At 12:29 AM 5/23/98 +0000, Barry Kutner wrote:
>The indicator on my TIC Ringrotor is starting to act up again -
>needle starts jumping around and rotor stops turning. I believe I
>read somewhere that TIC was working on a fix, like a different kind
>of indicator pot. Anyone know if they ever came up with something
>that keeps on TICking?
>Tnx/.Barry
Barry,
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 feelign 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.
73 John W0UN
--
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|