Xbee Digimesh 2.4 Design Notes; Xbee Board Layout; Xbee Power Supply Design; Xbee Antenna Performance - Digi XBee User Manual

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XBee/XBee-PRO DigiMesh 2.4 User Manual

XBee DigiMesh 2.4 Design Notes

The XBee modules do not require any external circuitry or specific connections for proper
operation. However, there are some general design guidelines that are recommended for
troubleshooting and building a robust design.

XBee Board Layout

XBee modules are designed to be self sufficient and have minimal sensitivity to nearby
processors, crystals or other PCB components. As with all PCB designs, power and ground traces
should be thicker than signal traces and should be able to comfortably support the maximum
current specifications. No other special PCB design considerations are required for integrating
XBee radios except in the antenna section.

XBee Power Supply Design

A poor power supply can lead to poor radio performance, especially if the supply voltage is not
kept within tolerance or is excessively noisy. To help reduce noise, place a 1.0 uF and 8.2pF
capacitor as near to pin one on the PCB as possible. If you are using a switching regulator for
your power supply, switch the frequencies above 500kHz. The power supply ripple needs to be
limited to a maximum 100mV peak to peak.

XBee Antenna Performance

Antenna location is an important consideration for optimal performance. For optimal antenna
performance, see the following placement tips and suggestions:
Point your antenna up vertically (up right):
Antennas radiate and receive the best signal perpendicular to the direction they point, thus, a
vertical antenna's radiation pattern is strongest across the horizon.
Position antennas away from metal objects whenever possible:
Metal objects between the transmitter and receiver can block the radiation path or reduce the
transmission distance. Objects that are often overlooked include metal poles, metal studs,
structure beams, concrete (it is usually reinforced with metal rods).
Use an external antenna if the XBee device is placed inside a metal enclosure:
Common objects that have metal enclosures include vehicles, elevators, ventilation ducts,
refrigerators, microwave ovens, batteries, and tall electrolytic capacitors.
Do not place XBee modules with the chip or integrated PCB Antennas inside a metal
enclosure:
There should not be any ground planes or metal objects above or below the antenna. For best
results, place the XBee at the edge of the host PCB on which it is mounted. Ensure that the
ground, power, and signal planes are vacant immediately below the antenna section. It is
recommended that you allow a "keepout" area, which is shown in detail on the next page.
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