I can understand why we want a short connection between the station
ground (the bonded chassis) and earth ground in the case of an RF
ground, especially for unbalanced antennas. But for a lightning
ground, I am not sure I understand why we want a short connection
between station ground and earth.

Let's take the example of an operator with whose only choice is a
second story ham shack and an antenna mounted on a pole some distance
from the house. If a balanced antenna system is used (so we don't need
a good RF ground) and the coax has an arrestor placed at the service
entrance ground where the shield is connected (cold water pipe in
basement), why do we need a ground wire at all? (The coax would run
from the antenna to the basement level [where grounded] and then up to
the second floor.) The chassis' can be bonded together and the bond
point can be connected to earth ground through the coax shield. The
lightning is not going to travel up to the second floor to get the
radio when it has a low impedance path right at ground, is it?

-JJ

wrote
I can understand why we want a short connection between the station
ground (the bonded chassis) and earth ground in the case of an RF
ground, especially for unbalanced antennas. But for a lightning
ground, I am not sure I understand why we want a short connection
between station ground and earth.

Because a large portion of the frequency spectrum of lightning is at RF.
Therefore the inductance of a conductor, not just it's dc-resistance, is
critical to maintain as low as possible. This is done by the shortest,
lowest impedance connection possible to the earth. The potential from all
bonded equipment in a shack and the potential at the grounding electrode of
the station ground should bever be more than 4' apart in elevation, and even
that is a stretch. 1' would be ideal!


Let's take the example of an operator with whose only choice is a
second story ham shack and an antenna mounted on a pole some distance
from the house. If a balanced antenna system is used (so we don't need
a good RF ground) and the coax has an arrestor placed at the service
entrance ground where the shield is connected (cold water pipe in
basement), why do we need a ground wire at all? (The coax would run
from the antenna to the basement level [where grounded] and then up to
the second floor.) The chassis' can be bonded together and the bond
point can be connected to earth ground through the coax shield. The
lightning is not going to travel up to the second floor to get the
radio when it has a low impedance path right at ground, is it?

-JJ

Good that you brought that up. A second story ham shack is the most
difficult, and almost an impossible location to safely provide a low
impedance ground for. Feedlines supplying a second-floor station should
never be allowed to enter from an above ground elevation. Think of inches of
elevation being equal to hundreds of volts each. A few feet above ground can
easily be 10,000v potential above ground. As long as the conditions you
described are followed, the feedlines have a safe path up to a second story,
wrt ground potential rise or attachment of lightning to a nearby antenna.

There are other issues that make the second floor difficult to protect, but
education can solve most of those problems. Lightning striking the nearby
antenna tower, telephone pole, tree in the yard, rooftoop, etc, can also
induce massive energy by electro-magnetic induction on house AC wiring,
phonelines and feedlines inside a structure. It won't matter if they were
grounded on the first floor if the energy in also induced at the second
floor level. Bonding, and a ground system, and adequate surge protection
control EMI from lightning. The problem that relying on a copper strap
connection to ground from 13' above ground is, it still allows a LOT of
potential when confronted with thousands of volts of potential from EMI.
"Wire" to ground from the second floor is useless at RF frequencies, and
even wide copper strap allows a dangerous level of potential to develop. But
it is better than nothing, because the electrical wiring on a second floor
is at a frightening potential wrt ground. If bonding and a lower impedance
path to ground is not provided, the prospect of at least minor damage is
possible from any nearby strike. Disconnecting the feedlines outside (only)
do not help prevent EMI damage at all. The wiring still carries it, and
feedlines still connected to the radios carry it as well. A Drake R8B I own
was originally crisped in a friend's second story shack, and it's feedlines
were disconnected outside. The entrance point of the damage? The RG-8X
feedline! Where did the lightning strike? 200' away on the tower. The
connection to AC ground (a horrible potential between earth and AC ground
exist on a second floor, remember?) was established via an AC powered sound
board that the Drake was connected to via speaker wire connection. My
friend thought disconnecting from main AC power and breaking the feedline
connection outside was enough to protect equipment. That's not always the
case.

73,
Jack Painter
Virginia Beach, Virginia

J.J. wrote:
"---why do we need a ground wire at all?"

Three reasons:
1) 50/60 Hz safety
2) R-F circuitry or suppression
3) Lightning abatement

Powerline frequencies have such wavelength that phase and voltage are
the same everywhere along a line in any particular vicinity. Wire
inductance is of little consequence.

Balanced R-F circuits don`t rely on ground wires to convey signal
between points. Transmission lines do this. Ground wires may be used to
supress some undesired R-F appearances.

Ground wires are essential to lightning abatement as the earth is nearly
always part of the circuit.

Best regards, Richard Harrison, KB5WZI

wrote in message
oups.com...
I can understand why we want a short connection between the station
ground (the bonded chassis) and earth ground in the case of an RF
ground, especially for unbalanced antennas. But for a lightning
ground, I am not sure I understand why we want a short connection
between station ground and earth.

