I HAD a tower up on the north side of the house for about 15 years, it
, top out at about 100feet. I built a 'tilt over' that is 52 feet tall
with a mast of about 25, = 77 give or take. been 'up' about 1.5 years
and lighting has 'hit' it twice. One was higher, never hit, this one
is lower, hit is there anything I can do to 'fix this'? Lost
antennas, need to do 'something'. thanks in advance. cl
73

"CIL" wrote in message
...
I HAD a tower up on the north side of the house for about 15 years, it
, top out at about 100feet. I built a 'tilt over' that is 52 feet tall
with a mast of about 25, = 77 give or take. been 'up' about 1.5 years
and lighting has 'hit' it twice. One was higher, never hit, this one
is lower, hit is there anything I can do to 'fix this'? Lost
antennas, need to do 'something'. thanks in advance. cl
73

Lightning is Female. 20 million volts & 100 thousand Amps will do as it damm
well pleases!

Hi CIL

Where lightning will hit, if it hits, can almost be calculated with a
fair degree of accuracy.

We did a small project in a college class and made a scale model of a
small city. We knew from past history some of the structures that
were hit and where. From this knowledge we made balls of certain
sizes so they would touch if sitting on the ground the place that was
actually hit. We ended up with only 4 such balls, each a similar size
factor to the others.

On our scale model town we outlined in red lines the most likely
places lightning would hit if it did hit in that area.

Every strike since that time, up until the project was abandoned, has
hit somewhere on the red lines we have drawn.
One such line was on a small single story U-Stor-It building between
two very tall radio station towers, that was assumed to be lightning
proof due to it's location. It was hit and hit hard when neither
tower was hit. We also indicated that if those towers were ever hit,
the location on those towers where the lightning would hit them.
Neither location was near the top either. Two small strikes to one of
the towers were both within 1 foot of where our red line was indicated
on the scale model.

We were so successful in our project we thought for sure some agency
would pick it up and make use of it. But long after I was at school
there, the project was abandoned with something like a record of 94%
accuracy on pinpointing areas where lightning can hit.

TTUL
Gary

CIL wrote:
"---is there anything I can do to fix this?"

Broadcasters have towers that are often struck by lightning. AM towers
sit on base insulators which makes them vulnerable to static buildup
too. Wind carries a static charge which falls out on the tower even when
no lightning is present.

The shape and positions of charged clouds are constantly changing, so
lightning strikes can come from anywhere.

The broadcaster starts his lightning protection at the tower top with a
small lightning rod extending above and beyond the beacon to take the
hit and avoid expensive repairs at the tower top.

Tower guy insulators are doubled and tripled where they connect to the
tower so that static breakdown occurs to the earth instead of at the
tower.

An air gap is installed across the base insulator to bypass a lightning
hit to earth. Often a turn or two is made in the feed to the tower. This
discourages lightning on the feedline and encourages breakdown of the
gap across the insulator.

A static drain choke is often added if needed to provide a d-c path
between the tower and the earth. It is used to bleed off charge which
might build to dangerous levels.

"Lightning elimination" is a name given to mounting a large number of
sharp points around a protected area in an attempt to drain the
atmosphere of charge. The reviews are mixed.

I`ve worked in several broadcast stations hit by lightning nearly every
time a charged cloud passed by. None ever caused significant damage. Al
of the stations had lighted towers but their tower lighting chokes kept
lightning off the a-c power source.

Berst regards, Richard Harrison, KB5WZI

I HAD a tower up on the north side of the house for about 15 years, it
, top out at about 100feet. I built a 'tilt over' that is 52 feet tall
with a mast of about 25, = 77 give or take. been 'up' about 1.5 years
and lighting has 'hit' it twice. One was higher, never hit, this one
is lower, hit is there anything I can do to 'fix this'? Lost
antennas, need to do 'something'. thanks in advance. cl
73



Can you describe how each tower was configured at the top and how it was
grounded?
What is important to know if the top ended up with sharp point (mast, VHF
vertical antenna, etc.) or Yagi type antenna, like tribander etc. without
anything pointy protruding above.

