Hardware Design notes
XBee®-PRO 900HP/XSC RF Modules
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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 we recommend to build and troubleshoot a
robust design.
Power supply design
A poor power supply can lead to poor radio performance, especially if you do not keep the supply
voltage within tolerance or if the noise is excessive. To help reduce noise, place a 1.0 µF and 47 pF
capacitor as near as possible to pin 1 on the PCB. If you are using a switching regulator for the power
supply, switch the frequencies above 500 kHz. Limit the power supply ripple to a maximum 50 mV
peak to peak.
For designs using the programmable modules, we recommend an additional 10 µF decoupling cap
near pin 1 of the device. The nearest proximity to pin 1 of the three caps should be in the following
order:
1. 47 pf
2. 1 µF
3. 10 µF
Board layout
We design XBee modules to be self-sufficient and have minimal sensitivity to nearby processors,
crystals or other printed circuit board (PCB) components. Keep power and ground traces thicker than
signal traces and make sure that they are able to comfortably support the maximum current
specifications. There are no other special PCB design considerations to integrate XBee modules, with
the exception of antennas.
Antenna performance
Antenna location is important for optimal performance. The following suggestions help you achieve
optimal antenna performance. Point the antenna up vertically (upright). Antennas radiate and receive
the best signal perpendicular to the direction they point, so a vertical antenna's omnidirectional
radiation pattern is strongest across the horizon.
Position the 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:
n Metal poles
n Metal studs
n Structure beams
n Concrete, which is usually reinforced with metal rods
If you place the device inside a metal enclosure, use an external antenna. Common objects that have
metal enclosures include:
n Vehicles
n Elevators
n Ventilation ducts
n Refrigerators
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