This is the :

ExcelRC DasMikro DSK-307 KO PROPO FHSS ANTENNA-FREE 4CH RX

This RC receiver unit is designed for KO PROPO FHSS 2.4G transmitters and RF unit (903FH/904FH)/EX-1/EX-2). This receiver supports KO PROPO 2.4G FHSS protocol and it offers full 4-channel support.

25.5 x 22 x 17.3 mm

Compatible Transmitters:

KO PROPO RF-903/RF-904FH
KO PROPO EX-1
KO PROPO EX-2
KO PROPO EX-RR