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Re: [TowerTalk] Lightning Protection

To: K8RI-on-TowerTalk@tm.net, towertalk@contesting.com
Subject: Re: [TowerTalk] Lightning Protection
From: N4KH Jim <n4kh@comcast.net>
Reply-to: N4KH Jim <n4kh@comcast.net>
Date: Sat, 06 Jul 2013 08:09:00 -0500
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
I remember back when I was a novice class op I kept hearing a tick tick tick 
pop sound sometimes. Finally figured out it was coming from somewhere inside my 
DX60B transmitter whenever a thunderstorm was approaching, even when quite a 
distance away. It was the arcing as you describe from voltage/static buildup on 
my dipole antenna, probably inside the tvi filter unit on the transmitter. It 
never did any damage to that old tube transmitter that I could tell but after 
that i learned to always disconnect my antennas. 
Jim


Sent from my Verizon Wireless 4G LTE Smartphone

-------- Original message --------
From: K8RI <K8RI-on-TowerTalk@tm.net> 
Date: 07/05/2013  10:46 PM  (GMT-06:00) 
To: towertalk@contesting.com 
Subject: Re: [TowerTalk] Lightning Protection 
 
On 7/5/2013 3:44 PM, Pete Smith N4ZR wrote:
> Every time Towertalk starts off on one of these threads I feel compelled
> to add one skeptic's viewpoint, and this time I'm actually going to do it.

I'm not a EE but I managed to get over in while earning a degree in CS.

I have a 100' 45G that had a 30' mast with a TH5 at 100', a 7L C3i 
6-meter Yagi at 115' and a cross boom at 130 feet with a pair of 11L 
440s ans a pair of 12L 144 antennas.
http://www.rogerhalstead.com/ham_files/Tower29.htm
When first installed this system took  at least 3 direct hits a year for 
a total of 17 visually verified hits the first 6 years it was up. The 
only loss was one Polyphaser at the entrance.
There is over 600 feet of bare #2 CadWelded to 32 or 33 8' ground rods. 
There are two parallel runs from the tower to the grounding panel and 
ground rods at the entrance.
http://www.rogerhalstead.com/ham_files/cablebox.htm ; The photo at the 
entrance is out of date as that panel/box has been replaced with a 
larger one.

During that time the rigs remained connected to the antennas, power, 
computers and network.  They stayed connected because the connections 
were very difficult to access.  I was more concerned about the 
connections to the computers and network as they are on a different 
circuit along with the cable connection.

BTW the stations in the house and shop are on serrate electrical feeds 
although from the same transformer,

> Unless you are an electrical engineer with deep understanding of
> lightning protection, I think that attempts to replicate a commercial
> 24/7 always-connected solution are far more likely to fail than to
> succeed.

Lightening protection is pretty well standardized and there is plenty of 
information available.  There is no 100% guaranteed, fail safe 
protection even for the 24 X 7 stations, but they are well protected 
from most strikes.  It's just that there is no guaranteed protection 
from the so called, "super strikes" that can be many times more powerful 
than your run of the mill, every day strikes.

So, yes, the best protection is to disconnect everything from everything 
else, not just the antennas and power.  Remember a strike a mile away 
can induce as much as a 1000 volts per meter into a piece of wire,

Another danger is precipitation static,  What heavy snow in high wind 
can induce into an ungrounded quarter wave, 40 meter vertical is 
something to behold and I've never seen an ignition coil produce that 
kind of voltage.

Twas about 35 years ago.  We were in the process of building a house on 
the NW corner of the family farm.  I had a 40 meter, 1/4 wave vertical 
about a 100 feet out.  The rig, a Kenwood TS820, was disconnected.  A 
very strong wind was blowing with heavy snow.  I kept hearing a loud 
snap or pop!  I looked behind the rig and was surprised to see a FAT 
blue ARC across the PL259.  The thing is, it wasn't just cross the end 
but rather arched out a good inch away from the end of the connector, 
forming a loop that appeared to be close to a couple of inches long and 
it was loud!. Rain with strong wind can also produce similar results.

I've seen similar results from nearby lightening strikes from the 
feedline to the 75 meter dipole.


<snip>

73

Roger (K8RI)

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