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@pacbell.net>
To: SM0HRP Kari Gustafsson <kari@sm0hrp.se>, towertalk@contesting.com
Subject: Re: [TowerTalk] Harmonics rectification in bearings or
Pro.Sis. Tel rotors?
Message-ID: <4396e89b-c67e-d672-28f0-e4fdb5ed23ef@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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> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>
------------------------------
Message: 3
Date: Sat, 8 Feb 2020 11:57:24 -0500
From: charlie carroll <k1xx@k1xx.com>
To: towertalk@contesting.com
Subject: [TowerTalk] center insulator material
Message-ID: <c827acc2-675f-c92c-b34c-a9625e2d2b18@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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