[time-nuts] GPS Antenna Grounding/Lightning protection.

djl djl at montana.com
Tue Jun 19 17:12:39 EDT 2018


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:
> 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
> 
>> On Jun 19, 2018, at 12:01 PM, Scott McGrath <scmcgrath at gmail.com> 
>> wrote:
>> 
>> 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 at 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
>> 
>> 
>> 
>>> On Jun 19, 2018, at 10:56 AM, Scott McGrath <scmcgrath at gmail.com> 
>>> wrote:
>>> 
>>> 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 at earthlink.net> wrote:
>>> 
>>> On 6/18/18 6:39 PM, Glenn Little WB4UIV wrote:
>>> 
>>>> To do the grounding correctly, all connections exterior to the 
>>>> building are to be welded.
>>>> The cable to ground rod welds are to be 18 inches below grade.
>>>> The exterior cable is to be number 2 copper or larger.
>>>> To bond numerous ground systems together, a number 2 copper cable is 
>>>> to be buried at 18 inches and welded to each ground system.
>>>> If using eight foot ground rods, a ground rod is to be driven every 
>>>> 16 feet along the connecting cable and the cable welded to the rod.
>>> 
>>> 
>>> 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.
>>> 
>>> 
>>>> A lot of work, but, cheaper, in the long run, than continuing to 
>>>> repair/replace equipment.
>>> 
>>> 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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-- 
Dr. Don Latham
PO Box 404, Frenchtown, MT, 59834
VOX: 406-626-4304




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