Hello:

Very interesting comments on my question of a few days ago re lightning
arrestors.
Thank you all for trying to educate me on this subject; really find it
confusing.
Thread is a bit buried by now, so thought I'd start another one.

I fully understand that the best approach is to (also) just disconnect
everything.

But if not around, here's what I don't understand and concerns me.

Assuming a "nearby" strike, and a subsequent emp pulse that's picked up by a
receive only antenna
wire strung outside:

No matter how quickly an arrestor's gas tube fires, and diverts the pulse to
a good RF ground, the fact that it takes
a few hundred volt threshold to fire makes "any" gas tube type of arrestor
almost worthless re the protection of a receiver whose front end certainly
won't take a few hundred volts, even for u-seconds, probably.

Do you agree with this statement, or am I missing something ?

Thanks,
Bob

Have you never static shocked a radio antenna? Why was that radio
not damaged by up to 18,000 volts? Radios have internal protection
which is why those 10,000+ volts did not damage. Parameters are
voltage ... and time.

Reason why a well earthed protection 'system' protect electronics
even from direct strikes includes internal electronics protection, fast
response of all protectors, and how well a protection system is
earthed. With properly earthed protection, then protection internal to
electronics is not overwhelmed; damage does not occur.

Disconnecting without earthing is not a best protection method. Ham
radio operators in the early days would disconnect an antenna lead, put
that connector inside a mason jar, and still suffer damage. When that
antenna lead was earthed, then damage stopped. Disconnecting - trying
to stop a destructive transient - works when the transient has a better
path to earth. Most essential is to provide a better path to earth.
Disconnecting would only enhance a good protection system. But
disconnecting without a non-destructive path to earth has been
demonstrated not sufficient. Idea is to keep protection inside that
electronics from not being overwhelmed even by a direct lightning
strike.

What was more than sufficient to protect telephone switching stations
- connected to overhead wires everywhere in town? Gas discharge tubes.
We have since obsoleted that technology (depending on other
parameters) twice over. But response of a gas discharge tube is not
'too slow'. Too often, people will blame 'slow GDT' for damage when
they failed to confirm the most critical component in a protection
system - earth ground and connections to that earthing 'system'.

Robert11 wrote:
Very interesting comments on my question of a few days ago re lightning
arrestors.
Thank you all for trying to educate me on this subject; really find it
confusing.
Thread is a bit buried by now, so thought I'd start another one.

I fully understand that the best approach is to (also) just disconnect
everything.

But if not around, here's what I don't understand and concerns me.

Assuming a "nearby" strike, and a subsequent emp pulse that's picked up by a
receive only antenna wire strung outside:

No matter how quickly an arrestor's gas tube fires, and diverts the pulse to
a good RF ground, the fact that it takes
a few hundred volt threshold to fire makes "any" gas tube type of arrestor
almost worthless re the protection of a receiver whose front end certainly
won't take a few hundred volts, even for u-seconds, probably.
...

"Robert11" wrote in message
...
Hello:

Very interesting comments on my question of a few days ago re lightning
arrestors.
Thank you all for trying to educate me on this subject; really find it
confusing.
Thread is a bit buried by now, so thought I'd start another one.

I fully understand that the best approach is to (also) just disconnect
everything.

But if not around, here's what I don't understand and concerns me.

Assuming a "nearby" strike, and a subsequent emp pulse that's picked up by
a receive only antenna
wire strung outside:

No matter how quickly an arrestor's gas tube fires, and diverts the pulse
to a good RF ground, the fact that it takes
a few hundred volt threshold to fire makes "any" gas tube type of arrestor
almost worthless re the protection of a receiver whose front end certainly
won't take a few hundred volts, even for u-seconds, probably.

Do you agree with this statement, or am I missing something ?

Thanks,
Bob


Hi Bob,
I'm Ace - WH2T.
Here's my story.
So far I have been very lucky. Neighbors closest on my north and south sides
have both been hit, BAD SEVERE strikes. We live on a hill.
I had a strike take out a cheap portable TV that was in the kitchen and it
blew a fuse in a VCR. It also came in the telephone line and blew up some FM
intercoms that were connected to the telephone line. After that happened I
had a commercial lightning arrestor installed by my electric power company
at the electric meter.

I use 2 HF antennas, a 272 ft delta loop and a 160 meter band 1/4 wave
inverted L antenna, both antennas go thru my MFJ-989C Tuner . When I am not
on the air I leave the antenna switch on the tuner in the "Dummy Load"
position. That connects a 300 watt 50 ohm resistor to the radio's antenna
jack and grounds both antennas.

