Signal Strength And The Rssi Pin - Digi XBee Zigbee Mesh Kit User Manual

Signal strength and radio frequency range
To achieve the greatest range, the football-shaped path in which radio waves travel (Fresnel
zone) must be free of obstructions. Buildings, trees, or any other obstacles in the path will
decrease the communication range. If the antennas are mounted just off the ground, over half
of the Fresnel zone ends up being obstructed by the curvature of the earth, resulting in
significant reduction in range. To avoid this problem, mount the antennas high enough off the
ground that the earth does not interfere with the central diameter of the Fresnel zone.

Signal strength and the RSSI pin

The Received Signal Strength Indicator (RSSI) measures the amount of power present in a radio
signal. It is an approximate value for signal strength received on an antenna.
Measuring the signal strength at the receiving antenna is one way to determine the quality of a
communication link. If a distant transmitter is moved closer to a receiver, the strength of the
transmitted signal at the receiving antenna increases. Likewise, if a transmitter is moved farther
away, signal strength at the receiving antenna decreases.
The RSSI is measured in dBm. A greater negative value (in dBm) indicates a weaker signal. Therefore, -
50 dBm is better than -60 dBm.
XBee® Zigbee® Mesh Kit
Signal strength and the RSSI pin
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