This is a Spektrum RC SLR300 3-Channel SLT Receiver Single Protocol.

Specifications:

Type: SLT Single Protocol Surface Receiver

# of Channels: 3

Modulation: FHSS

Band: 2.4 GHz

Length: 33.4mm

Width: 21mm

Height: 12.6mm

Weight: 6g

Voltage Range: 3.5–9.6V

Antenna Length: 140mm