Lightning arrestors
 

Having but recently returned to the world of shortwave radio, I'm
trying to be better informed about technical and safety issues than I
was as a kid. Now a homeowner with a mortgage and a homeowner's
insurance policy, I'm worried about lightning protection. I'm
receiving only, not transmitting. I have a ground rod just outside the
window where the antenna wire enters, and I intend to disconnect the
antenna outside the house when I'm not using the shortwave. But I
want to be extra careful!

So I'm considering some options. Which make sense to you seasoned
hams? Do any of these leave me open to my homeowner's insurance being
voided if I get a direct hit by lightning?
_____________________________

I ordered this before I read the disclaimer: just "better than
nuthin?"

http://www.universal-radio.com/catal...tect/4618.html

The Opek A7516 Lightning Arrestor is not the "state-of-the-art" in
radio protection. These "air gap" arrestors were OK for tube sets, but
are not the best for today's solid-state rigs. However, if you are on
a budget, this device is a whole lot better than nuthin! As with all
lightning protection devices; you must connect it to an earth ground
with thick ground wire, and it is not going to provide protection in
the event of a direct hit.
_____________________________

So, here's a better gas-discharge arrestor:

http://www.universal-radio.com/catal...tect/5611.html

The LDG SP-200 surge protector operates from DC to 1500 MHz with a 200
watt power capacity. The SP-200 protects coax feedlines from surges
exceeding 230V, such as caused by nearby lightning strikes and static
build-up. The SP-200 employs a gas-discharge tube that arcs-over when
230VDC is exceeded between the RF center pin and shield connections.
_____________________________

A variation, with different connectors:

http://www.radiolabs.com/products/an...protection.php

Ultra Fast Gas Discharge
0.4db Max Insertion Loss
350V or 90V Breakdown Voltage
VSWR Better than 1.5:1
Passes DC voltage
200W Operation
_____________________________

This doesn't say if it uses gas or air:

http://www.jetstream-usa.com/instructions/jtla1.pdf

# Model # JTLA1
# 1.5-200 Mhz
# 50 ohm
# 8 kW PEP, 4 kW DC
# Insertion Loss: Less than .1db
# Surge Current Capacity 20,000 Amperers
# VSWR Less Than 1.1:1 @ 1000Mhz
# Voltage Attack Time: 0 to 10 Billionths of a second
_____________________________

Can I use something like this? It's designed for fences, but could
easily be rigged for an antenna input:

http://www.zarebasystems.com/store/e...ccessories/la1

Protecting the fence charger from lightning strikes on the fence line.
This lightning arrestor creates a path of least resistance, diverting
lightning surges to the ground.
_____________________________

What's going on here?

http://ku5e.com/index-59869.html

The lower picture shows a device mounted atop the ground pole. Do you
recognize it?
_____________________________

Rees Chapman
Dahlonega, GA

Lightning arrestors
 

On Fri, 12 Aug 2011 02:23:13 -0700 (PDT), DrYattz
wrote:

Having but recently returned to the world of shortwave radio, I'm
trying to be better informed about technical and safety issues than I
was as a kid. Now a homeowner with a mortgage and a homeowner's
insurance policy, I'm worried about lightning protection. I'm
receiving only, not transmitting. I have a ground rod just outside the
window where the antenna wire enters, and I intend to disconnect the
antenna outside the house when I'm not using the shortwave. But I
want to be extra careful!

So I'm considering some options. Which make sense to you seasoned
hams? Do any of these leave me open to my homeowner's insurance being
voided if I get a direct hit by lightning?

Hi Rees,

For the Home:

If you implement an intention to control lightning hazard, I would
suspect a jury would see it your way if you sued the insurance company
for failing to uphold their policy with you. However, they might
grieve at yielding to the insurance's arguments against you.

It wouldn't get to trial if you could demonstrate that you met the
electrical code.

The elephant in the room is: have you properly installed that ground
rod? Driving a long one deep into the ground does not qualify for a
"yes" to that question.

