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Joined: Jan 2001
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Tom Offline
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Hopefully, the OP will post additional information about this installation. All the posts, including mine, seem to be based on a little bit of guessing what the owner wants to do.


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Joined: May 2004
Posts: 116
S
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Ham radio grounding is somewhat confusing, as there are three (3) types of "grounding" to consider; 1) Safety Ground, 2)Lightning Ground, and 3) RF Ground.

The 2002 NEC 810 Part III - Amateur Transmitting and Receiving Stations - Antenna Systems is the starting point to look at. 810.58 - Grounding Conductors -- Amateur Transmitting and Receiving Stations has you refer back to 810.21(A) through (J), which then refers you back to 250.50, 250.52, and 250.94. (are we confused yet?)

We need to find out just what type(s) of grounding this Ham operator is trying to install at the new location.

A good place to go for information about Ham radio grounding is "www.arrl.org". Doing a google search for "ham radio grounding" also brings up a great deal of useful (though at times contridiction) information.

If this were easy, it wouldn't be near as hard to do! (grin)


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Steve
Joined: Mar 2005
Posts: 1,213
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Even in big commercial transmit sites, they bond all the grounds together. The problem isn't that the grounds are bonded or connected electrically, it's that at radio frequencies, impedance through a traditional wire electrical ground is extremely high. Leads need to be kept shorter than normal to be effective. The best method is to install a large equipotential plane under the equipment- capacitive coupling between the plane and earth will reduce impedance and become a far more effective ground than the ground wire, even if there's no physical connection with the earth! Multipoint grounds like buried loops and multiple supplementary ground rods help, too.


Last edited by SteveFehr; 11/27/07 09:22 AM.
Joined: Jul 2004
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G
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I Inspected all the state radio shelters at the prisons and along the interstates (7 counties).
They had Ufers in every significant chunk of concrete, a ground ring around the shack and tower, 40' multipiece rods at the corners and radials going out from there.
Everything was CadWelded together at each intersection


Greg Fretwell
Joined: Mar 2004
Posts: 251
W
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The latest information revels that loops are not recommended. We have cut the loops on some sites. They use to install a loop around the structure and attach all the grounds and rods to it but it is now a practice not to make a complete circle. It was found that a closed loop can act as an inductor, causing resistance (or reactants ) to a lightning surge which is LF RF. Robert

Joined: Mar 2005
Posts: 1,213
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That doesn't sound right; the loop would be perpendicular to the electric field of the lighting strike and in-plane with the magnetic field, so there shouldn't be much induced current or inductance. And breaking the loop in a ground wire doesn't open the circuit, it just increases resistance a bit because the earth is still highly conductive. I'm interested in hearing the theory behind that- do you know of any technical papers or references talking about the issue?

Joined: Dec 2002
Posts: 327
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The closed loop does not act like an inductor in my understanding as it is perpendicular to the flow. To place them in to a grounding system at the base of the building helps to form an equal potential plane, but little to no current flows through them due to the equal potential plane they form, and, as such they do not provide additional "drain points" (for lack of being able to think of a better term) for the current of a lightning strike.

I close the loop everytime, but only have a ground loop installed at the base of the building. Loops further out away from the building are a waste of resources.

Been awhile since I've read tech papers on the subject. Try the military handbook "Grounding, Bonding, and Shielding for Electronic Facilities" mil-hnbk-419a, Motorola "Standard and Guidlines for Communication Sites" 68P81089E50-A, and if still available Polyphaser had some very well written manuals on the subject. Other references are to numerous and of the three mentioned I don't really care for the military handbook.

For deep stuff try the papers available at www.jolr.org (the Journal of Lightning Research).

Shane

Joined: Mar 2005
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I have a copy of MIL-HDBK-419A on my desk smile I haven't seen motorola or polyphaser's documents, but I speak fairly regularly to some of the nations top power experts, and none of them had mentioned this, even when we were specificlly discussing grounding at RF facilities. I was curious where the theory to break the grounding loop at come from, because it sounds wrong.

Joined: Mar 2004
Posts: 251
W
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It is in Motorola R56 site grounding. It is in a addendum released 2005 I think. My copy has the Ver# and release date but to smeared to read. (a COPY) I will see if I can find a better copy or a source online. This is a recent change and is not in the original R56. Robert

Joined: Mar 2005
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