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

[Glenn Little WB4UIV]

Unless all of your ground rods are bonded together, you are inviting 
disaster.

If you have two ground systems, one at the tower and the other at the 
house, you have a very dangerous situation.

If you have a unified (bonded) ground system and take a lightning strike 
every thing elevates to to same level, be it 10 Volts or 100 KV.
There is no difference in potential between equipments and everything is 
happy.
If there are two ground systems, they will not elevate to the same level 
at the same rate.
In this case, you have differences in potential between equipments and 
damage.


MIL-HDBL-419 is a very good grounding reference and is available for 
free download.

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.

I did lightning mitigation for seven years for a tower site monitoring 
company.
When these steps were followed, lightning damage was very minimal or 
non-existent.

You stated that the GPS antenna was on a tower.
To correctly install an antenna on a tower the feedline is to be bonded 
to the tower near the base of the antenna.
The feedline is again bonded to the tower where to leaves the tower 
heading for the building.
Prior to entering the building, the feedline is bonded to a copper plate 
called a ground window.
This ground window is bonded to the ground system.
The feedline goes through a surge suppressor the is bonded to the ground 
window prior to entering the building.

All equipment in the building should be bonded to a ground buss made of 
number 6 copper and bonded to the ground window.

A lot of work, but, cheaper, in the long run, than continuing to 
repair/replace equipment.

73
Glenn
WB4UIV




On 6/18/2018 2:29 PM, Dan Kemppainen wrote:
> Hi,
>
> I have (or had, I guess) a GPS antenna on a tower that took a 
> lightning hit yesterday.
>
> You can tell it's going to be a bad day when you walk into your shop, 
> and smell burnt electronics. Still have to troubleshoot exactly what 
> got hit, but the GPSDO was flashing no GPS signal, the 5V supply for 
> the antenna to the GPS splitter was dead, the data logging computer 
> had rebooted and the data logging computer monitor was dead. Other 
> network hardware was dead also.
>
> This is a bit surprising since the tower itself is grounded with 4 
> ground rods and bonded to a 150 foot deep well casing near by. The 
> antenna is on the end of 250 ft run of RG6. The GPS antenna cable 
> shield has a grounding block bonded to two ground rods driven down 
> below the basement foundation where it enters the house. I'm guessing 
> the surge ran the coax into the splitter, then through everything 
> connected to it, despite the grounding block.
>
> So, I'm wondering if there are better surge protectors for lightning 
> protection? Maybe something that actually protect the center conductor 
> also? Hopefully something that will pass GPS signal reasonably and let 
> DC power through. If so, can you recommend some starting points? Other 
> suggestions also welcome.
>
>
> Also, If you are considering upgrading your own lightning protection, 
> hopefully this will be some inspiration to get started. As I said 
> earlier, it's a bad day when you smell burnt electronics in the shop.
>
> Thanks,
> Dan
>
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-- 
-----------------------------------------------------------------------
Glenn Little                ARRL Technical Specialist   QCWA  LM 28417
Amateur Callsign:  WB4UIV            wb4uiv at 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"