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Author Topic: Best place to locate ground?  (Read 745 times)
KC2ELS
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« on: January 21, 2003, 02:22:24 AM »

I'm setting up an HF rig at home.  I'm about 15ft from a cold water pipe.  The HF rig is currently powered by wall current, but by Field Day it will be powered by batteries which will be constantly charged by a power supply.  The batteries will be connected to a Radio Shack power bus, which would then connect to all my 12V equipment including my HF rig.  There is also an antenna tuner in place.

Where should the ground go?  I'm torn between connecting it to the tranceiver directly and connecting it to the black terminal of the array of batteries.  Should the batteries be grounded or not?
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WB2WIK
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« Reply #1 on: January 21, 2003, 10:54:22 AM »

From a DC perspective, your chassis grounds and the negative battery terminal are one and the same.  From an RF or lightning preventive perspective, they're not, and the battery negative terminal being earth grounded is irrelevant.

Your RF ground should take the shortest possible path from your antenna tuner chassis and transceiver chassis to earth, and should be a broad, flat conductor (wire isn't particularly good) like aluminum or copper flashing.  I prefer copper simply because I can solder to it, and it's readily available.

A "lightning" ground should all be outside your home, and not even enter your shack.

Whether you actually need an RF ground, or any kind of low-impedance earthing, is another matter.  Many stations work perfectly without any grounding.  I know mine certainly does (160 meters through 70 cm, high power on all bands, zero ground of any kind, and no problems whatever).

Remember that for Field Day, "battery power" class does not allow for continuously charging your battery!  The equipment, including the battery, must remain independent of any AC mains power in order to be considered battery powered.  You can change batteries from a discharged to a fresh one, and recharge the discharged one off line while you're not using it, but the "station" battery should not be connected to a line powered charger.

WB2WIK/6
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KC2ELS
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« Reply #2 on: January 22, 2003, 05:35:50 PM »

I'm using the house itself as a lightning ground, as neither of my antennas is any higher than the house nor are they further than ten feet from my house.  Yes, it kills performance, but on the bright side, the  house itself will be more likely struck by lightning.  I will probably set up a lightning ground in the future as my antennas grow but since my backyard is only nine feet deep, there's not much that I can do there.

This is the second reference I've seen to flat copper instead of wire for RF grounding but I haven't seen any explanation for it.  I confess my experience with grounding is limited and I have none with RF grounding, so I'm terribly curious as to what's behind this rationale.  Also, is this something I can pick up at Home Depot?  I'll ask about "flat tinned grounding braid" but I suspect I'm going to come up dry.

Thanks for the reminder with regard to the Field Day rules.  My day-to-day operation will have four deep-cycle batteries between my equipment and the wall socket -- I'll have to be sure to set them up in pairs for the event.  Charging one pair while working the other is acceptable if I read the rules correctly -- feel free to correct me, please!
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WB2WIK
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« Reply #3 on: January 23, 2003, 11:34:08 AM »

The reason for flat, solid conductors used for RF grounding is that this construction minimizes inductance for any given cross-section.

Flat braided conductors, like the shield from coaxial cable, is not particularly good, compared with flat SOLID conductors.

Circular wire, solid or stranded (although solid's a bit better) is actually pretty bad for the application.

It's easy to measure the inductance in anything, if you have proper test equipment such as an inductance bridge.  6" wide copper sheeting, 10' long, has less inductance than #6 copper wire that's only 2' long.  Simple as that.  The measurement confirms it.

Copper sheeting, or aluminum sheeting, is quite available from contstruction materials supply centers as "flashing," which is used around chimneys, near the edges of roofs where rain gutters attach, and so forth.  The copper was very popular for 100+ years, but I suppose became a bit too expensive and I see now aluminum, and sometimes even galvanized steel, is used for this application.  Copper, obviously, is better -- it's the world's second-best conductor (silver is #1) and is easy to attach to, including soldering.  I can still get copper flashing, which comes in 12" wide rolls, cut to any length I wish, at my local construction materials supply house, although I see that Home Depot rarely has it.

I prefer "flashing" as opposed to thin "foil" as found in hobby shops because the foil, while pretty good, is also pretty weak and tears easily.  Real flashing is quite thick (about .030" or so) and strong, and you can twist and bend it and it doesn't tear; although, it's still very easy to cut with shears or tin snips.

WB2WIK/6
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