Re: Wireless Versus Ethernet

Jeff Liebermann <jeffl@comix.santa-cruz.ca.us> writes:
> I beg to differ. Lightning is DC. It does NOT conduct along the skin
> but goes through the highly conductive wet parts of the body, where it
> can do the maximum damage.

If lightning has only DC components why aren't lightning arrestors
simply a 1/4-wave shunt?. Certainly a 1/4-wave piece of copper will
have much better clamping than a gas tube that needs to get up to
ionization voltage first.

> However, the resistance of the armour is sufficiently high, and the
> lightning bolt current also very high, then the armour will probably
> get quite hot, resulting in burns or barbeque.

Yea, 20,000 amps for a hit is going to heat things up a bit. If it is
real armor with sliding plates and rivets I'd expect a few very hot
spots.

The really fun part comes when one looks at the magnetic fields
generated by the current flowing through on the armor. Since the
current is all flowing from top to bottom there will be quite a bit of
force pushing the armor in from all directions. Think
electro-forming. The armor and the guy wearing it are likely to end
up very thin after the hit.

Here is an example when you hit coins with this sort of a field. (The
geometry is a bit different from the armor case, but the concepts are
similar.)

http://205.243.100.155/frames/interesting1.html

-wolfgang
--
Wolfgang S. Rupprecht http://www.wsrcc.com/wolfgang/

On Fri, 21 Jul 2006 15:59:00 -0700, "Wolfgang S. Rupprecht"
<wolfgang+gnus20060721T153543@dailyplanet.dontspam .wsrcc.com> wrote:

>If lightning has only DC components why aren't lightning arrestors
>simply a 1/4-wave shunt?. Certainly a 1/4-wave piece of copper will
>have much better clamping than a gas tube that needs to get up to
>ionization voltage first.

Because DC is infinite wavelength. Only AC has wavelengths.

>Yea, 20,000 amps for a hit is going to heat things up a bit. If it is
>real armor with sliding plates and rivets I'd expect a few very hot
>spots.

I would expect a meltdown. I've seen what's left of a steel outdoor
cabinet and tower that received a direct hit. Whether anyone inside
the cabinet would have survived is rather dubious. However, it still
beats getting hit without any "protection".

>The really fun part comes when one looks at the magnetic fields
>generated by the current flowing through on the armor. Since the
>current is all flowing from top to bottom there will be quite a bit of
>force pushing the armor in from all directions. Think
>electro-forming. The armor and the guy wearing it are likely to end
>up very thin after the hit.

Actually, the electric field will tend to repel the lightning towards
the outside of the conductor. That's how skin effect works. My
guess(tm) is that a substantial amount of the current will be going
through the ionized air surrounding the suit of armour.

I don't think the magnetic field will have much effect. What was left
of the tower and cabinet looked melted, not deformed. Had there been
a substantial magnetic field involved, my guess(tm) is that there
would have been more mechnical deformation instead of just melting.

>Here is an example when you hit coins with this sort of a field. (The
>geometry is a bit different from the armor case, but the concepts are
>similar.)
> http://205.243.100.155/frames/interesting1.html

Wheee... 3000 to 7000 Joules at 100,000 amps.
--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558 jeffl@comix.santa-cruz.ca.us
# http://802.11junk.com jeffl@cruzio.com
# http://www.LearnByDestroying.com AE6KS

On Sat, 22 Jul 2006 04:42:11 GMT, Jeff Liebermann
<jeffl@comix.santa-cruz.ca.us> wrote in
<hha3c21o80o4hv0m9ufcj09a58vnq98dr1@4ax.com>:

>On Fri, 21 Jul 2006 15:59:00 -0700, "Wolfgang S. Rupprecht"
><wolfgang+gnus20060721T153543@dailyplanet.dontspa m.wsrcc.com> wrote:

>>Yea, 20,000 amps for a hit is going to heat things up a bit. If it is
>>real armor with sliding plates and rivets I'd expect a few very hot
>>spots.
>
>I would expect a meltdown. I've seen what's left of a steel outdoor
>cabinet and tower that received a direct hit. Whether anyone inside
>the cabinet would have survived is rather dubious. However, it still
>beats getting hit without any "protection".

