Here's are two quick-guides for a step-by-step base/rover setup with Leica Captivate system:  One with using internal UHF radio on the GS sensors,  and one for an external UHF base radio with a internal UHF Rover.

In cases for internal UHF radios bases, although the base or rover sensor can be interchangeable as long the base sensor unit have a internal Satel M3-TR4(+) or M3-TR3(OEM22), they can be configured to transmit using their internal radio. 

Note: Any GS sensor equipped with an M3-R3 (OEM20) has a receive-only radio and can only be used as a rover.

RTK Internal UHF Base Rover Quick-guide 

Other configurations/setup can also be used (For example, using a Satel HPR3/4 external radio):

RTK UHF Ext Base Rover Quick-guide