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 [email protected] 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"
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