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[TowerTalk] Wet coax

Subject: [TowerTalk] Wet coax
From: Red Haines <>
Date: Sun, 30 Dec 2007 21:21:27 -0600
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The first step is to measure the loss in the coax and determine that it 
is degraded.  An analyzer that can measure impedance is one good way to 
do that.  Open circuit one end and look for minimum impedance from the 
other end while increasing frequency.  A line with no loss will exhibit 
zero impedance when it is an odd multiple of 1/ wavelength, electrical.  
A few ohms is not uncommon near 30 MHz.

In the absence of an analyzer or other instrument that can measure 
impedance, make up some accurate dummy loads of 50 Ohms and multiples or 
integral fractions thereof and measure SWR at high and low frequencies.  
A lossy line will give you a lower than expected SWR when terminated 
with a load other than then characteristic impedance of the line.

Of course, if there is much water in the line, not only will the loss be 
increased but the characteristic impedance will be changed and that will 
appear as a mismatch.

If it is lossy and you suspect water, it may be easy to dry 9913, since 
it is practically hollow.  A vacuum cleaner can draw air through it to 
dry it, though it may be necessary to remove connectors from both ends. 

Make sure the open end is in a dry atmosphere, which may be the cold 
outdoor air at this time of year.  Bring the line into a warm area, to 
warm the moisture inside it, but leave the open end in the dry outdoor air.

All this takes time, but it may be a learning experience and part of the 
fun of the hobby.  HAVE FUN and HNY.  73 de Red


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