[RFI] Lightning Protection
dj2001x at comcast.net
Mon Jul 2 10:10:03 PDT 2012
I suspect during a direct strike the coax would be vaporized so loops probably won't do much. It was a way to take care of extra coax up there. I always like to have a little more in case I make changes, which I do from time to time. If you go to my QRZ page and arrow down you can see the antennas and the loops. The cover page they aren't installed because that picture is old, like me :)
I'm learning a lot with this discussion about mother nature's sparks and how to properly ground a tower.
On 02, Jul 2012, at 10:50, Missouri Guy wrote:
> Hmmm...loops in coax. I always wondered why
> the "pro" installers put loops in the coax feeds. This
> is on my satelite internet feed. The same kind of loops
> are on my Dish Network antenna feedlines. There's
> one just below the dish and one fastened to the pole.
> So, is this for lightning "protection" or is it just a "service loop"?
> Maybe both?
> See photo here:
> Charlie, N0TT
> On Mon, 2 Jul 2012 08:44:26 -0500 dalej <dj2001x at comcast.net> writes:
>> 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.
>> Interesting discussion about lightning.
>> 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
>>> Kim N5OP
>>> On Jul 1, 2012, at 23:21, "KD7JYK DM09" <kd7jyk at earthlink.net>
>>>> "I asked them about these corona brushes and was told that they
>>>> ineffective. Once the electric field exceeds about 50-100 kV per
>>>> everything -- grass, trees, fences, antennas -- are all in corona
>> and the
>>>> air is about as "saturated" with corona ionization as it can get.
>>>> 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,
>>>> even airports surrounded by towers with brush arrays a few tens
>> of feet
>>>> Not effective at all? What about a row of air teminals on a
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