The Raspberry Pi GMSK Modem board needs only a suitable N-FM radio .. add TWO radios and you get a D-Star repeater…add an internet connection for a fully functioning D-Star gateway, either simplex or full duplex! This boards CMX589 GMSK modem connects directly to the GPIO socket.
http://ki6zum.com/dstar/dv_overview.htm
Turning the Raspberry Pi into an FM Transmitter – PiFM