User's Manual

INSTALLATION

FIXED STATIONS

378 ENVOY™ TRANSCEIVER REFERENCE MANUAL

Earthing the antenna

For a fixed antenna, requirements of the earth plane depend upon the type of antenna

selected and the location of the antenna, that is, on open ground or on a roof-top.

When installing an antenna on open ground, earth conductivity is often insufficient to

provide adequate earthing, especially on well-drained sandy, rocky or loamy soils. An

earth plane should be used to provide adequate earthing of the antenna. For a vertical

antenna, an efficient earth plane is provided by a counterpoise consisting of at least

four radials extending from the base of the antenna. The radials should be buried

approximately 10 cm (4 in) below the surface. An earth mat for an antenna mounted

on open ground can be supplied by Codan (Codan part number 15-00158).

When installing an antenna on roof-tops where there is no existing earth plane, an

earth plane should be installed. The earth plane should be a conducting surface

extending several wavelengths in all directions around the antenna. This can be

provided by placing a screen of wire mesh or similar material over the roof of the

building. Usually, a counterpoise system is used to provide an efficient earth plane.

For example, the counterpoise system for a vertical antenna should consist of at least

8 to 10 radials bonded together at the base of the antenna. A radial earth plane for an

antenna mounted on the roof-top of a building can be supplied by Codan (Codan part

number 15-00159).

If an earth plane, such as a counterpoise, cannot be provided for the antenna, an earth

wire connected to a suitable earth stake can be used, but with reduced efficiency.

NOTE: As the earth wire forms part of the antenna system, any resistance in

the earthing network reduces the efficiency of the antenna.

CAUTION: The earth connections are subject to corrosion and oxidation. All joints

must be clean, and the hardware adequately tightened. The joints can

be protected by the application of silicone grease. In severe conditions,

joints should be covered with self-amalgamating tape followed by a

layer of good quality UV-stable PVC tape.

CAUTION: RF earthing should not be relied upon to provide protective earthing. It

can fail upon the removal of one of the interconnecting links. A

separate wire should always be connected to the item that you want to

protect.