HFU HF Underground
Technical Topics => Equipment => Topic started by: IQ_imbalance on January 23, 2018, 1312 UTC
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So this spring might be time for “operation permanently mount antennas”. One big part of that will be installing my station ground. I need to bond the feedpoint ground to the house’s entrance ground which is pretty much on the other side of the house, so I’ll be running a strip of copper (probably copper) flashing around to make that connection., and adding an extra ground rod about halfway where it goes around the corner of the house.
One question I’ve been pondering is how wide of a strip is sufficient given that it’s a fairly long run (60-feet or so)?
Thanks!
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Most sources I have read recommend copper strap normally .030 to .060 thick and 2 inches wide at a minimum. You can use .022 thick but only for mechanical attachment. Use the widest and heaviest copper strap you can find and afford from the station to the ground rod. Clamp it mechanically to the rod and then braise ( if you can) to the rod. If you have several pieces of strap to make up the required length to reach the station, overlap the strap at each joint and bolt the joint together with brass hardware and then braise (if you can) the joint. The wider the copper strap the harder it is to maneuver.
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This article is the best one I have ever read on radio station lightning protection/grounding
http://www.nautel.com/wp-content/uploads/2011/04/Lightning-Protection-Radio-Stations-Oct-1998.pdf
It is probably a bit overkill for a pirate/amateur/SWL station, but all of the rules and principles still apply.
It is probably also worth noting that some of the FM broadcast stations I maintain can withstand a direct lightning strike to the tower and stay on the air.
Of course the grounding dosen't only apply to lightning protection, but the same techniques will help reduce RFI and noise as well.
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The Nautel approach is the gold standard and it works well if you do it right. Basically bond everything you can together and tie it to a common earth ground preferably all at the same physical location. The things you can't bond, ferrite the Sh-- out of! Per their mantra, use the ferrite with the highest permiability and the lowest cutoff frequency you can get.
A later version of the same paper covers a few more areas that are still relevant to SWL stations.
http://www.nautel.com/wp-content/uploads/2011/04/Transmitter-Site-Preparation-Recommendations-Sep-2004.pdf (http://www.nautel.com/wp-content/uploads/2011/04/Transmitter-Site-Preparation-Recommendations-Sep-2004.pdf)
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"One question I’ve been pondering is how wide of a strip is sufficient given that it’s a fairly long run (60-feet or so)?"
Some people run a loop of regular ground wire around the foundation and have spaced ground rods attached. Then you ground what you need to that nice ground loop.
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Thanks for the Nautel reference. Looks like i have some options....run the antenna feed all the way around and ground at the electrical box on the other side of the house, ground it at the shack entrance and bond that ground to the electrical main ground with strap, or put a bunch of ground rods in between the shack entrance and the electrical box and use a ground wire.
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One of the other big points in the nautel article, the one that has helped me the most, is actually the part about all wires, coax, power, ground, signals, EVERYTHING, entering the shack at a single point. that way all interference and noise are common mode, and are very much easier to remove.
(p.s. I actually only have a 3 ft ground rod at home, and I still manage to avoid RFI, but, admittedly, its not really up to spec)
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As far as ground systems for lightning protection.. in the last few years QST has run some interesting in-depth articles on the subject. The most recent was within the last year and essentially concluded that the only way an effective lightning protection system can be designed and installed is by a professional LPS installer. There are companies that do this.
Almost anything short of that is useless or actually even riskier than having none at all. I wonder about the proliferation of solar panels on the roofs of homes that are installed by shady or untrained personnel, and the risk this presents in a lightning scenario.
RF ground is a different story, but this is worth noting the lightning aspect since life, limb and property are at stake.
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When I was kid we lived on a ridge that was a lightning magnet. Knowing what I know now, it was a ridge dominated by Virginia pines, they love iron rich soil. We had some near misses, and they play Hell on consumer electronics.
The on/off switch on the TV went due to a close strike during one storm. Did we spend money on getting it fixed? Nooo! Young Pigmeat crawled behind that behemoth to plug it in and unplug it at night. I was the remote before and after the great blast. Me plus a three ft. pipe wrench was the "antenna rotator". Baseball wasn't bad but I hated the Superbowl. Coldest weekend of the year, wind howling, and every time I let go of that wrench, hand capacitance caused the pic to go wonky. Big fun.
Common ground for the house is about 20-25 ft. out the shack window, and the outdoor faucet closer.
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UPDATE: OK I think i have the final plan. I'm going to add two more ground rods between the shack and the mains service entrance (so there will be one at service entrance, one at the shack entrance, and two in between (so about 20' between rods). I'll bond them together with 6 AWG Al wire, and the ground plate in the shack entrance box will be bonded to the ground rod there with 2" strap (or braid, whichever i can find). The coax from my LOG will go through a 75ohm surge protector/grounding block bolted to the ground plate in the shack entrance box. The coax from the LOG is buried for at least 40 feet before it makes a run across the back of the house, so i don't see much point in grounding it at its balun box (buried in the front yard).
Now, the AARL operating manual says to bond the RF bus to the AC safety ground and to bond everything together to the ac service entrance rod. Does this mean i need to also run a ground strap from the AC outlet I'll be using to my station ground? I think i recall seeing a powerstrip somewhere that had a connection for an additional ground.....
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You're not mixing metals here are you? Copper all the way.
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IIRC, aluminum grounding electrode conductor not permitted in direct contact with earth or masonry and not to be connected to the grounding electrode within 18" of the earth.