Not necessarily. Quite a few people survive direct lightning hits. If
instead the lightning hits a metal enclosure with a person inside (your
suit of armor), I think the odds of survival would be lower.

--
Best regards, FAQ for Wireless Internet: <http://Wireless.wikia.com>
John Navas FAQ for Wi-Fi: <http://wireless.wikia.com/wiki/Wi-Fi>
Wi-Fi How To: <http://wireless.wikia.com/wiki/Wi-Fi_How_To>
Fixes to Wi-Fi Problems: <http://wireless.wikia.com/wiki/Wi-Fi_Fixes>

Jeff Liebermann <jeffl@comix.santa-cruz.ca.us> writes:
> On Fri, 21 Jul 2006 15:59:00 -0700, "Wolfgang S. Rupprecht"
> <wolfgang+gnus20060721T153543@dailyplanet.dontspam .wsrcc.com> wrote:
>
>>If lightning has only DC components why aren't lightning arrestors
>>simply a 1/4-wave shunt?. Certainly a 1/4-wave piece of copper will
>>have much better clamping than a gas tube that needs to get up to
>>ionization voltage first.
>
> Because DC is infinite wavelength. Only AC has wavelengths.

Let me try again. If lightning only had energy at DC and one had an
antenna receiving 2.4ghz then one could short the center conductor of
the cable to the outer conductor with a big-honking (tm) piece of
copper that was cut to 1/4 wavelength. This lightning protector would
have much lower resistance than any gas tube.

The fact that folks don't regularly do this makes me suspect that
lightning does have significant RF components.

>>Yea, 20,000 amps for a hit is going to heat things up a bit. If it is
>>real armor with sliding plates and rivets I'd expect a few very hot
>>spots.
>
> I would expect a meltdown. I've seen what's left of a steel outdoor
> cabinet and tower that received a direct hit. Whether anyone inside
> the cabinet would have survived is rather dubious. However, it still
> beats getting hit without any "protection".

It is not clear. The picture of the guy with ipod that was hit
clearly shows horrible-looking burn marks where the earbud wires ran.
Looks like any conducting protection needs a layer of Nomex below it
just to be safe.

http://www.engadget.com/2006/07/07/i...-by-lightning/

> Actually, the electric field will tend to repel the lightning
> towards the outside of the conductor. That's how skin effect works.
> My guess(tm) is that a substantial amount of the current will be
> going through the ionized air surrounding the suit of armor.

If I'm not mistaken, the magnetic field in parallel wires that are all
carrying current in the same direction sucks the wires together. I
would expect a long hollow tube carrying a lot of current to collapse
at some point.

>> http://205.243.100.155/frames/interesting1.html
>
> Wheee... 3000 to 7000 Joules at 100,000 amps.

That site also has an amazing picture of a lightning bolt. (search for
"Huge positive lightning bolt"). What people do in the name of
science...

http://205.243.100.155/frames/longarc.htm

-wolfgang
--
Wolfgang S. Rupprecht http://www.wsrcc.com/wolfgang/

Wolfgang S. Rupprecht wrote:
> Let me try again. If lightning only had energy at DC and one had an
> antenna receiving 2.4ghz then one could short the center conductor of
> the cable to the outer conductor with a big-honking (tm) piece of
> copper that was cut to 1/4 wavelength. This lightning protector would
> have much lower resistance than any gas tube.
>
> The fact that folks don't regularly do this makes me suspect that
> lightning does have significant RF components.

Lightning is a major RF source. Those RF components cause so much
damage. The frequency spectrum is:
http://www.hubersuhner.com/hs-p-rf-l...e-image1-l.gif

> The frequency spectrum of the LEMP is also of interest,
> especially for RF applications. It reaches several 100 kHz.

