[TowerTalk] Static Discharge Porcupines - great for....

[Kim Elmore]

Exactly! No one should care about the mean: they should care about what 
part of the distribution they want protection for and for what part of 
the distribution they'll take the risk. This boils down to a 
conceptually simple economic cost/loss ratio: what's the cost of 
protection vs the cost incurred when protection fails?

Kim N5OP

On 8/9/2015 11:19 AM, Jim Lux wrote:
> On 8/8/15 6:11 PM, Roger (K8RI) on TT wrote:
>
>>
>> I'm glad Kim posted that information, but I wish the scientific
>> community would go back to averages rather than median.  The average is
>> much more meaningful than knowing the number that lies half way between
>> the highest and lowest figure measured, at least they are for me. Median
>> is an interesting number, but average seems to be much more informative
>> and typically what is used for design.  With a number of samples large
>> enough to be statistically valid a single, significant outlier, be it
>> high or low can substantially skew the median, but have little effect on
>> the average.
>
>
> Actually, the median is the one you want: half the strokes are higher, 
> half the strokes are lower.   it is not skewed as much by a outlier. 
> The mean (arithmetic sum divided by the number of entries) would be 
> skewed by a single very large number.
>
> In practice, what you'd really want is something like the 95th or 99th 
> percentile. And that's something that's in the standard scientific 
> literature.  I think pretty much any of Uman's books has a figure in 
> it of stroke current distribution.
>
> http://www.iclp-centre.org/pdf/Invited-Lecture-3.pdf
>
> has a lot of interesting charts..
> On page 10, it shows that 50% of the first strokes are around 35 kA or 
> less, and 90% are <100kA peak.
>
> http://surgelogic.com/documents/technotes/Lightning_Stroke_Tech_Note_1300DB1101.pdf 
>
> says 95% of positive strokes <30kA, 98%<60kA
> for negative strokes, 82%<30kZ, 98%<60kA
>
>>
>> The so called "super strikes", or Positive lightening, which is
>> associated with sprites can move the median, but happen so seldom, they
>> have little effect on the average and when it come to lightening, do we
>> design for the median, average, maximum, or the best we can afford?
>
>
> Design for what you can afford to lose. I suspect that designing for 
> the 99th percentile is inappropriate for hams..
>
>
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-- 

Kim Elmore, Ph.D. (Adj. Assoc. Prof., OU School of Meteorology, CCM, PP 
SEL/MEL/Glider, N5OP, 2nd Class Radiotelegraph, GROL)

/"In theory there is no difference between theory and practice. But, in 
practice, there is." //– Attributed to many people; it’s so true that it 
doesn’t matter who said it./