the basic problem of understanding the biggest lightning problems is throwing
away the traditional concepts of inductance and resistance, and even impedance.
most hams and even electrical engineers understand the lumped version of those
concepts, but to talk realistically about lightning effects you have to throw
them away and think distributed. yes, you could calculate the characteristic
impedance of a feedline shield above ground, and even the velocity factor of
it, but that doesn't let you calculate the voltages or currents from one end to
the other, you have to distribute those values and calculate the currents and
voltages as functions of time AND distance. it gets even more fun when you
have to consider the current and voltage distribution in the ground and realize
that the 'ground' has different voltages in different locations!
Sep 18, 2012 12:57:17 PM, jim@audiosystemsgroup.com wrote:
On 9/18/2012 9:36 AM, David Robbins wrote:
> yes, but its not the resistance that matters in the case of a lightning
> stroke (or even when talking about 'rf' grounds)... the length has MUCH more
> of an effect than the resistance.
David,
In Dale's first post on this topic, he made it quite clear that it was
the IMPEDANCE over the range of 100 kHz to 10 MHz that mattered, which
quite clearly is virtually all inductance. Further, by noting that
frequency range, it is also clear that rise time is the issue. Further,
I saw nothing in his posts that have emphasized resistance, they have
used the word impedance.
Perhaps some hams don't think about wires as having inductance (or
wavelength), but I'm sure that Dale does. :)
73, Jim K9YC
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