Therefore lightning causes radio frequency interference on AM
(longwave) radio. If lightning were DC, then radio frequency
interference would not occur.

On Sat, 22 Jul 2006 07:52:40 -0700, in alt.internet.wireless ,
"Wolfgang S. Rupprecht"
<wolfgang+gnus20060722T072107@dailyplanet.dontspam .wsrcc.com> wrote:

>
>Jeff Liebermann <jeffl@comix.santa-cruz.ca.us> writes:
>> On Fri, 21 Jul 2006 15:59:00 -0700, "Wolfgang S. Rupprecht"
>> <wolfgang+gnus20060721T153543@dailyplanet.dontspam .wsrcc.com> wrote:
>>
>>>If lightning has only DC components why aren't lightning arrestors
>>>simply a 1/4-wave shunt?.
>>
>> Because DC is infinite wavelength. Only AC has wavelengths.
>
>The fact that folks don't regularly do this makes me suspect that
>lightning does have significant RF components.

Had you thought about the fact that immediately prior to the lightning
strike, both voltage and current are effectively zero in the object,
then say 1e-5 seconds later, theyre a couple of hundred KV / Amps
etc? Sounds like a variable current to me.

--
Mark McIntyre

Mark McIntyre <markmcintyre@spamcop.net> writes:
> Had you thought about the fact that immediately prior to the lightning
> strike, both voltage and current are effectively zero in the object,

yes.

-wolfgang

"w_tom" <w_tom1@usa.net> writes:
> http://www.hubersuhner.com/hs-p-rf-l...e-image1-l.gif

More good general lightning information here (what a url!):

http://www.hubersuhner.com/mozilla/p...-bas-espec.htm

-wolfgang
--
Wolfgang S. Rupprecht http://www.wsrcc.com/wolfgang/

"Wolfgang S. Rupprecht"
<wolfgang+gnus20060722T072107@dailyplanet.dontspam .wsrcc.com> hath
wroth:

>Let me try again. If lightning only had energy at DC and one had an
>antenna receiving 2.4ghz then one could short the center conductor of
>the cable to the outer conductor with a big-honking (tm) piece of
>copper that was cut to 1/4 wavelength. This lightning protector would
>have much lower resistance than any gas tube.

Ok, you're 75% correct (which I guess makes me 25% wrong). Lightning
does have substantial energy content at RF frequencies. That's
because the spectra of any impulse includes a broad spectra of RF
junk. Incidentally, that's roughly the way pulsed type UWB (ultra
wide band) works. The problems are:
1. The spectra is not at any single frequency that can be tuned
with a 1/4 wave section.
2. The overwhelming bulk of the energy is strictly charge transfer,
which is DC current.
This is why you don't see "tuned" lightning rods.

>The fact that folks don't regularly do this makes me suspect that
>lightning does have significant RF components.

Well, the fact that you can hear lightning on any AM radio, or see it
on an over the air TV signal, such indicate something. Most of the HF
(high frequency) radio noise comes from approximately 50-100 lightning
hits per second somewhere on the planet. That's quite a bit of RF
noise, but nothing compared to the energy concentrated in a bulk
charge transfer.

>> I would expect a meltdown. I've seen what's left of a steel outdoor
>> cabinet and tower that received a direct hit. Whether anyone inside
>> the cabinet would have survived is rather dubious. However, it still
>> beats getting hit without any "protection".

>It is not clear. The picture of the guy with ipod that was hit
>clearly shows horrible-looking burn marks where the earbud wires ran.
>Looks like any conducting protection needs a layer of Nomex below it
>just to be safe.
> http://www.engadget.com/2006/07/07/i...-by-lightning/

Yuck. I wonder if Apple will honor the warranty on the iPod.

I suspect medieval knights in shining armour probably wore something
under all that metal. Googling.... Well, there's a line of sportsware
that offers UnderArmour clothing:
http://www.underarmour.com
Wikipedia says the armour is worn over linen or woolen clothes.

