It's easier with one or two cables - more
starts to cause coiling/uncoiling problems.
Cheers,
Steve K7LXC
TOWER TECH
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