Jerry wrote:
"I`m having trouble visualizing doing this grounding without affecting
antenna performance."

Shortwave radio antennas I`ve used were all made from Copperweld wire to
withstand lightning and weather. Also, copper wire can stretch and
fatigue. Copperweld`s steel core prevents this.

Signal Corps rhombic kits use (3) No.12 Copperweld wires twisted
together to make a cable used for antenna and transmission line. A
special Wihd Turbine Company insulator is included to space the line for
600-ohm impedance. These bolt atop short tower secttons used as
transmission line supports. Unless military surplus is available,
substitutions would be necessary. But, open-wire line is rugged and
withstands the challenges.

Pick a place outside your shack to drive ground rods to serve as a
ground bed for your antenna system to dump your lightning strikes to.
Place the rods at about the length of your ground rods away from each
other. The more rods, the better. Cost will prevent too many rods.

Interconnect all the ground rods and connect this ground system to your
electric service ground system. It`s the law in most jurisdictions.

Run your open-wire line from your antenna to a point above your ground
bed. You need arc-gaps between each transmission line cable and the
earth. Form copper vees to make arc-gaps. The vertex of one Vee is going
to face another to make a pair. Connect one Vee firectly to the earth.
Connect the other of the pair directly to the transmission line cable.
Do the sane for the other transmission line cable.

When the gaps are completed, adjust the space between them until they
flash over from your transmitter power, then back off until they just
don`t flash over. You should now be ready for lightning on the
transmission line. Connect your ladder line, twin lead, coax or whatever
you will use to complete the connection to your radio to your open-wire
line here above your ground bed.

Isolate the radio from the powerline through a brute-force filter with
MOV`s added for lightning suppression.

Audio, control, and any other wires connected to the radio also need
filters with MOV`s added but the current carrying capacity of the
filters can be lower than that required for the power wires in most
cases. A common ground point is required for all these filters.

If you don`t use coax somewhere between your radio and antenna, you will
lose some of the protection it provides. Its close internal spacing
couples its conductors tightly. We found even solid-state receiver
front-ends weren`t endangered by lightning because of grounded antennas
and the coax. It would flash over before it let lightning through.

Best regards, Richard Harrison, KB5WZI

Lightning attaching to a wire will instantly vaporize the wire.

Not always. Depends on the resistance of the
ground connection. If the resistance is low, a # 6 wire
can take a direct strike, and barely warm up at all.
Even a #10 is ok, if the connection to ground is good.
You might see a tiny pit where the point of contact
was. But a high resistance ground connection, and
yes, it will fry. I've taken two direct strikes on my mast,
and can see no damage at all. You can see a tiny pit
where the strike connected to the mast top, but even
it could be easily missed. According to my experience,
I think the quality of the ground connection also effects
the sound of the strike, not counting the sonic boom overhead.
A strike hitting my mast is very quiet. It's like a light bulb
being thrown on the ground, "plink", and you hear the overhead
sonic boom. But when it hits the trees with their high resistance
to ground, the strike is earsplitting. "CRACK-BAAAAAMMMM".
Thats the "local" sound, not the sonic boom, although they mix.
I don't operate during storms, and doubt I would, even if I could.
I unplug the antennas, and ground them out to ground outside
the window. If I *had* to operate during a storm, I would use my
attic dipole. It's the least likely to take a hit, in general.
MK

Richard Harrison wrote:
Chuck wrote:
"We all know of cases where electronics gets zapped but Jerry is
concerned about his house."

I`ve worked in many protected structures struck repeatedly by lightning
to their air terminals, rods, and towersm resulting in not one scintilla
of damage to occupants or equipment.

Transportation vehicles are struck by lightning every day and seldom
experience anything inside. An open convertible is not safe in a
lightning strike however.

The occasional stain on the seat tho' 8^)

- Mike KB3EIA -

Hal:

Actually, I have used the coherer on receiving antennas, in a couple
of lightning storms it has indeed shorted to ground and needed to be
shaken to restore the signals from the antenna (NOTHING near a direct
hit and this is central cal, not much lightning and of little
significance.)

Presently, I use MOV's... at best, -=maybe=-, better than nothing...

John

"Hal Rosser" wrote in message
.. .
Interesting, You made me look. (made me Look up coherer, that is).
An invention of Sir Oliver Lodge for detecting rf.
Your idea of using it as a lightning protection device seems to be a
misapplication.
But like I said, until now, I never heard of it.

"John Smith" wrote in message
...
For a receiving antenna, a coherer provides excellent lightning
protection.

Unfortuantly, on a transmitting antenna, the rf would immediately
make
the coherer conductive and a direct short to ground (perhaps very
low
QRP power could be used?)

One can easily be construted with a bottle filled with metal
filings,
two bare wires are inserted into the filings (not touching and
seperated by a substantial amount of the filings), one wire goes to
a
good earth ground, the other to the antenna.

If the coherer shorts to ground it only needs to be shaken to reset
(I
would suspect in a real lightning strike the metal would be fused,
quite possibly even vaporized.)

John

"Jerseyj" wrote in message
...
Hi all,
For years I lived in an apartment and just had antenna's in the
attic ,
but now having moved to a house in a few months I'll be putting
up a
10-160 wire type antenna in my trees. Given the recent spate of
serious
thunderstorms, and the accompanying lightning, I'm a bit
concerned
about
properly grouding the antenna so that I don't fry the house
*smile*.
I
know about some articles on the ARRL site, but was wondering if
anyone
else had some ideas or pointers on how to practically do this ?

Jerry

Jerry - I'll second that idea. I use banana plugs on the balanced feedline
from my inverted V wire antenna. If the weather looks like it might get
bad, I just unplug it from my transmatch and throw it out the window (the
feedline - not the transmatch!)

Warren KC8YKQ


Bob Miller wrote in
news
I have a 10-80 wire connected between 3 trees. It's fed with
ladderline. Lightning protection is simple -- with banana plugs and
jacks, I can unplug the ladderline just outside the window whenever it
looks rainy.