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5.2 With Line-of-Sight
When installing the Meter it is important to position your device in such a way to
optimize the antenna location within what’s known as the “Fresnel Zone”. The
Fresnel Zone can be thought of as a football-shaped invisible tunnel between
two locations that provides a path for RF signals between the End Device and
the Meter.
Figure 5.2 Fresnel Zone
In order to achieve maximum range, the football-shaped path in which radio
waves travel must be free of obstructions. Obstacles in the path (especially
metal) will decrease the communication range between the End Device and
Meter.
Also, if the antennas are mounted just barely off the ground or below the ceiling,
over half of the Fresnel zone ends up being obstructed resulting in significant
reduction in range.
Below is the calculated radius of the football-shaped tunnel for different distance
range:
Distance (feet) Radius (feet)
100 3.2
200 4.5
300 5.5
It is recommended that within the tunnel of the above radius, at least 60% of
space is free of obstruction.
Since signal reaches destination directly in a line-of-sight situation, it is important
to adjust the antenna properly to achieve maximum performance. Antenna for
the Meter and End Device should be perpendicular to the plane where the Meter
and End Device is located.