Many things I've read over the last couple of weeks on the proper
grounding of towers and ham stations all emphasize the importance of a
single point ground.

What if it's not possible to implement that?

My tower is on the other end of the house from where the electrical
service (and its associated ground) are. I did not put the tower there
and if it had been left up to me it wouldn't have gone there, but that's
another story for another time... point is that the tower and the service
ground are 50+ feet apart, and the shack (using the only available spare
bedroom) is on the end of the house where the service ground is.

I can beat a fistful of ground rods around the tower, and put another one
in the ground below the shack window (that's the one I'm doing now), and
bond it all together with buried heavy gauge copper wire that also bonds
to the service ground... but that ain't a single point ground, it's more
like a 50+ foot long distributed ground.

So, how do I achieve that ideal "single point ground" in a situation like
this?

On Sat, 14 Jul 2007 19:53:02 -0400, Rick (W-A-one-R-K-T) wrote:

So, how do I achieve that ideal "single point ground" in a situation
like this?

As I understand it, a "single point ground" means that everything is tied
to the same ground system however big or small that is. What you don't
want is the shack tied to a ground and the tower to its own ground with
the cabling tying the two together. The result will be unequal potential
at the tower and in the shack. A "single point ground" reference means
that the potential everywhere will be the same, rising and falling
together in the event of a strike.

I have seen it recommended to make that 50' run of #2 stranded copper and
place a ground rod approximately every eight feet along the run (no
closer than eight feet). You will have a much improved lightning ground
*and* a "single point ground". Beating a bunch of ground rods in the
ground is of little value unless they are at least eight feet apart.

Poke around Polyphaser's Web site for more detail information.

73, de Nate

--

"The optimist proclaims that we live in the best of all possible worlds,
the pessimist fears this is true."

"Nate Bargmann" wrote in message
news
On Sat, 14 Jul 2007 19:53:02 -0400, Rick (W-A-one-R-K-T) wrote:

So, how do I achieve that ideal "single point ground" in a situation
like this?

As I understand it, a "single point ground" means that everything is tied
to the same ground system however big or small that is. What you don't
want is the shack tied to a ground and the tower to its own ground with
the cabling tying the two together. The result will be unequal potential
at the tower and in the shack. A "single point ground" reference means
that the potential everywhere will be the same, rising and falling
together in the event of a strike.

I have seen it recommended to make that 50' run of #2 stranded copper and
place a ground rod approximately every eight feet along the run (no
closer than eight feet). You will have a much improved lightning ground
*and* a "single point ground". Beating a bunch of ground rods in the
ground is of little value unless they are at least eight feet apart.

Poke around Polyphaser's Web site for more detail information.

73, de Nate

--

"The optimist proclaims that we live in the best of all possible worlds,
the pessimist fears this is true."

the infamous 'single point ground' only refers to protecting equipment in a
single room or building... it does not refer to tying the grounds of
everything outside of a building or room together in any way... while that
is required by electrical code it is not going to protect your equipment,
all it does is make sure that if you touch 2 pieces of equipment their cases
are don't have power line voltage difference between them. The concept of a
single point ground is that you define a single point for your shack that is
the 'ground' and everything is connected to that one point, usually on an
outside wall of the shack. So any power, phone, catv, antenna, or other
wire coming into the shack is grounded and has lightning protectors on the
same panel at one spot on the wall. if this is done properly then
everything in the room will be at the same potential even during a surge
from a lightning stroke.

"Rick (W-A-one-R-K-T)" wrote in message
news

Many things I've read over the last couple of weeks on the proper
grounding of towers and ham stations all emphasize the importance of a
single point ground.

What if it's not possible to implement that?

My tower is on the other end of the house from where the electrical
service (and its associated ground) are. I did not put the tower there
and if it had been left up to me it wouldn't have gone there, but that's
another story for another time... point is that the tower and the service
ground are 50+ feet apart, and the shack (using the only available spare
bedroom) is on the end of the house where the service ground is.

I can beat a fistful of ground rods around the tower, and put another one
in the ground below the shack window (that's the one I'm doing now), and
bond it all together with buried heavy gauge copper wire that also bonds
to the service ground... but that ain't a single point ground, it's more
like a 50+ foot long distributed ground.

So, how do I achieve that ideal "single point ground" in a situation like
this?

Rick

You are thinking too deeply about this and worrying unnecessarily. If you
have grounding at the antenna and grounding 50+ feet away connected by a
heavy guage copper cable buried in the ground, the whole system will be at
the same potential and can be considered as a single point. The mistake that
gets made is when people put two separate earthing points in at different
locations and assume that both earth points are at the same potential. This
isn't necessarily the case if earth leakage currents are flowing to ground
and the earth electrode resistances are slightly different. Computers,
switch mode power supplies, washing machines, electric motors and electric
cookers all tend to generate some earth leakage current, usually only a few
millivolts, but for radio purposes you are receiving signals 1000 x fainter
in the microvolt range. This is where a lot of interference problems arise.
Bonding all the earth points together with thick cable is a perfectly valid
solution to ensuring that all the earth points are at the same common
potential.

If the antenna tower gets hit by lightning, the current will disipate into
the ground by the most direct route possible. Sure there will be an
instantaneous voltage gradient going out a few feet around the antenna base
for a couple of milliseconds immediately after the strike, but any equipment
damage will most likely be caused by electromagnetic pulse from the
lightning strike and not voltage flowing up the earth wire into your
equipment. A lightning strike that close can potentially damage equipment
that is completely disconnected and powered down.

The earth leakage currents are often caused by induced voltages in equipment
casings due to high currents flowing in rotary motors operating washing
machines and the like. In event of a nearby lightning strike the process is
effectively reversed. The equipment casing absorbs energy and a voltage
differential is created and absorbed across components inside the case.
Unless you are using valve equipment, a direct lightning strike will very
likely cause some damage to connected electronic equipment. With a decent
earth it may only take out the protection diodes across a receiver front
end - fairly easily fixable. Worst case, your insurance will have to pay out
for new equipment.

Just stick the ground rods in, connect them all together and job done.

Mike G0ULI

"Rick (W-A-one-R-K-T)" wrote in
news

Many things I've read over the last couple of weeks on the proper
grounding of towers and ham stations all emphasize the importance of a
single point ground.

What if it's not possible to implement that?

My tower is on the other end of the house from where the electrical
service (and its associated ground) are. I did not put the tower there
and if it had been left up to me it wouldn't have gone there, but
that's
another story for another time... point is that the tower and the
service
ground are 50+ feet apart, and the shack (using the only available
spare
bedroom) is on the end of the house where the service ground is.

I can beat a fistful of ground rods around the tower, and put another
one
in the ground below the shack window (that's the one I'm doing now),
and
bond it all together with buried heavy gauge copper wire that also
bonds
to the service ground... but that ain't a single point ground, it's
more
like a 50+ foot long distributed ground.

So, how do I achieve that ideal "single point ground" in a situation
like
this?


Rick,

I think you are envisaging too great a scope for your single point
ground, and it is unlikely to work as you want.

The reason for single point grounding is to make sure that you do not
have endesired current paths (and associated potential drops), and
prinipally between equipment in an equipment room.

If you thing about what it is trying to achieve, minimising potential
differences between equipment interfaces by avoiding potential
differences between the "ground" points of equipments, then you should be
able to intelligently design a single point grounding scheme in the
equipment room and bond it to your external grounds (tower, AC earthing,
others) in a similarly sensible way.

Owen