Station With Center-Fed Dipole - Best Grounding Technique?
 

On Mon, 04 May 2009, Richard Clark wrote:

A very good description of your set-up. You are already
grounded through a the haphazard path of your AC outlet
- if you chose to use three prong connections, if your outlet
is in fact grounded, if your equipment actually has a safety
ground to chassis. A lot of "ifs," hence my use of "haphazard."


Okay, I have checked each of those. The house was recently inspected
ensure compliance with recent building code requirements, with the
outlets and overall grounding system checked for proper wiring at that
time. The house wiring exceeded current building requirements, which I
was indeed happy to hear.

The radio uses a three-prong cord (a requirement here), with the
chassis apparently connected at several points to the ground of that.
It appears the antenna shield side of the connector is also bolted
directly to that chassis.


By deliberately adding a ground wire going to an ad-hoc
ground rod, you can easily introduce problems. (snip)


So you recommend no additional grounding?

stewart / w5net

Station With Center-Fed Dipole - Best Grounding Technique?
 

dave wrote:
Jim Lux wrote:


Do you use a balun at the antenna
feedpoint? How do you tune the inverted-V?

Good RF chokes on the coax at the feedpoint and at the point of entry
would go a long way to eliminating any "RF in the shack" problems. A
couple 2.4" 31 mix cores with half a dozen turns on them, for instance.

Whether the V is tuned or not won't have any effect on RFI or grounding.

A BalUn would help a lot.

Balun/choke.. tomato, tomato.. they're really all the same thing. Keep
the RF off the outside of the coax.



Since we are sticklers for the NEC, Homey needs a #6 wire from where the
transmission line enters the dwelling to an 8' copper clad rod driven
into the earth, as close as practicable.

The communications system (be it CATV, net powered broadband, amateur,
etc.) would need to be bonded to any of the usual things that form the
grounding/bonding system,e.g, one could "ground" through the metal conduit.

A ground rod is, of course, not recommended in the current codes as a
made electrode, and in any case, the code doesn't necessarily require a
specially installed ground for this purpose. If you DO install another
ground, then it has to be bonded with AWG #6 copper (or bigger) (can't
use the conduit)

Telephone has different rules. Must have electrode/grounding means as
close as practicible to point of entrance, and the ground wire has to be
AWG14 or large, insulated, in as straight a line as possible.

Metal structure supporting outdoor antenna systems have to be grounded
with AWG10 or bigger copper, AWG8 aluminum, or AWG17 copperclad steel,
straight line. (the size requirement is for mechanical strength, not
conductivity, which is why the copperweld(r) can be smaller)

So you have these weird situations where the phone protection block has
to be connected with AWG14 insulated to a grounding electrode as close
as practicible, but then, because of the "bonding of electrodes" rules,
you have to connect that electrode to the "house ground" with nothing
smaller than AWG6.

CATV is even different.. grounding block for drop has to be grounded to
an electrode close to block and an *insulated* AWG14 or bigger run to
bond with the rest of the house's grounding system.


This sort of thing is why most ham installations aren't "code
compliant"... heck, you could go insane trying to wend your way through
the thicket of rules for the NEC. And that doesn't even begin to get
into the transient suppression guidelines and/or NFPA 780 lightning
protection rules.

Station With Center-Fed Dipole - Best Grounding Technique?
 

Howard Lester wrote:
"dave" wrote

A BalUn would help a lot.

For what? If the antenna system is balanced (as are dipoles, inherently), I
seriously doubt a balun would be good for anything.



Most every practical dipole installation has some imbalance in the
installation (the trees are closer to one side than the other, etc.).. a
choke to prevent RF current from flowing on the outside of the feedline
will at least make the pattern more consistent with expectations.
Might make the tuning less "twitchy" too (because you've decoupled the
effect of things near the feedline).

Certainly, a choke at the entrance to the shack is a great way to keep
RF outside.

Station With Center-Fed Dipole - Best Grounding Technique?
 

