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
>>>
>> _______________________________________________
>> RFI mailing list
>> RFI@contesting.com
>> http://lists.contesting.com/mailman/listinfo/rfi
> _______________________________________________
> RFI mailing list
> RFI@contesting.com
> http://lists.contesting.com/mailman/listinfo/rfi
>
_______________________________________________
RFI mailing list
RFI@contesting.com
http://lists.contesting.com/mailman/listinfo/rfi
|