The 18” inch requirement is partially for damage resistance and partially to ensure adequate soil moisture for conductivity.

Content by Scott
Typos by Siri

On Jun 19, 2018, at 10:50 AM, jimlux jimlux@earthlink.net wrote:

On 6/18/18 6:39 PM, Glenn Little WB4UIV wrote:

It helps to know why some requirements exist - I suspect the 18" burial requirement is to avoid accidentally digging it up or damaging it. I can't think of an electrical reason for it.

It depends

Unless you're doing geodetic or precision timing work with a 2 or 3 band GPS, replacement GPS antennas are cheap.
I'd worry about the receiver and related equipment, but the antenna itself might be sacrificial.

As always, there's a risk/budget tradeoff

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Hi

18” down in a swamp likely is plenty for conductivity. 18” down in a sandy desert (or on an ice sheet) may be way
short in terms of conductivity :) The real answer to any of this is “that depends”. (Yes, the ice sheet grounding
problem is from a real case that shows up in some class notes from way back ….).

Some locations get multiple  hits on a weekly basis in the summer. Other locations get a close strike once every
few decades. What makes economic sense for one probably does not make sense for the other…. A “full up”
protection setup can easily run into hundreds of thousands of dollars. I’d much rather spend that kind of money
on a Maser … or two …. or three :) …. this is TimeNuts after all ….

Bob

Probably the easiest and most economical grounding system is the halo ground with antenna grounds bonded to the halo and the house ground bonded to the halo as well.

The halo conductor sizing is governed by local codes,  But really what you are doing ensuring that the entire structure and earth around it is at the same potential so a nearby strike does not cause ground currents to flow.

A direct strike is probably going to fry anything it hits because of the gigajoules of energy concentrated within the discharge

But a proper ground system also ‘bleeds off’ the potential difference thereby preventing discharge

Content by Scott
Typos by Siri

On Jun 19, 2018, at 11:19 AM, Bob kb8tq kb8tq@n1k.org wrote:

Hi

18” down in a swamp likely is plenty for conductivity. 18” down in a sandy desert (or on an ice sheet) may be way
short in terms of conductivity :) The real answer to any of this is “that depends”. (Yes, the ice sheet grounding
problem is from a real case that shows up in some class notes from way back ….).

Some locations get multiple  hits on a weekly basis in the summer. Other locations get a close strike once every
few decades. What makes economic sense for one probably does not make sense for the other…. A “full up”
protection setup can easily run into hundreds of thousands of dollars. I’d much rather spend that kind of money
on a Maser … or two …. or three :) …. this is TimeNuts after all ….

Bob

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About that "cone of protection"
http://lightningsafety.com/nlsi_pls/cone-of-protection-myth.html

-----Original Message-----
From: time-nuts time-nuts-bounces@lists.febo.com On Behalf Of Bill Hawkins
Sent: Monday, June 18, 2018 3:16 PM
To: oz@ozindfw.net; 'Discussion of precise time and frequency measurement' time-nuts@lists.febo.com
Subject: Re: [time-nuts] GPS Antenna Grounding/Lightning protection.

Oz has some useful observations.

I've worked on a 50 foot ocean-going fishing party boat that had a 10 foot aluminum mast on top of the wheel house. That will be the shortest path to ground on the open sea. The best you can do is to connect a 4"
wide copper strap from the mast to the keel, with as few bends as possible and none greater than 45 degrees. This seems to work.

I've also worked at a blasting cap plant where 50 foot masts were erected at both ends of an earth-covered powder magazine. They provide a "cone of protection" that prevents a direct hit on the magazine. The mast grounds were measured quarterly with a hand-cranked device specifically made for ground resistance. It had to be less than 100 milliohms.

But if you really want protection from a direct hit, you must disconnect the tower device(s) before the storm hits. The coaxial cable must have only one ground point. The other end should be far from a metallic ground. You'll probably lose any electronics in the antenna, but there are far more expensive things in your lab.

