TT:
I know I'm missing something important here, but what part of the
proposed balun needs to be sealed? If it's the spot where the leads emerge
from the coax jacket to connect to the feedpoint hardware, I have an
alternative for you to consider:
http://lists.contesting.com/archives//html/Towertalk/2002-10/msg00391.html .
I have a photo of my balun at
http://s83.photobucket.com/albums/j282/ersmar/?albumview=grid . I couldn't
get into the site to pick out the single shot, so you'se'll* have to wait
until it's back up and available.
73 de
Gene Smar AD3F
----- Original Message -----
From: "K8RI" <K8RI-on-TowerTalk@tm.net>
To: <TOWERTALK@contesting.com>
Sent: Tuesday, February 05, 2008 1:48 PM
Subject: [TowerTalk] Potting Baluns
> Just a thought here:
>
> When putting something together like a balun do you want to seal it,
> weather
> proof it, make it rugged, reliable?
> The odds are the answer is "all of the above". If it is then it's likely
> the
> job is going to be *permanent*! IOW the parts are not going to be
> reusable.
>
> Only one method is the most reliable and that is potting, but if potting
> then the capacity of the balun and the ability to get rid of heat have to
> be taken into account. If the balun is going to be inside a container such
> as a PVC sleeve/tube like the old KLM and many of today's the RTV, be it
> regular or non acetic is unlikely to cure properly or if it does it'll
> take
> months to do so. remember this stuff will cure in the tube eventually.
>
> One thing that should be pointed out right at the start: RTVs are not
> designed to be used as potting compounds. But that requires defining Room
> Temperature Silicones or RTVs. Originally they were the _one_part_
> materials
> that smelled like Acetic Acid and later the non-corosive types were
> developed. *Outside* industry the term RTV has been applied to anything
> the
> cures at room temperature. Last I knew there were no two part RTVs. Those
> are sealants and potting compounds. Another variant that came along is
> the
> CONDUCTIVE RTV . the only color in which I've ever seen the conductive
> *stuff* is black. That doesn't mean all black RTVs are conductive as they
> aren't.
>
> So, were it me, and it's not, I'd use either a two part Silicone potting
> compound which is likely to be quite expensive, or an epoxy of a fairly
> low
> viscosity. West Systems (TM) makes a very nice two part epoxy that should
> do the trick, it's inexpensive (expensive and inexpensive are relative
> terms
> here),easy to use, and readily available at most boating supply stores.
> Like many epoxies it is exothermic and it does get HOT.<:-)). This
> approach
> has a number of advantages over the RTVs. It is STRONG (If you want even
> stronger you can mix in what are called "mill fibers"), It is water AND
> moisture proof. RTVs are water proof, but not moisture proof. Also the
> cure
> time is a known factor that can be varied a bit to suit conditions. I
> prefer Vinyl Ester Resin as it has a lower viscosity than the epoxy and I
> have a lot of it. Unfortunately it only comes in gallons and it has a very
> short shelf life compared to the epoxy family. It also uses a rather nasty
> catalyst that makes it expensive to ship.
>
> It may take a little practice to do a good job of potting, but the results
> are worth the time. Also, any potting job should be considered
> *Permanent*.
> IOW the parts are unlikely to be reuseable but there's nothing in a balun
> that should be considered expensive. OTOH I do realize some of us have to
> pinch pennies by necessity where even PL-259s and SO-239s get reused.
> (been
> there and done that)
> The nice thing is by rolling your own, you can build a balun with ratings
> high enough to withstand considerabley higher voltages and currents
> handled
> by the regularly available "store bought" stuff.
>
> 73, good luck, and happy potting,
>
> Roger (K8RI)
>
> BTW I retired as a project manager from one of the major corporations that
> produces a series of RTVs.
>
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>
>
>
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