Hello:

Anyone have any thoughts on (hopefully not experiences) whether putting a
loop of, e.g. 1 foot in diameter,
on a coax run from an outdoor receive-only antenna has any merit as far as
helping any emf lightning induced pulses from traveling into a house ?

Have heard about this, but it's hard to believe it would actually do
anything in practice.
But,... ?

B.

All the grounding info I have seen mentions no sharp bends, or any bends
if you can help it when bonding tower legs, etc to ground rods or ground
rings as it raises the impedance to the ground connection. I can see a
loop in the coax being beneficial as a supplement to a ground system,
but definitely not as the only precaution. It takes a well designed
lightning ground system to take a direct hit without any damage and I
have never seen one in a residential setting. I know several mountain
top repeater sites that take hits all the time with no apparent damage
but the entire site including the building, tower and electrical system
were designed from the start with lightning in mind.
Bob


Robert11 wrote:
Hello:

Anyone have any thoughts on (hopefully not experiences) whether putting a
loop of, e.g. 1 foot in diameter,
on a coax run from an outdoor receive-only antenna has any merit as far as
helping any emf lightning induced pulses from traveling into a house ?

Have heard about this, but it's hard to believe it would actually do
anything in practice.
But,... ?

B.

Do you think a loop will stop what three miles of sky could not?
Effective protection is not about stopping a transient. That does not
work and is they myth even used to promote plug-in protectors. A most
trivial earth ground is a massive improvement in protection. That
incoming wire must be earthed - directly or through a protector -
before entering the building. That simplest earthing is many times
more effective than 100 loops. Effective for direct strkes - which
means induced trasnients would be made irrelevant.

The US Forestry Service has documented that most direct strikes to
trees do not leave appreciable indication. Even a standard household
earth ground in conductive soil will provide protection from most
lightning strikes. Then we enhance that earthing for other, more
violent and less frequent direct strikes.

Quality of earthing determines how many direct strikes will be
earthed without damage. Even some earthng to a single point is a
massive improvement in transistor protection. But the loop is about
as useful as bad science fiction. For loop to be effective, then loop
also must seriously degrade radio reception. How many reasons why that
loop is useless? Five?

Robert11 wrote:
Hello:

Anyone have any thoughts on (hopefully not experiences) whether putting a
loop of, e.g. 1 foot in diameter,
on a coax run from an outdoor receive-only antenna has any merit as far as
helping any emf lightning induced pulses from traveling into a house ?

Have heard about this, but it's hard to believe it would actually do
anything in practice.
But,... ?

B.

Robert11 wrote:

Hello:

Anyone have any thoughts on (hopefully not experiences) whether putting a
loop of, e.g. 1 foot in diameter,
on a coax run from an outdoor receive-only antenna has any merit as far as
helping any emf lightning induced pulses from traveling into a house ?

Have heard about this, but it's hard to believe it would actually do
anything in practice.
But,... ?

B.


you been hanging out on 11 meters?

W_Tom wrote:
"Do you think the loop will stop what three miles of sky could not?"

Depends on what kind of loops and how many.

I`ve worked in several broadcast stations that often got struck by
lightning. Their towers were the tallest things around. None of these
stations got significant damage from lightning. In addition, none of the
station equipment powered from the mains or appliances plugged into the
mains at the station ever was damaged.

All these stations used tower lighting chokes, one coil for each tower
lighting wire including the neutral going up the tower. Three wires,
beacon, side lights, and neutral were usually accommodated with tower
lighting chokes. Their primary function is to avoid sapping any of the
r-f energy from the tower. Another benefit is that the chokes reject
lightning too. They are substantial and all turns are wound side by side
(trifiler?) around a large ceramic coil form. The wire is large enough
to easily handle the load current. I never worked at a station that used
Austin tower lighting transformers instead of chokes, but I`ve seen
enough of them to suppose they must isolate about as well as chokes do.
One station I worked in had an FM antenna atop one if its AM broadcast
towers. Its FM coax was coiled at ground level to isolate the AM r-f and
it rejected lightning too. So, if you have enough of the right turns the
choke does effectively reject lightning. Inductance is proportional to
the size of the coil.

Best regards, Richard Harrison, KB5WZI

The OP asked:
Anyone have any thoughts on (hopefully not experiences)
whether putting a loop of, e.g. 1 foot in diameter, on a coax
run from an outdoor receive-only antenna

One turn of coax is all but not a choke. Then the loop is not
located after a better path to earth. It is just a coax loop 1 foot
diameter that will somehow stop lightning - without some other path for
lightning to seek earth. Somehow it will block lightning and while not
impeding radio reception. How many henries stops - not diverts - stops
lightning?

Richard Harrison has previously described this choke as part of a
system where lightning also has a conductive path to earth. Only with
earthing is lightning further discouraged - diverted - by a choke.

Choke can only discourage lightning when lightning has a
significantly more conductive path to earth elsewhere. A 1 foot
diameter loop of coax does not even begin to accomplish what that choke
would, nor is it defined as part of a system that includes earthing.
Just some of maybe five reasons why that single coax loop does nothing
useful.