Cecil Moore wrote:
dave wrote:
Since we are sticklers for the NEC, Homey needs a #6 wire from where
the transmission line enters the dwelling to an 8' copper clad rod
driven into the earth, as close as practicable.

What if it is 1/4WL long?

The NEC cares not one whit for RF performance. The NEC rules are
designed to keep the house from burning down or people dying if
something happens: like a power line falling on the antenna. I read a
quoted statistic (for which I can't find the original source, so it
might not be trustable) that electrocution is the leading cause of death
in connection with antennas.

Station With Center-Fed Dipole - Best Grounding Technique?
 

I was skeptical, but did as he suggested. Dug a hole (about a foot
deep) around each ground rod, drove the rods in a bit deaper, poured
in a generous helping of rock salt, and then watered the area long
enough for the salt to spread into the soil.

Of course, the radio was fine immediately after adding the water, but
the real test was the next day once the water drained away. The radio
did operate just fine that next day, and the day after that. In fact,
the rock salt added to the soil (more added every two to three months)
resolved the problem entirely the remainder of my time at that
location.


The professionals use something like bentonite or montmorillion clay
(kitty litter) as a soil admixture. The stuff is like a sponge and
holds the water real well (by surface tension) and is very ionic as
well, so the conductivity is good. You have to be careful, because too
much causes an expansive soil problem.

Station With Center-Fed Dipole - Best Grounding Technique?
 

On Tue, 05 May 2009 17:10:16 +0200, noname wrote:

On Mon, 04 May 2009, Richard Clark wrote:

A very good description of your set-up. You are already
grounded through a the haphazard path of your AC outlet
- if you chose to use three prong connections, if your outlet
is in fact grounded, if your equipment actually has a safety
ground to chassis. A lot of "ifs," hence my use of "haphazard."


Okay, I have checked each of those. The house was recently inspected
ensure compliance with recent building code requirements, with the
outlets and overall grounding system checked for proper wiring at that
time. The house wiring exceeded current building requirements, which I
was indeed happy to hear.

Hi Steve,

So, in fact your three prong plugs find their way to the panel ground.
Can YOU find that ground?


The radio uses a three-prong cord (a requirement here), with the
chassis apparently connected at several points to the ground of that.
It appears the antenna shield side of the connector is also bolted
directly to that chassis.

So, by this explicit statement, your "balanced" antenna has been
unbalanced at the rig (which only further enforces the unbalance by
virtue of the coax connection).

By deliberately adding a ground wire going to an ad-hoc
ground rod, you can easily introduce problems. (snip)


So you recommend no additional grounding?

This is a loaded question because there are TWO grounds which
discussion often gets mixed. They may both go to the same point of
zero potential, but their paths are what distinguish them. The TWO
grounds are safety ground and RF ground. Any wire that is
significantly long at a wavelength of your operation, will qualify
more as a radiator than it will as a ground wire.

Consider you are sitting at your transmitter, it has a dedicated newly
applied ground wire that runs the shortest distance to what you think
of as ground. Maybe that is all of 10 feet. You are operating on
10M. Ground is a quarterwave away. That puts your equipment at the
high potential end of a wire with zero potential at ground. How
grounded does that sound?

The solution there is to add an artificial ground tuner to move that
potential away from you (this would be an attempt to "balance" the
distribution so that your equipment sits at an artificially imposed
neutral - ground of another mother).

Thing is, as I said, you already have a ground connection. The safety
ground is a necessity unless you are very practiced in the art of
isolation. You can add another path, and, again, that path may be a
different length to the one you already have. Given that situation,
you may find one path now spilling current into the new one - as
dependant upon the wavelength of operation and the physical path
lengths. When this spilling from one path into the other occurs,
strange things happen compared to if you hadn't added that new path.

More's to be said, but that's enough for now.

73's
Richard Clark, KB7QHC

Station With Center-Fed Dipole - Best Grounding Technique?
 

Richard Clark wrote:
On Tue, 05 May 2009 17:10:16 +0200, noname wrote:

On Mon, 04 May 2009, Richard Clark wrote:
A very good description of your set-up. You are already
grounded through a the haphazard path of your AC outlet
- if you chose to use three prong connections, if your outlet
is in fact grounded, if your equipment actually has a safety
ground to chassis. A lot of "ifs," hence my use of "haphazard."

