Fig, 3. A method for improving uround-rod effectiveness in very dry or sandy soil.

short in the first place. The 4-foot size is always too short, and a 6-foot rod is considered marginal The best is the 8-foot size, driven into the ground so that only 4 to 6 inches show as seen in Pig. 2(a),

The wire lead between your equipment and the buried ground rod should be low inductance, For this reason, small-diameter wire is not suitable Perhaps best is braid wire, or, if braid is too expensive, use the shield from a length of heavy coax (e.g., RG-8 or M W In either event, the wire between the equipment and the ground should be as short as possible.

The eiectrical connection between the ground rod and the wire must be competent both electrically and mechanically. It should go without saying that a good electrical connection is first a good mechanical connection For this reason, I prefer to both sweat-solder the braid and damp it to the ground rod. The clamps that come on the ground rod are marginal, so I use the kind that electricians use. The big problem with the regular clamps is that they are fastened with only a slot-head screw, and they tend to work loose after a while.

The main idea in building a good ground system

BítJUO 1 J
Fig. 2(b). Three ground rods connected in para//e/

is to reduce the impedance as much as possible. The resistive component of this impedance is mostly the resistance between the ground rod and the earth. 1 hereforeF the biggest improvement comes from increasing the surface area of the ground rod that is in contact with the earth. This is the main reason why we want the ground rod to be driven in all the way and its length to be 8 feet.

A way to increase the surface area in contact with the earth is to use more than one ground rod, Fig. 2(b) shows three ground rods connected in parallel; I have seen as many as six in one system, A method shown in a book on lightning protection uses five arranged with four on the corners of a square and one in the center of the square.

The 8-toot ground-rod length assumes a reasonably moist soil (even though the surface may be dry). If the soil is very dry or if it is sandy, then some other tactic will be necessary A method advocated for many decades in ARRL and other amateur publications is shown in Fig. 3, The idea is to dig a 6- to 8-inch-deep trench around the ground rod at a radius of 1 foot or so. The trench is filled with a chemical such as copper sulphate and re-covered. The chemical leaches into the soil and reduces tts electrical resistance, The chemical must be renewed every several years.

Another high-surf ace-area, low-resistance ground is shown in Fig. 4. Here we see a 1-inch-dianneter (or larger) copper plumbing pipe used as a ground rod. These pipes normally come in 8-foot and 10-foot lengths. Unfortunately, copper pipes do not survive the pounding required to drive them into the earth. Ordinary ground rods are not actually all

Fig. 4. Copper pipe used as a ground rod.

copper, but are steel with a copper coating on the outside to reduce the rf resistance. The well-known "skin effect" makes the rf current How only in or near this low-resistance copper coating, and very little flows in the steel core. The steel core, then, can be used for strength.

The 1-inch (or larger) copper pipe will yield greater surface area in contact with the earth (and if we do it right, even the inside Will be in contact with the earth) and so should yield a lower-resistance ground. I he problem is, however, that the copper pipe is not strong enough to be driven into the ground,

Two people gave me ideas concerning this problem.. One was a man at our church who said he used to use a garden hose and water pressure to drive the pipe into the earth, as shown in Fig. 5(a). I he end of the pipe is beveled slightly, and then the water hose nozzle is inserted into the upper end. This connection must be held tightly by hand in order to build up water pressure in the pipe. By applying a downward mechanical pressure on the pipe while the water is applying its pressure to drive soil out from under the beveled point, the pipe will sink into the earth rather easily.

During the period when I


F ig. 5(a). One meth od o f driving copper pipe into the earth.

Figs 7, Wire mesh ground system.

73 for Radio Amateurs * April, 19Ö5 31


copper plate

Fig 6. Grounding a vertical.


Fig. 5(h). Improved method for driving copper pipe into the earth.

Fig 6. Grounding a vertical.

copper plate


was writing a monthly column for Wortdradio newspaper, I discussed this method and used illustrations similar to Figs. 4 and 5(a), A reader wrote in and told me that he has been using that method for many decades of hamming and has improved on it a bit. He demonstrated by drawing the method shown m Fig 5(b). Here we see a copper tee connector at the top end of the ground pipe. A short (6-inch or so) piece of matching copper pipe is extended out one end of the tee and capped to prevent the leakage of water (sweat-soldering is probably necessary), ihe


0 0

Post a comment