Ground is a very complex and mysterious thing for many, many people.
The electrical code doesn't go any great distance to inform you of its
mysteries, but it does give you solutions that work.

For the Receiver:

As for protecting your receiver from the lightning risk presented by
putting wire up into the air. All of the lighting protectors you have
links to guarantee you will see a couple of hundred volts across the
terminals. The receiver is not going to survive. The distinction
between near strike and direct strike are not really material to the
problem of frying the receiver. The difference is merely one of
personal drama.

You may encounter this potential even on a seemingly cloudless day.

Receiver solutions:

Short the potential. This may be accomplish by using the "Folded
Dipole" design of horizontal antenna. A "Folded Monopole" design for
a vertical antenna. Other designs that employ loop coupling would
also reduce the risk. All such options offer a DC short, but with an
RF impedance. This insures static electricity drain, but allows an RF
voltage (the short wave signal) to develop. A large inductor across
the feedline or conventional dipole feed point provides the same
protection. The coil acts as a DC short, but as an RF open.

Some SWL lightning protectors employ paired diodes to reduce the
voltage risk to less than 10V - trivial indeed. Unfortunately, these
same diodes will conduct in the presence of large RF fields (recall my
discussion about nearby AM transmitters, and "nearby" is relatively
near for RF but seemingly distant if you had to walk or even drive to
it). This conduction will ruin listening opportunities with a jungle
of mysterious signals "that shouldn't be there." Example, hearing an
FM rock station feed on the 60M band.

Having a Tuner between your radio and antenna shifts the dynamics such
that the gap arrestors are useful - until you throw the bypass switch.

73's
Richard Clark, KB7QHC

Lightning arrestors
 

Thanks, Richard!

But help me understand this:

All of the lighting protectors you have
links to guarantee you will see a couple of hundred volts across the
terminals.

http://www.universal-radio.com/catal...tect/5611.html says

* 230V DC discharge voltage ±15%
* Max 1000V surge (1x 40 µS duration)
* Max 6000A surge (1x 40 µS duration)

Which tells me that if the incoming current exceeds 230V, it dumps up
to 1000V and 6000A to ground. Right?

Rees

Lightning arrestors
 

On Sat, 13 Aug 2011 05:52:34 -0700 (PDT), DrYattz
wrote:

Which tells me that if the incoming current exceeds 230V,
.... if the incoming voltage exceeds...
it dumps up to 1000V and 6000A to ground. Right?
Sort of (voltage does not dump, so to speak).

Hi Rees,

The voltage in excess of 230V sustains the dumped current. The 230V
is still there, all the same.

That is to say that the resistance of the gap is (for all practical
purposes) infinite at voltages below 230V. For voltages applied that
exceed 230V, the resistance of the gap is 230V/2300A = 0.1 Ohm.

I chose 2300A both for ease of math, and as being representative.

Hence the gap undergoes a astronomical change in resistance in a very
short time (about a microsecond or less).

This is great fortune to the house's protection. This is poor fortune
to the radio's first transistor which resides in an environment of, at
most, 9V to 12V as a supply for gain, and 0.5V as typically the
highest voltage seen at the input. Transistors are rated to sustain
higher voltages, typically in the 10s of volts, sometimes higher.

230V to 1000V surge (as guaranteed) offer a speedy death. Of course,
of the original source being orders of magnitude greater, lightning
boosts speedy death to instantaneous (within nanoseconds).

Let's take a scenario closer to experience, and one that could easily
be likened to a near death experience at that. Open the hood of your
car, grab an unconnected spark plug lead with the end just a tenth of
an inch from the engine block (a common test of the ignition system).
You observe a spark. Dare you hold the metal clip where that spark is
jumping from it to the block? Dare you even hold the lead on its
insulation? The gap guarantees a certain voltage, and the system
guarantees a certain current (otherwise you would be forever stalled
in the driveway).

Why the hesitation in holding this lead, IF ALL the voltage and
current is dumped into the block? Experience will inform you of why
you hesitate, and why the transistor fears elevated potential.

