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Re: [TowerTalk] Potting Baluns

To: K8RI <>
Subject: Re: [TowerTalk] Potting Baluns
From: Jim Lux <>
Date: Tue, 05 Feb 2008 12:23:28 -0800
List-post: <>
K8RI wrote:
> 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"), 

In the high power electronic components business, they often mix 
something with high thermal conductivity (alumina, beryllia?) with the 
potting compound.  Then, there's the whole issue of how do you make sure 
there aren't voids in the potting (important for HV and thermal properties).


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