User Manual

2
1
1. Line of sight
2. Obstruction in the
"lobe" (Fresnel zone)
of the radio signal.
Despite a clear line of sight, obstructions in the Fresnel zone, a three-dimensional ellipsoid formed with the two antennas
as the foci, will still interfere with the radio signal and cause multi-path fade. Raise the antennas high enough to clear any
obstructions. Ideally there should be no obstructions in the Fresnel zone. If a radio network site is spread over a large area
with multiple obstructions or a variety of terrain, conduct a site survey to determine optimum antenna locations, antenna
mounting heights, and recommended gains for reliable performance.
Omni-Directional Antennas
Omni-directional antennas mount vertically and transmit and receive equally in all directions within the horizontal plane.
Omni-directional antennas are used with the SureCross
®
Gateway, because the Gateway is usually at the center of the
star topology radio network.
An omni-directional, or omni, antenna transmits and receives radio signals in the ‘doughnut’ pattern shown. Note the lack
of a signal very close to the antenna. Most dipole omni antennas have a minimum distance for optimum signal reception.
Antenna
3 miles
From the top view, the signal radiates equally in all
directions from the antenna. For this reason, omni-
directional antennas are best used for the device in the
center of a star topology network.
Viewed from the side, however, the radiation pattern of an
omni-directional antenna is doughnut shaped.
With the star topology network, using the omni-directional antenna on the Gateway ensures that all Nodes fall within the
antenna radiation pattern.
Antenna Basics
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