This is the third of several parts about grounds. This time we'll look at RF (Radio Frequency) grounds. In this case I am talking about the ground in your radio shack. The grounding system for your antenna is a part of this RF ground, but we'll save that for another month.

There are two reasons for having a good RF ground in your radio shack. The first is safety; that is, preventing electrical shock. The second is to provide a low impedance path for unwanted stray RF energy in your shack. This reduces Radio Frequency Interference (RFI). I am sure your family and friends would not appreciate hearing you talk on their phone lines or TV because of RFI.

To get a good low impedance ground you have to consider skin effect. That is, at RF frequencies the current in a conductor travels on the surface of the conductor and not through the cross-section (center) of the conductor. The higher the frequency the more this effect comes into play. Hence, a good low impedance ground has lots of surface area.

Now for the practical aspect of this ground, you'll need three things, besides minor hardware such as nuts, bolts, and connectors. These are a good quality copper-clad ground rod 8 to 10 feet ling, a copper ground bus and copper-braided ground strap that is tinned and ampacity rated (wider is better). The ground rod is obvious: it's your interface between your equipment and the earth and gives you the ground potential that protects you and your equipment. The copper ground bus provides a place for you to mount your equipment grounds and is in turn tied to the ground rod. It is also a part of your lightning ground protection. The braided ground strap provides the ground connectivity between your equipment and the ground bus.

If you are lucky, your ham station is close to the existing power panel ground rod; that is less than 10 feet. If not, then drive the ground rod into the earth at a location less than 10 feet from your station. Leave the top 8 inches above ground. Make sure the ground rod is not loose or you'll end up with a poor ground reference. If your ground gets very dry then before driving the ground rod in, dig a 2 foot deep by 2 foot in diameter hole and at the center of the hole drive in the ground rod. Fill the hole with loose gravel than will not compact. Don't use sand or lime as these will compact and prevent water from seeping into the earth. When the weather gets real dry you can soak the gravel and add salts to increase the loose ions, thus improving your earth ground.

Next attach a copper strip on the wall behind your bench or at the rear of your bench. This will be the buss bar that you'll ground each of your individual radios and supporting equipment to. The buss bar should have at least a 26 gauge thickness. A strap that is 3/4 inch wide and 10 inches long is sufficient to ground 4 pieces of equipment. If you have more equipment than that, make the bar longer. Drill a hole in each end for mounting the bar to the wall or bench. Use standoffs to allow you room to work, 1 to 1-1/2 inches will usually be sufficient. Drill a hole for grounding each piece of equipment, plus one to ground to the grounding rod between the 2 mounting holes. The size of the holes will depend on your mounting hardware. Centrally mount the bar to keep the runs from your equipment to the bar as short as possible.

Finally, attach a ground strap to each piece of equipment and then to the buss bar. Do the same from the ground rod to the buss bar. Use a washer to press the strap into the buss bar insuring a tight, solid contact. Use a conductive grease to prevent corrosion between dissimilar metals. Bends on the straps should be not less than 8 inches. Coat the strapping to prevent shorts. Be sure that the straps don't touch anything else but the buss bar and your equipment.

The above should give you a good, low maintenance station ground that will last for many years. About every 6 months check the connections for corrosion and tightness.

Last updated on March 30, 2006