The BLK-721N from Synergy Microwave Corporation is a DC Block with Frequency 5 to 500 MHz, Insertion Loss 0.10 to 0.25 dB, Breakdown Voltage 2500 V, VSWR 1.12:1, 1.30:1. Tags: Module with Connectors, Inner-Outer DC Block. More details for BLK-721N can be seen below.