You will also have to deal with the electromagnetic pulse, so all of your equipment, including the computers, must have a common ground point. This provides a ground plane that can change potential relative to the Earth without inducing potentials between devices. Every connection to/from the ground plane must have a surge arrestor. If the risk of nearby direct hits is high enough, isolate the ground plane from all external connections before the storm. You'll need battery backup on the ground plane for all temperature controlled ovens and crystal oscillators. Maybe the Cs and Rb packages also need to keep running.

It would help to move away from Florida, or high hilltops.

Bill Hawkins

-----Original Message-----
From: time-nuts [mailto:time-nuts-bounces@lists.febo.com] On Behalf Of Oz-in-DFW
Sent: Monday, June 18, 2018 2:25 PM
To: time-nuts@lists.febo.com
Subject: Re: [time-nuts] GPS Antenna Grounding/Lightning protection.

Not sure I have much to specific offer, other than some observations.

1. A path to ground is only a small part of the story.  What's really
   important is the ground reference of all equipment to all other
   equipment. The huge currents and substantial risetimes can cause
   large voltage spikes across even large conductors (>8 AWG.) You want
   everything to stay at the same voltage reference, and you'd really
   like to keep that close enough to ground to prevent arcs from that
   equipment to ground and other equipment.
2. Long wire runs of even large gauge wire are inductors and can be of
   little value during an event.
3. No matter what you do, it's unlikely you can do anything within
   economical reason to survive a direct strike and the 10's to 100's
   of kiloamps involved. The real question is how close of a near miss
   can you survive.
4. Most of the non-telecom smoking fails I've seen have been power line
   transients. If you took a direct tower hit it's more likely than not
   that your RG-6 would now be plating on a tower leg. An old tower can
   be a pretty poor ground for the microseconds (or sometimes
   milliseconds when you consider return strokes) it takes the
   corrosion in the leg joints to flashover and fuse, or resistance
   heat and weld.
5. The large currents of a direct strike have predictable but less than
   obvious physical effects like conductor shortening (if they don't
   fuse,) and other significant forces caused by magnetic attraction of
   conductors. One failure case I saw years ago collapsed the conduit
   around a ground conductor. Made no sense until we discovered that
   the conduit was the actual ground path. I'll see if I can find the
   pictures.
6. Even near misses can induce huge currents (kiloamps) on their own,
   particularly in long vertical cable runs.  I've seen solder joints
   in small empty copper water pipes melt and reflow from a strike a
   100 feet away.
7. The best coax lightning suppression units I have seen are
   essentially 1/4 wave grounded stubs. These are common is cell site
   installations (and the top /AND/ bottom of the lines.) These are
   always at DC ground and the coax is a the weak point (and ultimately
   the fuse.)  I've seen them surplus and at hamfests and some cover
   GPS freqs.
8. A near strike will induce some really impressive voltages on
   Ethernet cable runs. Most residential buildings are
   electromagnetically transparent and the protection on most Ethernet
   interfaces is oriented toward ESD.

Oz (in DFW)

On 6/18/2018 1:29 PM, Dan Kemppainen wrote:

--
mailto:oz@ozindfw.net
Oz
POB 93167
Southlake, TX 76092 (Near DFW Airport)

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Hi

If indeed a proper ground system could be depended on to “bleed off” and prevent discharge things
would be much simpler. Indeed I’ve been on towers and decided to exit that location as the bleed
process became audible. It very much does happen. It simply is not a 100% sort of thing.

Bob

First, I recommend the following:
http://www.arrl.org/shop/Grounding-and-Bonding-for-the-Radio-Amateur/
well worth the price.
second, bleeding off does not prevent discharge. Many such systems are
garbage or worse. "bleeding off" is corona discharge from sharp points
submitted to a large electric field, such as under or near a
thunderstorm. It's gonna happen.
I think what's meant here by a halo system is a conductor dug in to a
shallow trench? If so, Scott is correct.
next, most of the time, damage is done by induced currents rather than
direct hit by the stroke terminus. These can be eased by proper power
treatment and good single point grounds. I personally do not trust MOV
ground protectors. They are only good for a certain, unknown, number of
hits, and are useless after that. There is no way to tell if the limit
has been reached.  Surge protection on AC power needs doing only at the
main breaker box from each side of the 220 to ground.
and, if you are on a tower and hear the sizzling noise of corona, get
down pronto.
Hope this helps.
Don

