[TowerTalk] Rotor loop coax

[Grant Saviers]

The ball bearings in the rotator should have an oil film between them 
and the races. That oil film will break down with a few to several dozen 
volts of potential and the discharge will make noise,  and also pit the 
bearing and race.  Normal static from wind might make enough potential 
difference.    Maybe also make PIM if the film is really thin.

If the oil film isn't replenished with regular rotation then fretting 
corrosion can also damage the balls and bearings.  So this poor contact 
made of corrosion products might make also make PIM.

Another source of voltage differential is corona discharge from the top 
antenna, described by W8JI on his website as what is often called p-static.

So small voltages and currents over time cause a couple of problems.  
Maybe a welding cable around the rotator might help protect the rotator 
in a lightning strike but who knows. Otherwise, I think most any modest 
gauge sufficiently flexible wire has the capacity to protect rotator and 
top bearings and reduce noise.  A lug on each end of the wire to a 
convenient bolt would also work IMO.

Discharge noise and resulting bearing damage are historical problems in 
disk drives and inverter driven AC motors.

Grant KZ1W


On 8/23/2018 8:37 AM, k7lxc--- via TowerTalk wrote:
>   
>>    W3LPL has alerted us to the fact that passive intermod is often
> generated within rotor housings, the solution for which is to bond
> around the rotor. What do you recommend for making the connection to the
> mast above the rotor?
>   
>      I dunno. What does the new N0AX grounding book say? My answer would probably be to use some sort of stranded insulated wire with a hose clamp on the mast and the bottom end connected to the tower - connection type your choice with some anti-oxidant on each end.
>   
>      To be honest I've never done this.
>   
> Cheers,
> Steve     K7LXC
> TOWER TECH -
> Professional tower services for amateur and commercial
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