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Re: [TowerTalk] R7 traps

To: towertalk@contesting.com, Barry Fox <foxbw@comcast.net>
Subject: Re: [TowerTalk] R7 traps
From: AI4WM Bill <ai4wm@yahoo.com>
Date: Sat, 5 Sep 2009 08:07:33 -0700 (PDT)
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
These traps have caps on the end opposite the piston.  IF the cap is good it 
will keep water out.  The same for the heat shrink integrity for the piston 
end.  The original heat shrink has a liner that melts when the heat shrink is 
heated.  This makes a water tight seal IF the heat shrink was correctly heated 
and correctly shrunk (as it was from the factory).  

Over time the heat shrink can deteriorate from being out in all kinds of 
weather.  If someone replaced the heatshrink with the regular heatshrink or 
used some other method of repair water can enter the capacitors.  In this case 
the capacitor must be taken apart and cleaned.  There are 2 good websites that 
detail this, just google R5 or R7 traps or trap repair.  There are cross links 
to the sites from several amateur radio sites also.  Here is one of the sites: 

http://www.iol.ie/~bravo/r7_vertical.htm

The capacitors are plain old coaxial capacitors and there is no electrical 
reason to have piston up or piston down.  The constraint comes with how the 
capacitor will interfere with the trap below it or above it. 

The problem would be if the brackets move and you end up with a different 
capacitance thus changing the frequency.

I 
have an AP8A that is very similar to the R7.  I have resonated these
on the bench and find no difference with the direction of mounting the 
capacitor since this was my thought on one
that was missing an end cap.  However I have found a cap and did not reverse 
the capacitor mounting.

73,

Bill

AI4WM

--- On Sat, 9/5/09, Barry Fox <foxbw@comcast.net> wrote:

From: Barry Fox <foxbw@comcast.net>
Subject: [TowerTalk] R7 traps
To: towertalk@contesting.com
Date: Saturday, September 5, 2009, 7:37 AM

I'm no antenna designer, but it seems to me that if the trap capacitor
clamps were swapped such that the center rod were at the bottom, no 
water could then enter.  Would that work?
Barry - W1HFN

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