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Re: [TenTec] RFI Issues

To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Subject: Re: [TenTec] RFI Issues
From: "chacuff" <chacuff@cableone.net>
Reply-to: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Wed, 23 May 2012 07:37:15 -0500
List-post: <tentec@contesting.com">mailto:tentec@contesting.com>
----- Original Message ----- 
From: "Don Jones" <ko7i@comcast.net>


> Cecil,
> You are spot on. A direct ground strike will develop up to 400 kA-pk. At 5
> ohms that is a serious voltage surge. The Voltage Surge will have a very
> fast rise time (less than 100nS), the current surge will have a lower rise
> time 40uS or so. Within 1mS the impulse will have decayed back to zero.
> If your tower takes a direct strike, the grounding at the base of the 
> tower
> had better be able to "take it" up.
> W8JI claims his towers have taken direct strikes and has a section of his
> web site dedicated to lightning protection. Lots of straight talk and no 
> BS.
>
> I feel blessed to live in Western Washington. Very rarely do we have 
> serious
> lightning activity.
> 73, Don KO7i

That's why I am concerned about guys that drive 3 ground rods at the base of 
their tower and expect it will be good enough.  Mine has been struck 3 times 
in the last year and the net result was the loss of one hot air workstation 
and a tripped breaker in an electrical panel.  The tripped breaker is an 
indication that I probably still have a bit of work to do. (all radio gear 
was still plugged in but antennas disconnected)  I have lots of 2/0 copper 
in the ground as radials leading away from a ring around the base of the 
tower with 10' rods driven every 20'. (probably 18 to 24 total..can't 
remember) Everything is cadwelded.  No clamps...they degrade...especially 
when buried.

As you can see with a 400Ka current peak and a ground system as good as 5 
ohms you are still talking about 2 million volts to have to sink off.  Less 
than 5 ohms would be more desireable but becomes difficult to attain.  With 
things happening so fast, distance is your friend as well...having the tower 
100' from the shack buys you some time for the ground system to do it's work 
hopefully decaying the energy significantly before reaching the shack 
equipment and your home electrical systems.  Thats why bonding those 
together is important so they all come up to potential together..any 
differences causes current to flow and damage to occur.

I live in one of the most lighning prone areas of the country...the Gulf 
Coast of MS. Second only to the central FL area...

Cecil
K5DL 

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