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Author Topic: Water in Hard Line  (Read 9368 times)
AF6D
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« on: April 11, 2014, 10:44:23 PM »

We moved into our new site today. We thought that we were blessed to be offered 1 5/8 hard line to connection to our new Station Commander until I put my low budget MFJ-269Pro on the cable and got a high SWR. The cable came to the bottom of the tower and switched to what appears to be an old piece of 1/2" SuperFlex. When I unscrewed the N connector water poured out. It is obvious that the 1/2" has to go, especially since the connector could be disassembled without a wrench. The center pin was black and corrosion obvious. This is snow country and it was just black taped - no monkey snot (Buytl) - just black tape.

Now then, the 1 5/8 actually looks serviceable but I have 1.58:1 SWR. I don't know the affect of water in hard line. It has been suggested that it may have come in from the top and traveled down to the screw in pin and that I may be able to disassemble and rejuvenate the connector.

I know that water in the line is bad. I have new hard line that could have been put up but I'd like to try and save this line. I'll be honest, I don't know how to test to see if the cable is shot or if it is affecting the receive. I have little reflected power.

Humbly, how should I proceed? I can pay their crew to put up my new Andrews 1/2" or try to save the 1 5/8"

Suggestions?

Sometimes free comes at a high price...
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NJ1K
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« Reply #1 on: April 12, 2014, 05:20:07 AM »

What is the 1-5/8 line connected to at the top? 

IS this andrews line with a hollow center conductor?

Have you checked the calibration on your MFJ 269?

What band are you using the 1-5/8 for?

If it's hollow center conductor, they make a fitting/connector to connect a nitrogen cylinder to it.  You slightly pressurize the line with dry nitrogen and over time the gas flow will dry out the hollow core.  It won't however dry out a saturated dielectric.
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AF6D
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« Reply #2 on: April 12, 2014, 03:38:43 PM »

Thank you very much for your reply. I sincerely appreciate it.

The band for the 1 5/8 is overkill at 2 meters. It was free. But free seems to be a little wet.

The MFJ reports a 1.0:1 and 49 ohms into a Cellwave dry dummy load and a 1 foot RG-214 jumper.

The next step is to either keep it simple and just run my 1/2" hard line or pull the 1 5/8 connector and see if/where it's wet.

The antenna is a Commander Technologies 220-N and is spec'd at 1.6:1 at the edges, which means that it should be 1.3:1 at 148MHz. I am driving back up now to make sure that the guys put the radials on the antenna. That as I recall lowers the characteristic impedance to closer to 50 ohms. Or are they used to decouple?
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KD0REQ
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« Reply #3 on: April 14, 2014, 10:53:42 AM »

the trick is to keep the line under a couple pounds positive pressure to start with.  obviously, it was a spare run of hardline "just in case," perhaps abandoned in place to run something nicer.

so first, see if it will hold pressure for 20 min or so (standard a/c testing.)  if so, running low power for a while should get the dielectric strip dried out.

if this is a designed-lossy installation in which you constantly bleed air, you're either going to have to get a climber to check the topside out, or run low power for a while.  in the telco, we dry wet lines after they're slit for coarse drainage, by putting a welder across the pairs and cook 'em.  run it half a day, and recheck SWR.  a $100 buzz box is fine, you typically don't run full power or you'd melt the 26-gauge.  you have a larger center conductor, so I'm not even going to ask an outside guy how many amps they run to heat the wire, you will need to put more power on for that larger wire.  get a K-probe pushed up the center onto the wire, and dial up the current until you show heating over ambient.
« Last Edit: April 14, 2014, 10:58:22 AM by KD0REQ » Logged
W6LAR
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« Reply #4 on: May 06, 2014, 10:22:51 AM »

Is your 1 1/8 coax solid foam or air dielectric? Either way the center conductor is hollow and if water got into the center conductor it should not be a problem other than being a route to pass the water on to the connector. If the 1/18 is air dielectric it should have a connector that has a small plug on it to attach a brass fitting for placing a very low pressure nitrogen bottle with regulator or airdryer to keep the cable dry.
On air dielectric cable or wave guides it is best practice to test them for leakage after connectorizing them. Otherwise see if it will hold pressure over time. All the stuff I maintained had air dryers.

I've always used testing the cable or wave guide by installing a very good 50 ohm load at one end and run a return loss measurement. You can spot a wet cable / wave guide and bad connector that way.
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AF6D
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« Reply #5 on: May 06, 2014, 10:51:48 AM »

Thank you both for your replies. I sincerely appreciate them.

We abandoned the use of the 1 5/8th. It just keeps filling up with water even though its hollow center at the top IS sealed. We placed a sandwich baggy over the bottom and lt it hang at an angle and it still fills with water. We ran less than 100 feet of LDF40-5. It all good in the end.

But thank you for your replies.
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KD0REQ
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« Reply #6 on: May 07, 2014, 08:46:11 AM »

probably holed from lightning, then.  enjoy the reach.
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