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Author Topic: High SWR from summer antenna  (Read 359 times)
SM5ZBK
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Posts: 4




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« on: June 21, 2007, 09:40:50 AM »

Hi.

I have a Hy-Gain 14-AVQ vertical mounted in my parent's garden at their summer cottage. I put up the antenna last summer and have not used it since then. I have not changed anything, all equipment is the same.

Last summer I had SWR at least lower than 2 on 40, 15, 10 m but higher on 20 m. Now I have an SWR over 10 on all bands except 15 m where I have 1.8.
I don't really know how to solve this, so my questions are:

1.The cable to the antenna is buried under ground in PVC-pipes from the house to the antenna.
Could there be a problem whit the cable? Since SWR on 15m is MUCH better than on the other bands, could it really be a cable problem? Wouldn’t that affect all bands?

2. If there is a problem whit the antenna, how do I proceed then? I was thinking off disassemble the antenna and then put it together again.

73 de SM5ZBK, Martin
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K1CJS
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Posts: 6012




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« Reply #1 on: June 21, 2007, 09:52:15 AM »

Have you examined the antenna for damage?  The conduit with the co-ax in it for water?  If there is just corrosion on the antenna, disassembling it and cleaning the connection points may solve the problem.

If everything looks OK, disconnect the antenna and put a dummy load on the cable at the antenna end, then see if you still have SWR problems.  If you do, the problem is probably the cable.  If not, and you get a low SWR on all bands, the cable is OK, and the antenna is at fault.

Troubleshooting is always simpler if you divide the possible causes of the problem and narrow it down.

Good luck!
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KB9CRY
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« Reply #2 on: June 21, 2007, 10:20:44 AM »

Disconnect the coax from the antenna out at the antenna.  Install a dummy load out there and test the coax.

Then attach your antenna analyzer to the antenna and look for issues.

Too many places where you can have a change over a year's time to cause problems.

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WA3SKN
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Posts: 5457




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« Reply #3 on: June 21, 2007, 10:23:10 AM »

Sounds like a bad/corroded connection.  Disconnect cable at the antenna and connect dummy-load.  If you still have a problem, it is in the coax, if not... the antenna.  Check antenna and radials for bad connections.  Break out the ohm-meter... check for shorts, as well as opens.
Good Luck!

-Mike.
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K8AG
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Posts: 351




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« Reply #4 on: June 21, 2007, 10:48:41 AM »

CRY is right.  Divide and conquer.  Separate the cable from the antenna.  If the dummy load looks good (without a tuner) then the problem is in the antenna.  If not then you have a coax problem at least.

Sounds like a water or corrosion problem, but finding what is the cause is the only way to fix it.

73, JP, K8AG
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WA9FZB
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Posts: 171




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« Reply #5 on: June 21, 2007, 11:30:01 AM »

Another place to look with the 14-AVQ is the internal connections inside the traps.  If the antenna is subject to wind whipping and if it bends back and forth, over time the solid wire inside the traps can fatigue and break, causing an open circuit at that trap.  Your problems that show up on all bands above 15 meters (did you check 10 meters?) might indicate an open circuit inside the 15 meter trap.

Carefully open the traps and look for breaks.  If you find one, solder a piece of wire across the break and check it again.

73 es gud luck!
Steve  WA9FZB
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K8KAS
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Posts: 569




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« Reply #6 on: June 21, 2007, 01:30:27 PM »

PCV tube and coax is not a good thing. I have lost two feed lines I placed in PCV. Both tubes had water in them plus the coax, not good. I sealed the PCV very well with RTV and besides the ends were above the ground level, you tell me. Since then I bury the stuff
using the proper cable and have not had a trouble. In the sand the water leaches off, in the PCV it just collects when it sweats. Denny
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K1CJS
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Posts: 6012




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« Reply #7 on: June 22, 2007, 04:06:29 AM »

PVC is nice--if you need to pull the cables out or change the configuration often.  The thing you need to do is install the PVC properly.  Many think just dig a trench and bury it, but that's not the correct way.

There has to be a way for water to drain away from the pipe--and a way to get water out of the pipe also.  Sealing the pipe isn't the answer, putting holes in it every one or two feet and laying it in a bed of gravel is.  If you have to use PVC, you should install it that way.

For cable runs out to a tower where you don't have to pull new cable or change it, get direct bury cable and be done with it.

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SM5ZBK
Member

Posts: 4




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« Reply #8 on: June 29, 2007, 12:11:33 PM »

Hi everyone, and thanks for all answers.

I have now bought a dummy load and tested the cable, it was all ok.
I took the antenna apart and measured the resistance in the traps. The 10-m trap had very high resistance (3k ohm - 3M ohm) and the value changed when moving the trap. I took the trap apart and checked the wire, it was not broken. But when doing more measurements I found that the screw connection that connects the coil to the lower antenna element was very dirty. The other traps had no problems so it must have something to do with the manufacturing. After cleaning the connection SWR dropped to more normal values.
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