[TowerTalk] Conductive Concrete and Grounding

[K8RI on Tower Talk]

Trying to remember my theory... It's been a long time.
I hope this makes a little sense.

I think of lightning as a poor square wave.  It has an fairly abrupt rise 
time and a bit slower fall time as I recall.
It's also complex, with changes in amplitude and usually consists of 
multiple closely spaced strikes appearing as one flash that might flicker a 
bit. It may even have several distinct separate flashes.

Even if the stroke were always in the same direction the rapid varying 
amplitude would make it basically an AC signal.  If you pick the mean 
current and then measure either side you will see substantial voltage swings 
which would be positive and negative in reference to that point.

Taking the square wave of short duration.  Tom remembers this stuff much 
better than I so he may need to expand (or correct).
The theory part is a tad confusing as a perfect square wave consists of an 
infinite series of harmonics.  If that sounds confusing you should try to 
figure the band width of a network signal which is basically DC.  Yet, it's 
DC only in the sense that it stays positive (I believe it's positive) in 
reference to the common, or return path.  The faster the rise time, or fall 
time the broader the signal.  Remember even CW is not zero band width but 
depends on the sending speed as well as the characters being sent.

The power for the perfect square wave would be a summation of an infinite 
series, but in real life the lightening is a far cry from a perfect square 
wave.  In that case the power is basically a summation with some limit and 
the power drops off at a given rate with frequency.

It's that rapid rise time that sometimes causes lightning to strike a tower 
and then get off part way down.
The magnetic field is so intense the current takes a different path.  I've 
seen guy wires on a commercial tower glow blue with the fire but it did no 
damage.

Roger Halstead (K8RI, EN73 & ARRL Life Member)
N833R, World's Oldest Debonair (S# CD-2)
www.rogerhalstead.com

> Tom:
>>
> Even when flowing in one direction a waveform can contain multiple high
> frequency components and act just like AC.
> Lightning can never be treated like DC.
>>
>
> This is difficult for me to comprehend.  Either is current is flowing in 
> one
> direction or the other.
>
> Are you saying that there are multiple waveforms?
>
> Keith NM5G
>
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