[RFI] Lightning Protection
Pete Smith N4ZR
n4zr at contesting.com
Mon Jul 2 12:22:08 PDT 2012
We just had DirecTV installed, and the installer did those loops. I
asked him why, and he said they are there for the next technician, when
the connector fails - not if - to provide plenty of cable length for
putting on a replacement connector.
73, Pete N4ZR
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On 7/2/2012 11:50 AM, 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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