I wonder if the insulation might form a capacitor between the armour
and the body?
http://video.google.com/videoplay?do...94361927520529
Never mind. Pretend I didn't suggest it.

Anyway, my original point is that wearing armour (over an insulator)
will divert most of the lightning current around the body and
hopefully into the ground.

>If I'm not mistaken, the magnetic field in parallel wires that are all
>carrying current in the same direction sucks the wires together. I
>would expect a long hollow tube carrying a lot of current to collapse
>at some point.

You're correct (again). The do attract which will cause the armour to
collapse somewhat. Maybe lightning armour idea isn't such a great
idea.

>That site also has an amazing picture of a lightning bolt. (search for
>"Huge positive lightning bolt"). What people do in the name of
>science...
> http://205.243.100.155/frames/longarc.htm

High voltage is so much fun:
http://video.google.com/videosearch?q=arc+volt
Lots of lightning photos:
http://video.google.com/videosearch?q=lightning

One of my friends sometimes takes pictures of high voltage phenomenon
at his work. He mentioned something about destroying 5 digital
cameras (so far).


--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

In article <vak4c2967s814fcp385t9tek1p7mau3muf@4ax.com>,
Mark McIntyre <markmcintyre@spamcop.net> wrote:

> On Sat, 22 Jul 2006 07:52:40 -0700, in alt.internet.wireless ,
> "Wolfgang S. Rupprecht"
> <wolfgang+gnus20060722T072107@dailyplanet.dontspam .wsrcc.com> wrote:
>
> >
> >Jeff Liebermann <jeffl@comix.santa-cruz.ca.us> writes:
> >> On Fri, 21 Jul 2006 15:59:00 -0700, "Wolfgang S. Rupprecht"
> >> <wolfgang+gnus20060721T153543@dailyplanet.dontspam .wsrcc.com> wrote:
> >>
> >>>If lightning has only DC components why aren't lightning arrestors
> >>>simply a 1/4-wave shunt?.
> >>
> >> Because DC is infinite wavelength. Only AC has wavelengths.
> >
> >The fact that folks don't regularly do this makes me suspect that
> >lightning does have significant RF components.
>

A true "DC" signal (i.e., theoretically pure DC) is constant *for all
time*, from -infinity to +infinity. The spectrum (Fourier transform) of
such a signal has a component at zero frequency only.

Any other signal (including an "almost pure DC" that is constant for
long periods of time, short of infinite), will always have components at
non-zero frequencies, due to the transition from zero current to the
specified DC when the signal appears, and back to zero when the signal
is removed. The amplitude of these non-zero frequency components is
determined by the time since the transition (longer time since
transition yields lower non-zero frequency amplitudes), the amplitude of
the resulting current, and the slew rate (faster transitions yields
higher non-zero frequency amplitudes).

Although we commonly speak of "DC" when discussing practical circuits
and systems, we never encounter true DC, since the signal is never
constant for infinite duration; however, a signal that is constant for
long times (relative to the time periods we care about) can be
approximated as DC for most engineering purposes. Lightning is NOT such
a signal.

When he referred to the concept that lightning is DC, I believe that
Jeff L. meant that the current in a lightning strike never changes
*direction*. However, it clearly changes amplitude during the time of
interest, on the order of thousands of amperes in tens of milliseconds.
Thus, the resulting spectrum will have significant components at
non-zero values of frequency, as the various posted data indicate.

The amplitude of the lightning signal will be non-zero for all values of
frequency from -infinity to +infinity (as for any impulse-like current
function). Thus, while it contains "RF" (i.e., signals in the RF
spectrum), it will generally not have narrowband (CW) components at any
particular frequency; thus, a narrowband filter (such as a 1/4 wave
transmission line shunt) will not be effective to direct or contain
lightning.

