GPS antenna selection
Hi
Ummm ….. It’s a lot more fun to focus on the 0.001% case :)
Bob
On Aug 5, 2016, at 9:31 PM, Chris Albertson albertson.chris@gmail.com wrote:
You guys, well some of you are mixing to things
-
the building code requirement to ground an antenna is for the protection
of the building. The building code don't care if you electronics is fried
or not. The wire and ground rod keep the antenna mast at earth potential. -
Those surge protectors and grounding your electronics to a common point
an al other advice then grounding the most to a rod by the nearest route
down the side of the house. These are different things
So, outdoor antenna are different from indoor antenna in that if you indoor
antenna is struck the house is already pretty much toasted. You still
might want a surge protector to protect the receiver.
The question is if you need to buy a $40 surge protector for your $8
Motorola Encore receiver? But no question if you need a group wire in the
mast, even for that $8 gps receiver because that wire protects the house
Part of the equation is where you live. In many years of living in Redondo
Beach, CA I never hear of anyone or anything being =damaged by lightening.
We don't even get lighting here but twice a year if that. On the other
hand I had god protection on my sailboat as that 60 for aluminum mast might
be the highest thing around on the ocean for miles. That mast has a very
solid connection straight to saltwater. You have to evaluate the risk and
consequence. You get different answer in Orlando Florida then I get here.
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A very good reference for EMP protection is MIL-HDBK-419.
This is downloadable for a number of web sources.
It is about 600 pages and is in two volumes.
This discusses a number of different sources of EMP such as nuclear and
lightning.
A lot is for protection of military industrial complexes, but, there is
a lot that pertains to us.
I worked for a military complex that assembled nuclear missiles.
The site was built to this handbook specs.
We had no EMP related damage at the site.
Number one rule, bond all grounds together. If something on your
property takes a hit, you want everything on your property to elevate to
the same level and the same rate.
If you have multiple, non bonded grounds, there is a different reference
for each ground. This is a major source for disaster.
I spent seven years in lightning mitigation. I was told by professionals
that I was wrong. The third time that their tower was struck, destroying
all of the lights and attached equipment, they followed my
recommendations. That was ten years ago. The three hits were within four
months of each other. The site has been free of destructive hits since then.
73
Glenn
WB4UIV
On 8/5/2016 10:37 AM, Eric Scace wrote:
Unfortunately, an antenna, cable, or piece of electronics located indoors is just as susceptible to lightning surges as one that is outdoors.
Lightning-induced surges couple into these systems electromagnetically across a wide range (VLF to SHF) of frequencies. When you think about your home from an electromagnetic viewpoint, just imagine your structure with all non-conductive materials absent. For a typical wood or brick/stone house in North America, what you are left with is:
metal plumbing pipes and fixtures, with their geometry suspended in space
house wiring, CATV, Ethernet, and telephone cabling, and their service drops, all suspended in space
electrical & electronic circuits of every kind (WiFi note, computer, appliances), their power supplies and AC power cords, also suspended in space
metal furniture? That’s hanging out there, suspended in space, too.
any I-beam or other steel structural elements, some random aluminum flashing, door knobs, and other similar metal construction materials used in the home.
That is what an electromagnetic pulse sees as it approaches and sweeps over your home… all hovering over a lossy ground plane (earth) its varying dielectric constant.. Each one of those pieces of metal, hanging in space, is an unintentional antenna that experiences voltage differentials and current flows.
A GPS antenna and its coax line that is installed next to a window is no different from the same antenna/coax installed one meter outside the window… or 10 meters away outside the window. All three installations are effectively “outdoors” from an electromagnetic viewpoint, and all three need effective surge protection from lightning-, cloud-, and precipitation-induced voltage surges.
(N.B.: Snow can be particularly bad for voltage surges. I’ve seen thousands of volts per meter potential differences in moderate-to-heavy snowfall that produced very significant current flows on cables.)
Surge protection for your antenna, its attachment to your receiver(s), AC/DC power supply lines, and any other signal lines of significant length is cheap insurance.
My continuously-operating electronics lives in an enclosed rack cabinet — not too much worse than a proper Faraday cage. Every cable entering the cabinet has surge protection at the point of entry. The cabinet is bonded to earth ground by 2” copper flashing. In the past this system lived 22 years on a mountaintop home, 1200 ft above surrounding terrain. Lots of thunderstorms — zero damage/disruptions during that time… a sample size of one, admittedly, but during the first 18 months at that site I had two lightning-surge damaging events before I got serious about protection.
