You might consider building yourself a hi-q parallel resonant tank circuit
that you can put in parallel with a dummy load. This will allow you try
various coatings and compare for self heating of the inductor (set the
Xl such that the circulating current in the tank will he high). Otherwise,
you will need a network analyzer or impedance analyzer capable of making
accurate Q measurements when Q is several hundred or more.
I was going to suggest contacting W6ANR, but the blurb about his
loading coils in ON4UN's book suggests PVC shrink tubing, so you have
probably already thought of that. As far as coatings go, the military
space folks use polyurethane coatings on circuit boards to protect them.
I have seen people get away with using this stuff on RF boards running up
to a few hundred megahertz, so it might be worth a try. There is also another
material that will allegedly work on microwave PWBs, but I can't remember
the name of it. I have never tried it myself.
Good luck !
----- Original Message -----
From: "Steve Miller" <firstname.lastname@example.org>
Sent: Friday, August 31, 2001 1:54 PM
Subject: [TowerTalk] Weatherproofing for copper coils?
> I am upgrading Cushcraft 402-CDs. The plan is to replace the stock
> loading coils with high-Q coils made from 1/4 inch copper tubing.
> I'd prefer to apply a low loss protective coating directly to the
> copper tubing rather than construct housings for the coils.
> Heat shrink tubing seemed a possible solution but finding the right
> combination of UV resistance, low RF loss, and price has been
> unsuccessful. (PTFE heatshrink has good properties but runs almost
> Are there any low loss paints or coatings that adhere well to copper
> and can withstand a north Texas environment for several years?
> Any suggestions on how best to weatherproof the coils is welcome....
> Steve Miller N8SM email@example.com http://www.dma.org/~millersg
> List Sponsored by AN Wireless: AN Wireless handles Rohn tower systems,
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List Sponsored by AN Wireless: AN Wireless handles Rohn tower systems,
Trylon Titan towers, coax, hardline and more. Also check out our self
supporting towers up to 96 feet for under $1500!! http://www.anwireless.com
FAQ on WWW: http://www.contesting.com/FAQ/towertalk
Administrative requests: towertalk-REQUEST@contesting.com