ABB AWIN GW120, User Manual

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ANTENNAS AND CABLING WIR ELESS HART S YS TEM PLANNING
22 4JNO0 0030 8 A
4.4 Antennas and Cabling
The single most important item affecting radio performance is the antenna system. Consider
carefully this part of an installation, or the performance of the entire system will be compro-
mised. Quality high gain antennas should be used at all stations. The antennas should be
specifically designed for use at the intended frequency of operation and with matching im-
pedance (50 ohm).
Antennas are made by several manufacturers and fall into two categories – omnidirectional
and directional (see
Figure 3) . An omnidirectional antenna provides equal radiation and re-
sponse in all directions and is, therefore, appropriate for use at master stations which must
communicate with an array of remote stations scattered in various directions. Omni-anten-
nas should also be used where clients will be mobile.
At remote fixed stations, a directional antenna, such as a Yagi, is typically used. Directional
antennas confine the transmission and reception of signals to a relatively narrow beam
width, allowing greater communication range and reducing the chances of interference from
other users outside the pattern. It is necessary to aim these antennas in the desired direction
of communication (i.e., at the master station).
The end of the antenna (farthest from support mast) should face the associated station. Fi-
nal alignment of the antenna heading can be accomplished by orienting it for maximum re-
ceived signal strength.
Figure 3: Omnidirectional and directional antenna performance characteristics