[Towertalk] Grounds, UFER grounds

[Steve G.]

Jim and Kelly,

Interesting thread...

While the in the USAF several years ago (less than 10 yrs), I made ground 
point resistance/impedance measurements using a bridge device like you've 
mentioned.  The test equipment device is known as a "vibraground"  or 
"vibroground" and measures the ground system's impedance in ohms.  In 
practice, three connections are made. One to the ground point under test, 
and the other two were made with insulated wire to short copper rods about 
18" long.  These rods were driven about 33 feet and 100 feet from the 
ground point under test (rod, plate or system) at a 3:1 spacing ratio from 
the point under test.  The device, I believe, made these measurements in 
the ULF frequency range, or at several KHz.

BTW, the few UFER ground measurements I made were surprisingly good, 
considering where I made them (Elmendorf AFB in Anchorage, AK).  Anchorage 
is sitting on a rocky moraine with questionable quality and amounts of 
soil.  If my memory serves me right, they measured around 5 to 10 
ohms.  But, these were big bldg's with large cement pads/foundations.

If I were to build a house, I'd do some more reading on them, and specify 
the contractor to install a copper network around and through the bldg's 
foundation.  I made the measurements, and seen them work.

Oh, I suppose a similar device might be found gov't surplus, or at one of 
the used test equipment company websites.

73 de Steve, KZ9G/7

At 09:42 AM 4/11/2002 -0700, you wrote:

>I suppose that one could make some sort of impedance bridge measurement to 
>measure the impedance between your "ground connection" and some 
>standardized electrode, for which the characteristics can be known by 
>calculation.  Like, for instance, a big sphere, or maybe a flat plate, or 
>a single wire suspended at a fixed height above the ground.
>
>Ground resistance/impedance measurements are one of the ways used for 
>subsurface exploration, so there should be some technical literature 
>available.  Once one knows what the "electromagnetic structure" of the 
>soil is, then you could use any of a variety of modeling techniques to see 
>how close your scheme comes to "ideal".
>
>This comes down to "what is ground"?  A non-trivial question that really 
>can only be answered, it depends....
>kelly johnson wrote:
> >
> > So, how do you know if you have a good ground
> > or not?  If there's stray RF all over the place
> > I usually assume there's a bad ground, but unless
> > it's really obvious like this, how do you tell?
> >
> > On Wed, 10 April 2002, "Jim Lux" wrote
> >
> > >
> > > Nope.. I haven't tried it for RF (got a standard
> > ground rod hammered into
> > > the ground).. My house's electrical service, though,
> > does use a UFER ground.
> > > A bit of web searching should turn up some info on RF
> > properties though..
> > > Lightning protection and RF are very similar
> > applications...
> > >
> > > I was more interested in pointing out that the
> > surface area of a ground rod
> > > isn't all that huge... so a buried 2x2 foot copper
> > plate could actually be a
> > > "better" ground...
> > >
> > > A lot also depends on where your water table is, how
> > wet the soil is,
> > > capacitive coupling, etc.
> > >
> > >
> > > ----- Original Message -----
> > > From: "Bill Axelrod" <bill@axelrods.org>
> > > To: <jimlux@earthlink.net>
> > > Sent: Wednesday, April 10, 2002 8:32 PM
> > > Subject: Re: [Towertalk] Grounds, UFER grounds
> > >
> > >
> > > > This is an interesting thread since one of my goals
> > this spring is to
> > > > install a better system ground.  Jim, if I read
> > your posting correctly,
> > > you
> > > > say that I would be essentially equally served with
> > a 10x10 inch plate
> > > than
> > > > I would with a 1/2" diameter rod 10 feet long.
> > > >
> > > > Does that pertain to the RF ground as well as the
> > DC ground?  If you use
> > > > such a ground, how have you fared with it?
> > > >
> > > > Thanks and 73...   Bill K3WA  bill@axelrods.org
> > >
> > >
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