However, if the signal you are trying to *protect* is narrowband (e.g.,
a 2.4 GHz signal), a transmission line shunt can appear as a low
impedance for all of the lightning components other than the desired 2.4
GHz. Thus, to the extent that the shunt is really a low impedance (good
connection to earth, good conductivity, etc.) it *may* help somewhat. Of
course, the filtering characteristics of a simple transmission line
shunt are not spectacular; IIRC it appears as a single-pole filter,
rolling off at only 6 dB/octave. Finally, if the lightning current melts
the shunt conductor, all is again lost.

--
Rich Seifert Networks and Communications Consulting
21885 Bear Creek Way
(408) 395-5700 Los Gatos, CA 95033
(408) 228-0803 FAX

Send replies to: usenet at richseifert dot com

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Wolfgang S. Rupprecht wrote:
> The most important take-home point I see here is that a 1/4-wave
> filter for 2.4Ghz constructed out of heavy copper and grounded well
> would be a very good thing to use in addition to a gas-discharge tube
> lightning arrestor.

Earthing of lightning energy is why some use a J pole type antenna.

The RF nature of lightning is why short wire length, no sharp bends,
not inside metallic conduit, etc are all important for that earthing
connection. Due to the RF nature of lightning, wire impedance (not
just wire resistance) is an essential part of a lightning protection
'system'. Not only is that copper wire 'heavy'. A shorter length and
how it routes to earth is also critical for better protection.

Due to lightning's RF characteristics, an earthing wire bundled with
other cable wires may induce transients on those adjacent wires. Just
another RF effect that must be considered when installing an effective
lightning protection 'system'.

w_tom wrote:
(snip)

> Due to lightning's RF characteristics, an earthing wire bundled with
> other cable wires may induce transients on those adjacent wires. Just
> another RF effect that must be considered when installing an effective
> lightning protection 'system'.

Not only RF. Look at the 60Hz impedance of a copper wire in
a steel conduit. In the case of a single wire running through
a steel conduit carrying 60Hz, how much current travels in the
wire, and how much in the conduit?

-- glen

"w_tom" <w_tom1@usa.net> writes:
> Earthing of lightning energy is why some use a J pole type antenna.

Thanks Tom. Those J-Poles look pretty nice from a grounding
standpoint. (One plan I found was just a J-shaped antenna made from
soldered copper water pipe.)

http://www.n7qvc.com/amateur_radio/copper.html

As an aside, I did notice that a company is selling 1/4-wave stubs for
lightning protection. (They act as a normal N-to-N coupler at the freq
of interest and act as a short at anything off frequency.)

http://www.globec.co.uk/emc/lightnin.../protect2.html

-wolfgang
--
Wolfgang S. Rupprecht http://www.wsrcc.com/wolfgang/

Jeff Liebermann <jeffl@comix.santa-cruz.ca.us> writes:
> 1. The spectra is not at any single frequency that can be tuned
> with a 1/4 wave section.
> 2. The overwhelming bulk of the energy is strictly charge transfer,
> which is DC current.
> This is why you don't see "tuned" lightning rods.

My idea wasn't to tune anything for the lightning. What I think you
can do is to put a 2.4Ghz 1/4-wave "short" in your antenna cable. The
1/4-wave "short" by the magic of out-of-phase addition looks like an
open at the frequency of interest (and any harmonic where the stub is
N+1/4 wave long). At very low frequencies the stub looks almost like
a dead short. The thing that is enticing to me is that the shorting
stub can be made out of very beefy parts and can be clamped directly
to a copper rod pounded into the ground. That should give you as very
good grounding.

-----------------+----------------------
from antenna | to radio
-----------------|-+--------------------
| |
| | 1/4 wave shorted stub.
| | (1/4 wavelength of 2.4Ghz)
| |
+-+

(Pretend the above is coax. I'm too lazy to draw all those ascii
lines and curved sections.)

