David Robbins wrote:

"Andy Cowley" wrote in message
...
CW wrote:

Effective lightning protection can be done in the amatuer station for a
reasonable cost. Most though, don't do so.
"Andy Cowley" wrote in message
...

As I understand it, there is nothing that can work if
a direct lightening strike occurs.

How? How do you deal with thousands of amps? It's for certain sure that
a simple spark gap will be blown to kingdom come in the first millisecond,
so what happens in the next millisecond? and the one after...........

I think your method must be untried, untested and 'whistling in the dark'.

Andy, M1EBV

lightning doesn't go on for milliseconds, 50 micro-seconds is a relatively
long stroke. 30kA can go through a 12ga copper wire with no damage for
10-20 microseconds. in most cases there will actually be very little
voltage between wires of a coax or twin lead just because their insulation
will break down or the feedpoint of the antenna will arc over... both are
naturally occuring spark gaps that actually work very well to protect
equipment from direct strikes. assuming of course the tower and feedline
have good grounds. where people have problems is they don't ground the
shield of the coax to a single point ground along with the power lines, so
they get differential voltages between grounds that has no place to go but
through the equipment. properly grounded installations with relatively
small arresters to limit voltage on the center conductor of the coax
relative to the shield are very effective. for tube type receivers a simple
spark gap is adequate, for transistorized stuff you may need lower voltage
protection and should probably get something commercially made for the job.

I had not realised that the current was so 'spikey' I was aware that the
duration of a stroke, including restrikes, was of the order of a second
for large strikes.

I found this info:
0.2 MA for 200 uS, then ~10 kA for another 200 uS, then 300-500 A for ~0.75
seconds. This followed by an average of 3 to 4 (max 26) restrikes at 0.1 MA
(possibly decaying to 25 kA) for 200 uS for a big stroke.

There is a MIL standard for this - MIL-STD-464.

If your Coax breaks down then you have a PD in the tens of kV range for
common coax and arc over in solid dielectric is permanently damaging.

Sorry if I mislead anyone but we don't really suffer badly from
lightning in G-land.

Here are some interesting links.

http://www.weighing-systems.com/Tech...Lightning1.pdf
http://www.lightningsafety.com/nlsi_lhm/NFP_780.html
http://www.mil-std-464.com/
http://www.kolacki.com/MIL-STD-464.htm

I'm a little wiser now. Thanks

vy 73

Andy, M1EBV

"Andy Cowley" wrote Here are some interesting
links.
http://www.weighing-systems.com/Tech...Lightning1.pdf
http://www.lightningsafety.com/nlsi_lhm/NFP_780.html
http://www.kolacki.com/MIL-STD-464.htm

Excellent reading, thanks. And thanks to all who contributed. In all these
informative discussions, the precautions seem to be centered only around
towers. My HF antennas consist of 3 long wires and 1 dipole suspended from
and between pine trees, all some 80' in the air. Of course disconnecting
constantly in thunderstorm season works, but should the feedlines all be
connected to a ground system outside at time of disconnect? Is grounding a
dipole for instance just guaranteeing a fry job when there might have been
only dielectric-puncture? The latter is certainly an easer repair. I would
think grounding might help to disintegrate the Balun also - but you guys are
clearly the experts so I look forward to your advice.

As far as rooftop antennas go, I now plan a much better down conductor
system than the rado shack aluminum ground wires that probably melt just a
wee bit slower than solder ;-)

Jack
Virginia Beach

On Wed, 17 Dec 2003 00:05:58 -0500, "Jack Painter"
wrote:

"Andy Cowley" wrote Here are some interesting
links.
http://www.weighing-systems.com/Tech...Lightning1.pdf
http://www.lightningsafety.com/nlsi_lhm/NFP_780.html
http://www.kolacki.com/MIL-STD-464.htm

Excellent reading, thanks. And thanks to all who contributed. In all these
informative discussions, the precautions seem to be centered only around
towers. My HF antennas consist of 3 long wires and 1 dipole suspended from
and between pine trees, all some 80' in the air. Of course disconnecting
constantly in thunderstorm season works, but should the feedlines all be
connected to a ground system outside at time of disconnect? Is grounding a
dipole for instance just guaranteeing a fry job when there might have been
only dielectric-puncture? The latter is certainly an easer repair. I would
think grounding might help to disintegrate the Balun also - but you guys are
clearly the experts so I look forward to your advice.

As far as rooftop antennas go, I now plan a much better down conductor
system than the rado shack aluminum ground wires that probably melt just a
wee bit slower than solder ;-)

Although some have already addressed part of the issue with wire
antennas, I'll try to elaborate a bit without repeating...and will
probably fail...but...

Two things about ungrounded wire antennas and ungrounded verticals.
Static electricity (precipitation static) and lightening strikes
(nearby and direct hits)

BE it rain of snow and snow is particularly bad, just the
precipitation and build many thousands of volts on an antenna.
Some years back...welllll...actually quite a few (back in 1966) I was
in the process of living in a mobile home while building a new home.

I had a 40 meter quarter was vertical set up about 100 feet from the
trailer. The station was used on the kitchen counter and stored in a
broom closet.

One evening as we st there watching television I heard a popping
noise. It was pretty loud. A bit of searching showed the noise to be
coming from the closet. When I opened the door I was greeted by a
blue white flash accompanied by a loud "pop". The static was arcing
across the PL259 with enough current that the arc was extending a good
half to one inch out from the connector and it put any ignition I've
ever used to shame. That includes some pretty strong magnetos.

