Don't get too hung up on a perimeter ground ring. That is good if you have
things outside at various places that need to be tied into the ground
system. It also equalizes the ground currents flowing around the building
during a strike.
Don't worry that your radials are a different length than the ground ring.
What Polyphaser was doing in the example was to show how the current divides
among all the radials and ring. Many shorter radials are better than long
radials. Too long a radial and the inductance becomes too high and it is
not as effective.
The whole idea is to dissipate the energy away from the building.
An ideal SPG box would be a bulkhead panel where everything entered the
house thru that panel via protection devices. Not always practical in a
home. Mounting the box right near where the cables are going to enter the
house is the place for the protection devices and the ground system to
start. Radials should go out from that point.
The box should be as close to your ground system as practical. You want a
short length of large strap from the SPG panel to where your ground system
starts.
73
Gary K4FMX
> -----Original Message-----
> From: towertalk-bounces@contesting.com [mailto:towertalk-
> bounces@contesting.com] On Behalf Of Jeff kb2m
> Sent: Saturday, June 19, 2010 7:25 AM
> To: 'Tower and HF antenna construction topics.'
> Subject: Re: [TowerTalk] SPG or whatever it is called now,to coax entrance
> ground question
>
> Ok. I have lots of info available about grounding to follow but as I
> didn't
> get the SPG to start with I'm thinking of doing the following...
>
> >EZ Rhino wrote:
> > Since you're starting from scratch, and since you apparently want to do
> this right the first time, what about doing a >complete ground system like
> we read in the Polyphaser papers (and elsewhere, including ARRL articles)
> in
> which you surround >the entire house with copper, with grounds rods at the
> corners and interspersed between? And how about using copper strap
> >(lower
> inductance) rather than cable? Just a thought. Sure is nice to do this
> before the landscaping and concrete go in.
>
> !From the PolyPhaser website....
>
> !All radials should be run away from the equipment building. The more
> radials there are, the more the current is divided. A !perimeter ground
> system (ring) around the building will help form an equipotential plane.
> If
> this ring is approximately equal !(in length) to each radial and if eight
> radials are used, each will have 1/9 the total surge energy. This will
> leave
> only 1/9 !the strike energy to the equipment building perimeter ground.
>
> But what happens if I don't put the other recommended 8 equal length
> radials
> in? The perimeter wire around the house will be 240'. I don't see how I
> can
> do all of this with the TWO towers that are within 70' of each other. If I
> can't put in the 15 other 240' radials what is a good compromise? Should I
> not encircle the house ?
>
>
> Also I'm still not sure if I want to place the boxes right on the
> foundation. I have plenty of room as I have a full basement and can simply
> mount them right on the concrete. Or should I be a few feet away. I would
> prefer flush mounting.
>
> Like I've been reading here, all of this involves compromise. I was really
> looking for some input from people who have gone either way (on just these
> two items) had a hit and would advise to do, or do otherwise.
>
> Giving a cup of coffee to the hired laborer with shovel :>)
>
> 73 Jeff kb2m
>
>
>
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|