Okay, I have checked each of those. The house was recently inspected
ensure compliance with recent building code requirements, with the
outlets and overall grounding system checked for proper wiring at that
time. The house wiring exceeded current building requirements, which I
was indeed happy to hear.

Hi Steve,

So, in fact your three prong plugs find their way to the panel ground.
Can YOU find that ground?

The radio uses a three-prong cord (a requirement here), with the
chassis apparently connected at several points to the ground of that.
It appears the antenna shield side of the connector is also bolted
directly to that chassis.

So, by this explicit statement, your "balanced" antenna has been
unbalanced at the rig (which only further enforces the unbalance by
virtue of the coax connection).

By deliberately adding a ground wire going to an ad-hoc
ground rod, you can easily introduce problems. (snip)

So you recommend no additional grounding?

This is a loaded question because there are TWO grounds which
discussion often gets mixed. They may both go to the same point of
zero potential, but their paths are what distinguish them. The TWO
grounds are safety ground and RF ground. Any wire that is
significantly long at a wavelength of your operation, will qualify
more as a radiator than it will as a ground wire.

Consider you are sitting at your transmitter, it has a dedicated newly
applied ground wire that runs the shortest distance to what you think
of as ground. Maybe that is all of 10 feet. You are operating on
10M. Ground is a quarterwave away. That puts your equipment at the
high potential end of a wire with zero potential at ground. How
grounded does that sound?

Worse than that. You've basically made a big loop antenna: greenwire
ground to panel, panel to ground rod, ground rod to rig.





The solution there is to add an artificial ground tuner to move that
potential away from you (this would be an attempt to "balance" the
distribution so that your equipment sits at an artificially imposed
neutral - ground of another mother).

Or, easier.. put a choke around the feedline where it comes into the
shack, so that there's no appreciable RF current through the chassis and
green-wire ground.




Thing is, as I said, you already have a ground connection. The safety
ground is a necessity unless you are very practiced in the art of
isolation. You can add another path, and, again, that path may be a
different length to the one you already have. Given that situation,
you may find one path now spilling current into the new one - as
dependant upon the wavelength of operation and the physical path
lengths. When this spilling from one path into the other occurs,
strange things happen compared to if you hadn't added that new path.


Exactly.. one DC/Line frequency path is all that's needed for safety.

Station With Center-Fed Dipole - Best Grounding Technique?
 

Jim Lux wrote:
Howard Lester wrote:
"dave" wrote

A BalUn would help a lot.

For what? If the antenna system is balanced (as are dipoles,
inherently), I seriously doubt a balun would be good for anything.


Most every practical dipole installation has some imbalance in the
installation (the trees are closer to one side than the other, etc.).. a
choke to prevent RF current from flowing on the outside of the feedline
will at least make the pattern more consistent with expectations. Might
make the tuning less "twitchy" too (because you've decoupled the effect
of things near the feedline).

Certainly, a choke at the entrance to the shack is a great way to keep
RF outside.

A choke wastes power.

Station With Center-Fed Dipole - Best Grounding Technique?
 

Jim Lux wrote:
Howard Lester wrote:
"dave" wrote

A BalUn would help a lot.

For what? If the antenna system is balanced (as are dipoles,
inherently), I seriously doubt a balun would be good for anything.


Most every practical dipole installation has some imbalance in the
installation (the trees are closer to one side than the other, etc.).. a
choke to prevent RF current from flowing on the outside of the feedline
will at least make the pattern more consistent with expectations. Might
make the tuning less "twitchy" too (because you've decoupled the effect
of things near the feedline).

Certainly, a choke at the entrance to the shack is a great way to keep
RF outside.

A choke wastes power.

Station With Center-Fed Dipole - Best Grounding Technique?
 

dave wrote:
A choke wastes power.

I certainly wish that the RF power that left my lip
with an RF burn scar had been wasted by a choke.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com