Rick, I think you hit the nail squarely on the head. As the overlap goes
to its minimum the leverage of the extended tower portion vs the
overlapped region's leverage begins to bind the overlapped portion with
side load. Some users of the DB42 add on aerodynamic winglets to
balance the center of effort (or center of lateral resistance or drag,
if you prefer) so that winds do not create a torque around the vertical
axis.
I wonder how much weight, strategically located and fastened so as to
not change electrical characteristics it would take to make the antenna
"neutral?"
I have a DB42 on my shop floor in 4 boxes awaiting it's turn on my
priority list. Its going on a Tashjian tower with a dead weight
carrying capacity of 550 lbs. I too estimate the weight of the load at
300 lbs or so without cables and coax. I haven't gotten past the musing
stage but it looks like there is plenty of margin to do some
counterbalancing if I have stiction issues with the raising or
lowering. It is power down with a 1/2 horse power motor via a 40:1 so
it will come down, smoothly or otherwise.
Patrick NJ5G
On 6/11/2015 12:36 PM, Richard (Rick) Karlquist wrote
On 6/11/2015 10:07 AM, kr2q@optimum.net wrote:
Hi all,
2. What point is the weak link for the 200 pounds?
Here is the surprising thing I ran into with my HDX-5106,
a MUCH bigger tower. It has a MonstIR on top, figure
250 lbs. Also a short mast and a prop pitch, figure
another 50 lbs. Figure another 100 lbs for cables,
so lets call that 300 lbs. Should be fine.
What happens is that when I get within about 5 feet
of full extension, I start to get noise and vibrations.
The working theory is that this is due to IMBALANCE of
weight, rather than just the weight itself. The sections
start to bind a little when the overlap gets small.
I removed the antenna to change the cables in the tower,
and ran it up and down a few times, and the problem
went away under those conditions. The MonstIR has a
very flexible boom that exascerbates the imbalance
problem. Once it starts to lean a little, the boom
flexes in the direction that makes it worse.
What I am doing as a workaround is manually stopping
the raising winch just before the problem begins.
I know from experience where this point is.
Rick N6RK
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