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Author Topic: Arcing from Antenna  (Read 2406 times)
VA3GUY
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Posts: 172




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« on: May 05, 2012, 02:12:34 PM »

The other day, it was raining and I was on the air doing some CW.  My neighbor came to me the next day (after the rain had stopped) and told me that he saw arcing coming from my antenna..."bright enough to light the roof", he said..."kind of like an arc welder".  Unfortunately, he could not tell me where the arcing was coming from or going to.  I was doing CW running 100W.
Here is my station:

GlenMartin roof-top tower grounded to the earth with '00' copper cable clamped to a true grounding plate, using proper copper connectors on tower and plate.  The plate is buried into the ground a few feet.  Antenna is a Cushcraft A3S with the 40M add-on.  Mast is approx 8' and antenna is mounted at the top.  Rig is IC-7200.  Power supply is MFJ-4125.  Coax is LMR-400 (approx 40') with a 6-turn 'Ugly Balun' at the feedpoint.  I have 1 counterpoise connected to the external ground lug on the rig as I found this helped to stop interference in my house when I was using my old rig (Yaesu  FT-757GXII) so I just kept the counterpoise on the 7200.  No other grounding other than what is in the standard 110V socket.

Any idea as to what may be going on and how to avoid it?  The next time it rains, I am going to get help and have them key the rig while I go outside and see for myself.

Thank you and 73,

- Guy
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STAYVERTICAL
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Posts: 854




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« Reply #1 on: May 05, 2012, 04:41:15 PM »

Hi Guy,

There are many possibilities, but it may help to narrow the culprits if you noticed if your SWR was higher than normal.
I would imagine that if arcing was on the antenna, that your impedance would be changed, and the SWR would reflect this.
If the SWR was stable, then perhaps the arcing was between some metal on the tower or roof.

The antenna is not that high off the roof so perhaps induction is strong enough to do something there.

Another possibility is that water entered a trap which may have caused some arcing inside.

Unfortunately, I can't give any definitive answer, but if you setup a diagnostic checklist for next time, it may help.

Good luck, and clear skies.

73s
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N4NYY
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Posts: 4742




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« Reply #2 on: May 05, 2012, 04:59:54 PM »

Quote
Unfortunately, I can't give any definitive answer, but if you setup a diagnostic checklist for next time, it may help.

He should try to have another ham transmit while he is out there looking at where the arc is happening. Granted, he had to wait for rain and might get wet, but at least he could end the guesswork.
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W0BTU
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« Reply #3 on: May 05, 2012, 05:13:41 PM »

Can you spray it down with a garden hose and try again?
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N4CR
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Posts: 1655




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« Reply #4 on: May 05, 2012, 07:19:27 PM »

I can't imagine where an A3S might arc other than at the driven element insulators.

It would probably be a good idea to inspect them.

Certainly eyeballing it arcing would give you an indication of where to start your search.
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73 de N4CR, Phil

We are Coulomb of Borg. Resistance is futile. Voltage, on the other hand, has potential.
K2OWK
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Posts: 1041




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« Reply #5 on: May 05, 2012, 08:43:20 PM »

If the arcing from the antenna was bright enough to light up the roof. I would imagine that there wold be a carbon trace or some melted metal at that point. Have you inspected the antenna for this?

73s

K2OWK
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K0ZN
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Posts: 1536




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« Reply #6 on: May 05, 2012, 08:52:05 PM »


Hmmm??   I wonder if it was some kind of static electricity discharge??  I would think if that was the case, you would have been hearing all kinds of loud
noises in the receiver, however.

"Bright lights" with 100 W seems kind of a stretch..... possible I guess, but who knows......

73,  K0ZN
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W5FYI
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Posts: 1044




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« Reply #7 on: May 05, 2012, 09:34:40 PM »

It could be coronal discharge; check out these YouTube videos:

http://www.youtube.com/watch?v=LWJPA4WdXXA

http://www.youtube.com/watch?v=bL4UdLZ1mNc

Or it could be St. Elmo's fire, either from precipitation static (which you should have heard) or from an electrically-charged cloud overhead.

A metal ball on the end of the elements might prevent arcing; the larger the better (some high-power mobile ops in days of olde used copper toilet floats. Nowadays they all seem to be made of plastic).
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VA3GUY
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Posts: 172




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« Reply #8 on: May 06, 2012, 06:23:48 AM »

Ok, after having talked with the neighbor more, I was able to get more detail from him.  He said that it wasn't arcing as much as it was just a spot...like spot welding.  I finally got a chance to get on the roof and do a visual inspection.  As K2OWK suspected, there are carbon traces around the 15M trap on the driver element.  It looks like there is a very small opening in the side of the trap where it connects to the element.  I am going to hazard a guess that is where the 'arcing' is coming from.  Any suggestions on how to properly seal this?

Thanks again...Guy
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W5FYI
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Posts: 1044




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« Reply #9 on: May 06, 2012, 06:59:21 AM »

Before you seal it, do two things first:

1) Check to see if there is there a small hole in the other traps? If so, the hole may be a drain hole for any condensation that may collect inside the trap.  Unless the trap is completely sealed, and filled with a dry atmosphere, water will condense on the inside walls of the trap. For an antenna like yours, the drain hole should be aligned with the bottom of the trap and on the end that is furthest from the beam.

2) Disassemble the trap, if possible, to see what damage may be inside. Quite frequently, small spiders will get inside and, provided there is enough food for them, they become big spiders and spin webs that to collect more food. If you seal the drain hole, and there's a lot of debris still in the trap, things will only get worse.  While it's disassembled, check all connections and clean the coil and capacitor. If you decide to inspect all traps, make sure you identify which trap is which and on which element it goes so you can put them all back where they belong. GL
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N4CR
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Posts: 1655




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« Reply #10 on: May 06, 2012, 08:37:26 AM »

Ok, after having talked with the neighbor more, I was able to get more detail from him.  He said that it wasn't arcing as much as it was just a spot...like spot welding.  I finally got a chance to get on the roof and do a visual inspection.  As K2OWK suspected, there are carbon traces around the 15M trap on the driver element.  It looks like there is a very small opening in the side of the trap where it connects to the element.  I am going to hazard a guess that is where the 'arcing' is coming from.  Any suggestions on how to properly seal this?

Thanks again...Guy

Don't seal the trap. If you do, you'll have even more problems.

First, it's possible that the trap was installed wrong with the drain hole(s) pointed up instead of down. If that's the case, you'l have to remove the trap, do a visual inspection, repair any damage and reinstall it in the correct orientation.

The other already mentioned possibility is bugs as was already mentioned. But the same process ensues.
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73 de N4CR, Phil

We are Coulomb of Borg. Resistance is futile. Voltage, on the other hand, has potential.
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