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Author Topic: Lightning STrike  (Read 1930 times)
KB1PXU
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Posts: 33




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« on: April 09, 2012, 08:05:37 AM »

Last summer my Buckmaster dipole received I believe a direct lightning strike. That antenna no longer exists. I was using a LMR400 Times Microwave feed cable which was interupted near ground by an ICE lightning arrestor prior to the feed entering my shack as well as arrestor being grounded to the house's service ground rod.  The lightning arrestor's gas tube also disintergrated.  My rig which is out for repair was unplugged but unfortunately I forgot to disconnect the antenna feeds.

I'm wondering if my coaxial cable can still be used?  What's the best way to test it?  Can I just do a continuity test or is there something else?

Also I was running a Diamond X510 on 2 meters.  The balun of the dipole was within a meter of the mast for the vertical antenna. The ice arrestor for the feedline of this antenna is fine.  Just wondering how do I make sure the x510 is fine?  Do I just make sure that the antenna is resonant with a low SWR or would you do something else?

Thanks
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KB1PXU
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Posts: 33




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« Reply #1 on: April 09, 2012, 12:26:37 PM »

I went ahead and contacted Times Microwave and Diamond.

Times Microwave told me to connect a dummy load to the feed line and then observe the swr.  If the swr is within spec for the frequency transmitting on then the cable should be fine.  They also suggested to visually inspect the cable.

Diamond suggested that I remove the RF connector at the bottom of the antenna and then slide out the internal element and visually inspect two different sets of capacitors.  Additionally too look along the length of the internal element for any discoloration or burning.  If I don't observe anything then the antenna should be OK.

Both manufacturers said if I did have any issues they would help me.  Couldn't ask for more than that. Hope the above may help someone.

73s
Will
KB1PXU
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WA0CRI
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Posts: 35




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« Reply #2 on: April 09, 2012, 01:24:08 PM »

The only way to guarantee the integrity of your coax after the lightning strike would be to "hi-pot" the cable to make sure the dielectric has no carbon paths created by the electric potential of the strike.  Most electrical contractors have a hi-pot instrument and could probably test your cable for little or no cost.

Doug
WA0CRI
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KB1PXU
Member

Posts: 33




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« Reply #3 on: April 09, 2012, 02:12:48 PM »

Doug -

Could you explain in lay terms what "hi-pot" the cable is?

Will
KB1PXU
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N4NYY
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Posts: 4758




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« Reply #4 on: April 09, 2012, 02:23:01 PM »

Quote
Could you explain in lay terms what "hi-pot" the cable is

I did this like 20 years ago. It is a high voltage test that see where the dielectric is as far as breakdown. If it is shorting at a lower voltage, the dielectric was compromised.

Personally, I would not bother with this even though it is correct way of testing. It appears you did get a strike and there was significant damage. I would just replace it.
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WA0CRI
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Posts: 35




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« Reply #5 on: April 09, 2012, 02:36:15 PM »

Will,
"Hi-potting" is a static voltage test which checks, non-destructively, that the dielectric of coax or insulation on other types of conductors do not have microscopic defects which could contribute to current leakage between conductors.  The instrument itself is portable and about the size of a shoe box.  I worked for an industrial electrical contractor for many years and we pulled many miles of cable through buried conduits.  After each pull we would "hi-pot" all cables at a voltage just below the breakdown voltage to guarantee that no damage occurred during the pull, and also that there were no manufacturing defects in the cables.  In your case I would hi-pot your coax at about its maximum working voltage, i. e. 3700 volts for typical RG-213.  If you took your cable in to a contractor it would only take about 2 minutes to check it out.

Doug
WA0CRI
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KB1PXU
Member

Posts: 33




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« Reply #6 on: April 09, 2012, 04:12:13 PM »

Thanks - I really appreciate the suggestion.

Will
KB1PXU
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K7KBN
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Posts: 2801




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« Reply #7 on: April 10, 2012, 08:27:30 PM »

The term "Hi-Pot", however you choose to spell it, stands for "HIgh POTential", which is what the tester applies to the device being tested: a high electrical potential (aka voltage).
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73
Pat K7KBN
CWO4 USNR Ret.
KK4IKO
Member

Posts: 67




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« Reply #8 on: May 08, 2012, 05:23:55 PM »

Food for thought:

Hi-potting a cable may be considered non-destructive, but it has been known to compromise insulation, even in new cable.  I was involved in such testing on new 17,000 volt feeders where I worked.  Recent research has shown that hi-pot testing, especially more than once, may not be recommended on new cable, even though there might be a requirement to do it, unless there is some question about the installation.  The jury is still out on that.  It will however, find a fault if there is one.

Reminds me of an article I once read on proof testing firearms...yes, I know this has nothing to do with ham radio, but the question put forth was whether or not the proof test itself introduces stresses which will show up later under normal use.  I don't know about now, but all gun makers used to proof test each and every one with at least a double load.

73

Bruce, KK4IKO
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KK4IKO
Member

Posts: 67




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« Reply #9 on: May 08, 2012, 05:32:05 PM »

BTW...over 40 years experience as an industrial electrician who has seen the results of lightning strikes first hand, has led me to believe that lightning does whatever it wants, and very often the unexpected.  I highly recommend solid lightning protection and good ham shack practice (disconnecting), but even that might not be enough.

73

Bruce, KK4IKO
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