Harris Platinum HT EL 2000LS, Technical Manual

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C.2.3
DC Ground
DC grounds in the transmitter are connected to a ground bus,
which in turn is routed to a common cabinet ground and then
connected to an earth ground. The use of separate ground busses
is a suggested method of isolation used to prevent cross-coupling
of signals. These ground buses are then routed to the cabinet
ground and to earth ground.
C.2.4
Earth Ground
The transmitter must be connected to earth ground. The connec-
tion 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 coun-
terpoise 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 resistivi-
ties 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 meas-
ured to ensure that the resistance remains within installation
requirements.
C.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 mini-
mizes 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 electrical continuity. Equipotential planes
for existing facilities may be installed at or near the ceiling above
the equipment.
Each individual piece of equipment must be bonded to its rack
or cabinet, or have its case or chassis bonded to the nearest point
of the equipotential plane. Racks and cabinets should also be
grounded to the equipotential plane with a copper strap.
RF transmission line from the antenna must be grounded at the
entry point to the building with copper wire or strap equivalent
to at least no. 6 AWG. Wire braid or fine-stranded wire must not
be used.
All building main metallic structural members such as columns,
wall frames, roof trusses, and other metal structures must be
made electrically continuous and grounded to the facility ground
system at multiple points. Rebar, cross over points, and vertical
runs should also be made electrically continuous and grounded.
Conduit and power cable shields that enter the building must be
bonded at each end to the facility ground system at each termi-
nation.
Platinum™ Series
C-2 888-2457-001
WARNING: Disconnect primary power prior to servicing.