Yuri, K3BU

I would suspect a poor grounding system on the tower. If the ground is a
rod driven into the Earth, then the impedance needs to be as low as
possible. Once the ground system takes a surge, glass crystalls will form
in the dirt on and around the rod. The impedance then climbs and the number
of strikes to the tower increase. The amount of impedance in your ground
network determines the amount of static charge that can build on the tower
and how fast the charge can bleed. The formula for calculating the bleed
rate is 5 times (Resistance times Capacitance). The resistance is the
ground impedance and the capacitance is the amount of surface area of the
tower relative to the air flow over it (think of two plates on a capacitor
with a dielectric between them). Any charge above that of the Earth makes
that point more likely to get hit by lightning. The tower is only one item
to concern yourself about because a floating antenna can be just as bad.
Ground everything on the tower during a storm if it is not in operation such
as a repeater. Surge arrestors on the antenna feeds then become imparative
for repeater installations. A very large grounding system is required to
mitigate the potential for lightning strikes on a tower. If a strike does
occur, then the grounding structure needs to be able to dissipate the charge
back into the Earth very quickly or the ground will be lost until the
voltage on the ground falls. Again, R x C for the Earth.

Good Luck,
Frank N1SIF


wrote in message
...
I HAD a tower up on the north side of the house for about 15 years, it
, top out at about 100feet. I built a 'tilt over' that is 52 feet tall
with a mast of about 25, = 77 give or take. been 'up' about 1.5 years
and lighting has 'hit' it twice. One was higher, never hit, this one
is lower, hit is there anything I can do to 'fix this'? Lost
antennas, need to do 'something'. thanks in advance. cl
73

On 19 Oct 2004 09:32:10 EDT, am (Gary V.
Deutschmann, Sr.) wrote:
It was hit and hit hard when neither tower was hit.

Hi Gary,

If lightning strikes a tower, and it doesn't burn down, did any power
dissipate? (Apologies to the trees falling in the forest cliche.)

How did your team "know" what was struck?

73's
Richard Clark, KB7QHC

I would suspect a poor grounding system on the tower. If the ground is a
rod driven into the Earth, then the impedance needs to be as low as
possible. Once the ground system takes a surge, glass
(( (crystalls?)))
will formin the dirt on and around the rod. The impedance then climbs
and the numberof strikes to the tower increase. The amount of
impedance in your groundnetwork determines the amount of static charge
that can build on the towerand how fast the charge can bleed.

(((The tower sites are only about 100 feet apart, ground substance is
the same, clay/rocks, 1st foot then clay…… The first tower ground, is
a 4 ft hole, with ¾" rebar then driven deeper,1.5ft, w/ horz bars 1ft
on center from bottom of hole to top, where a ¾ steel plate was welded
to vertical bars, and to the plate, strong hinge plate connected to 25
rohn tower. The 'other site', is two 4" pipe, 5ft, in the ground, and
welded to fence. Fence is 2"2/8 upset tubing that goes around
property/everything welded. ((fence is 5 foot tall) and as stated part
of the 'gournding system',,,? The first 'site' was not connected to
the primenter fence,,problem???)) If you are familur with the ''bird
tilting over and drinking from the cup", you can picture in your minds
eye, my 'tilting tower'. It is about 75ft tall, with a uhf/vhf duel
band at top of mast, four ft. below that is a two meter horz omni
ground plane.)))

Can you describe how each tower was configured at the top and how it
was grounded? What is important to know if the top ended up with sharp
point (mast, VHF vertical antenna, etc.) or Yagi type antenna, like
tribander etc. without anything pointy protruding above.
Yuri, K3BU

((( Both towers carried almost the same 'items', vhf/uhf , and 4 ft
below that, clover leaf horz ground plane.)))


but their tower lighting chokes kept
lightning off the a-c power source.

((( What do you call these chokes, I know I have read about, but at
the moment I am blank.)))


The broadcaster starts his lightning protection at the tower top with
a small lightning rod extending above and beyond the beacon to take
the hit and avoid expensive repairs at the tower top.


((( Is this something like the antennas I have seen that have a
'center core' copper rod???)))

Tower guy insulators are doubled and tripled where they connect to the
tower so that static breakdown occurs to the earth instead of at the
tower.


((( Where do I 'see/read' about this??)))


One such line was on a small single story U-Stor-It building between
two very tall radio station towers, that was assumed to be lightning
proof due to it's location. It was hit and hit hard when neither
tower was hit

……"How did your team "know" what was struck?

"""…my question was and is,,,, why?




(((((((((((((((((((This statement is the one that makes the
most sense to me)))))))))))))))

Lightning is Female. 20 million volts & 100 thousand Amps will do as
it damm
well pleases!

