Putting in some new ground rods today.

Dirt in the yard (Maryland) is semi-rocky. House is on a hill and
certainly well above the water table.

I sank 5/8" copper-clad 8-foot ground rods around the yard. Some went
in fairly easy others required some pretty good sledgehammer action.
No two ground rods are closer than 16 feet apart.

Random measurements between two nearish (20 to 25 feet) ground rods
give resistances in the 50 to 100 ohm range. The ones that went in
easiest seem to have highest resistance. (Possibly construction fill
near the house foundation?)

Paralleling a bunch on one side of the yard, and a bunch on the other
side of the yard, gives resistances between the bunches in the 15-20
ohm range.

Resistance measurements done with homebrew fall-of-potential tester
that puts about 100mA between the probes. Tested both polarities and
results seem similar. If I scope the potential between the probes
there's clearly already a fair amount of 60Hz AC current flowing in
the ground as well as a DC component (there is a substation across the
street and about 100 yards down if that means anything...)

I'm guessing this means that when I tie everything together I can
guesstimate the resistance to "true" ground being in the 10 to 20 ohm
range.

I kinda wonder why I spent money on all this heavy 6 AWG copper wire
to hook everything together, when the resistance of the ground itself
is bigger than the resistance of the wire. I mean, it wouldn't feel
right wiring it with 22 gauge hookup wire, but isn't 6 AWG overkill?
10 Ohms of 6AWG is like 5 miles of copper that I can't afford :-(.

Tim KA0BTD

On Sun, 17 Jun 2007 10:35:06 -0700, Tim Shoppa
wrote:

I kinda wonder why I spent money on all this heavy 6 AWG copper wire
to hook everything together, when the resistance of the ground itself
is bigger than the resistance of the wire. I mean, it wouldn't feel
right wiring it with 22 gauge hookup wire, but isn't 6 AWG overkill?
10 Ohms of 6AWG is like 5 miles of copper that I can't afford :-(.

Hi Tim,

The choice of 6 AWG, I suppose, was driven (or should have been
driven) by code.

The alternative to your 10 Ohms would be infinite Ohms. In that
sense, quite an improvement. Driving it down to 1 Ohm will take much
more effort (and grief).

Yet and all, it has nothing to do with RF ground (sorry). What you
have accomplished serves your safety from lighting strokes. On the
plus side (when we get beyond survival techniques) you also gain from
removing a lot of ground currents getting into your gear. This can be
especially painful in the sense of Signal to Noise ratio. Worse, if
untreated, it can lead to component failure or shock hazards (you DID
connect all these grounds together, didn't you?).

Laying radials would have reduced your ground resistance, faster, and
lower - but this is not conventional code. Radials will help with
near RF ground, but will not otherwise help with obtaining those low
DX launch angles (not, unless you invest in 5 mile radials).

The discussion of the benefits/pay-back for radials drives a lot of
discussion. Simple advice (if you are building a vertical) is to make
them as long as your antenna is high, and plant a dozen or two about
an inch below the soil, or beneath the grass above the soil.

73's
Richard Clark, KB7QHC

"Tim Shoppa" wrote in message
ps.com...
Putting in some new ground rods today.

Dirt in the yard (Maryland) is semi-rocky. House is on a hill and
certainly well above the water table.

I sank 5/8" copper-clad 8-foot ground rods around the yard. Some went
in fairly easy others required some pretty good sledgehammer action.
No two ground rods are closer than 16 feet apart.

Random measurements between two nearish (20 to 25 feet) ground rods
give resistances in the 50 to 100 ohm range. The ones that went in
easiest seem to have highest resistance. (Possibly construction fill
near the house foundation?)

Paralleling a bunch on one side of the yard, and a bunch on the other
side of the yard, gives resistances between the bunches in the 15-20
ohm range.

Resistance measurements done with homebrew fall-of-potential tester
that puts about 100mA between the probes. Tested both polarities and
results seem similar. If I scope the potential between the probes
there's clearly already a fair amount of 60Hz AC current flowing in
the ground as well as a DC component (there is a substation across the
street and about 100 yards down if that means anything...)

I'm guessing this means that when I tie everything together I can
guesstimate the resistance to "true" ground being in the 10 to 20 ohm
range.

I kinda wonder why I spent money on all this heavy 6 AWG copper wire
to hook everything together, when the resistance of the ground itself
is bigger than the resistance of the wire. I mean, it wouldn't feel
right wiring it with 22 gauge hookup wire, but isn't 6 AWG overkill?
10 Ohms of 6AWG is like 5 miles of copper that I can't afford :-(.

Tim KA0BTD

Ground rods have to "settle" for a few weeks - at least - before
measurements make some sense. Give them water, as you would do with plants.
Borrow a genuine earth resistance "Megger" (or similar) and operate it by
the rules.

the idea on 6ga is to have something heavy enough to handle the current of a
power line fault or lightning surge. so yes, use the 6ga. note that as you
bury the wire it will also reduce the total resistance some more, so its not
a total waste to take what you have left over and add it as buried
radials... don't do the tuck them into the grass trick though, trench or
make a good slit for them so they are in contact with solid dirt, the deeper
the better.


"Tim Shoppa" wrote in message
ps.com...
Putting in some new ground rods today.

Dirt in the yard (Maryland) is semi-rocky. House is on a hill and
certainly well above the water table.

I sank 5/8" copper-clad 8-foot ground rods around the yard. Some went
in fairly easy others required some pretty good sledgehammer action.
No two ground rods are closer than 16 feet apart.

Random measurements between two nearish (20 to 25 feet) ground rods
give resistances in the 50 to 100 ohm range. The ones that went in
easiest seem to have highest resistance. (Possibly construction fill
near the house foundation?)

