Westermo RM-80 - Manual (Page 11)

11 6193-4201
2.2.2 Yagi antennas.
A Yagi antenna provides high gain in the forward direction, but lower gain in other direc-
tions. This may be used to compensate for coaxial cable loss for installations with mar-
ginal radio path.
The Yagi gain also acts on the receiver, so adding Yagi antennas at both ends of a link pro-
vides 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 polarized) or in a horizontal plane (horizontally polarized).
For a two station installation, with both modules using Yagi antennas, horizontal polariza-
tion is recommended. If there are more than two stations transmitting to a common
station, then the Yagi antennas should have vertical polarization, and the common (or
“central” station should have a collinear (non-directional) antenna.
Also note that Yagi antennas normally have a drain hole on the folded element – the
drain hole should be located on the bottom of the installed antenna.
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