[TowerTalk] Mast slippage

[Les Brown]

Hi Dave,
   It's not the torsional twist on the mast. I was up the tower when the wind was blowing and saw the small movement back and forth on the rotator plate itself. Since this noise started after replacing the clamshell mast clamp with the more rigid K7NV tubular mast clamp, I'm beginning to wonder if the slight movement in the rotator was always there due to gear play and maybe the sound is due to an ever so slight misalignment of the rotator off center causing the gears to make a kind of binding sound when they start to move. Perhaps the old clamshell clamp had more flex so as not to apply as much twisting pressure on the gears. It's just a thought.
73, Les

-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of David Gilbert
Sent: Wednesday, May 26, 2021 10:28 PM
To: towertalk at contesting.com
Subject: Re: [TowerTalk] Mast slippage


Are you certain that what you are seeing isn't simply torsional twisting of the mast itself?  I have a 20 foot 2 inch diameter chromoly mast with
5 feet inside the tower, an Optibeam OB16-3 about 3 feet above the tower and an OB2-40 about 10 feet above that ... all driven by a PST-71D with a homebrew mast clamp similar to the one by K7NV.  Granted that your 3 inch mast would have less twist than my 2 inch mast, but under strong swirling winds I can see the antennas swing back and forth and I know that it's just the mast twisting because the upper OB2-40 twists a bit further than the lower OB16-3.

I used to have a PST-61D up there turning the same antennas and the winds did indeed strip some teeth on the toothed gear, but that involved swings about +/- 20 degrees and was pretty obvious.  I don't think there is enough slop in the PST-17D gears to explain what you are seeing, and I'm pretty certain that there is no clutch in the rotator since none is needed.

For what it may be worth ...

73,
Dave   AB7E




On 5/26/2021 6:06 PM, Les Brown wrote:
> Hi guys,
>     Last year, I reported mast slippage with my PST-71D clamshell mast clamp.
> Well, after replacing the clamshell clamp with the nice K7NV 3 inch 
> mast clamp, no more mast slippage. However, the weak link now seems to 
> be the rotator itself. In a strong wind, I hear a creaking sound as 
> the rotator slips a couple of degrees one way then the other. Is this 
> actually turning the gears all the way back to the worm gear or is 
> there a clutch pad in the PST-71D that could be slipping?
>     I have 2 Optibeams up top for a total of 44 square feet of wind 
> load and the PST-71D is rated at 80 square feet.
> 73, Les VE3NNT

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