Reference Manual

Design notes Power supply design
Digi XBee® RR RF Module Hardware Reference Manual
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Power supply design
A poor power supply can lead to poor device performance, especially if you do not keep the supply
voltage within tolerance or if it is excessively noisy. To help reduce noise, place a 1.0 µF and 8.2 pF
capacitor as near as possible to the VCC connection on the XBee RR RF Module (pad 2 for micro and
surface-mount, and pin 1 for through-hole). Adding a 10 µF decoupling capacitor is also
recommended. 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 best results,
place the lower capacitance capacitors closest to the XBee RR RF Module.
Board layout
We design XBee RR RF 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 RR RF 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
n Batteries
n Tall electrolytic capacitors
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
n Microwave ovens
Use the following additional guidelines for optimal antenna performance:
n Do not place XBee RR RF Modules with the embedded antenna inside a metal enclosure.
n Do not place any ground planes or metal objects above or below the antenna.
n For the best results, mount the device at the edge of the host PCB. Ensure that the ground,
power, and signal planes are vacant immediately below the antenna section.