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

Sun Feb 9 09:23:56 EST 2020

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
>>
>> _______________________________________________
>>
>>
>>
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> 
> 
> ------------------------------
> 
> 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
> 
> 
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