Radio Station Grounding
There are three types of ground systems to be
considered within a radio station environment:
1) Safety Ground
This ground is simply the AC power neutral
system, formed by a single driven ground. This is found in most residential
installations. Some electrical codes still allow a connection to a cold water
pipe. This seems to be going out of style with the installation of PVC or other
“non-conductive” carriers of water. Never chop off or isolate the
3rd pin ground on any power supply or other equipment. It is there to prevent
electric shock in the event a component fails.
2) Lightning Ground
This ground is found on most antenna
support structures (towers), buildings and other tall structures. Several ground
rods are driven and spaced equally around the base of the tower. These ground
rods must be connected to each other as well as the tower in the form of a ring
or circle. The spacing should be about 2 - 2.5 meters. All conductors must be
attached using the lowest possible resistance connection possible (i.e. crimp,
clamp and cad-weld). The goal is during a lightning strike the energy is
dispersed to as large an area as possible.
3) RF Ground
The station ground must provide both an effective DC and RF ground. Creating
a good DC ground is not a problem, but an effective RF ground must be carefully planned.
- The ground wire should be as short as possible,
it should also be shorter than a quarter-wavelength long on the highest
frequency band operated.
- The ground wire should be very large. The braid removed from a piece of RG-8
or 213 coax works well. Copper flashing strap is a better choice if you can find it.
- Clamp this short, heavy ground wire to your ground rod(s) or radial system.
- Several different lengths of ground wire should be used, each connected to a separate
ground rod. This configuration provides multiple, parallel ground paths.
All grounds should be bonded together !
This includes a house ground, exterior antenna tower ground and station shack ground.
This “bonding” should occur at a single point ground (SPG) located
immediately outside the structure (house or operating location). During a nearby
lightening strike the energy is dispersed over a wide area (several thousand
feet in all directions). Should there be two driven grounds in the area, a “step
voltage” is produced and these grounds are not at the same potential.
Allowing a difference in potential will allow
large currents to travel from one point to another. The path between the two
separate grounds may be through the house electrical system or radio equipment
causing damage and danger to the radio operator.
The various ground connections in the shack (shown above) must be grounded to a SPG (single point ground)
in the radio room. Connections which leave the
radio room and cross the line shown in RED
must be protected. This can be accomplished via lightning arrestors or
other surge suppression methods at the bulkhead (as they enter the
house/structure) Following these basic rules prevents noisy ground loops or a dangerous difference in electrical potential
during a lightning strike event.
The radio room SPG should then be bonded to the exterior SPG at the entrance
bulkhead into the building. (see below)