The BWLF-R4 from Sainty-Tech Communications Limited is a Low Pass RF Filter with Frequency DC to 0.4 GHz, 3 dB Cutoff Frequency 0.4 GHz, Insertion Loss 1.8 dB @0.4 GHz, Rejection 20 dB @0.9GHz, 40 dB @1.4GHz, Power 30 dBm. Tags: Die. More details for BWLF-R4 can be seen below.