INSTALLATION
FIXED STATIONS
416 ENVOY™ TRANSCEIVER REFERENCE MANUAL
NOTE: The transceiver and antenna do not have to be positioned close to each
other if connected by coaxial cable. The transceiver and the feed point
of the antenna can be up to 20 m (22 yd) apart before heavier low-loss
coaxial cable, such as RG213, is necessary.
Horizontal wire antennas, including the dipole, broadband and long wire antennas,
have maximum radiation along their length. Radiation is lowest at the ends of the
antenna. Therefore, position these antennas at right angles to the desired direction of
communication.
Vertical antennas, such as the vertical whip antenna, have an omnidirectional
radiation pattern. Therefore, the direction that vertical antennas face is not important
as the radiation pattern is generally equal in all directions.
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.
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