[TowerTalk] Station grounding on granite

[Joe - WDØM]

Here in the Rockies, the professional tower installers use 1.5 inch wide 
copper strips, spread out across the rocks to disburse lightning strikes on 
their tower installations in the mountains.  Based upon their telling me 
how well it works, I chose that method for my installation.  It's hard to 
put a ground rod into rock, and not very effective.  I had a problem 
installing my tower, because virtually all of my 5 acres has bedrock just a 
few inches under it.  I placed a copper ring around the base of the tower 
and connected it to the tower base with copper #6 wire and copper 
tubing.  I ran 50 foot lengths of 1.5 inch wide copper strips out away from 
the base and away from the house.  At the house (I was able to put in a 
ground rod near the foundation) I also ran copper #6 wire out away from the 
house in 20 - 30 foot sections to disburse the strike, and connected it all 
to the single point ground.  My web page shows how I did 
it.  Congratulations on your SteppIR - my antenna of choice as well!

http://home.centurytel.net/WD0M/

Hope this helps!

73,
Joe
WDØM

>>>Folks,
>>>
>>>Having invested in a SteppIR, a roof-top tower, a
>>>rotor, and several wire antennas, I find I have a lot
>>>of copper running out to the sky from my shack.  Too
>>>much to easily disconnect when I hear thunder.  Time
>>>to think about a better protective ground system.
>>>
>>>Inside the shack, I am thinking of a single-point
>>>ground plane near the feedline entrances.  All
>>>connections including AC power, telephone, computer,
>>>SteppIR/rotor control, etc. pass through surge devices
>>>on that plane, and all equipment is hopefully
>>>connected by low inductance strapping to the SPG.
>>>
>>>My problem is how to get a good "earth ground" for the
>>>SPG.  My house is on a granite ledge with only 1-2 ft
>>>of soil nearby. We are about 80 ft from salt water,
>>>but that doesn't help. The house does have lightning
>>>rods with 3 or 4 downleads (more on this in a moment).
>>>The 20-ft rooftop tower is connected to a lightning
>>>rod ground, but feedlines are not.
>>>
>>>I was wondering how the lightning rod grounds were set
>>>up, so I partly excavated one.  The results are
>>>visible on my web site:
>>>http://www.aa6e.net/aa6e/grounding .
>>>
>>>Is this approach - dual buried horizontal ground rods
>>>- good enough even for home protection?  Should I do
>>>something like this for my station? (The shack is not
>>>near any of the existing ground connections.)
>>>
>>>It's clear that not even an "excellent" ground
>>>connection can prevent kilovolt surges from a near
>>>hit, because that is what happens to the earth itself.
>>>And full protection from a direct hit to the house is
>>>hard to achieve (IMO) no matter how you try in a
>>>typical home retrofit. The whole shack should be
>>>inside a grounded metal box...
>>>
>>>My philosophy now is to concentrate on the SPG system
>>>and not to obsess on the low-Z ground, which must be
>>>pretty hard to realize over rock.  (I would put in
>>>something like what I see on the existing lightning
>>>rod system.) If the SPG is really good, and the
>>>equipment is all referred to that carefully, then it
>>>shouldn't matter if the whole system floats up and
>>>down by kilovolts.  (Hopefully the op is elsewhere!)
>>>
>>>The "kilovolt" scenario doesn't quite catch the full
>>>impact of a direct hit to the antenna.  10,000 amps
>>>into a one ohm ground (?) is 10 kV.  No one expects
>>>the Spanish Inquisition! (i.e., worst-case event)
>>>
>>>I would appreciate suggestions, especially from anyone
>>>who has faced a similar problem -- and survived the
>>>worst.
>>>
>>>73, Martin, AA6E
>>>
>>>p.s. Fortunately here in CT, we have fairly low
>>>lightning incidence.  Even so, we had a close strike a
>>>couple of years ago.  A BIG crack, and both my close
>>>neighbors lost their telephones and other electronics.
>>>We had no troubles here.  My tower was down then;
>>>maybe our lightning rods actually caught one. Thank
>>>you, Ben Franklin.