[TowerTalk] M2 KT36XA SWR Problem

[Tony Brock-Fisher]

Cross posted to Towertalk and KTantennas:

Re: Water in KT34/36 antennas

The question is: What can be done to increase the ability of the plastic 
capacitor caps to keep water out of the capacitors?

In increasing order of effectiveness and risk:

 1. The most important key to getting the plastic caps to keep water out
    is to make sure they are installed properly. The latest version
    black caps are extremely durable -- I replaced a set after seven
    years and they looked just as good as the brand new ones after all
    that time in the UV. But they have to be installed fully to seal
    properly on the outer tube. After installation, measure the inside
    distance between the end caps. This should be no more than 11/16 of
    an inch less than the outer tube length. This measurement tells you
    if you have them pressed on fully. I built a clamp-like tool to
    apply significant force to push the caps onto the outer tube, using
    threaded rod and slotted bars.

 2. You can wrap the larger diameter side of the caps with scotch 33
    tape. I did this andit seems to work with no side effects. This
    doesn't help with the smaller diameter tubing though.

 3. You could try silicone RTV sealant on both the outer and inner areas
    of the caps. Non-acetic version would be preferred, but the regular
    stuff would probably work. This would have been my next step.

One other idea I had for drying out traps with water in them without 
complete disassembly: Use a vacuum pump with a rubber hose connected to 
one end of the inner tube. Block the other end. Pull a vacuum on the 
assembly for 45 minutes. The vents in the inner tube will allow the pump 
to evacuate the capacitors. This is how they pull water out of air 
conditioning system -- water boils at room temperature if the pressure 
is low enough. I was going to try this but found out my problem was not 
water in the traps -- it was water in the feedline instead!

-Tony, K1KP