[TowerTalk] Indicator wiper issues

[Roger (K8RI) on TT]

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 at 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)