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Re: [RFI] Lightning Protection

To: rfi@contesting.com
Subject: Re: [RFI] Lightning Protection
From: "Roger (K8RI)" <k8ri@rogerhalstead.com>
Date: Mon, 02 Jul 2012 13:48:15 -0400
List-post: <rfi@contesting.com">mailto:rfi@contesting.com>
On 7/2/2012 9:44 AM, dalej wrote:
> I put large loops in my coax at the top of the tower.  The idea being the 
> lightning striking the antenna goes down the coax and won't make the bend so 
> it just shoots out the coax and not down to the rig.  I suppose it's not very 
> effective, but I had some extra up there so I figured why not.

I call those drip loops to keep water/moisture out of the coax.
I ground the coax shield at both the top and bottom of the tower so I 
don't worry about the lightning having to jump anywhere and my system 
has taken many direct strikes.  Most of those strikes do nothing, but I 
have had a couple that removed the plating (and weatherproofing) from 
every connector up there and with 6 antennas that is a lot of 
connectors.  17 if I counted correctly with power dividers and rotator 
loops.  They were just bare brass (with a very rough finish).  The 
weatherproofing  which was the self sealing tape covered with regular 
Scotch 66 tape looked like sheets of expanded metal.
That was when I realized the fallacy in believing a good job of weather 
proofing will always keep water out of the coax.

73

Roger (K8R)


>
> Interesting discussion about lightning.
>
> 73
> Dale, k9vuj
>
>
>
> On 02, Jul 2012, at 8:08, Kim Elmore wrote:
>
>> No, not effective. Again, because *everything else* is in corona (tower 
>> legs, rivets, weld sputters, bolt threads, nut shoulders, joints of all 
>> kinds) and because lightning propagation isn't driven by small variations in 
>> the local electric field, which is all these devices can accomplish. 
>> Lightning begins well aloft in the cloud, when the e-field approaches 1 M 
>> V/m and propagates at the very high e-field at the tip of the stepped 
>> leader. The downward propagating stepped leader is typically met 100-200 m 
>> above the surface by an upward-propagating streamer, which is caused by the 
>> local e-field induced by the stepped leader. All of this happens faster 
>> (think relativistic speeds) than corona currents can diffuse away from the 
>> source.
>>
>> Kim N5OP
>>
>>
>>
>>
>> On Jul 1, 2012, at 23:21, "KD7JYK DM09" <kd7jyk@earthlink.net> wrote:
>>
>>> "I asked them about these corona brushes and was told that they are
>>> ineffective. Once the electric field exceeds about 50-100 kV per meter,
>>> everything -- grass, trees, fences, antennas -- are all in corona and the
>>> air is about as "saturated" with corona ionization as it can get. These
>>> corona brushes have no effect"
>>>
>>> Several of htese at a site won't lower the potential in the immediate area
>>> preventing charges in the 50-100 kV per meter range?
>>>
>>> I see the diasharge brushes on remote sites, radar, repeaters, surveillance,
>>> even airports surrounded by towers with brush arrays a few tens of feet
>>> across?
>>>
>>> Not effective at all?  What about a row of air teminals on a house?
>>>
>>> Kurt
>>>
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