((((Last, but not least,,,,,,, thank you, WILL implement input,
cl&73))))

Sorry for the spelling error crystalls should be crystals. When lightning
hits the Earth, the heat it generates is enough to make glass which is an
insulator. The ground rod becomes isolated from the Earth. If you spread
out the contact area with the Earth as with the fence around the perimeter
of the property, then the energy is not concentrated to one spot. The over
all impedance is also much lower. I would install a ring grounding system
around the tower. A 32ft. diameter ring would do nicely in a clay/rocky
soil. Place 8ft. ground rods in the ground every 16 ft along the 32 ft.
diameter circle (approx. 6 rods). Each rod is then connected to the tower
base with a multistrand 00 copper wire and a ring of 00 copper to connect
each rod together. The connections should be cad welded or at least treated
with a deoxit coating to prevent corrosion. I have had excellent luck with
this approach, no lightning hits and my tower sits up at 870ft. ASL or 650
ft. above average terrain. Note: the tower has a strike counter hooked up
to it so I know no hits have happened. Go to this link to read more
http://www.polyphaser.com/ppc_pen_home.asp .

Frank N1SIF

"CIL" wrote in message
...

I would suspect a poor grounding system on the tower. If the ground is a
rod driven into the Earth, then the impedance needs to be as low as
possible. Once the ground system takes a surge, glass
(( (crystalls?)))
will formin the dirt on and around the rod. The impedance then climbs
and the numberof strikes to the tower increase. The amount of
impedance in your groundnetwork determines the amount of static charge
that can build on the towerand how fast the charge can bleed.

(((The tower sites are only about 100 feet apart, ground substance is
the same, clay/rocks, 1st foot then clay.. The first tower ground, is
a 4 ft hole, with ¾" rebar then driven deeper,1.5ft, w/ horz bars 1ft
on center from bottom of hole to top, where a ¾ steel plate was welded
to vertical bars, and to the plate, strong hinge plate connected to 25
rohn tower. The 'other site', is two 4" pipe, 5ft, in the ground, and
welded to fence. Fence is 2"2/8 upset tubing that goes around
property/everything welded. ((fence is 5 foot tall) and as stated part
of the 'gournding system',,,? The first 'site' was not connected to
the primenter fence,,problem???)) If you are familur with the ''bird
tilting over and drinking from the cup", you can picture in your minds
eye, my 'tilting tower'. It is about 75ft tall, with a uhf/vhf duel
band at top of mast, four ft. below that is a two meter horz omni
ground plane.)))

Can you describe how each tower was configured at the top and how it
was grounded? What is important to know if the top ended up with sharp
point (mast, VHF vertical antenna, etc.) or Yagi type antenna, like
tribander etc. without anything pointy protruding above.
Yuri, K3BU

((( Both towers carried almost the same 'items', vhf/uhf , and 4 ft
below that, clover leaf horz ground plane.)))


but their tower lighting chokes kept
lightning off the a-c power source.

((( What do you call these chokes, I know I have read about, but at
the moment I am blank.)))


The broadcaster starts his lightning protection at the tower top with
a small lightning rod extending above and beyond the beacon to take
the hit and avoid expensive repairs at the tower top.


((( Is this something like the antennas I have seen that have a
'center core' copper rod???)))

Tower guy insulators are doubled and tripled where they connect to the
tower so that static breakdown occurs to the earth instead of at the
tower.


((( Where do I 'see/read' about this??)))


One such line was on a small single story U-Stor-It building between
two very tall radio station towers, that was assumed to be lightning
proof due to it's location. It was hit and hit hard when neither
tower was hit

.."How did your team "know" what was struck?

""".my question was and is,,,, why?




(((((((((((((((((((This statement is the one that makes the
most sense to me)))))))))))))))

Lightning is Female. 20 million volts & 100 thousand Amps will do as
it damm
well pleases!

((((Last, but not least,,,,,,, thank you, WILL implement input,
cl&73))))

The broadcaster starts his lightning protection at the tower top with a
small lightning rod extending above and beyond the beacon to take the
hit and avoid expensive repairs at the tower top.

An air gap is installed across the base insulator to bypass a lightning
hit to earth. Often a turn or two is made in the feed to the tower. This
discourages lightning on the feedline and encourages breakdown of the
gap across the insulator.

We used to call em "johnny balls" at the base of the AM towers. One
station I was chief engineer of was hit constantly without any damage. NOT
fun to be in the transmitter room when lightning was hitting tho! I felt
like Dr. Frankenstein in my lab during the storms, when I had to go into the
xmitter room.

A static drain choke is often added if needed to provide a d-c path
between the tower and the earth. It is used to bleed off charge which
might build to dangerous levels.

A static drain choke is an EXCELLENT idea, I have used it on my ham
antennas in the past.

73
WB7FFI