User's Manual

E2 Wireless I/O Page 17
already shielded from lightning strike by an adjacent earthed structure, a lightning rod
may be installed above the antenna to provide shielding.
Dipole and Collinear antennas.
A collinear antenna transmits the same amount of radio power in all directions - as such
they are easy to install and use. The dipole antenna with integral 15 ‘cable does not
require any additional coaxial cable; however a cable must be used with the collinear
antennas.
Collinear and dipole antennas should be mounted vertically, preferably 1 wavelength
(dependent on frequency) away from a wall or mast to obtain maximum range.
Yagi antennas.
A Yagi antenna provides high gain in the forward direction, but lower gain
in other directions. This may be used to compensate for coaxial cable loss
for installations with marginal radio path.
The Yagi gain also acts on the receiver, so adding Yagi antennas at both
ends of a link provides a double improvement.
Yagi antennas are directional. That is, they have positive gain to the front
of the antenna, but negative gain in other directions.
Hence, Yagi antennas should be installed with the central beam horizontal
and must be pointed exactly in the direction of transmission to benefit from
the gain of the antenna. The Yagi antennas may be installed with the
elements in a vertical plane (vertically polarised) or in a horizontal plane
(horizontally polarised). For a two-station installation, with both modules
using Yagi antennas, horizontal polarisation is recommended. If there are
more than two stations transmitting to a common station, then the Yagi