[RFI] ISOBAR

[David Robbins]

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 at 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
_______________________________________________
RFI mailing list
RFI at contesting.com
http://lists.contesting.com/mailman/listinfo/rfi