[RFI] Lightning Protection

[Pete Smith N4ZR]

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
The World Contest Station Database, at www.conteststations.com
The Reverse Beacon Network at http://reversebeacon.net, blog at reversebeacon.blogspot.com,
spots at telnet.reversebeacon.net, port 7000 and
arcluster.reversebeacon.net, port 7000

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:
> http://i913.photobucket.com/albums/ac332/MissouriGuy/th_LOOPSINCOAX.jpg
>
> 73,
> 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.
>>
>> 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 at 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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