[SBE] "modifying co-ax" to drain moisture

[Mark Heller]

Dean, 
First and foremost, I'd get pressure in that line 24/7, at least three pounds above normal atmosphere.
Nothing good can come from what you described, especially with winter setting in.  Nitrogen doesn't
chase out ice, through that weep hole.  If your FM transmitter is lowering power, it's telling you something
is seriously out of whack.  And, moisture is found in normal air, you don't need a rain event or even fog
to collect moisture in a line.  Power amplifiers are just not designed to operate at high reflected SWR 
conditions, over a long period of time.   That seal on the top, is a $10 part.  The end connector is a $650 to
$1000 part.  You could be making a costly mistake, but prematurely aging your power amplifier, or if a power
tube is used, your output equipment.  I wouldn't open that 'weep hole' at all.  You're inviting a spider, hornet or wasp to enter your system, and just get worse.  They'd get attracted by your liquid exiting.  Joy dishwashing soap, in a plastic squeeze bottle, will give you a sign of where the moisture is entering...but it will require getting a tower climber to reach the top of your tower.  Just my two cents.  I was recently in your neighborhood, retrieving an AM transmitter from Paoli, and I stayed in Bedford, across the street from the cemetary, so you know where I was....

Mark Heller WGBW / WLWB
mheller at sbe.org

----------------------------------------
 From: "Dean" <dspencer at hpcisp.com>
Sent: Wednesday, October 03, 2012 11:45 AM
To: "sbe member discussion mail list" <sbe at sbe.org>
Subject: [SBE] "modifying co-ax" to drain moisture

  I have a 300 foot run of 1-5/8" air-filled coax up one of our towers that apparently has a bad seal at the top end, and it seems to be admitting water (sort of like an open drinking straw) which is collecting at the bottom in a "loop" of co-ax we left deliberately when it was installed to collect water outside the transmitter and transmitter building.  The "low point" is collecting water as we planned, but eventually it "fills" the insulation space where the drip loop is, and causes the transmitter to drop way back in power, due to high reflected power through the water route.     I can give the co-ax a blast of compressed nitrogen, and after about 15 seconds the water is "forced out" through a small drain hole we have drilled in the co-ax jacket and outer conductor, and the reflected power drops to a normal value, the transmitter output current and power return to normal and we're off and running.   My problem is:  I cannot leave the co-ax pressurized or the leaky seals at the top will bleed down my bottle of nitrogen in a short time (about an hour or so).  So, whenever it looks like a rainy siege is coming, I give the co-ax a "blast" of nitrogen, and hope it will keep the water out for the duration of the rain storm.   What if I increased the size of my co-ax "weep hole" to about ½ inch diameter.  Would this cause any problems?   What if I coupled a small air compressor (with a dryer attached) operating off 120 volts to the co-ax and left it running (cycling on and off on pressure)?  Would this work?   I'm looking for a long range answer, without having to climb the tower, replace the co-ax, etc.     Any suggestions?     DEAN SPENCER WBIW/WQRK/WPHZ dspencer at hpcisp.com P.O. Box 1307 Bedford, IN. Ph.812-275-7555  Fax 812-279-8046 Cell 812-797-3612 wbiw.com  superoldies.net      

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