RE: [TowerTalk] Ring Rotor problem

[W0UN -- John Brosnahan <shr@swtexas.net>]

I discovered that early TIC rings would blow out the POT from
strong RF overload.  And the overload depended on how
you dressed the leads, the frequency, etc.

I stopped having problems with the POT once I started
using bypass caps (0.01uFd) on the leads at the terminal
strip on the rotator.

Here is my original post from 23 MAY 98 to contesting.com

--John  W0UN


I had an original Clarostat pot fail in my TIC RIng and replaced it
with a similar pot only to have it fail quickly thereafter.

Subsequently I examined both pots and the failures seemed to be
at the point of contact of the wiper arm, or in the wiper arm lead.
I ultimately replaced the pot with a  Bourns 3590S-4-501, which is
what TIC Ring is supplying now.  This pot is not listed in the
usual distribution sources (they only go down to 1K, not 500 ohms)
but it can be special ordered through the usual distribution channels.

My gut feeling was that there was a chance that the failure mode
was that of picking up RF on the control leads with the RF itself
actually burning up the pot at the point of contact of the wiper arm
or on the fine lead to the wiper arm.   Failures would then be
associated with lead dress to some extent and not consistent, which
might explain why some have had failures and others have not.  Since
the control leads are almost in the middle of any antenna mounted on
the ring the level of RF could be quite high.  If the leads are pulled
open into a loop that is terminated by the pot resistance the
amount of dissipated power could be significant!  I once had
an extension cord that was tied in a knot to a small drill actually
melt while in the field of a 10 KW FM transmitter.  I have to stop
working those antennas when they are hot!   In fact my metal frame
glasses got very hot to the touch, as well!

So, I decided to add bypass capacitors on the terminal strip in the
motor enclosure when I changed to the Bourns pot.   I have not had
any more failures but can't be sure if it was just due to the Bourns
pot or to the bypassing of the pot leads.

The whole arrangement of mounting and engaging the teeth on
the pot gear leaves a lot to be desired, so there is still some
suspicion that it is more a mechanical or environmental issue rather
than an RF one, but so far so good.

Hope this info helps.





At 12:57 PM 10/24/2004, Jon Zaimes AA1K wrote:
> Dave,
>
> Thanks for the tips. This box is as you describe....vintage 1993, though 
> it was unused till I installed about 2 years ago.
>
> I'll do an ohmmeter test on the pot.
>
> 73/Jon AA1K
>
> At 09:28 AM 10/24/04, you wrote:
> >For ring rotors you have to specify the type of control box you have.  I
> >assume from the mention of meter and start button that it is one of the
> >ones that has a knob for setting the direction you want and then you
> >momentarily press the start button and it turns the right direction to
> >match the knob.  And that this uses a pot at the motor to indicate
> >position... this type of problem is likely an open in the pot or the
> >wires to it.  If it's the one I think it is it has a 10 turn wirewound
> >pot that does the direction, those pots were prone to opening and
> >depending on where you where the needle on the box could follow the
> >control knob position or just pin one way or the other.  You can force
> >it to turn by putting a pot across the indicator terminals on the
> >control box and watching the beam to point it where you want it... but
> >the real fix is to find the open, probably in the indicator pot, and fix
> >or replace it.
> >
> >Oh, and if it is the one with the 500 ohm 10 turn wirewound pot I just
> >happen to have a couple spares... $20 shipped.
> >
> >David Robbins K1TTT
> >e-mail: mailto:k1ttt@arrl.net
> >web: http://www.k1ttt.net
> >AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net
> >
> >
> >> -----Original Message-----
> >> From: towertalk-bounces@contesting.com [mailto:towertalk-
> >> bounces@contesting.com] On Behalf Of Jon Zaimes AA1K
> >> Sent: Sunday, October 24, 2004 12:06
> >> To: towertalk@contesting.com
> >> Subject: [TowerTalk] Ring Rotor problem
> >>
> >> My Tic Ring Rotor has been working fine for a couple of years, turning
> >a
> >> HyGain Explorer 3-el 40m yagi. I last used it a couple of days ago.
> >>
> >> This morning when I turned on the control box, the meter indicator
> >> immediately pinned to the left. (The beam had been
> >> left around NNE).
> >>
> >> When I changed the preset a few degrees and hit the start button,
> >there
> >> was no change. When I changed the preset
> >> a greater amount (to 150) and hit start again, the meter initially
> >pinned
> >> to the right. And the beam did not move. Then
> >> I hit start again, and the relay in the box clicked intermittently as
> >long
> >> as I held the start button on, and the meter
> >> moved back to about 135 degrees but wobbled. Still no movement of the
> >> beam.
> >>
> >> Any ideas for debugging?
> >>
> >> 73/Jon AA1K
> >>
> >> _______________________________________________
> >>
> >> See: http://www.mscomputer.com  for "Self Supporting Towers",
> >"Wireless
> >> Weather Stations", and lot's more.  Call Toll Free, 1-800-333-9041
> >with
> >> any questions and ask for Sherman, W2FLA.
> >>
> >> _______________________________________________
> >> TowerTalk mailing list
> >> TowerTalk@contesting.com
> >> http://lists.contesting.com/mailman/listinfo/towertalk
>
> _______________________________________________
>
> See: http://www.mscomputer.com  for "Self Supporting Towers", "Wireless 
> Weather Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with 
> any questions and ask for Sherman, W2FLA.
>
> _______________________________________________
> TowerTalk mailing list
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> http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________

See: http://www.mscomputer.com  for "Self Supporting Towers", "Wireless Weather Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with any questions and ask for Sherman, W2FLA.

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