Harris DiamondCD Series, Техническое руководство

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B-4 888-2463-001 3/6/08
WARNING: Disconnect primary power prior to servicing.
Diamond Series™
Appendix B Surge, Lightning and
B.2.4 Earth Ground
The transmitter must be connected to earth ground. The connection must have an
impedance of 5 ohms or less. For example, a one-inch metal rod driven 20 feet into
moist earth will have a resistance of approximately 20 ohms, and a large ground
counterpoise buried in moist earth will exhibit a resistance on the order of 1 to 5 ohms.
The resistance of an electrode to ground is a function of soil resistivity, soil chemistry
and moisture content. Typical resistivities of unprepared soil can vary from
approximately 500 ohms to 50 k ohms per square centimeter.
The resistance of the earth ground should be periodically measured to ensure that the
resistance remains within installation requirements.
B.2.5 RF Ground
Electrical and electronic equipment must be effectively grounded, bonded, and shielded
to achieve reliable equipment operation. The facility ground system forms a direct path
of low impedance of approximately 10 ohms between earth and various power and
communications equipment. This effectively minimizes voltage differentials on the
ground plane to below levels which will produce noise or interference to
communication circuits.
The basic earth electrode subsystem consist of driven ground rods uniformly spaced
around the facility, interconnected with a minimum of 1/0 AWG bare copper cable. The
cable and rods should be placed approximately 40 inches (1 meter) outside the roof drip
line of the structure, and the cable buried at least 20 inches (0.5 meters). The ground
rods should be copper-clad steel, a minimum of eight feet (2.5 meters) in length and
spaced apart not more than twice the rod length. Brazing or welding should be used for
permanent connections between these items.
Where a resistance of 10 ohms cannot be obtained with the above configuration,
alternate methods must be considered.
Ideally, the best building ground plane is an equipotential ground system. Such a plane
exists in a building with a concrete floor if a ground grid, connected to the facility
ground system at multiple points, is embedded in the floor.
The plane may be either a solid sheet or wire mesh. A mesh will act electrically as a
solid sheet as long as the mesh openings are less than 1/8 wavelength at the highest
frequencies of concern. When it is not feasible to install a fine mesh, copper-clad steel
meshes and wires are available. Each crossover point must be brazed to ensure good