I have equipment at a coastal site with multiple 130-ft towers. That site had damage events every 2 years or so — even when cables to the “outside” were disconnected, and AC mains power was shut off at the main circuit breaker box. After implementing comprehensive surge protection, we have had zero damage over the last 12 years.
— Eric
On 2016 Aug 04, at 19:46 , Bob Camp kb8tq@n1k.org wrote:
Grounding the antenna is always a good idea.
A surge suppressor in the line could save you some
real cost if there is a lightning strike.
I did a quick search for SMA/BNC/TNC based surge
protectors and not much did come up, any suggestions
what to use there?
There are a lot of them on eBay. Many of them have N connectors on them.
I don’t know about Austria, but here in the US,
both are required.
Outside definitely, "inside" I'm not sure, but it
won't hurt to have additional protection for the
receiver(s).
It is a good bet that the antenna will be outside. I’d plan it that way.
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--
Glenn Little ARRL Technical Specialist QCWA LM 28417
Amateur Callsign: WB4UIV wb4uiv@arrl.net AMSAT LM 2178
QTH: Goose Creek, SC USA (EM92xx) USSVI LM NRA LM SBE ARRL TAPR
"It is not the class of license that the Amateur holds but the class
of the Amateur that holds the license"
Glenn wrote:
A very good reference for EMP protection is MIL-HDBK-419.
This is downloadable for a number of web sources.
Tisha Hayes has a big fat folder full of good stuff relating to
"Grounding Surge and Filtering" at her dropbox site, and another one
full of "Transient Protection Documents." See:
https://www.dropbox.com/sh/qjnu6cp03ahajpc/AAABcWVmOZdyPWquiz3az58Ha?dl=0
Best regards,
Charles
This thread grows old, so here's one person's summary:
There are two ways to be damaged by lightning:
-
A direct hit pumps 100 kiloamps of electrons into an ohm or so of
your local wiring. There is no way to survive a direct hit except to
implement stuff only the Military can afford. The probability is so low
(outside of Florida and mountain tops) that your homeowners insurance
may cover it. -
A 100 KA strike goes to ground near you, with two effects:
a. The ground resistance allows a large range of volts per meter to
kill cows but not golfers with their feet together.
b. A mighty electromagnetic pulse (EMP) induces voltages in anything
inductive that is not shielded or twisted.
Case 'a' argues for a single point earth ground. When the ground voltage
goes up, you want all of your equipment to go up with it, as if it was
on an isolated ground plane. It seems best to use the Electric Power
Company's house ground for that reference point in your home. If you use
a UPS for a set of equipment, everything on it should ground to that UPS
(which should have a high capacity surge arrestor). You are left with
telephone cords, TV cables, and antennas as peripheral connections to
protect with surge arrestors. Marine supply stores sell rolls of 4 inch
wide copper strap for connecting the mast on the wheelhouse cabin with
the keel of fiberglass boats. This is also the ground for all electronic
equipment. The strap is considerably less inductive than a wire.
Case 'b' argues against long wires inside the area that contains the
common ground and the surge arrestors at its periphery.
Surge arrestors have energy ratings that refer to the energy of the EMP
that caused the surge. I have no idea how that relates to lightning EMP
energy so I buy the most capacity I can afford.
I used these principles in a home that had a pair of HP GPS antennas
four feet apart on a twenty foot mast of six inch plastic pipe, using N
connectors and 50 feet of RG-8 to a pair of Z3801A receivers. The
neighbor's tree took a direct hit (was split apart) less than 100 feet
away. He had extensive electrical damage originating at the outdoor
flood light six feet from the tree. I lost the GPS antenna closest to
the tree but nothing else. FWIW, I had wireless G access points
separating the area connected to the antenna from the rest of the house
network. No attempt was made to beef up the grounds.
Regards,
Bill Hawkins
Hi Bill,
A lot of us are hams. The ARRL handbook has a section on grounds, including the need for bonding additional grounds to the power line ground. A loop of heavy gauge wire around the house that has periodic 8' ground rods is seen as a good thing as long as it's bonded to the power line ground. This is something entirely different from "multi-point ground". It is said to provide a circle of protection around the house, but yea, it's a lot more complicated than that. Check the handbook, or read whatever grounding documents you have access to and trust.
OK, I've had my say.
