"Richard Harrison" wrote
Coax rejects common-mode
lightning energy. We used zero protection across coax and never had a
burnt transistor receiver front-end.

Richard, could you please explain the term "common mode lightning"? I've
seen you reference that many times and meant to ask what that is. Apparently
an uncommon mode burned through 300' of RG8 (literally melting the end
connected at the radio) and disintegrated the internal coax post inside a
Drake R8B.

I sent the radio to Drake, and they explained that the lightning protection
inside the radio was literally exploded, but it did it's job and the radio
was easily and inexpensively repaired.

The coax in question was disconnected about 150' from the house, but
lightning apparently jumped from the tower feed across a foot of air space
and back into the PVC pipe channel housing several coax, which led to the
house. The Drake was the luckiest of the second-story ungrounded shack gear.
The protecton on this particular installation was multiple radial-grounds
from the base of the tower. It was a very nasty strike or set of strikes, as
several outbuildings on the property all suffered equipment damage. _Maybe_
this was a case of ground current from the strike jumping into the coax, but
in any case several coax carried very high charges into the home.

Jack

Jack Painter wrote:
"---explain the term "Common mode lightning"."

A folded monopole or another antenna with a 1/4-wave short-circuited
stub across its drivepoint is a low impedance except at resonance. At
other frequencies containing most of the lightning energy, the exposed
antenna is a short to the grounded tower. At the resonant frequency, the
same voltage with the same polarity is imposed on both the center
conductor and the inside of the coax shield.

Inside the coax, currents in one conductor induce opposing and near
equal currents in each other, cancelling. It worked for me in hundreds
of locations over decades of time including countless lightning strikes
to what was often the most exposed and salient structure for miles
around.

Best regards, Richard Harrison, KB5WZI

Thanks Richard, I remember your explanation about a dipole being no
attractor of anything except it's resonant freq. But I guess the the
currents in the coax weren't "near enough equal" in this one case. Kind of
defines lightning as it's own anomoly when it wants to be, huh.

Jack

Richard Harrison wrote
Inside the coax, currents in one conductor induce opposing and near
equal currents in each other, cancelling.

On Mon, 26 Jan 2004 14:14:21 -0500, "Jack Painter"
wrote:

But I guess the the
currents in the coax weren't "near enough equal" in this one case.

This is the definition of Common Mode.

Kind of
defines lightning as it's own anomoly when it wants to be, huh.

It means you lacked the Common Mode protection. Your earlier posting
of:

The coax in question was disconnected about 150' from the house, but
lightning apparently jumped from the tower feed across a foot of air space
and back into the PVC pipe channel housing several coax, which led to the
house. The Drake was the luckiest of the second-story ungrounded shack gear.

screams this big time. There was nothing anomalous about that
lightning strike, it did what it was enabled to do.

73's
Richard Clark, KB7QHC

"Richard Clark" wrote

It means you lacked the Common Mode protection. Your earlier posting
of:

The coax in question was disconnected about 150' from the house, but
lightning apparently jumped from the tower feed across a foot of air
space
and back into the PVC pipe channel housing several coax, which led to
the
house. The Drake was the luckiest of the second-story ungrounded shack
gear.

screams this big time. There was nothing anomalous about that
lightning strike, it did what it was enabled to do.

Richard, do you mean that if the coax had been left connected to the dipole
it would have afforded common-mode protection? I think I understand what
you're saying but would appreciate you tying that principle together.
Thanks.

Jack

On Mon, 26 Jan 2004 16:02:38 -0500, "Jack Painter"
wrote:


Richard, do you mean that if the coax had been left connected to the dipole
it would have afforded common-mode protection? I think I understand what
you're saying but would appreciate you tying that principle together.
Thanks.

Jack

Hi Jack,

Ask yourself "Where is ground in this picture?"

THAT is the Common of the Common Mode. I see it discussed nowhere in
your description. There is the inference of it being back in the
house (code requires it) where lightning eventually found it, the hard
way.

As you describe it:
The coax in question was disconnected about 150' from the house,
disconnected where, how? Up the tower? At the bottom of the tower?
Is the tower grounded? Does the tower ground meet code in being tied
to the house ground? Is the coax grounded? Where? Does it supply
ground? Where?

The Drake was the luckiest of the second-story ungrounded shack gear.
No ground? There are two problems with this statement.
1.) It is unlikely due to code;
2.) It means you accept Common Mode problems.

It being unlikely does not mean you are protected (experience proves
this), it means you went with the flow - of several KV.

73's
Richard Clark, KB7QHC

Jack Painter wrote:
"But I guess the currents in the coax weren`t "near enough equal" in
this case."

Yes, and I can`t guarantee common-mode or equal currents. If the folded
unipole gets zapped, equal or non-equal currents may flow in both
conductors. Induced currents are likely to be differential-mode. But if
they are differential-mode currents, something else likely happens. The
line flashes over.

I seem to be very lucky to never have damage with so many opportunities
for damage. We never lost a transistor radio front end with countless
strikes as evidenced by the pitted antennas. We know the coax arcs in
broadcast stations. Most stations have automatic circuits to kill the
transmitter when the coax arcs.


