AL-800H Instruction Manual
12
Grounding
Connect a good RF and dc ground to the ground post on the rear panel of the amplifier. Use the heaviest
and shortest connection possible. The best materials to use for ground connections are (in order of
effectiveness) smooth wide copper flashing, copper tubing, or solid copper wire.
Never
use braided or
woven conductors unless the lead needs to be flexible.
Braided or woven conductors offer a high
impedance to both lightning and RF.
Water pipes, metal heating ducts, metal fences and other large metallic masses offer convenient RF
grounds. If a water pipe ground is used, inspect all the pipe connections to be sure that no plastic or rubber
connections are insulating the pipes. Insulated pipe connections will interrupt the electrical continuity to
the water supply line. Install a jumper around any insulated pipe connections you find. Use heavy copper
wire or flashing with stainless hose or pipe clamps for the jumpers.
The following tips will help prevent lightning damage and RF grounding problems:
1.
Avoid using braided or woven conductors, they have very high resistance to both RF and lightning
currents. RF and lightning flows along the surface of conductors, almost no current flows in the center
of the conductor. The lowest RF resistance occurs with wide, smooth conductors.
2.
Avoid routing a single small gauge grounding conductor along the various pieces of equipment (or to
connect multiple ground sources). Instead, use multiple ground leads that connect to a single wide
buss at the operating position. Keep all ground leads as short and wide as possible.
3.
Buried radials provide much better lightning and RF grounds than ground rods do, although both are
needed for safety.
4.
Avoid sharp bends in ground leads. When changing the direction of a ground lead use a gradual radius
turn.
5.
Avoid second story operation. A good ground is much easier to obtain on the first floor or in the
basement of a structure.
6.
Air-core choke baluns should be used on all coaxial feedlines. The feedlines should be coiled into
several 4" to 6" diameter turns
before
they
enter the building. Either directly bury the feedlines a few
inches deep in the ground for a minimum distance of ten feet or ground the shields to a separate
outside ground on the antenna side of the choke.
