[TowerTalk] [Bulk] Re: RF Ground is a Myth

[Roger (K8RI) on TT]

I'd prefer an installation a bit more secure<:-)) but "Usually" 
something is better than nothing <LOL>
And with Lightening is a "sometimes"event that is  unpredictable 
event.    IOW Even with a "good ground system" you can not provide 
protection for all events.  The bigger, the better, BUT you soon reach 
the area of diminishing returns.  A relatively simple and relatively 
inexpensive ground system will "Probably" give you protection for a good 
percentage of strikes   A few more will up the percentage substantially, 
but there is no way of predicying whether the next strike will be 
typical, or a super strike.  Wk know they "tend" to be related to the 
seasons, but it's that "tend to" meaning a higher percentage of them 
come in spring or fall, no that "they will" happen only in spring or 
fall and not in summer. IOW, we are playing the odds

The first 6 years my tower was up with the elaborate ground system, it 
took 17 visually verified direct hits. AFAIK it has received none in the 
last 6 years.  Why the difference?  I have no idea.  OTOH The first week 
we spent in this house, there were several, really strong thunderstorm 
with many, many major strikes within a couple hundred yards of our 
house.  They were the kind that sounded like a large caliber rifle shot, 
and felt like someone hit the side of the house.  We've had nothing like 
those in many years.

73

Roger (K8RI)


On 1/21/2015 8:48 PM, Jim Lux wrote:
> On 1/21/15 1:41 PM, Jim Brown wrote:
>> On Wed,1/21/2015 1:01 PM, Patrick Greenlee wrote:
>>> I'm confused...    (still, yet, again...)
>>>
>>> There are recommendations to place ground rods (8 footers) 8 ft apart
>>> in a circle (octagon.) If my 14 ft apart Ufer grounds are too close
>>> together so as to act as a single point, what about the 8 ft rods 8 ft
>>> apart?
>>
>> Forget about "single point" with respect to these various earth
>> electrodes. Multiple electrodes (rods, Ufer, etc.) simply provides
>> multiple paths in parallel to discharge a strike. Each of those paths is
>> R + jwL, and the impedances to earth of the combination of those paths
>> adds like any other combination of resistance and inductance, except to
>> the extent that mutual coupling between the electrodes increases the
>> combined impedance.
>>
>> Lightning is NOT a DC event, it is an RF event, with the energy
>> concentrated in very broad spectrum, roughly centered (on a log
>> frequency scale) around 1 MHz (in other words, spread roughly between 50
>> kHz and 20 MHz). Thus, the inductance dominates the impedance.
>> Resistance matters primarily to the extent that we would like the
>> conductor to carry as much as possible of the strike current before it
>> vaporizes. :)
>>
>
> And just plain old redundancy.  Install 3 rods of various length in 
> various parts of your yard with manky old clamps cobbled together out 
> of stuff you found in the parts bin in your garage, don't look at them 
> for 10 years, and hopefully not all the clamps have fallen off.  I 
> have used stainless steel hose clamps to connect ground wires to a 
> rod.  Clearly not to code, clearly not a good long term solution, but 
> hey, I'm pretty sure that if something "bad" had happened while I had 
> it hooked up, it would have been a heck of a lot better than nothing.
>
>
>
>
>
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-- 

73

Roger (K8RI)


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