In article ,
Owen Duffy wrote:

Roy Lewallen wrote in
:

Ed wrote:

Roger, Lightning is DC. How could it be " RF " if it has no
"frequency" ?


Ed

If you're not convinced after reading the responses, turn on your radio
the next time a lightning storm is anywhere nearby -- or for that
matter, anywhere within skip propagation range. Then explain how it is
your radio is hearing DC.

Roy Lewallen, W7EL


Indeed Roy, rather than argue that lightning doesn't contain AC
components, one could more cogently argue that it is *not* DC.

It is evident that many hams treat lighting as DC in the design of their
lightning protection system (eg small conductor diameter, sharp bends,
loops, u-turns etc in down conductors), but if you pick up the simplest
models for analysing a lightning down conductor, they treat it as excited
by a double ramp current, and the down conductor as an inducance.

Such a model is not a DC model.

Owen

Lightning is pulsed dc. The pulse can be examined by fourier analysis,
as every sophomore electrical engineering student knows, revealing that
the lightning pulse is made up of a superposition of ac waves of many
frequencies.

One can get away with explaining some things about lightning using
simple dc analysis but most of the interesting stuff requires ac
analysis.

And then there is the business of a nearby lightning strike raising the
voltage of ground lines so that during the strike; they are no longer at
ground potential. This requires ac analysis with impedances rather than
resistances.