To top it off the thing was flashing every few seconds.
Now this was one of those things where the choke across the coax
connector would have bled off the charge big as it was. A lightening
arrestor (spark gap) would have kept the voltage down, but most likely
would not have protected a receiver input without a choke across the
connection.

Nearby lightening strikes do something similar for ungrounded antennas
although they also induce a current in grounded ones as well.

Now we are getting into the realm where the choke across the terminals
may not be enough to protect the rig and I'm assuming the rig is
properly grounded. That a protective device across the input will
protect the rig is some what problematic. It just depends on the
strength of the induced voltage and current. OTOH, some protection is
better than no protection.

Now as to direct hits to wire antennas and ungrounded verticals.
There are precautions to take such as cable routing and grounding of
the shield at the base of the antenna and prior to entering the
house/ham shack, but again these come with no guarantee.

*Generally* installations using a few wire antennas and ungrounded
verticals are configured in such a way that the antennas can be
disconnected. With these stations I would always disconnect and
ground the coax. Then unplug the AC mains from the station.

I would resort to one other step which is to ground any other cables
and even rotor cables if any exist.

The easiest way to ground a group of coax cables is to take three
aluminum plates (or copper). clamp the plates together and drill
them to take bulkhead connectors (the clamping only assures the
connectors will properly align after the thing is assembled.) One
plate is for the connectors going into the house, one is for the coax
cable connectors from the antennas and the third is for the grounding.

I should really make one of these up and shoot some photos to show how
well they can work.

At any rate, The plates can be configured several ways as long as it
allows the user to unplug the cables from the antennas from the house
and plug it into the grounding plate. The slip on PL-259 equivalents
work very well for this.

The same thing can be done one cable at a time, but I find that with a
rapidly approaching storm I'd not want to be spending time
disconnecting one cable at a time and then reconnecting said cables to
a grounded set of connectors.

I'd go so far as to attach a pair of rack panel handles to the one
plate to allow for easy unplugging and reinserting it into the
grounding receptacle. I's also ground the metal plate that holds the
feed throughs into the house and install PolyPhasers for each line.
it and the grounding receptacle both need to be thoroughly grounded
and make no sudden or sharp turns in the cables.

Another tract would be to have all cables enter the house through a
well grounded panel using bulkhead connectors and PolyPhaser.
By well grounded I don't mean tieing the plate to a single ground rod
with a #8 wire, but rather bonding the plate to at least two 8' ground
rods and connecting those to a grounding network. Even then in this
kind of installation I'd consider disconnecting the cables and
grounding them.

BTW, ground rods can be easy to install if you don't have rocky soils,
by using a hydraulic drill. (Another thing I need to write up and
photograph). Actually I have the photos. I just need to write up how
to make and use one. Maybe soon.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair?)
www.rogerhalstead.com
Return address modified due to dumb virus checkers


Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair?)
www.rogerhalstead.com
Return address modified due to dumb virus checkers
Jack
Virginia Beach

Sorry if this doubles, it didn't show up after almost an hour the 1st time:

"Andy Cowley" wrote Here are some interesting
links.
http://www.weighing-systems.com/Tech...Lightning1.pdf
http://www.lightningsafety.com/nlsi_lhm/NFP_780.html
http://www.kolacki.com/MIL-STD-464.htm

Excellent reading, thanks. And thanks to all who contributed. In all these
informative discussions, the precautions seem to be centered only around
towers. My HF antennas consist of 3 long wires and 1 dipole suspended from
and between pine trees, all some 80' in the air. Of course disconnecting
constantly in thunderstorm season works, but should the feedlines all be
connected to a ground system outside at time of disconnect? Is grounding a
dipole for instance just guaranteeing a fry job when there might have been
only dielectric-puncture? The latter is certainly an easer repair. I would
think grounding might help to disintegrate the Balun also - but you guys are
clearly the experts so I look forward to your advice.

As far as rooftop antennas go, I now plan a much better down conductor
system than the rado shack aluminum ground wires that probably melt just a
wee bit slower than solder ;-)

Jack
Virginia Beach

Jack wrote:
"My HF antennas consist of 3 long wires and 1 dipole suspended from and
between pine trees, all some 80 feet in the air."

I worked for years in a shortwave broadcasting plant. One building
contained 12 transmitters, 8ea. 50KW, and 4ea 100 KW, plus several lower
powered transmitters.

We had dozens of antennas which included several curtain antennas for
each of 3 frequency ranges, low, medium, and high. The curtain array
requires 4 towers for support. It has 4 dipoles in a radiating plane,
all driven in-phase. It has 4 reflecting dipoles in a parallel plane
directly behind the radiators. Height of the drive point of the array,
its midpoint, was about 1-WL, or about 165 feet as I recall. That makes
the tower height well over 300 ffeet at 6 MHz. For economy, the curtains
for a particular frequency range are hung from a double row of towers
which support curtains on both sides.

The transmission lines from nearly all antennas, curtains, rhombics, or
whatever, are brought into a cross-bar switching area so that any
transmitter can be connected to any antenna.

Transmission lines are all open-wire spaced at about 15 inches, or more,
for a 600-ohm impedance if memory serves. Where the antenna line enters
the switching area, boomerang arc gaps provide a flashover-point
opportunity, line-to-line, and line to ground.This works.

Open wires, like coax, have a high common-mode impedance. This tends to
make a gap more conducive than the transmission line. Use large ground
wires to keep inductance and resistance low. This keeps voltage drop low
and handles the kiloamps for the short period of the surge.

Best regards, Richard Harrison, KB5WZI