I may not have explained properly. I have long SO-239 barrals installed
though my boom-to-mast plates as well as the bonding bars at the top and
bottom of the tower. The coax feedlines connect to the barrels, and
those connections are weatherproofed with silicon and vinyl tape.
There is no exposed braid.
I used to have #2 stranded wire bypassing my rotator and plan to do so
again before the monsoon lightning storms next summer, but this thread
started with non-lightning considerations .... harmonic rectification
and static bleed off.
73,
Dave AB7E
On 2/9/2020 12:10 PM, Tim Duffy wrote:
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@contesting.com] On Behalf Of David
Gilbert
Sent: Sunday, February 9, 2020 12:36 PM
To: towertalk@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@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
_______________________________________________
_______________________________________________
TowerTalk mailing list
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
------------------------------
Subject: Digest Footer
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|