Bob - AE6RV
-----------------------------------------------------------------
AE6RV.com
GFS GPSDO list:
groups.yahoo.com/neo/groups/GFS-GPSDOs/info
From: Bill Hawkins <bill.iaxs@pobox.com>
To: 'Discussion of precise time and frequency measurement' time-nuts@febo.com
Sent: Sunday, August 7, 2016 10:06 PM
Subject: Re: [time-nuts] GPS antenna selection - lightning
This thread grows old, so here's one person's summary:
There are two ways to be damaged by lightning:
-
A direct hit pumps 100 kiloamps of electrons into an ohm or so of
your local wiring. There is no way to survive a direct hit except to
implement stuff only the Military can afford. The probability is so low
(outside of Florida and mountain tops) that your homeowners insurance
may cover it. -
A 100 KA strike goes to ground near you, with two effects:
a. The ground resistance allows a large range of volts per meter to
kill cows but not golfers with their feet together.
b. A mighty electromagnetic pulse (EMP) induces voltages in anything
inductive that is not shielded or twisted.
Case 'a' argues for a single point earth ground. When the ground voltage
goes up, you want all of your equipment to go up with it, as if it was
on an isolated ground plane. It seems best to use the Electric Power
Company's house ground for that reference point in your home. If you use
a UPS for a set of equipment, everything on it should ground to that UPS
(which should have a high capacity surge arrestor). You are left with
telephone cords, TV cables, and antennas as peripheral connections to
protect with surge arrestors. Marine supply stores sell rolls of 4 inch
wide copper strap for connecting the mast on the wheelhouse cabin with
the keel of fiberglass boats. This is also the ground for all electronic
equipment. The strap is considerably less inductive than a wire.
Case 'b' argues against long wires inside the area that contains the
common ground and the surge arrestors at its periphery.
Surge arrestors have energy ratings that refer to the energy of the EMP
that caused the surge. I have no idea how that relates to lightning EMP
energy so I buy the most capacity I can afford.
I used these principles in a home that had a pair of HP GPS antennas
four feet apart on a twenty foot mast of six inch plastic pipe, using N
connectors and 50 feet of RG-8 to a pair of Z3801A receivers. The
neighbor's tree took a direct hit (was split apart) less than 100 feet
away. He had extensive electrical damage originating at the outdoor
flood light six feet from the tree. I lost the GPS antenna closest to
the tree but nothing else. FWIW, I had wireless G access points
separating the area connected to the antenna from the rest of the house
network. No attempt was made to beef up the grounds.
Regards,
Bill Hawkins
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and follow the instructions there.
On 8/7/16 8:06 PM, Bill Hawkins wrote:
This thread grows old, so here's one person's summary:
Marine supply stores sell rolls of 4 inch
wide copper strap for connecting the mast on the wheelhouse cabin with
the keel of fiberglass boats. This is also the ground for all electronic
equipment. The strap is considerably less inductive than a wire.
No - strap is about the same inductance as a wire of the same length.
The advantage of strap is a lower RF resistance, which is important if
the strap is part of your antenna system, because it's less resistive
loss than a wire.
For lightning impulses, either conducted or radiated, the inductance
dominates the voltage rise (e.g. Xl is much larger than Rac).
Strap or bar may be easier to make connections to (drill a hole in some
1/8x1" bar, tap it, and hook your lug up)
Hi
We tend to look at all this lighting / EMP stuff very much as a “get to the ground”
sort of thing. For whatever reason the whole thought process stops once we get
to a coper weld rod driven however far into the dirt.
If you try to operate a vertical antenna against that same rod in the middle of a nice dry
summer. You will quickly find out that dirt != ground. The same fun and games
that get you a low impedance ground for your antenna also apply to a low impedance
ground for your protection system. Its not an identical process, but it’s the same idea.
You can argue that a good bond of everything to a single point is sufficient. Looking around
my house, there is most certainly not a single point of entry for everything. Various
utilities and other wires / chunks of conductive stuff go off in a variety of directions. Like
most homes in the US, it’s a wood frame structure. There is no nice steel frame to
tie everything to. I suppose the first step would be to tear the house down and re-build
it from scratch …..
Bob
On Aug 8, 2016, at 10:00 AM, jimlux jimlux@earthlink.net wrote:
On 8/7/16 8:06 PM, Bill Hawkins wrote:
This thread grows old, so here's one person's summary:
Marine supply stores sell rolls of 4 inch
wide copper strap for connecting the mast on the wheelhouse cabin with
the keel of fiberglass boats. This is also the ground for all electronic
equipment. The strap is considerably less inductive than a wire.
No - strap is about the same inductance as a wire of the same length. The advantage of strap is a lower RF resistance, which is important if the strap is part of your antenna system, because it's less resistive loss than a wire.
For lightning impulses, either conducted or radiated, the inductance dominates the voltage rise (e.g. Xl is much larger than Rac).
Strap or bar may be easier to make connections to (drill a hole in some 1/8x1" bar, tap it, and hook your lug up)
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