A coax loop is really not a choke. A choke by itself does not even
stop what three miles of sky could not. But a choke can be part of a
system that diverts lightning to some other earthing path. Without
earth ground, even a choke would not be very effective. And a one loop
of coax does not even perform as a choke would. So many reasons why
that coax loops does nothing effective.

Then the numbers. How many henries does a single 1 foot loop of coax
cable create? Ballpark - maybe 1 microhenry. How does a microhenry
stop or block lightning? Would inductance existing in an uncoiled coax
wire actually do more to stop lightning? A significant difference
exists between stopping and diverting.

Richard Harrison wrote:
w_tom wrote:
"Do you think the loop will stop what three miles of sky could not?"

Depends on what kind of loops and how many.

I`ve worked in several broadcast stations that often got struck by
lightning. Their towers were the tallest things around. None of these
stations got significant damage from lightning. In addition, none of the
station equipment powered from the mains or appliances plugged into the
mains at the station ever was damaged.

All these stations used tower lighting chokes, one coil for each tower
lighting wire including the neutral going up the tower. Three wires,
beacon, side lights, and neutral were usually accommodated with tower
lighting chokes. Their primary function is to avoid sapping any of the
r-f energy from the tower. Another benefit is that the chokes reject
lightning too. They are substantial and all turns are wound side by side
(trifiler?) around a large ceramic coil form. The wire is large enough
to easily handle the load current. I never worked at a station that used
Austin tower lighting transformers instead of chokes, but I`ve seen
enough of them to suppose they must isolate about as well as chokes do.
One station I worked in had an FM antenna atop one if its AM broadcast
towers. Its FM coax was coiled at ground level to isolate the AM r-f and
it rejected lightning too. So, if you have enough of the right turns the
choke does effectively reject lightning. Inductance is proportional to
the size of the coil.

Best regards, Richard Harrison, KB5WZI

stananger wrote:

Robert11 wrote:
Anyone have any thoughts on (hopefully not experiences) whether putting a
loop of, e.g. 1 foot in diameter,
on a coax run from an outdoor receive-only antenna has any merit as far as
helping any emf lightning induced pulses from traveling into a house ?

you been hanging out on 11 meters?

Reminds me of what I once told my secretary back in the 70's.
Our lab soldering irons were simple AC devices with standard
AC cords attached. We tied a half-hitch knot in them and used
that loop to hang them on nails on the wall. I was at the
bench one day and my secretary asked me what the knot was for.
I told her that by tightening the knot, I could regulate the
flow of electrons and thus control the temperature of the
soldering iron. Later that night, over drinks at Charlie
Brown's, she and I had a good laugh about that.
--
73, Cecil http://www.qsl.net/w5dxp

W_Tom wrote:
"How does a microhenry stop or divert lightning?"

Alone, not effectively. I think "driploops" are almost usless in
lightning protection.

W_Tom is right. You need to make a path unattractive to protect and
divert the lightning to an easier path to earth.

Best regards, Richard Harrison, KB5WZI

On Sun, 12 Mar 2006 10:59:56 -0500, "Robert11"
wrote:

Hello:

Anyone have any thoughts on (hopefully not experiences) whether putting a
loop of, e.g. 1 foot in diameter,
on a coax run from an outdoor receive-only antenna has any merit as far as
helping any emf lightning induced pulses from traveling into a house ?

Have heard about this, but it's hard to believe it would actually do
anything in practice.
But,... ?

Your station can be thought of as a cluster of "black boxes" with
interfaces (eg power, audio in, rx RF in, control, etc) that are
suceptible to damage if large voltages are impressed across those
interfaces.

Hardening a station against lightning usually involves minimising the
voltage impressed across those interfaces in the event of lightning,
and two main approaches are followed (usually together):
1. - reducing the current that enters the station in a strike; and
2. - reducing the voltage drop in conductors within the station that
would cause high voltages across interfaces.

Item 1 is usually done by diverting the bulk of the lightning current
via an alternate path to ground. This means shunting the current
through a low impedance path to ground before it enters the station.
Series impedance on the path to the station may assist in increasing
the portion of the strike current that flows by the alternate shunt
path to ground, but series impedance without the upstream shunt path
is not likely to have much effect. The series impedance you propose is
very small, so its effect will be quite limited.

Item 2. is usually addressed by the design of the earthing system and
equipotential bonding (eg single point earthing).

In summary, a one turn loop in the coax alone is not going to provide
a significant improvement in lightning protection in a station that is
not otherwise hardened against lightning or EMP.

Owen
--

I wouldn't think anything but extremely good grounding
at the antenna will do much.

Long ago, when I lived on the west central coast of
Florida (lightning alley), I had a 6-meter repeater on
a tall building. The transmit and receive antennas were
at diagonal corners of the building (no duplexer).
We got a direct hit on BOTH antennas. The damage
was something to see. Antennas had no damage except
some scorch marks, but the coax was another matter.
There would be 2-3' of coax, then 2-3' of nothing but
scorched roofing. This repeated across the entire 150' or
so length of the coax! A whole bunch of RG-8 simply
vaporized.

Steve