On 11/9/2014 2:05 AM, Tod wrote:
My thoughts:
I've seen two distinct problems with the same results.
#1 is the vibration already discussed and
#2, is a short oscillation of the antenna system back and forth. It
takes very little wind. Just a light breeze for anything from a medium
size tri-bander and larger. The more mass (antenna weight, element
length, and boom length.) the easier it is for the oscillation to start
which is counter intuitive. If there are more than a few feet of mast
between the antenna and rotator, it can act as a torsion bar/spring to
slow the period and add energy.
The more mass and the longer the mast, the longer the period of
oscillation and the more power the entire system must handle when the
direction reverses at the end of each half cycle and more movement in
the rotator shell, but that is physically limited by the wedge, or gear
train to a few degrees.
The longer that mast, the easier it is to start the oscillation and the
lower the frequency.
Both cause a small and repeated movement over a small area causing wear
and both are almost continuous except for very calm periods.
If the rotator is not used a lot, if possible the parked position should
be changed every few days. I think that rotators used regularly would
be less likely to suffer this problem unless they were always parked on
the same heading as into the prevailing winds. So there is a down side
to where you park the antenna(s)
Just a few thoughts,
73
Roger (K8RI)
I have seen this too. Steve's analysis is the same one I came too. You have to
somehow eliminate or at least dampen the vibration.
Tod, K0TO
Sent from my iPad air
On Nov 8, 2014, at 7:46 AM, Steve London <n2icarrl@gmail.com> wrote:
N7EF wrote:
The one direction pot failure we ever had, at autopsy, revealed the
rotator had been back and forth so many times
that the brush riding on the resistance wire torus had completely worn
away. What was left of it had sprung down
so it was touching intermittently on inside diameter of the
resistance wire torus...it was not a corrosion.issue.
-----------------------------------------------------------
I have never had this happen to one of my rotators, however I have seen it
happen repeatedly to a local ham - and he was rarely turning his rotator. The
issue was an incredible amount of wind-induced vibration on his TH7DXX-topped
HDBX48 free-standing tower. Even on calm days, you could feel it. I finally
convinced him to stretch a piece of black dacron rope between the top of his
tower and a tree to dampen the vibration.
73,
Steve, N2IC
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73
Roger (K8RI)
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