R603GF is 2.4GHz FHSS 3-Channel Receiver. It is designed for 2PL and 3PL.
However, 4PL is using the S-FHSS system which is differ from that of 2PL and 3PL. 4PL is able to select between FHSS/S-FHSS modes, which allow you to use R603GF or R2004GF FHSS receivers, or take advantage of the higher frame rates available with the included high-voltage R2104GF receiver.