Ground rods should be placed along the entire length of each radial. The most cost effective spacing between rods for normal (grassy) soil is two times the length of a rod into the ground. If 8 foot rods are used, they should be placed on 16 foot centers.

If the soil is not normal (e.g., very dry or sandy), the separation may be reduced in order to minimize the interconnect inductance. It doesn’ t hurt to have the rods too close, it only costs more in material and labor.

Since most soils are stratified, the best way to determine the effectiveness of a ground system is to measure it. The simplest way to determine the sub-layer conductivity is to measure the first ground rod, one foot at a time, as it is hammered into place. This technique can provide a profile of the lower layers relative to the first foot. (For additional information see our book: The ‘ Grounds’ for Lightning and EMP Protection or the November 1992 issue of Striking News.) Most earth resistance meters measure only dc or low frequency ac resistance of the ground system. Since the lightning strike energy is predominately RF energy, the inductance of the ground system is important. Without using very expensive specialized test methods, the only way to ensure a low impedance ground system is to follow the suggestions given for conductors, doping and radials.

No one should consider using a non-conductive structure for an antenna support. Only conductive towers or metal poles should be used for mounting antennas high into the air. If the tower or pole has sliding contacts (crankup or push-up), the joints should be jumpered using short sections of copper strap attached with PolyPhaser TK clamps. Normal self support and guyed towers will not need such jumpers.

Guyed towers are better from a lightning protection perspective if the guy anchors are grounded properly. Because the anchors are located away from the tower base, at least some of the strike energy will traverse the inductive guy wire to the ground. The more the strike energy is divided, the less there is to go to your equipment.

Copper should never touch galvanized material directly without proper joint protection. Water shedding from the copper contains ions that will wash away the galvanized (zinc) tower covering. Stainless steel can be used as a buffer material. However, be aware that stainless steel is not a very good conductor. If it is used as a buffer between copper and galvanized metals, the surface area of the contact should be large and the stainless steel should be thin. Joint compound should also be used to cover the connection so water can not bridge between the dissimilar metals.

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