[TowerTalk] Mast slippage

[David Gilbert]

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