Re: Lightning protection

w_tom wrote: 
  You are hung up on a pulse.  True, the sine waves that
combine to create a pulse exist with boundary conditions.  A
true sine wave goes forever - has no boundary conditions.  But
how do we measure the frequency response of circuits?  We
apply a signal that is chock full of 'sine waves' at various
frequencies (for a limited time - the boundary condition) and
then learn which sine waves come out the other end. We apply a
pulse.  We measure those 'sine waves' with a spectrum
analyzer.  If pulses did not create sine waves at all those
frequencies, then the spectrum analyzer would do nothing
useful.  Just another example of how a pulse is far more than
just a pulse.



Certainly pulses can excite tuned circuits.  That's different
from what you have been saying.


  A radio receives electromagnetic radiation at its tuned
frequency (assuming the signal is not so strong as to
overwhelm filters).  If a pulse is only a pulse then the radio
does not receive anything.  But since a pulse is AC
electricity at numerous frequencies, then the radio receives
only its unique frequency from that pulse.

I made it easy. Chart provides a frequency spectrum for a
lightning pulse. How can the pulse have a frequency spectrum
if a pulse is only a pulse? Yes some of those RF frequencies
are so low as to be same as audio frequencies. But they are
electrical - not mechanical motion. The electricity is still
RF frequencies. Some of the most destructive energy is found
in those higher (and less amplitude) frequencies. 


You seem to be using "RF frequencies" to mean "electromagnetic
radiation."  I think that's another example of imprecise language.

I guess you are finally coming to accept the fact that a
lightning pulse is not just a pulse (and not a DC pulse as
TimPerry claimed). You don't provide any supporting facts,
numbers, or citations for your claim that "a pulse is only a
pulse". Provided were numerous reasons why a lightning pulse
is composed of AC electricity at numerous RF frequencies. 

I've deliberately steered clear of the DC vs AC controversy.
If pressed, I'd probably come down on the side of TimPerry,
because I find his flashlight analogy persuasive.  But I don't
think the distinction is particularly useful, so I find it
uninteresting.  You and TimPerry could probably resolve your
differences by careful definition of the terms DC and AC.  I
suspect that under your definition, there has never been a true
DC (i.e. unvarying, as I understand your position) source.

Numerous sine waves summed together to create a pulse. To
repeat some supporting facts: We measure the frequency
spectrum of a pulse because a pulse is composed of so many
different frequencies. That lightning pulse is affected by
impedance because it contains radio frequencies - not DC. The
pulse contains frequencies that create noise on tuned radios. Wire impedance created by sharp wire bends can undermine a
protection system because lightning is composed of AC
electricity. 

Without some calculation to support it, that's a vacuous
statement.  I think it's probably also incorrect in general.

You cited a surge arrestor company's Web site earlier.  Do
you think the ground wires associated with surge arrestors
must similarly avoid sharp bends?

A chart with the frequency spectrum for a
lightning pulse is provided showing energy even at the
megahertz range. The so called DC arc is really AC
electricity. Even Fourier analysis demonstrates that all
waveforms (such as pulses) are summations of sine waves at
various amplitudes, frequencies, and phases. 

At the risk of sounding too much like a former President, that
depends on your definition of "are."  "Can be analyzed for
certain purposes as if they were" might be closer to the truth.

Lighting pulse 
contains many sine waves (with boundary conditions).  The
sharper that pulse, then the more frequencies are contained in
a pulse.

  Meanwhile your concept of earthing a steel building is
flawed.  The steel frame is sufficient to be an earth ground.
It does not have high impedance to obstruct a lightning
strike.  However, for better protection, the lightning rod is
earthed using wire outside the building.  Better protection
means a building's earthing meets lightning rod's earthing at
a point beneath the building - the single point grounding
concept.  A building structure is not some big 'lightning
impeding' inductor.   However even wire has impedance which is
why shorter connections to earth ground mean superior
lightning protection.  Wire impedance is also why plug-in
protectors are not effectively earthed.


