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Re: [TowerTalk] SteppIR vertical

To: towertalk@contesting.com
Subject: Re: [TowerTalk] SteppIR vertical
From: David Gilbert <xdavid@cis-broadband.com>
Date: Mon, 27 Sep 2010 13:47:24 -0700
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
I used to be an engineer, and later an operations manager, for one of 
the largest manufacturers of semiconductors in the world.  Most of our 
components were plastic encapsulated with materials far more 
sophisticated than the PVC, nylon, polypropylene, etc, commonly used in 
general purpose enclosures and yet we knew for a fact that moisture 
would very quickly penetrate the package and get to the silicon.   The  
key was to make sure that the manufacturing process was very clean and 
that the encapsulating materials had very low ionic impurity levels so 
that when the moisture did get to the silicon chip it wouldn't create 
leakage paths and corrosion.  In the early years of such semiconductors, 
one of the more popular molding compounds was silicone based.  It was 
quite clean for those times but also very porous relative to other 
materials ... it didn't do a good job of keeping out moisture but 
neither did it trap the moisture in, and some of our most reliable 
products used silicone for years before better materials were developed.

Anyone who thinks a plastic case is going to keep out water vapor is 
kidding themselves, and the more tightly sealed it is the greater the 
chance for it to eventually cause problems.

73,
Dave   AB7E



On 9/27/2010 1:10 PM, TexasRF@aol.com wrote:
> And further, if you don't let the housing breathe, that  condensation can
> accumulate and eventually fill it with water.
>
> Trying to seal a box like that will never prevent vapor laden atmosphere
> from entering the box but can seal condensation from escaping. Air apparently
>   will travel through much smaller spaces than water.
>
> I have seen this process take place inside hollow Heliax center conductors
> and in a few days flood the downhill connector with water droplets. In this
>   case, the answer was sealing the center pin as if it were a water pipe by
> use of  plumbers tape around the center pin before installation.
>
> If you could actually totally seal the box in question, you might be able
> to prevent the problem. But, the problem is: you can't. And if you could,
> you  have to evacuate all air from the box otherwise there will be some water
> vapor  and condensation of that. You can't win!
>
> 73,
> Gerald K5GW
>    
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