On Tue, 06 May 2008 12:09:33 -0400 Eric <me@[EMAIL PROTECTED]
> wrote:
| In assessing the high frequency content of any wave form, including a
| lighning pulse, the rise time is not significant. The actual
| calculation is based on the slew rate, or slope of the wave form. A
| lighning pulse of 1.2 microseconds has a slew rate of many thousands of
| amps per microsecond. That is why there is much high frequency content
| in a lightning pulse.
The slew rate is not even consistent throughout the rise. A lightning
strike
surge, even the ones induced by a nearby strike to ground or other
objects,
do not look nice and smooth in their wave form. It's a bunch of noise.
You
can see this on analog TV transmissions inversely proportional to the
strength
of the TV signal. The low VHF band, of course, gets more energy. UHF
gets
less, but it can still be seen there. When you see it, it is not always a
simple black or white bar. It is a blast of noise. This is particularly
so
when the lightning steps through multiple strokes, which often vary
because
subsequent strokes can involve additional areas of cloud or ground
discharging.
A strike a mile away will definitely "pop" your AM radio or pulse a bar
across
channel 2 on your analog OTA TV. You won't see much on UHF, depending on
the
strength of that strike. But if it hits YOUR power line service drop
triplex,
you will see it even on UHF. You will see it even on the SHF C-band
analog FM
TVRO signal. Your Ku-band digital TV signal will even freeze up for a
frame
or so. And that's assumping you have the proper protections in place (and
your
power line didn't melt through).
Lightning can, and has (I've seen it twice myself, and read reports from
others) caused damage even to completely and totally disconnected
equipment,
that is not even turned on (assuming it even had a battery to be powered
from).
--
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