single point ground

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I am finding differing opinions about a single point ground.  Here are two discussions:

KY6LA Howard: In his paper at around page 21 - Use a single point ground


K9YC Jim Brown: In his presentation around page 107 - Single point madness

Two respected sources with a difference in opinion.

My preference is a water pipe in the shack for a very low impedance connection between each station's "single point ground"; a Canadian compromise may be a "T" connection joining computer and rig with the long lead going to the ground bus.

One thing I don't see in most presentations is Kirchhoff's Current Law.  If garbage escapes the box it must complete the circuit by some method even if that is a long path through many wires.

Comments Howard?

Stan - VA7NF

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Stan - VA7NF

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Posted 5 years ago

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Jay / NO5J

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Single Point Ground and single path to ground aren't 2 competing stratagies, you don't want any piece of equipment to have multiple paths to ground. Bonding the external ground rods and Single Point Grounding all equipment inside to a common ground point before attaching that Common ground point to any external ground rod still eliminates alot of alternate paths to ground. The tough one is the ground shield on the coax. both ends should be grounded, at both the tower ground rod and the shack ground rod. Both the shack ground rod and the tower ground rod should be bonded. Keep the bonding conductors "Large,Low Resistance, and As Short As Possible". Inside the shack, single point rules, although safety grounds are involved too. Outside the house or shack it's more about lightning and safety grounds.  Bond all ground rods, break up long paths in the bonding with additional ground rods remember also that inside the equipments there are multiple paths to chassis ground but there should only be one path to ground for the chassis, so inside the chassis there is only a single path to ground. when you come to a fork in the ground path try to eliminate it. I still feel better disconnecting the Coax at the entrance panel during thunderstorms, Lightning has about as much magic as I can tolerate.  Dirt is a lousy bonding conductor, use copper instead. Daisy chaining is better left to florists. Plastic flowers in the shack make better insulators and don't require watering, water and amplifiers should not be mixed, stirred or collocated. 

And If I've implied anything incorrectly, correct me before anything magical happens. I have no personal attachements with being wrong.

Ben Franklin just didn't know any better, but I bet he had suspicions. Better suspicious the superstitious.  

I studied the Powerpoint and didn't find anything contradictory, but of course I couldn't hear the Presentation that went with it.  

Jay - NO5J
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KY6LA - Howard, Elmer

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Basically Jim Brown and I totally agree on the need for bonding of EVERYTHING.

The difference is the choice of topology.

Jim seems to be advocating a ring or Line ...   While I am advocating a Star (or a modified bus)

Ultimately the intend is to keep the impedance and hence the potential noise voltages between the devices as low as possible.  

In audio work, where Jim has much expertise, a ring works because the distances are shorter than the noise wavelengths

In RF, even short bonding distances are long compared to the wavelengths.  

The ring topology and its variants tends to act as a huge antenna.. hence the Star or Modified Bus tends to have much better results.

Ultimately this is all theory.. and we can argue this until we are blue in the face...

In practice there are always local unknowns, couplings, paths, etc that can bite you in the butt....and change a star into a ring and a ring into a mesh and a mesh into a Star, etc. 


Don't let Kirchhoff's Current Law confuse the situation.  I am concerned with getting rid of RF noise... The current is conserved by converting it to something other than current at Noise Frequencies...    Yes Garbage can escape the box but it does not need to come back at Noise just needs to return as current....
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Jay / NO5J

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My tree layout looks like a star layout when viewed from below the bottom end of my ground rod. None of the branches are in contact with each other. I still have to get past the lightning round though. Lightning never hits trees does it?
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Paul Christensen, W9AC, Elmer

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> "Ultimately the intend is to keep the impedance and hence the potential noise voltages between the devices as low as possible."

Excellent advice.  Despite our efforts to strive for one form of grounding topology or another, our intent is undermined by things for which we have little control.  We almost always end up approximating the "mesh" structure that Howard shows. 

Let's say we bring one large conductor from each piece of shack equipment directly to a ground rod driven into the floor of our shacks.   That ground rod is further connected to a copper bulkhead outside the shack window where coaxial lines are bonded - and that bulkhead is tied to another ground rod that connects our grounded tower(s) in a ring that includes the AC power entry.  We don't have, nor do we want a "single point ground."  Ground should be established at many locations for the reason Howard states in the quote above. 

Compounding the "single point" issue is that our equipment is further meshed with many grounded and interconnected RCA, BNC, and coax connectors.  Oh, and what of the 3rd pin AC power cords that now tie the whole residence together in an even larger mesh?  Almost forgot the grounded CATV coaxial bulkhead required by every cable TV operator (for those with CATV service).  That coax forms another pathway into the meshed system.

When considering lightning avoidance, we definitely don't want a "single point" ground.  We want low-Z grounding paths everywhere.  We don't want lightning induced-surge currents to create a voltage divider in the grounding network.  High Z ground paths result in surge currents that create a large voltage difference between equipment.  What we want is a multiple-point ground where coax lines are bonded at the top of the tower, the bottom of the tower, and a low Z connection back to the shack cable entry and AC power entrance.  Strikes on a tower need to divert to ground on a short path directly to the tower base. We want to try and a achieve a perfectly conducting, multipoint ground. This grounding method is used by every cellular telephone company.

For most conversations dealing with grounding, we would be well-off to avoid terms like "ground loop" and "single point ground."  These terms have morphed in time and always come up because old habits, perceptions and theories are slow to die. 

Paul, W9AC

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Two thumbs up to both presentations! I like seeing both -- helps reinforce the important points. Boy are we hams mostly confused about all of it. Thanks so much for sharing your expertise with us!

73 de Dave, N7AIG

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Jay / NO5J

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Lightning chooses the most direct path you provide it. RF will try to resonate every path you give it, Noise will travel across any shortcuts you provide. Above all try to never be part of the path to ground yourself. Be wary of stray electrons, they tend to travel fast, and follow the leader well.

Ma Bell tried hard to teach me, but I got zapped plenty, and usually knew why. Survived anyway. 

Jay - NO5J