Gary,
Your thinking isn't 'crooked', so it doesn't need straightening.
You are confused by the term SPG. It does NOT mean that EVERYTHING is
tied to ONE POINT!
The ground you have outside your shack is the SPG for your
equipment/shack, provided all 'boxes' in the shack are tied to it and
not simply to each other.
The common practice, many years ago, was the 'daisy-chain' the ground
from box to box to box, etc ... and then ONE wire went to ground.
This is a problem waiting to happen.
Tie EACH of the 'boxes' in the shack to the SPG outside with SEPARATE
ground wires. Thus, the SPG you have serves its purpose.
The grounds at each tower are great for dissipating the initial 'blow'
if struck, but NOTHING will keep the 'strike current' from travelling
from tower to shack.
The idea is to MINIMIZE the potential damage.
Good luck
73
Don
N8DE
Quoting "Gary E. Jones" <garyejones@cmaaccess.com>:
> I have read the threads on SPG over the years, but I think I don't really
> understand a couple of concepts that are fundamental. Maybe someone can
> help.
>
>
>
> I live in a 4000 square foot ranch house which is in the shape of a "U" with
> sleeping areas on one end of one leg of the U, and Garage/laundry/den on the
> other leg of the U, and the traditional living areas in the center of the U.
> The house has two 200A 240 volt distribution panels as the house was all
> electric initially. The phone and power services all come into the house on
> the garage end of one leg of the U. The shack is one of the bedrooms on the
> other leg of the U.
>
>
>
> Further, the house is 500' from the two 90' crank up towers, each with two
> yagis stacked on them. The towers are grounded through three ground rods per
> tower. Further, the feedlines for the yagis (buryflex) enter into
> weatherproof boxes mounted on 4x4 weather resistant posts. The boxes have
> remote coax switches in them to switch the various yagis on each tower. The
> remote switches are grounded and I will be separately grounding each piece
> of buryflex at the base of the towers. There is Heliax from the remote
> switches (500' for one tower and 600' for the other tower) to the house.
>
>
>
> Now, I assume there is no logic of trying to put the house and the two
> towers at the same common ground point and that the towers have to be
> separately grounded at their base (the way that I have it now). That means
> there is a 500 and 600 foot separation between the towers and the house.
> Further, the shack is on one side of the house and the common utility
> grounds are in the center of the house. I have a separate ground rod right
> outside the shack window, so it is not a SPG even for the house.
>
>
>
> Now, is the conventional wisdom that I have a problem?
>
>
>
> I can't see an easy or even possible solution. It seems to me that the
> towers have to be grounded separately, and short of running a ground strap a
> hundred feet and boring either under my slab or around my swimming pool,
> there is no easy way to even have a SPG for the house.
>
>
>
> One more thing, it has always seemed to me that at the exact instant that a
> tower or antenna gets hit with lightening, the tower ground is going to be
> many volts higher than a second ground 500' away as the charge dissipates
> into the tower "ground". That is going to put a very large voltage
> difference between the two and is my understanding of the whole logic of
> SPG. Am I correct or wrong in my assumptions? However, if they are all tied
> together, for that same fraction of a second, isn't everything "hot" (even
> the "ground") relative to any other ground that is separated from the common
> ground?
>
>
>
> Straighten out my thinking.
>
>
>
> Thanks in advance
>
>
>
> 73
>
>
>
> Gary W5FI
>
>
>
>
>
>
>
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>
>
>
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