[TowerTalk] Harmonics rectification in bearings or Pro.Sis. Tel rotors?

[K9MA]

I just use a piece of braid inside the tower from the mast to the tower. 
Because of the small diameter of the mast, it doesn't take much to make 
a loop. It bypasses both the rotator and the thrust bearing.

73,
Scott K9MA



On 2/9/2020 08:23, Grant Saviers wrote:
> Kari,
>
> Not sure if you have a rotating tower or rotating mast.  For my masts, 
> the ground wire loop is the same design as the coax service loop at 
> the top of the tower, they can be taped together.  A u-bolt on the 
> mast for one end and a lug onto a screw on the tower top for the 
> other.  Or perhaps inside the tower on a rotator top clamp bolt and 
> then to the tower.
>
> I use 10ga wire but that is because I had some high flex.  1mm would 
> be fine.
>
> btw corona discharge (aka p-static) is another mast current that kills 
> ball bearings.
>
> Grant KZ1W
>
> On 2/9/2020 05:57, SM0HRP Kari Gustafsson wrote:
>> Interesting Grant. I wonder though how common this problem is. So I  
>> need to
>> make ground loop that can make revolution round the tower when the 
>> antenna
>> is being rotated. Yes I agree, to model a Yagi above a rotor would be
>> interesting to do. Perhaps someone already have done that?
>> 73s Kari SM0HRP
>>
>>
>> From: Grant Saviers <grants2 at pacbell.net>
>> To: SM0HRP Kari Gustafsson <kari at sm0hrp.se>, towertalk at contesting.com
>> Subject: Re: [TowerTalk] Harmonics rectification in bearings or
>>     Pro.Sis. Tel rotors?
>> Message-ID: <4396e89b-c67e-d672-28f0-e4fdb5ed23ef at pacbell.net>
>> Content-Type: text/plain; charset=utf-8; format=flowed
>>
>> Considering that the oil film in a well lubricated ball bearing is 
>> only a
>> few microns thick, it doesn't take much voltage to bridge that gap.
>> However, it is likely there are wear particles and worse rust added 
>> to the
>> mix.  Then there is the additional problem of metal to metal contact and
>> fretting corrosion when the balls don't rotate enough to be lubricated.
>> Which happens when rotators sit on a heading and move a bit in the 
>> wind.  So
>> the noise could be rectification or just arcing.
>>
>> All lubricated bearings should have a ground lead jumper around them.  I
>> learned this long ago making disk drives and used rotating contacts of
>> various types. Grounds are also needed in inverter driven motors 
>> where high
>> (RF) frequencies couple to the armature and arc thru the well lubed 
>> bearing
>> to the frame.  It kills the bearings. google it.
>>
>> It might be informative to model a free space mast with a top yagi at 
>> QRO
>> and see what the voltage would be at the rotator end.
>>
>> Grant KZ1W
>>
>> On 2/8/2020 03:42, SM0HRP Kari Gustafsson wrote:
>>> Hi,
>>>
>>> I have discovered what it seems like rectification in my HD Alu Tower
>>> where on the top there is antenna ball bearing thrust (SKF) below a
>>> 61D Prosistel rotor. I used various techniques to pin poin to the 
>>> tower.
>>>
>>> The harmonics is growl sounding on 20 m (TX on 40 m) and is some -120
>>> dB below the fundamental (40 m) after double low- and high as filters
>>> (giving some 100 dB of combined out of band suppression) in TX and RX
>> chain.
>>>
>>> I have read that some have encountered harmonics rectification in
>>> thrust bearings. Anyone has any experience from ball bearings and
>>> rectification? Or rectification in Prosistel rotors (in the
>> potentiometer?).
>>>
>>> Being a physicist I wonder how the mechanism is with this kind of
>>> rectification in bearings and grease which I assume is isolating. Or?
>>>
>>> I am close to getting a skylift and do the shortening of the bearing
>>> with a jumper and see if it helps bit it is winter her. Brr.cold.
>>>
>>> 73s Kari SM0HRP
>>>
>>> _______________________________________________
>>>
>>>
>>>
>>> _______________________________________________
>>> TowerTalk mailing list
>>> TowerTalk at contesting.com
>>> http://lists.contesting.com/mailman/listinfo/towertalk
>>>
>>
>>
>> ------------------------------
>>
>> Message: 3
>> Date: Sat, 8 Feb 2020 11:57:24 -0500
>> From: charlie carroll <k1xx at k1xx.com>
>> To: towertalk at contesting.com
>> Subject: [TowerTalk] center insulator material
>> Message-ID: <c827acc2-675f-c92c-b34c-a9625e2d2b18 at k1xx.com>
>> Content-Type: text/plain; charset=utf-8; format=flowed
>>
>> I need some help selecting some type of material to build some custom 
>> center
>> insulators.? I have what approaches zero experience in this area.
>>
>> The insulators will be used to support near vertical dipoles for
>> 160-meters.? The antennas will be installed in the Caribbean and will 
>> need
>> high resistance to UV and salt water.? I also want to install an
>> SO-239 and home made common-mode choke on the insulator.? It would be
>> preferable that I be able to fabricate the final shape with common home
>> workshop tools and not have to rely on a machine shop.? The 
>> insulators won't
>> be under a lot of tension because of their orientation, but low weight
>> material would be preferred.? The insulators may be subject to some 
>> winds
>> containing sand particles.
>>
>> I'm looking for some help selecting some appropriate material (UHMW, 
>> Ultem,
>> UV augmented HDPE, ...) that I can investigate further.
>>
>> thanks
>>
>> 73 charlie, k1xx
>>
>>
>> ------------------------------
>>
>> Subject: Digest Footer
>>

-- 
Scott  K9MA

k9ma at sdellington.us