The main lightning problems I have had in the 12 years at this QTH are
surges coming in the telephone line.
I noticed when I moved here that all the telephone jacks in the house were
black. I lost 9 computer modems in short order. I installed the smallest
fast blow fuses I could find in both sides of the telephone line (they are
under 100 ma) . The next time there was a nearby strike it blew both fuses
and still blew my computer modem.
After that I installed three 130 Volt MOVs outside the house in the
telephone box , one across the telephone line and one from each side of the
telephone line to ground. I also installed a very small pigtail neon lamp
between or across the 2 sides of the telephone line. It acts as a gas tube
type of arrestor, and lights when the telephone rings, or when lightning
strikes nearby; the threshold to fire is under 100 volts. I also installed a
DPDT knife switch , to break the telephone line when the computer is not
connected to the internet. No further problems. I live out in the country
dial up is all that is available here other than expensive satellite access.
Anyway , now on to your question.

I got the following Info from another ham.

From my commercial broadcast days the lightning control solution for
tall insulated base AM towers (which were always experiencing direct
lightning strikes) was to use 2 inch diameter copper balls spaced 1/4
to 1/2 inch from each other (depending on peak RF voltage present) at
the base of each tower on heavy arms as a lightning spark gap. Then
the 1/4 inch tubing feeding station RF into each tower base would be
formed into a 3 turn loop with a 12 inch diameter, with about 2 inch
spacing between each turn. I would do the same with the coax feeding
repeaters and studio-transmitter links on these towers. I never lost
any equipment using these techniques.



I realized I have to mention that I use an inductive RF coupling-
impedance transformer in my homemade transmatch in order to eliminate
a direct dc path from the ladder line to the transceiver input. I
also use high tension teflon coated wire for the primary turns in the
transformer. Lightning would be common mode on the transmission line
and therefore not inductively coupled through the transmatch. The
issue then becomes voltage breakdown between transformer primary and
secondary windings (along with minor capacitive coupling), hence the
teflon coated wire.

Concerning possible lightning on the ladder line, I use adjustable
spark gaps from each conductor to ground outside of my building.



I hope this is of some help.

Ace - www.WH2T.com

Note the voltage on that fuse. No matter how fast it is, if a
transient exceeds that voltage, then the fuse remains a conductor.
Furthermore, destructive transients occur in microseconds. That fuse
takes tens of milliseconds to open. Two reasons - both numbers - that
demonstrate why one cannot stop or block destructive transients.

Meanwhile, the phone line should already have a protector installed
for free that looks something like boxes at:
http://www.alarmsuperstore.com/bw/bw%20connectors.htm
But again, the protector is not protection. A protector is simply a
connection to earth. If that box is not properly earthed, then a
transient will seek earth ground, destructively, via household
appliances.

Most destructive transients enter on AC main seeking earth ground.
Incoming on AC electric, into telephone appliances such as portable
phone base station, fax machine, computer modem - or that intercom.
Then outgoing to earth ground via telephone line. To have damage,
first, a path to earth ground must be both incoming and outgoing
through damaged electronics. Incoming on that intercom AC electric;
outgoing via phone line. It also explains why some appliances are
damaged while others are not.

But again, what is the protection? Earth ground. Fuses, power strip
protectors, and anything else that will 'stop or absorb' a surge is
myth. Ben Franklin demonstrated the solution in 1752. Give a
transient a better (shorter, low impedance, etc) path to earth so that
it need not find a path, destructively, via electronics.

Those fuses only might blow. And if they did, maybe 300 consecutive
and separate transients could have already damaged the electronics.
More often, fuses trip due to and after damage created by a destructive
transient. If one suffers damage, one discovers why the dwelling was
not properly earthed. Why was lightning seeking earth ground inside a
building? The answer is often directly traceable to human failure.
Protection is about earthing before a transient enters the building.

Dr.Ace wrote:
Hi Bob,
I'm Ace - WH2T.
Here's my story.
So far I have been very lucky. Neighbors closest on my north and south sides
have both been hit, BAD SEVERE strikes. We live on a hill.
I had a strike take out a cheap portable TV that was in the kitchen and it
blew a fuse in a VCR. It also came in the telephone line and blew up some FM
intercoms that were connected to the telephone line. After that happened I
had a commercial lightning arrestor installed by my electric power company
at the electric meter.

I use 2 HF antennas, a 272 ft delta loop and a 160 meter band 1/4 wave
inverted L antenna, both antennas go thru my MFJ-989C Tuner . When I am not
on the air I leave the antenna switch on the tuner in the "Dummy Load"
position. That connects a 300 watt 50 ohm resistor to the radio's antenna
jack and grounds both antennas.

The main lightning problems I have had in the 12 years at this QTH are
surges coming in the telephone line.
I noticed when I moved here that all the telephone jacks in the house were
black. I lost 9 computer modems in short order. I installed the smallest
fast blow fuses I could find in both sides of the telephone line (they are
under 100 ma) . The next time there was a nearby strike it blew both fuses
and still blew my computer modem.
After that I installed three 130 Volt MOVs outside the house in the
telephone box , one across the telephone line and one from each side of the
telephone line to ground. I also installed a very small pigtail neon lamp
between or across the 2 sides of the telephone line. It acts as a gas tube
type of arrestor, and lights when the telephone rings, or when lightning
strikes nearby; the threshold to fire is under 100 volts. I also installed a
DPDT knife switch , to break the telephone line when the computer is not
connected to the internet. No further problems. I live out in the country
dial up is all that is available here other than expensive satellite access.
Anyway , now on to your question.
...