-wolfgang
--
Wolfgang S. Rupprecht http://www.wsrcc.com/wolfgang/

"Wolfgang S. Rupprecht"
<wolfgang+gnus20060724T094432@dailyplanet.dontspam .wsrcc.com> hath
wroth:

>
>Jeff Liebermann <jeffl@comix.santa-cruz.ca.us> writes:
>> 1. The spectra is not at any single frequency that can be tuned
>> with a 1/4 wave section.
>> 2. The overwhelming bulk of the energy is strictly charge transfer,
>> which is DC current.
>> This is why you don't see "tuned" lightning rods.
>
>My idea wasn't to tune anything for the lightning. What I think you
>can do is to put a 2.4Ghz 1/4-wave "short" in your antenna cable.

That's done all the time with antennas. Most mountain top VHF/UHF
antennas use one of numerous designs that offer a grounded feed or
grounded elements. The main reason is not for lightning protection,
but too reduce noise pickup from nearby frequencies. The grounded
antenna is by it's very nature a resonant bandpass of sorts. There's
also a big advantage as a grounded antenna does not pickup much of a
static electricity charge.

>The
>1/4-wave "short" by the magic of out-of-phase addition looks like an
>open at the frequency of interest (and any harmonic where the stub is
>N+1/4 wave long).

More common is a half wave "stub", which acts as an open circuit at
the resonant frequency, and a short at all other frequencies. Oh,
it's the same as what you drew below.

>At very low frequencies the stub looks almost like
>a dead short. The thing that is enticing to me is that the shorting
>stub can be made out of very beefy parts and can be clamped directly
>to a copper rod pounded into the ground. That should give you as very
>good grounding.
>
> -----------------+----------------------
> from antenna | to radio
> -----------------|-+--------------------
> | |
> | | 1/4 wave shorted stub.
> | | (1/4 wavelength of 2.4Ghz)
> | |
> +-+

The problem with that scheme is that there's still a small possibility
for some of the energy to leak past the stub. The stub might also
decide to become a fuse and there goes your protection. The stub
would also need to be shielded as it would act as quite a good antenna
or unintentional radiator.

More common is a bandpass filter, where there is no physical
connection between input and ouput. Something like this:
http://802.11junk.com/jeffl/pics/lig...yphaser-02.jpg
The two wires are a 1 section interdigital filter at 800-900Mhz. It
could easily be done at other frequencies. Of course, there's some
losses involved. Incidentally, the reason the photo shows 4 spark
gaps in series is that gives you 4 lightning hits before your
protection is gone and the line shorts out.

>(Pretend the above is coax. I'm too lazy to draw all those ascii
>lines and curved sections.)

Well, there's:
http://www.jave.de
This is cute:
http://www.asciimaps.com
More ASCII art tools:
http://www.artcontext.org/ascii/dire...&first=0&time=


--
Jeff Liebermann jeffl@comix.santa-cruz.ca.us
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

glen herrmannsfeldt wrote:
> w_tom wrote:
> (snip)
>
>> Due to lightning's RF characteristics, an earthing wire bundled with
>> other cable wires may induce transients on those adjacent wires. Just
>> another RF effect that must be considered when installing an effective
>> lightning protection 'system'.
>
> Not only RF. Look at the 60Hz impedance of a copper wire in
> a steel conduit. In the case of a single wire running through
> a steel conduit carrying 60Hz, how much current travels in the
> wire, and how much in the conduit?
>
I did the math back in 74 but I forget the answer. :)

I think most is in the wire. But after about 1" or 2" of wire diameter
there's only trivial amounts being carried in the center. Which is why
they use pipes in many high current situations and I think high tension
lines use a center core for strength and the outer windings for current.

DLR <news23@raleighthings.com> wrote:
(snip, I wrote some months ago...)

>> Not only RF. Look at the 60Hz impedance of a copper wire in
>> a steel conduit. In the case of a single wire running through
>> a steel conduit carrying 60Hz, how much current travels in the
>> wire, and how much in the conduit?

> I did the math back in 74 but I forget the answer. :)

You might have missed an important point. I mentioned
a steel conduit, that is, a high permeability material.

The answer is very different for aluminum.

Some National Electrical Code rules are based on this.
For steel, it is mostly in the conduit.

-- glen