ArcPad supports SiRF Star III based GPS receivers and Static Navigation (SN), yet it is recommended that users disable this property.
Many PDAs are now using the SIRF Star III chip. Problems may occur when using GPS in ArcPad unless the SN property is turned off.
For more information about Static Navagation, refer to the link below:
GPS Passion, Advanced Configuration for SiRF based GPS Receivers.