An antenna invites access to elevated potentials from many sources
other than lightning. Even on a clear day, a dipole can accumulate
enough charge to make the spark gap sizzle. This would be
extraordinary circumstances in some parts of the US, and typical in
other parts. Yet and all as this may be commonplace, radios still
play and life goes on. There are many other factors to consider
insofar as what the input transistor has to suffer or enjoy.

73's
Richard Clark, KB7QHC

Lightning arrestors
 

Rees,

The use of a device such as this that purports to protect the radio from
a differential signal impressed across one interface could lure you into
a false sense of security.

It does not eliminate the effects of elevation of the 'grounded' sided
of the interface above real ground, and especially relative to other
equipment. Of course, if the radio has more than one interface (eg a
power lead), the problem is much greater than protecting it against a
differential transient on that interface.

It is entirely possible that you do such a good job of protecting the
input interface, that the receiver is destroyed by a transient from the
power cord (if it uses one). You must take the bigger picture into
account.

Then there is a question of the damage threshold (current / time
profile) for the interface, the expected current waveshape, and the
response characteristic of the device.

Whilst a high performance FET might be destroyed long before a gas tube
fires, even one doped with radioactive isotope, on the other hand, the
input stage of a HF receiver with the input attenuator in circuit might
survive without protection.

It is a really complex problem, and the risk is that spending some small
money migth delude you into a false sense of security.

I am with Richard, don't take less than competent measures for possibly
worse outcomes.

Owen

Lightning arrestors
 

Rees,

The use of a device such as this that purports to protect the radio from
a differential signal impressed across one interface could lure you into
a false sense of security.

It does not eliminate the effects of elevation of the 'grounded' sided of
the interface above real ground, and especially relative to other
equipment. Of course, if the radio has more than one interface (eg a
power lead), the problem is much greater than protecting it against a
differential transient on that interface.

It is entirely possible that you do such a good job of protecting the
input interface, that the receiver is destroyed by a transient from the
power cord (if it uses one). You must take the bigger picture into
account.

Then there is a question of the damage threshold (current / time profile)
for the interface, the expected current waveshape, and the response
characteristic of the device.

Whilst a high performance FET might be destroyed long before a gas tube
fires, even one doped with radioactive isotope, on the other hand, the
input stage of a HF receiver with the input attenuator in circuit might
survive without protection.

It is a really complex problem, and the risk is that spending some small
money migth delude you into a false sense of security.

I am with Richard, don't take less than competent measures for possibly
worse outcomes.

Owen

Lightning arrestors
 

Rees,

The use of a device such as this that purports to protect the radio from
a differential signal impressed across one interface could lure you into
a false sense of security.

It does not eliminate the effects of elevation of the 'grounded' sided of
the interface above real ground, and especially relative to other
equipment. Of course, if the radio has more than one interface (eg a
power lead), the problem is much greater than protecting it against a
differential transient on that interface.

It is entirely possible that you do such a good job of protecting the
input interface, that the receiver is destroyed by a transient from the
power cord (if it uses one). You must take the bigger picture into
account.

Then there is a question of the damage threshold (current / time profile)
for the interface, the expected current waveshape, and the response
characteristic of the device.

Whilst a high performance FET might be destroyed long before a gas tube
fires, even one doped with radioactive isotope, on the other hand, the
input stage of a HF receiver with the input attenuator in circuit might
survive without protection.

It is a really complex problem, and the risk is that spending some small
money migth delude you into a false sense of security.

I am with Richard, don't take less than competent measures for possibly
worse outcomes.

Owen

If you are going to go to the expense of trying to keep the lightning out of your shack and your radio - you need to do several things.

The first is the use of something called Polyphasers - Although I have talked to the man who founded the company and he seemed like a real bung hole - he did have many valid points and his equipment is used here exclusively for the install of CELL Towers.

In the world of towers - there is a formula of how to expect lightning strikes.
With a 350' tower - you can expect on average 2 strikes per a year and a catastropic strike once every 4 years.