On 2018-06-19 12:55, Bob kb8tq wrote:

--
Dr. Don Latham
PO Box 404, Frenchtown, MT, 59834
VOX: 406-626-4304

If you see St Elmos fire ‘corona discharge bleed process is working as expected

Content by Scott
Typos by Siri

On Jun 19, 2018, at 3:55 PM, Bob kb8tq kb8tq@n1k.org wrote:

Hi

If indeed a proper ground system could be depended on to “bleed off” and prevent discharge things
would be much simpler. Indeed I’ve been on towers and decided to exit that location as the bleed
process became audible. It very much does happen. It simply is not a 100% sort of thing.

Bob

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and follow the instructions there.

The "Cone of Protection" is a thumbrule.  It's not a myth, but it's also
not an absolute law of nature. It's a self-fulfilling prophecy to some
degree because it drives component design guidelines. 

Bunker spacing is also a thumbrule, based on a lot of horrible
experience. It's also a function of many variables and differing
requirements, largely the explosive involved.  It's also self-fulfilling
prophecy because it enters into design guidelines for explosives
packaging. There's a multitude of reasons those bricks are in a foil
bag. This is one of them.

I'm not a lightning protection expert, but I do a bit of work where I
have to be concerned about it. I look at that thumbrule, but I'm also a
belt and suspenders guy and apply many others. And I build shipping gear
as if it's going to South Africa (much worse that Florida.)

Back to my original statement early in this thread (rope?) "No matter
what you do, it's unlikely you can do anything within economical reason
to survive a direct strike and the 10's to 100's of kiloamps involved.
The real question is how close of a near miss can you survive." for a
small business/residential install, as a minimum I would:

1. Make sure your tower is grounded.
2. Make sure your tower is electrically sound (a good electrical
   conductor - all sections are well connected electrically. this is
   */NOT /*a given with used or old tower.) If you are going to clamp
   copper straps to the tower or antennas, use some stainless shim
   stock as a barrier.
3. Mount your antenna(s) with grounding as specified by the manufacturer.
4. Use a lightning/drip loop at the top of the tower as a absolute
   minimum.  Better to use a real suppressor, preferably of the 1/4
   wave stub type.
5. Ground the coax shield to the tower at the top and the bottom.
6. If you have control lines (power, rotator controls, etc.) use
   shielded cable, ground, and suppress as with coax.
7. Use a master ground bar entry into your building, and make sure you
   have effective lightning suppression on /everything/ that enters
   the building: Coax, AC power, phone lines, ethernets, hopes, wishes,
   etc.
8. Make sure the master ground bar is well grounded to the tower.  See
   https://www.solacity.com/docs/Polyphaser/Coaxial%20cable%20entry%20panels%20and%20coax%20grounding.PDF 
   Commercial installs are copper bus bar.  I use it where I can, but I
   also have ham installs that use unistrut and copper strap.  In an
   ideal world this is next to the electrical service panel and ground
   there with suppressors on the AC lines into the building. The world
   is rarely ideal. 
9. I /try/ to bury at least 8 AWG ground wire around the building, but
   I'm usually lucky to get it between the AC panel,  coax entry, and
   tower.  One time I used scrap 1/2" copper water pipe. 
10. Get a good suppressor on the input feed to the AC panel. The /vast/
    majority of failures I've seen come in the AC line. Or phone line if
    you still have copper.
11. Make sure your grounds really are.  A six foot 14 AWG wire is not a
    ground, even for a cable TV entry block. Use wide braid, strap, or
    welding cable size wire. And be careful how you route it.  There is
    a lot of literature on this alone. don't run it across the attic  ;-)
12. If you want the buried stuff to last, look at some form of cathodic
    protection.

