User manual

WI-MOD-9-E Wireless Ethernet User Manual
WI-MOD-9-E Manual V1.9 Page 14
2.2.2 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
polarized) or in a horizontal plane (horizontally polarized). For a two station installation, with
both modules using Yagi antennas, horizontal polarization 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.
WI-MOD-9-E
Antenna installed
with drain holes
down
Coax feed
looped
90
o