When I say catastropic - I mean a lightning strike which does about $40,000 of damage.
When you add it all up, it averages about $6,000.00 per a strike.
There is also something called the big 7 - that is 7 people who owns 1000 or more cell towers each.
Their maintenence bill is something in the order of about $36.5 million dollars per a year - due to lightning strikes.

The things that we do to subdue lightning strikes is covered under the Motorola codes for towers. It's a simple formula
We bond everything in the candleabra - each antenna carries it's own ground.
Every 30 feet down the tower - the heliax gets connected / bonded to a ground along the ladder mount.
At the bottom of the tower - each coax ( Heliax) gets bonded to ground.
Before it goes into any type of transmitter building, it gets bonded to a ground.

Each leg of the tower is bonded to a ground.
There is a loop around the transmitter building and tower with stakes spaced evenly all around and sometimes a wire mesh is placed under the tower and around the building to absorbe the lighting and displace it.
Everything gets bonded to the grounds by way of thermal welded joints - Cadweld. All of the equipment inside of the transmitter building is cadwelded to the ground and the electrical service is also bonded to all the other grounds.

The towers here - are not ran off of the consumer power lines.
It is attached to a battery bank and the battery bank is connected to the power supply. Even if the power goes out - there is enough power to run the tower two more days. If after that the power does not come back on - there is provisions to switch service to a different tower or to connect the battery bank to alternate power sources - generators.

These standards - called R 56 is not written in stone - but is pretty much the industry standards for cell tower construction.

http://lightning-protection-institut...f%20damage.htm

http://www.esgroundingsolutions.com/...quirements.php

Lightning arrestors
 

On 8/12/2011 2:23 AM, DrYattz wrote:
Having but recently returned to the world of shortwave radio, I'm
trying to be better informed about technical and safety issues than I
was as a kid. Now a homeowner with a mortgage and a homeowner's
insurance policy, I'm worried about lightning protection. I'm
receiving only, not transmitting. I have a ground rod just outside the
window where the antenna wire enters, and I intend to disconnect the
antenna outside the house when I'm not using the shortwave. But I
want to be extra careful!


Separate two issues:
1) having the house not burn down
2) protecting the front end of your radio

#1 is fairly straightforward and what your homeowner's insurance company
might care about

#2 is pretty darn tricky, but the homeowner's insurance company doesn't
care much about your radio.


As others will point out, a single rod pounded in does not generally a
code compliant ground make. And a single rod pounded in might actually
make things worse, as far as damage and destruction goes.

The goal is to get the lightning energy to go "somewhere else" than in
your house. A secondary goal, since sending ALL lightning energy
somewhere else is very difficult, is to not have the remainder destroy
the radio.


First off.. almost all amateur antenna installations do not fully comply
with the electrical code (and before I get flamed.. let me ask all you
would be commenters: do you have a listed antenna discharge unit? are
all your conductors no less than AWG 14 hard drawn copper or copper clad
steel? Is your antenna lead in entirely contained within a metallic
raceway? I thought not.. pace...we're going for practical here)

That said, I think that a "good faith" effort to do the right thing will
help, and besides, unless you're in a disaster area, insurance companies
generally don't work to try and deny claims on flimsy basis. there's
the whole "reasonable person" aspect and your looking for decent
information is a good start of what a "reasonable person" would do.

You might take a look at the safety chapter in the ARRL handbook as a
start (the library has it, almost certainly, or you can find someone who
will loan it to you).


A antenna discharge unit (open spark gap with a spacing of a few tenths
of an inch) to a ground rod or rods will go a long way towards keeping
most of the lightning current out of the house. It takes several kV to
jump the gap, but once the gap is conducting, the voltage drops to a few
tens of volts, and that's nothing in the overall scheme of things where
there are many kilovolts along your wire.

The real problem comes in with the fact that no matter how good a job
you do in connecting that gap to the rod, there's going to some
distance, and some voltage drop between the voltage at that arrestor
(during the strike) and "the rest of the house ground potential". If
your radio is sitting in the middle, it WILL conduct, and it WILL be
exciting.

