This is the Futaba R2104GF S-FHSS High Voltage 4-Channel 2.4Ghz Receiver
NOTE: This receiver is NOT compatible with 2.4GHz FASST or FASSTest systems. It will work with FHSS and T-FHSS transmitters, but the transmitter mode will need to be changed to from T-FHSS/FHSS to S-FHSS mode.
Specifications:
Dimensions: 1.54x1.02x0.39" (39x26x10mm)
Weight: 8 g (0.28 oz)