Let's take the example of an operator with whose only choice is a
second story ham shack and an antenna mounted on a pole some distance
from the house. If a balanced antenna system is used (so we don't need
a good RF ground) and the coax has an arrestor placed at the service
entrance ground where the shield is connected (cold water pipe in
basement), why do we need a ground wire at all? (The coax would run
from the antenna to the basement level [where grounded] and then up to
the second floor.) The chassis' can be bonded together and the bond
point can be connected to earth ground through the coax shield. The
lightning is not going to travel up to the second floor to get the
radio when it has a low impedance path right at ground, is it?

don't ever say that lightning won't do something. the voltages and currents
and frequency range combination in lightning can do things that are often
hard to understand. it will go up, down, and sideways, often at the same
time. and just because it hits the ground doesn't mean it won't come up
again somewhere else and still be deadly or destroy equipment.

Dave wrote:
don't ever say that lightning won't do something. the voltages and currents
and frequency range combination in lightning can do things that are often
hard to understand. it will go up, down, and sideways, often at the same
time. and just because it hits the ground doesn't mean it won't come up
again somewhere else and still be deadly or destroy equipment.

The scariest thing I ever heard of lightning doing is
killing someone out of a clear blue sky, coming from
clouds that were hidden by mountains.
--
73, Cecil http://www.qsl.net/w5dxp

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"Cecil Moore" wrote

Dave wrote:
don't ever say that lightning won't do something. the voltages and
currents
and frequency range combination in lightning can do things that are
often
hard to understand. it will go up, down, and sideways, often at the
same
time. and just because it hits the ground doesn't mean it won't come up
again somewhere else and still be deadly or destroy equipment.

The scariest thing I ever heard of lightning doing is
killing someone out of a clear blue sky, coming from
clouds that were hidden by mountains.
--
73, Cecil http://www.qsl.net/w5dxp

Cecil, the "bolt from the blue" is a fairly common way for Americans to be
struck and injured or killed from lightning. In a few cases each year,
witnesses offer that there was either no warning that the storm was arriving
when the victim was struck, or they had only heard thunder but not seen the
storm. Last year I believe there were three such document cases, two of
which resulted in fatalities. The National Lightning Safety Center and
National Weather Bureau have both recently revised upwards the number of
miles from a storm that lightning can be expected to strike. That number
varies according to agency but is generally accepted to be at least 10 miles
ahead of the storm and an unknown (smaller) number of miles behind it.
Agreed is the now universal warning that if outdoors you should find cover
immediately when you hear thunder, and not leave cover until 30 minutes have
passed without hearing thunder.

A good friend who I have known for years and who provided many professional
documents for my lightning systems review over the years was just struck
(and injured) last summer. He waited a couple minutes in his driveway in
Virginia for the rain to let up a bit, and then made his forty foot "dash
for the door". Lightning struck a pine tree next to the driveway just then,
and it struck sideways into his shoulder and out his feet onto the wet
driveway. His wife found him unconscious a few minutes later, and he was
fortunate to survive and make good recovery so far. More than half of all
survivors of lightning strikes experience mental and/or physical
disabilities or complications following the incident. Another good friend
was in his Virginia workshop three summer ago when lightning struck the
tower, and he was the lucky survivor but unfortunate witness to massive
damage, some of it explosive, both to the room he was in, and other
buildings on his property. after a lifetime of close calls myself, it was my
close friend's experience three years ago that finally helped me get the
message and change the way I operated.

Jack Painter
Virginia Beach, Virginia

Jack Painter wrote:
A good friend who I have known for years and who provided many professional
documents for my lightning systems review over the years was just struck
(and injured) last summer.

I was once caught in a thunderstorm riding my bicycle at night in AZ.
I looked down and there were four continuous arcs running from my
wheel rims to the pavement on both sides of both tires. I'll never
forget it.
--
73, Cecil http://www.qsl.net/w5dxp

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Jack Painter wrote:
A good friend who I have known for years and who provided many professional
documents for my lightning systems review over the years was just struck
(and injured) last summer.

I got caught in a thunderstorm while riding my bicycle at
night in Queen Creek, AZ. I looked down and there were
four continuous bright arcs on both sides of my two wire
rims across the tires to ground. I'll never forget that.
--
73, Cecil http://www.qsl.net/w5dxp


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"Justín Käse" wrote
in message news:4228fee2.2075649@chupacabra...
In posted on Thu, 03 Mar 2005
17:40:27 -0600, Cecil Moore wrote:

Dave wrote:
don't ever say that lightning won't do something. the voltages and
currents
and frequency range combination in lightning can do things that are
often
hard to understand. it will go up, down, and sideways, often at the
same
time. and just because it hits the ground doesn't mean it won't come
up
again somewhere else and still be deadly or destroy equipment.

The scariest thing I ever heard of lightning doing is
killing someone out of a clear blue sky, coming from
clouds that were hidden by mountains.

To believe that an errant lightening bolt could navigate around or over
the obstructing mountains, and then single someone out for a lethal
strike is a bit of a stretch, scary thing is that some people believe
this nonsense.
--

JK

All right Justin,

In case your FLAME was just a case of ignorance, you can look this stuff up
for yourself before your foot has to be inserted any further down your
mouth.

http://www.crh.noaa.gov/pub/ltg/crh_boltblue.php

Jack Painter
Virginia Beach, Virginia

Justín Käse wrote:
To believe that an errant lightening bolt could navigate around or over
the obstructing mountains, and then single someone out for a lethal
strike is a bit of a stretch, scary thing is that some people believe
this nonsense.

Well, it was re-enacted on the Discovery Channel. If I
remember right, it happened to a lady on horseback.
--
73, Cecil http://www.qsl.net/w5dxp

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