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

Sun Feb 9 14:10:24 EST 2020

Exposed braid will wick water and become useless pretty quick. I use covered stranded welding cable for all of my bearing and rotor bypasses. The ends of each cable terminates in a lug which is waterproofed. The lug allows low resistance connections to the mast or the tower.

73
Tim K3LR

-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of David Gilbert
Sent: Sunday, February 9, 2020 12:36 PM
To: towertalk at contesting.com
Subject: Re: [TowerTalk] Harmonics rectification in bearings or Pro.Sis. Tel rotors?

I use braid as well ... that of my coax feedlines.  The shields of the 
feedlines of my yagis are bonded to their respective boom-to-mast clamps 
(so if for any reason my coax gets wrapped around the mast I don't have 
to replace the section along the boom), and then again to a bar at the 
top of the tower ... and then again to a bar at the base of the tower.  
That's not likely enough to handle a direct lightning hit on the tower, 
but then again neither is 1 mm.

73,
Dave   AB7E

On 2/9/2020 9:59 AM, K9MA wrote:
> 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
>>>
>

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