The FN-3980W from Filtronetics is a Low Pass RF Filter with Frequency DC to 3 kHz, Stopband Frequency 4.5 to 5.7 KHz, 3 dB Cutoff Frequency 3 kHz, Insertion Loss 0.5 dB, Rejection 20 to 60 dB. Tags: Module with Connector. More details for FN-3980W can be seen below.