The idea, then, is to make sure that no big voltages occur across two
terminals of the radio (that could either be antenna and ground
terminal, e.g. coax, or antenna and power supply).

The big deal is the AC power.. your wall socket is close to ground
potential (in terms of kilovolts, anyway). So if your radio's antenna
is at 2 or 3 kV, and the power cord is at ground, your radio will fry.

Run the radio off batteries? As long as you're not touching it, and
it's not hooked up with an audio cable to your PC or something, then it
just floats up to a few kV, and then, floats back down.


Most UL listed wall wart power supplies these days can hold off several
thousand volts between inside and outside (that's the so called "hi pot"
test rating).


Beyond that, it starts getting into gas tubes, and similar stuff to try
and protect the innards of the radio. How much does your radio cost?
Do you want to spend hundreds of dollars on surge suppressors to protect
a $200 radio?

it's also remarkably hard to build a very sensitive receiver that will
tolerate even a few tens of volts on the input.

Lightning arrestors
 

Jim Lux wrote in
:

....
Most UL listed wall wart power supplies these days can hold off
several thousand volts between inside and outside (that's the so
called "hi pot" test rating).

That may be so at DC or 60 Hz, but it may be relatively transparent to
the spectral components of lightning discharge current, components that
may me significant to 100MHz or more.

There is no simple broadband equivalent circuit of the power
transformer, but at 100MHz, it might look more like some series
capacitance of the order of 100pF from primary to secondary for common
mode excitation... and that may well allow damaging currents to flow
(without insulation breakdown or permanent damage to the transformer),
whether driven from the coax shield, the power line, or more likely,
both.

Just another factor that makes design of bullet proof solutions so
challenging.

Owen

Lightning arrestors
 

On 8/15/2011 4:46 PM, Owen Duffy wrote:
Jim wrote in
:

...
Most UL listed wall wart power supplies these days can hold off
several thousand volts between inside and outside (that's the so
called "hi pot" test rating).

That may be so at DC or 60 Hz, but it may be relatively transparent to
the spectral components of lightning discharge current, components that
may me significant to 100MHz or more.


yes.. although for the most part, if you're looking at the transient
from a "spark gap arrested lightning impulse" you probably don't have
quite that spectrum.


There is no simple broadband equivalent circuit of the power
transformer, but at 100MHz, it might look more like some series
capacitance of the order of 100pF from primary to secondary for common
mode excitation... and that may well allow damaging currents to flow
(without insulation breakdown or permanent damage to the transformer),
whether driven from the coax shield, the power line, or more likely,
both.

Could be.

Standler's book on transient protection comments that several studies
have shown that most modern consumer electronics can tolerate standard
transient impulses (both the 1 us and 6 us rise time variety) of several
kV. The not so halcyon ESD days of TTL gates connected directly to the
device connector pins are long gone.




Just another factor that makes design of bullet proof solutions so
challenging.

Owen

Lightning arrestors
 

On Aug 12, 5:23*am, DrYattz wrote:
Having but recently returned to the world of shortwave radio, I'm
trying to be better informed about technical and safety issues than I
was as a kid. *Now a homeowner with a mortgage and a homeowner's
insurance policy, I'm worried about lightning protection. *I'm
receiving only, not transmitting. I have a ground rod just outside the
window where the antenna wire enters, and I intend to disconnect the
antenna outside the house when I'm not using the shortwave. *But I
want to be extra careful!

So I'm considering some options. *Which make sense to you seasoned
hams? *Do any of these leave me open to my homeowner's insurance being
voided if I get a direct hit by lightning?

Choice of device seems to be what you're concentrating on but I don't
think the brand name of any device will figure into the solution at
the insurance and electrical code level.

Correct bonding of the equipment ground/RF ground to the house ground
at the entrance panel is the key for any of this. See e.g. W8JI's
webpages.

Tim.