I am upgrading from an HT to a Kenwood TM-V71A. Yay! But this means I need to install some antennas and run feed lines into my shack.

I'm going to be installing antennas in my attic (the feed lines will exit the attic, run down the side of the house, and re-enter in the shack, for a total length of ~30ft). I've read many articles that suggest external cable runs like this should be grounded near the point they re-enter the house.

I am planning on standardizing on BNC connectors. What are my options for grounding these cables? I haven't been able to find a BNC grounding block. There are lightning arrestors, but these are pricey and seem like overkill given that the antennas are in the attic.

These feed lines are located on the opposite side of the house from the ground spike. What is my best option for a ground connection? Would I need to install a new ground spike?

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    $\begingroup$ First, I recommend you try it without additional grounding. Depending on how your site's electrical system is wired, local ground conductivity, inductance of grounding wires, coupling to other systems, etc., you could introduce ground loops and other problems. At one QTH my electrical utility's "ground" was 50VAC above earth ground! Unless I unplugged the rig, I would receive a nice tingle every time I connected the grounded coax to the radio. $\endgroup$ – Brian K1LI Oct 5 '18 at 15:27
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    $\begingroup$ This isn't really about the central question of grounding, but it seems worth mentioning: BNC connectors seem like a bad choice for outdoor use because they are not weathertight at all. BNC is ideal for frequently changed cabling as in test equipment or portable systems, but there are better options for any permanent uses (though any outdoor connection should also be protected with suitable tape or an enclosure, and have drip loops). $\endgroup$ – Kevin Reid AG6YO Oct 5 '18 at 20:26
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    $\begingroup$ @BrianK1LI it sounds like it is time to rework your safety ground! $\endgroup$ – Glenn W9IQ Oct 5 '18 at 21:56

First, although it increases your cable cost slightly, I recommend using only plenum rated cable for attic installation. It's a fire concern. Second, as long as you have good grounding on your radio and power source and you have no exposed metal outside the house, you should be fine without grounding your cable. References to grounding just prior or after the cable enters the shelter normally assumes exterior mounting of your antenna on a tower or mast.

Also, depending on the size of coax you're using and the care given to installation, ground kits may do more harm than good in your application. The LMR and RG cables with woven outer conductors are easy to damage when removing the section of jacket necessary for installing a ground kit, effectively changing the cable impedance at that point (insertion loss). Some insertion loss is natural and unavoidable, but excessive loss is excessive. Coax with solid outer conductors are more sturdy and thus easier to install grounding on without cutting into or deshaping the outer conductor.

That said, I always recommend grounding your outer shield as much as you reasonably can. Ensure your grounding is the shortest electrical path to earth ground. Ground wires should never run up, zigzag, etc.

When planning your grounding, dont forget to consider the type and alkalinity of the ground you're sitting on. Sand or sandy loam is excellent for frying appliances and radios. If you have that type of soil, I strongly recommend an UPS, surge arrestor or polyphaser, in addition to a ground kit and bussbar.

As you described your planned install, I would suggest a small bussbar mounted in the attic just below your cable exit port. Install a polyphaser, or at the very least a ground cable with ring connector, inline between your antenna pigtail and the coax run.

Run a length of #6 jacketed stranded ground wire from whichever you installed there directly to your bussbar. Then, on a separate lug on the bussbar, run jacketed stranded #2 ground wire outside and straight down the side of the house to a ground rod sunk at least six feet below ground, eight feet would be better. (I'm sure there's a video on youtube of how to drive a ground rod in the most compacted soil using a bottle of water. It works.)

Because of skin effect, your #2 cable, bussbar, and ground rod can all be copper coated aluminum which will be just as effective and less expensive. For a clean install, use crimp on lugs and heat shrink all connectors. For the connection to your ground rod, a welded connection is best, because you avoid oxidation developing between your #2 and ground rod connection. A mechanical ground rod clamp works well too and is less difficult to install, although I recommend applying ample No-lox and periodic inspection of the tightness of that connector.

If it's highly important to you to replace your radio as seldom as possible, I would also install a second bussbar and #2 run just below your shelter cable entry port. This run of #2 can exit your cable port, run down the side of your shelter, and be buried at least a foot deep along the straightest path to your ground rod. If the distance from your shelter to the ground rod is more than ten or twelve feet, install a second ground rod closer to your shelter and connect to that instead.

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  • $\begingroup$ Thanks for the detailed response. If I sink a ground rod for this purpose, does it need to be bonded to the existing house electrical ground? My radio is unfortunately located as far as possible from the house electrical ground, and any physical connection from point A to point B is going to be tricky at best. $\endgroup$ – larsks Oct 7 '18 at 20:57
  • $\begingroup$ @larsks Yes, if you add a ground rod, it needs to be bonded to the existing rod. See ham.stackexchange.com/questions/51/… for more info. $\endgroup$ – mrog Oct 8 '18 at 18:40
  • $\begingroup$ @mrog Thanks for the link, that was a good read. $\endgroup$ – larsks Oct 8 '18 at 20:52

If you are in a jurisdiction that requires compliance with the US NEC (National Electric Code), you will probably find that there is no requirement for grounding the cable or having a lightning arrestor on the cable. This is because the NEC grounding requirement (article 810) starts with the presence of a mast mounted or tower mounted antenna or associated equipment. This obviously does not fit your situation. You might, however, find that an electrical inspector will interpret the NEC differently and can insist that you comply with his/her interpretation.

The NEC states that if you are using coaxial cable with an outdoor antenna that you only need a grounding block to ground the shield. If the grounding block connects to a ground rod other than the same ground rod that serves as the safety ground for your electrical service, you must bond the new ground rod to the electrical service ground. This bonding must be done with 6 AWG or larger wire. You can elect to use a listed lightning arrestor in place of the grounding block as this still grounds the shield.

Aside from the NEC issue, I would not install a ground connection to this cable. It introduces a failure point at the junction, it may increase RF noise on the coax, and it creates a fair bit of work and expense for no discernible return.

If you later add outdoor antenna(s), then you should revisit this issue and look at the best practices for a single point ground connection for your station.

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