Apparently I was unclear.  :-)  I'm not aware of any requirement
that the wire grounding a lightning rod not be encircled at any
point by the building's girders.  Another post of yours seemed
to imply such a requirement.

  Lastly cited is how BT and other telcos earth their
switching stations to not suffer lightning damage.  Every
incoming wire is earthed ideally 50 meters before those wires
connect to the computer.  Connection from each incoming wire
to earth is as short as possible.  A larger separation between
'earthing connection to computer' provides more impedance -
better computer protection.  Short connection 'from incoming
wire to earth' means less impedance - a better path for
lightning.  Why do we mention this?  Because lightning
protection is about low impedance earthing.  Better lightning
protection means the protector is where utility wires enter
the building, with a shortest connection to a single point
earth ground, and not adjacent to electronics.

  A lightning pulse is not just a pulse.  Lightning is many AC
waves in a wide frequency spectrum - AC electricity - that
seeks earth ground.  Protection from lightning involves RF
principles that radio engineers best appreciate.

CJT wrote:
w_tom wrote: 
  The radio is tuned only to receive a specific frequency.
That pulse is composed of many frequencies.

The pulse is a pulse.

Frequency that 
interferes with radio reception is a unique sine wave
frequency
within that pulse.

You're really hung up on those sine waves for some reason.
Fourier analysis is a mathematical construct (admittedly
a very useful one), but it's a fiction (in the best sense
of the word).  The lightning isn't "created" from sine
waves.

Just one of so many frequencies that 
create the pulse.  Pulses - like all waveforms - are a
summation of basic sine waves at different frequencies,
amplitudes, and phases.

So what's the phase of the third sine wave in the series?
What physical phenomenon results in that phase?  Does the
Fourier series you contend results in the single lightning
pulse match it through all time?  Think about what you're
saying.

The radio does not receive a pulse. 
Huh?  Why not?

It receives only parts of a waveform that are specific to its
tuned frequency.  Fourier analysis demonstrates the concept.
The radio does not receive a pulse so much as it receives one
frequency that was part of that pulse.

So what magic keeps the other parts of the pulse away from the radio?
Face it, the radio gets the full pulse and processes it into whatever
you hear.

  A chart for the frequency spectrum of lightning is available
in:
http://www.hubersuhner.com/products/hs-p-rf-lp-kb/hs-p-rf-lp-kb-bas/hs-p-rf-lp-kb-bas-fre.htm
.

Did you look at the scale on that chart?  Is that your idea of RF?
Looks more like audio to me.

  What does DC arcing create?  That was how radios worked.
Sparking DC electricity created AC electricity that resulted
in radio waves.  Telsa did not transmit DC electricity.  To
perform electricity transmissions, DC electricity was
converted to AC.  DC arcing is detected how?  By measuring AC
components created by that arcing.

You're arguing with yourself.  I didn't say it was DC (or AC for
that matter -- the DC/AC distinction, as explored recently in
another thread, is not necessarily useful in a discussion such
as this).

  Meanwhile TimPerry repeatedly refers to DC pulses.  That
would be DC analysis.  Lightning pulse is AC electricity.  It
creates electromagnetic waves of same frequencies.  You even
have a chart for that frequency spectrum.  What the chart does
not show is how the energy content quickly tapers to zero as
frequency approaches DC.  That pulse called lightning is
composed of electricity at RF frequencies.

I suspect we're more in agreement than would appear.  But my problem
with your position is twofold:

- your insistence that a pulse in nature is somehow created from lots
of sine waves; maybe it's just the words you use, but I have a
philosophical problem with projecting a mathematical analysis
technique onto nature as more than an analogy

- (not explored here yet, but related) your claim in one of your
posts that a sharp bend in a ground wire would necessarily destroy
its effectiveness in shunting lightning to ground because of effects
on its impedance.  I think you also contend that wrapping a coil
around the wire would cause a similar problem.  I assume you would
then contend that all skyscrapers run their lightning rod ground wires
outside their girder structures, to avoid being encompassed by single
turn coils consisting of metallic girders.



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