Of course you can do all of this and take losses from a hit, or none of
it and never see a problem.  This is, as the Polyphaser paper mentions,
insurance.

Oz

Shutting up now, sir.

On 6/19/2018 10:56 PM, Bill Hawkins wrote:

--
mailto:oz@ozindfw.net
Oz
POB 93167
Southlake, TX 76092 (Near DFW Airport)

Part of the problem is lightning protection is not sexy,  its not like getting a 5071A or a H-maser,  But it DOES provide a measure of insurance for those sexy items

Content by Scott
Typos by Siri

On Jun 20, 2018, at 6:45 PM, Oz-in-DFW lists@ozindfw.net wrote:

The "Cone of Protection" is a thumbrule.  It's not a myth, but it's also
not an absolute law of nature. It's a self-fulfilling prophecy to some
degree because it drives component design guidelines.

Bunker spacing is also a thumbrule, based on a lot of horrible
experience. It's also a function of many variables and differing
requirements, largely the explosive involved.  It's also self-fulfilling
prophecy because it enters into design guidelines for explosives
packaging. There's a multitude of reasons those bricks are in a foil
bag. This is one of them.

I'm not a lightning protection expert, but I do a bit of work where I
have to be concerned about it. I look at that thumbrule, but I'm also a
belt and suspenders guy and apply many others. And I build shipping gear
as if it's going to South Africa (much worse that Florida.)

Back to my original statement early in this thread (rope?) "No matter
what you do, it's unlikely you can do anything within economical reason
to survive a direct strike and the 10's to 100's of kiloamps involved.
The real question is how close of a near miss can you survive." for a
small business/residential install, as a minimum I would:

1. Make sure your tower is grounded.
2. Make sure your tower is electrically sound (a good electrical
   conductor - all sections are well connected electrically. this is
   */NOT /*a given with used or old tower.) If you are going to clamp
   copper straps to the tower or antennas, use some stainless shim
   stock as a barrier.
3. Mount your antenna(s) with grounding as specified by the manufacturer.
4. Use a lightning/drip loop at the top of the tower as a absolute
   minimum.  Better to use a real suppressor, preferably of the 1/4
   wave stub type.
5. Ground the coax shield to the tower at the top and the bottom.
6. If you have control lines (power, rotator controls, etc.) use
   shielded cable, ground, and suppress as with coax.
7. Use a master ground bar entry into your building, and make sure you
   have effective lightning suppression on /everything/ that enters
   the building: Coax, AC power, phone lines, ethernets, hopes, wishes,
   etc.
8. Make sure the master ground bar is well grounded to the tower.  See
   https://www.solacity.com/docs/Polyphaser/Coaxial%20cable%20entry%20panels%20and%20coax%20grounding.PDF
   Commercial installs are copper bus bar.  I use it where I can, but I
   also have ham installs that use unistrut and copper strap.  In an
   ideal world this is next to the electrical service panel and ground
   there with suppressors on the AC lines into the building. The world
   is rarely ideal.
9. I /try/ to bury at least 8 AWG ground wire around the building, but
   I'm usually lucky to get it between the AC panel,  coax entry, and
   tower.  One time I used scrap 1/2" copper water pipe.
10. Get a good suppressor on the input feed to the AC panel. The /vast/
    majority of failures I've seen come in the AC line. Or phone line if
    you still have copper.
11. Make sure your grounds really are.  A six foot 14 AWG wire is not a
    ground, even for a cable TV entry block. Use wide braid, strap, or
    welding cable size wire. And be careful how you route it.  There is
    a lot of literature on this alone. don't run it across the attic  ;-)
12. If you want the buried stuff to last, look at some form of cathodic
    protection.

Of course you can do all of this and take losses from a hit, or none of
it and never see a problem.  This is, as the Polyphaser paper mentions,
insurance.

Oz

Shutting up now, sir.

--
mailto:oz@ozindfw.net
Oz
POB 93167
Southlake, TX 76092 (Near DFW Airport)

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