In medium wave broadcast stations there is almost always a Faraday
screen to keep down the harmonic radiation. It gets countless zaps as
evidenced by pock marks and metal splattered about its shield box.Even
so, the coax gets arcs. When you are on the air, transmitter energy
keeps the arc alive once a transient has struck the arc. Most
transmitters are equipped with a momentary kill relay whose d-c coil
circuit is completed by the coax arc. As soon as the transmitter is
killed, the relay is de-energized and the transmitter returns to the
air.

In the 2-way radio world, the transmitter is going to drop out in a
moment when the mike button is released, or the station was in the
receive mode when the lightning hit and there is no energy to sustain
the arc.

The arc prevents conveyance of the energy to the radio. I never saw a
broadcast transmitter with evidence of lightning inside the transmitter
and we have a good ides that these stations get struck almost every time
a dark cloud passes by.

Best regards, Richard Harrison, KB5WZI

Richard, my earlier posts described the grounding my friend, here is quick
summary:

1.Well grounded 100' tower, hundreds of feet of many radials, rods, etc.
Survived many strikes.
2. Feedline from tower's dipole was disconnected about 20' from tower where
it enters a buried pvc conduit that travels 150' to house, then up to second
story shack. Where nothing is grounded, except by virtue of house AC
wiring - a bad I know (not mine either).
3. Ground current from the tower strike most likely entered the coax
feedlines at the disconnect point as they entered the pvc conduit then
traveled on into house.
4. House current also took huge jolts, zorching all kinds of connected
equipment, phones, tv's etc.
5. Outbuilding with radio equipment connected took huge hit, ball lightning
inside room fried test cords connected to nothing, hanging on test bench,
where the leads touched tile floor, huge blow-out of tile. AC power blew
wall warts across room, computers next to each other had .22 rifle bullet
sized hole between them. Equipment in this bldg was grounded, and some that
was was damaged, others not touched. In short, a massive, multiple
strike-path hit that may not be protectable from - but I realize there was a
lot missing from a good ground picture here also.

Jack

"Richard Clark" wrote
Ask yourself "Where is ground in this picture?"

THAT is the Common of the Common Mode. I see it discussed nowhere in
your description. There is the inference of it being back in the
house (code requires it) where lightning eventually found it, the hard
way.

As you describe it:
The coax in question was disconnected about 150' from the house,
disconnected where, how? Up the tower? At the bottom of the tower?
Is the tower grounded? Does the tower ground meet code in being tied
to the house ground? Is the coax grounded? Where? Does it supply
ground? Where?

The Drake was the luckiest of the second-story ungrounded shack gear.
No ground? There are two problems with this statement.
1.) It is unlikely due to code;
2.) It means you accept Common Mode problems.

It being unlikely does not mean you are protected (experience proves
this), it means you went with the flow - of several KV.

73's
Richard Clark, KB7QHC

On Mon, 26 Jan 2004 21:07:24 -0500, "Jack Painter"
wrote:

Richard, my earlier posts described the grounding my friend, here is quick
summary:

1.Well grounded 100' tower, hundreds of feet of many radials, rods, etc.
Survived many strikes.
2. Feedline from tower's dipole was disconnected about 20' from tower where
it enters a buried pvc conduit that travels 150' to house, then up to second
story shack. Where nothing is grounded, except by virtue of house AC
wiring - a bad I know (not mine either).
3. Ground current from the tower strike most likely entered the coax
feedlines at the disconnect point as they entered the pvc conduit then
traveled on into house.
4. House current also took huge jolts, zorching all kinds of connected
equipment, phones, tv's etc.
5. Outbuilding with radio equipment connected took huge hit, ball lightning
inside room fried test cords connected to nothing, hanging on test bench,
where the leads touched tile floor, huge blow-out of tile. AC power blew
wall warts across room, computers next to each other had .22 rifle bullet
sized hole between them. Equipment in this bldg was grounded, and some that
was was damaged, others not touched. In short, a massive, multiple
strike-path hit that may not be protectable from - but I realize there was a
lot missing from a good ground picture here also.

Jack

Hi Jack,

You know, it sounds like the lightning hit your house/out-building and
went toward the tower.

73's
Richard Clark, KB7QHC

Many thanks to all you you.
I will probably contact you personally very soon.

73's
Thierry
ON4SKY

"Thierry" To answer me in private use
http://www.astrosurf.com/lombry/post.htm wrote in message
...
Hi,

Was your house/shack stroken by Thor's hammer, I mean a lightning recently
?
I am interested in your experience...

If your installaiton was damaged by a strike event, I would like to now if
:
- you used a central ground point bonded to an external grounding system,
as
well as the home ground.
- you left some gears switched on during the strike event
- you left the TX switched on and the coaxial plugged without protection
- you installed or not lightning controllers in your electric distribution
panel
- you had installed another protection
- you swicthed off and unplugged all devices
- you think that the energy came back via the grounding network (probably
dut to a difference of potential in a device)

Tell me only in a few words what was the most probable cause of the
accident.

At last, if you master the subject, do you really think that a grounding
system, as best it could be as the advice provided by PolyPhaser for
example, will never protect you against a direct strike on your antenna or
on the house lightning conductor
Why ?

All this will help me to conclude the article dealing with this matter :
http://www.astrosurf.com/lombry/qsl-...protection.htm

Thanks in advance

NB. Answer preferably through these forums to please everybody.

Thierry
ON4SKY