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

Bob kb8tq kb8tq at n1k.org
Tue Jun 19 15:55:57 EDT 2018


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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