Paralleling a bunch on one side of the yard, and a bunch on the other
side of the yard, gives resistances between the bunches in the 15-20
ohm range.

Resistance measurements done with homebrew fall-of-potential tester
that puts about 100mA between the probes. Tested both polarities and
results seem similar. If I scope the potential between the probes
there's clearly already a fair amount of 60Hz AC current flowing in
the ground as well as a DC component (there is a substation across the
street and about 100 yards down if that means anything...)

I'm guessing this means that when I tie everything together I can
guesstimate the resistance to "true" ground being in the 10 to 20 ohm
range.

I kinda wonder why I spent money on all this heavy 6 AWG copper wire
to hook everything together, when the resistance of the ground itself
is bigger than the resistance of the wire. I mean, it wouldn't feel
right wiring it with 22 gauge hookup wire, but isn't 6 AWG overkill?
10 Ohms of 6AWG is like 5 miles of copper that I can't afford :-(.

Tim KA0BTD

Dave wrote:
the idea on 6ga is to have something heavy enough to handle the current of a
power line fault or lightning surge. so yes, use the 6ga. note that as you
bury the wire it will also reduce the total resistance some more, so its not
a total waste to take what you have left over and add it as buried
radials... don't do the tuck them into the grass trick though, trench or
make a good slit for them so they are in contact with solid dirt, the deeper
the better.

In fact I measured the resistance-to-a-ground-rod from a 20-foot
section of buried bare 6AWG stranded wire, and it was in the hundreds
of ohms. My conclusion was that buried radials, while great for a
vertical antenna installation, were pretty crappy as a DC ground. Of
course it's a lot easier to slit the ground (I have random mixed rocks
but ignore them) than to drive down a ground rod - I did several rods
this morning and am pretty sore from the sledgehammer work tonight.

It is no coincidence that the rods are laid out in a radial-type
pattern (at least until I get up to the driveway).

Tim.

Richard Clark wrote:
On Sun, 17 Jun 2007 10:35:06 -0700, Tim Shoppa
wrote:
The choice of 6 AWG, I suppose, was driven (or should have been
driven) by code.

That's true. It also seemed stupid to use 22AWG wire after driving
down a 5/8" diameter ground rod :-). Still, copper is so damn
expensive today!

The alternative to your 10 Ohms would be infinite Ohms. In that
sense, quite an improvement. Driving it down to 1 Ohm will take much
more effort (and grief).

Yet and all, it has nothing to do with RF ground (sorry). What you
have accomplished serves your safety from lighting strokes. On the
plus side (when we get beyond survival techniques) you also gain from
removing a lot of ground currents getting into your gear. This can be
especially painful in the sense of Signal to Noise ratio. Worse, if
untreated, it can lead to component failure or shock hazards (you DID
connect all these grounds together, didn't you?).

While the rods were laid out in a roughly radial pattern from the
entrance panel, the driveways kept me from doing the world's best
radial pattern :-).

Yes, these are all bonded to the existing older ground system at the
entrance panel. I also measured the resistance to the older ground
system and it seems the old system barely met code.

Laying radials would have reduced your ground resistance, faster, and
lower - but this is not conventional code. Radials will help with
near RF ground, but will not otherwise help with obtaining those low
DX launch angles (not, unless you invest in 5 mile radials).

The discussion of the benefits/pay-back for radials drives a lot of
discussion. Simple advice (if you are building a vertical) is to make
them as long as your antenna is high, and plant a dozen or two about
an inch below the soil, or beneath the grass above the soil.

All my antennas are dipoles hung between trees right now, but I used
to have a vertical (4BTV) a few decades ago. I look at pictures of the
AV-18HT in the catalogs with a lot of envy in my eyes!

Tim.

"Tim Shoppa" wrote in message
ups.com...
Richard Clark wrote:
On Sun, 17 Jun 2007 10:35:06 -0700, Tim Shoppa
wrote:
The choice of 6 AWG, I suppose, was driven (or should have been
driven) by code.

That's true. It also seemed stupid to use 22AWG wire after driving
down a 5/8" diameter ground rod :-). Still, copper is so damn
expensive today!
===================
The ground rod diameter is large because of (physical) necessity since it
must endure a pounding on one end without bending, so don't feel like the
diameter of the ground rods make it necessary to use large wire.
I have used 12 ga (as radials) (not as bonding conductors per the NEC).
You're right copper is high.
=================

While the rods were laid out in a roughly radial pattern from the
entrance panel, the driveways kept me from doing the world's best
radial pattern :-).

Yes, these are all bonded to the existing older ground system at the
entrance panel. I also measured the resistance to the older ground
system and it seems the old system barely met code.

================
it would be interesting to see what difference it would make if you just
burried the same dollars-worth of 12ga wire about 2 or 3 inches and omit
most of the ground rods..
==========
All my antennas are dipoles hung between trees right now, but I used
to have a vertical (4BTV) a few decades ago. I look at pictures of the
AV-18HT in the catalogs with a lot of envy in my eyes!

Tim.

On Sun, 17 Jun 2007 22:30:12 -0400, "Hal Rosser"
wrote:

it would be interesting to see what difference it would make if you just
burried the same dollars-worth of 12ga wire about 2 or 3 inches and omit
most of the ground rods..

Hi Hal,

That has been discussed here at depth (no pun, well maybe) and it
works nearly as well (barring the current density vaporizing it during
a lightning strike).

Depth does not bring any great boon to lowering resistance that cannot
be served with a lateral bar of the same length. As usual, simple
answers have their problems, but this simple answer serves many
trivial concerns (RF ground being one).

73's
Richard Clark, KB7QHC