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Author Topic: grounding question  (Read 774 times)

KD2HPQ

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grounding question
« on: June 11, 2020, 10:03:24 AM »

During a recent outdoor project I discovered a length of grounding braid that originally ran from our underground fuel tank (since removed) to a pipe.

One end of this "wire" is still deep underground, where the tank once was; the other end terminates in an above-ground pipe that goes through my patio floor and into the earth at least four feet deep. Approximately 3 feet of this braid is accessible.

Unfortunately my shack is in the attic, around 30 feet from this "wire." My current ground -- the less said the better. Is this newly found wire a suitable ground for a radio station? What sort of grounding braid do you recommend for this setup? Moving the station is not in the cards at this point.

Thanks.
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K1KIM

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Re: grounding question
« Reply #1 on: June 11, 2020, 10:51:10 AM »

I personally would not use a ground of unknown conductivity. Best is you drve 2  4' rods 9-10' apart. This will give you about 1 1/2 times the benefit of a single 8' rod. My ground is a long run also. I use 3/4" tinned braid on all the equipment toa copper buss bar and then 25' of # 10 or 12 stranded wire to the ground rods which are daisy chained.  I also ground my shielding on my coax at the rod again in addition to at my vertical antenna. Hope his helps.

Andy
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KD6VXI

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Re: grounding question
« Reply #2 on: June 11, 2020, 11:02:16 AM »

By code, you would have to bring that to the service panel.

'ground' for a radio transmitter is a misnomer.

You ground and bond for lightning protection.

You choke your antenna feedline to force the antennas to work correctly and to keep rf off the feedline exterior (in the case of coax).

You shouldn't rely on a ground to keep rf where you want it.  Thats an old way of doing things, and doesn't comply with the NEC.

Ground for your station?  That's done by using a 3 pin power connector to the AC outlet.  Lightning protection?  That's done by bonding every piece of equipment, tower, etc to the service panel and increasing surface area contact with the earth.

Take that braid and run it to your service panel if you really want to make a better ground.

--Shane
KD6VXI
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N6MST

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Re: grounding question
« Reply #3 on: June 11, 2020, 12:42:52 PM »

I personally would not use a ground of unknown conductivity. Best is you drve 2  4' rods 9-10' apart. This will give you about 1 1/2 times the benefit of a single 8' rod. My ground is a long run also. I use 3/4" tinned braid on all the equipment toa copper buss bar and then 25' of # 10 or 12 stranded wire to the ground rods which are daisy chained.  I also ground my shielding on my coax at the rod again in addition to at my vertical antenna. Hope his helps.

Andy

Yeah, so, giving specific ground system advice for a site you aren't personally familiar with is not a good idea. Calling your method "best" is REALLY not a good idea. You trying to get this guy killed?
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W9IQ

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Re: grounding question
« Reply #4 on: June 11, 2020, 01:04:50 PM »

I personally would not use a ground of unknown conductivity. Best is you drve 2  4' rods 9-10' apart. This will give you about 1 1/2 times the benefit of a single 8' rod. My ground is a long run also. I use 3/4" tinned braid on all the equipment toa copper buss bar and then 25' of # 10 or 12 stranded wire to the ground rods which are daisy chained.  I also ground my shielding on my coax at the rod again in addition to at my vertical antenna. Hope his helps.

Andy

Andy,

If you are subject to NEC, it doesn't sound like this is a compliant installation.

- Glenn W9IQ
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

W9IQ

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Re: grounding question
« Reply #5 on: June 11, 2020, 01:08:11 PM »

Angelo,

As Shane suggested, you need to specify what is the purpose of the ground connection. It can be for lightning protection of outdoor antennas, an RF ground or an electrical safety ground - or a combination of the three.

- Glenn W9IQ
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

WA9AFM

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Re: grounding question
« Reply #6 on: June 11, 2020, 04:46:11 PM »

Before you proceed, get a copy of "Grounding  and Bonding For The Radio Amateur" by Ward Silver, N0AX.  It covers the three principle grounding protocols; electrical, lightning protection, and RF.  All three are related.
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KB1NO

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Re: grounding question
« Reply #7 on: June 11, 2020, 05:25:16 PM »

Good advice from WA9AFM.   That book by Ward Silver is excellent.   
One comment: For RF ground,  braid is not the best,  especially outside.  The individual strands tend to oxidize/corrode and make it a poor RF conductor.  Copper strap is best;  2nd best heavy copper wire, or multiple wires. 
Good luck,
John, KB1NO
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WA9AFM

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Re: grounding question
« Reply #8 on: June 12, 2020, 06:50:43 AM »

To follow up on KB1NO's comment.  Braid should only be used for very short runs, i.e. from the equipment to grounding buss permitting movement of the equipment.  If you must use braid, use material that is really 'braid'.  DON'T use coax braid (a Ward Sliver no-no).  Coax braid will begin to degrade physically and chemically the moment you remove it from the cable.
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KD6VXI

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Re: grounding question
« Reply #9 on: June 12, 2020, 09:21:27 AM »

To follow up on all of this.  You shouldn't be grounding any rf.

Grounding and bonding are for your protection.  From lightning and from getting shocked.

If you are bleeding any rf into ground, you have a problem that needs to be addressed elsewhere.

RF is expensive to make.  Why on 'earth' would you want to dump it into the ground?

Proper feedline dressing and choking will invalidate the need for an rf ground.


--Shane
KD6VXI
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AA4PB

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Re: grounding question
« Reply #10 on: June 12, 2020, 11:43:57 AM »

To follow up on all of this.  You shouldn't be grounding any rf.

Grounding and bonding are for your protection.  From lightning and from getting shocked.

If you are bleeding any rf into ground, you have a problem that needs to be addressed elsewhere.

RF is expensive to make.  Why on 'earth' would you want to dump it into the ground?

Proper feedline dressing and choking will invalidate the need for an rf ground.


--Shane
KD6VXI

I think it depends on what type of antenna you are using. If its a dipole then you don't need an RF ground. If it's a 1/4 wave vertical mounted on the ground then a bunch of buried radials will definitely improve the performance. It's not a matter of "dumping" RF into the ground, it's a matter of providing an efficient termination for the other side of the antenna circuit. Think about a battery and a flashlight bulb. Will the bulb light if you only connect it to the + terminal of the battery? No, you need to provide a return path back to the other terminal of the battery in order to make current flow through the bulb.
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Bob  AA4PB
Garrisonville, VA

W9IQ

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Re: grounding question
« Reply #11 on: June 12, 2020, 11:54:59 AM »

The efficiency "fix" for a 1/4 wave vertical is a better ground plane e.g. more radials. Several ground rods will make no appreciable difference in efficiency.

You should use at least one balun where the coax exits from the radial field on the way to the shack. A second balun near the shack is also prudent. With this treatment, no RF ground will be necessary.

As an external antenna, the NEC lightning protection requirements will apply.

- Glenn W9IQ
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

N6MST

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Re: grounding question
« Reply #12 on: June 12, 2020, 02:03:06 PM »

You should use at least one balun where the coax exits from the radial field on the way to the shack. A second balun near the shack is also prudent. With this treatment, no RF ground will be necessary.

By balun you mean choke?
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W9IQ

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Re: grounding question
« Reply #13 on: June 12, 2020, 02:54:44 PM »

A current balun and a choking balun are functionally the same device.

- Glenn W9IQ
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

N6MST

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Re: grounding question
« Reply #14 on: June 12, 2020, 04:30:25 PM »

A current balun and a choking balun are functionally the same device.

- Glenn W9IQ

Why would you put a balun at the shack? Where is the balanced transmission line at that point?
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