Drotek XL RTK
The Drotek XL RTK GPS receiver is a competitively priced RTK module that can be configured as either base or rover. Using RTK, PX4 can get its position with centimetre-level accuracy, which is much more accurate than can be provided by a normal GPS.
Drotek XL RTK (drotek.com)
RTK setup and use on PX4 via QGroundControl is largely plug and play (see RTK GPS for more information).
The Drotek UCenter tool is not required for configuration - everything is handled by QGroundControl.
Wiring and Connections
The module inputs/outputs are shown here (Drotek docs).