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

[a9xw at cs.com]

Depending on how much oxidation your inner conductor has from your leak, you may have to replace the entire line. The weep hole is likely letting in more moisture than letting out because temperature changes are causing your line to "breath" Since it is causing VSWR shut down, you might even have internal arcing burning your inner conductor and that will lead to line failure.  Considering thecost of labor for 2-3 trips up the tower and the low cost of coax, you are likely better off replacing the coax now before it fails and you are off the air for days/weeks. Make sure you don't have a lightning hole in the antenna. If the antenna is also pressurized from the coax line, it is much more likely you have an antenna hole than a coax hole. Having a weep hole at the bottom is never a good idea, and whomever "planned" that was no engineer. The correct method would be to have an airseal at the end of the coax and pressurize from the end to the top. You could already have insect eggs in the line from the hole. 

Henry Ruhwiedel (ret) 46 yrs CE R_TV


 




-----Original Message-----
From: Dean <dspencer at hpcisp.com>
To: sbe member discussion mail list <sbe at sbe.org>
Sent: Wed, Oct 3, 2012 11:48 am
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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