Ace, WH2T wrote:
"I realized I have to mention that I use an inductive RF coupling -
impedance transformer in my homemade transmatch in order to eliminate a
direct d-c path from the ladder line to the transceiver input."

Lightning is a threat to antennas and to items connected with them.
Static charges may build in a time of clear skies, especially ahead of a
thunderstorm. Guy-wire insulators often flashover to announce a storm
is approaching.

Radio towers in broadcast stations get lightning strikes over and over
again, but loss of equipment or even air time is minimal.

The beacon atop a tower is most exposed, but it is protected by a
vertical metal rod attached to the tower near the beacon and extending
well above it. Often this rod is an 8-ft Copperweld groundrod bolted to
the tower with its tip point skyward. Pits on the rod show it takes
hits. Beacon survival shows it does not take hits. The protection works.

Guy-wire insulators are often doubled or tripled at the tower attachment
points to discourage flashovers here.

An air gap is provided across the tower base insulator. In theory,
lightning ionizes rhe air in the gap and shunts the charge to ground
before it gets into the feeder system. Spacing is usually adjusted to
only slightly wider than the gap will breakdown on the transmitted
signal. I`ve examined many of these ball gaps and horn gaps and seen no
evidence of flashover.

To discourage lightning, a turn or two is often made in the conductor
feeding the tower. I haven`t seen pts on the balls or horn gaps
indicating that the tiny inductance added by a turn or two in the
feedwire does any good.

A static-drain choke which has a very high impedance at the operating
frequency, but has a low d-c resistance, is often connected across the
tower`s base insulator on the line side of the base impedance matching
unit. It may be placed on the tower side of the matching unit if there
is no d-c continuity through the matching unit.

All the stations I`ve worked in had an air-core 1:1 coupling transformer
in the tower matching unit. Primary and secondary share the same axis
but are seoarated by a metal rake which serves as a Faraday screen. It
is a picket fence between the coils. The tines of the rake have no
electrical connection at one end, but the backside of the rake connects
all the tines together and firmly grounds them.

The rake allows magnetic coupling between the coils but prohibits
electric field coupling between the coils. The rake is a very effective
lightning stopper. It is full of pits where lightning has struck.

Best regards, Richard Harrison, KB5WZI

When lightning directly strikes either the antenna or the dwelling,
despite all the precautions, ANYTHING can happen.

The direct strike is just as likely to be on the dwelling and its
occupants as the ordinary radio antenna.

So concentrate precautions on your house, the more valuable of your
possessions. Only then think about your inverted-L and your radio
equipment.

Just a logical way of thinking about things.

A direct strike will probably never happen anyway.
=========================================

Reg, G4FGQ wrote:
"The direct strike is just as likely to be on the dwelling and its
occcupants as the ordinary radio antennas."

True, unless the antennas are much taller than the dwelling. That was
the case of the radio stations. Occupants were safe, protected by the
tall radio towers. Just as the towertop rod protects the beacon. the
tower protects the nearby structures under it (within its "cone of
protection"). Agreed that people are more important than radios. I don`t
want to cede people or radios.

Here on the Gulfcoast of the U.S.A., the climate is semitropical and
thunderstorms are abundant. Radio towers are struck by lightning
repeatedly by nearly every passing thunderstorm and these are frequent.

Where I`ve worked, buildings on the station`s property were never
struck, nor was a serious electric surge ever transmitted into any
building other than one of the "dog houses" at the towers where it is
expected.and prepared for the stroke.

The buildings on radio station properties are protected by big lightning
rods, the towers, just as Benjamin Franklin predicted in 1735.

Best regards, Richard Harrison, KB5WZI

On Fri, 20 Jan 2006 04:58:48 -0500, "Dr.Ace"
wrote:



I use 2 HF antennas, a 272 ft delta loop and a 160 meter band 1/4 wave
inverted L antenna, both antennas go thru my MFJ-989C Tuner . When I am not
on the air I leave the antenna switch on the tuner in the "Dummy Load"
position. That connects a 300 watt 50 ohm resistor to the radio's antenna
jack and grounds both antennas.

I have the same tuner. Are the antennas really grounded when in dummy
load position? Looking at the circuit diagram, I can see the coax
braid is always grounded, and one side of the balanced line is always
grounded. But are both sides of all antennas grounded when in the
dummy load position? From what I can see, the coax center conductors,
and one side of the balanced line are left floating.

bob
k5qwg




I hope this is of some help.

Ace - www.WH2T.com