|To:||Jon Zaimes AA1K <firstname.lastname@example.org>,"David Robbins K1TTT" <email@example.com>, firstname.lastname@example.org|
|Subject:||RE: [TowerTalk] Ring Rotor problem|
|From:||W0UN -- John Brosnahan <email@example.com>|
|Date:||Sun, 24 Oct 2004 13:44:40 -0500|
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
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:
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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