The 2539 from KR Electronics (A Division of NIC) is a Low Pass RF Filter with Frequency DC to 65 MHz, Stopband Frequency 75.1 MHz, 3 dB Cutoff Frequency 65 MHz, Lower Rejection 45 [email protected] MHz, Upper Rejection 4 [email protected] MHz. Tags: Plug In. More details for 2539 can be seen below.