An approved ADS-B system does require high integrity GPS position source to be a valid ADS-B client. It is recommended to have at least a TSO-C145/146 GPS/WAAS position source. Please refer to AC20-165 (appendix 2) for position source requirements. FreeFlight Systems offer the 1201 and 1203C series GPS/ WAAS Sensors to supply position source options that fully meet the ADS-B requirements worldwide.